Content:

G – Geodesy

G1.1 – Recent Developments in Geodetic Theory

The Global Ionosphere Maps (GIMs) are generated on a daily basis at the Center for Orbit Determination in Europe (CODE) using the observations from about 200 Global Positioning System (GPS)/GLONASS sites of the International GNSS Service (IGS) and other institutions. These maps contain Vertical Total Electron Content (VTEC) values, which are estimated in a solar-geomagnetic reference frame using a spherical harmonics expansion up to degree and order 15. Although these maps have wide applications, their relatively low spatial resolution limits the accuracy of many geodetic applications such as those related to Precise Point Positioning (PPP) and navigation. In this study, a novel Bayesian approach is proposed to improve the spatial resolution of VTEC estimations in regional and global scales. The proposed technique utilises GIMs as a prior information and updates the VTEC estimates using a new set of base-functions (with better resolution than that of spherical harmonics) and the GNSS measurements that are not included in the network of GIMs. To achieve the highest accuracy possible, our implementation is based on a transformation of spherical harmonics to the Slepian base-functions, where the latter is a set of bandlimited functions that reflect the majority of signal energy inside an arbitrarily defined region, yet they remain orthogonal within this region. The new GNSS measurements are considered in a Bayesian update estimation to modify those of GIMs. Numerical application of this study is demonstrated using the ground-based GPS data over South America. The results are also validated against the VTEC estimations derived from independent GPS stations.

Key words: Spherical Slepian Base-Functions, Spherical Harmonics, Ionospheric modelling, Vertical Total Electron Content (VTEC)

How to cite: Farzaneh, S. and Forootan, E.: A Bayesian Approach to Improve Regional and Global Ionospheric Maps using GNSS Observations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-282, https://doi.org/10.5194/egusphere-egu2020-282, 2020.

G1.1 Session: Recent Developments in Geodetic Theory

 

Estimability in Rank-Defect Mixed-Integer Models: Theory and Applications

 

PJG Teunissen1,2

1GNSS Research Centre, Curtin University, Perth, Australia

2Geoscience and Remote Sensing, Delft University of Technology, The Netherlands

Email: p.teunissen@curtin.edu.au; p.j.g.teunissen@tudelft.nl

 

Although estimability is one of the foundational concepts of todays’ estimation theory, we show that the current concept of estimability is not adequately equipped to cover the estimation requirements of mixed-integer models, for instance like those of interferometric models, cellular base transceiver network models or the carrier-phase based models of Global Navigation Satellite Systems (GNSSs). We therefore need to generalize the estimability concept to that of integer-estimability. Next to being integer and estimable in the classical sense, functions of integer parameters then also need to guarantee that their integerness corresponds with integer values of the parameters the function is taken of. This is particularly crucial in the context of integer ambiguity resolution. Would this condition not be met, then the integer fixing of integer functions that are not integer-estimable implies that one can fix the undifferenced integer ambiguities to non-integer values and thus force the model to inconsistent and wrong constraints.

In this paper we present a generalized concept of estimability and one that now also is applicable to mixed-integer models. We thereby provide the operationally verifiable necessary and sufficient conditions that a function of integer parameters needs to satisfy in order to be integer-estimable. As one of the conditions we have that estimable functions become integer-estimable if they can be unimodulair transformed to canonical form. Next to the conditions, we also show how to create integer-estimable functions and how a given design matrix can be expressed in them. We then show how these results are to be applied to interferometric models, cellular base transceiver network models and FDMA GNSS models.

 

Keywords: Estimability, S-system theory, Mixed-integer Models, Integer-Estimability, Admissible Ambiguity Transformation, Interferometry, Global Navigation Satellite Systems (GNSSs)

 

How to cite: Teunissen, P.: Estimability in Rank-Defect Mixed-Integer Models: Theory and Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1797, https://doi.org/10.5194/egusphere-egu2020-1797, 2020.

Removal of the Common Mode Error (CME) is very important for the investigation of Global Navigation Satellite Systems (GNSS) technique error and the estimation of accurate GNSS velocity field for geodynamic applications. The commonly used spatiotemporal filtering methods cannot accommodate missing data, or they have high computational complexity when dealing with incomplete data. This research presents the Expectation-Maximization Principal Component Analysis (EMPCA) to estimate and extract CME from the incomplete GNSS position time series. The EMPCA method utilizes an Expectation-Maximization iterative algorithm to search each principal subspace, which allows extracting a few eigenvectors and eigenvalues without covariance matrix and eigenvalue decomposition computation. Moreover, it could straightforwardly handle the missing data by Maximum Likelihood Estimation (MLE) at each iteration. To evaluate the performance of the EMPCA algorithm for extracting CME, 44 continuous GNSS stations located in Southern California have been selected here. Compared to previous approaches, EMPCA could achieve better performance using less computational time and exhibit slightly lower CME relative errors when more missing data exists. Since the first Principal Component (PC) extracted by EMPCA is remarkably larger than the other components, and its corresponding spatial response presents nearly uniform distribution, we only use the first PC and its eigenvector to reconstruct the CME for each station. After filtering out CME, the interstation correlation coefficients are significantly reduced from 0.46, 0.49, 0.42 to 0.18, 0.17, 0.13 for the North, East, and Up (NEU) components, respectively. The Root Mean Square (RMS) values of the residual time series and the colored noise amplitudes for the NEU components are also greatly suppressed, with an average reduction of 25.9%, 27.4%, 23.3% for the former, and 49.7%, 53.9%, and 48.9% for the latter. Moreover, the velocity estimates are more reliable and precise after removing CME, with an average uncertainty reduction of 52.3%, 57.5%, and 50.8% for the NEU components, respectively. All these results indicate that the EMPCA method is an alternative and more efficient way to extract CME from regional GNSS position time series in the presence of missing data. Further work is still required to consider the effect of formal errors on the CME extraction during the EMPCA implementation.

How to cite: li, W. and jiang, W.: Extracting Common Mode Errors of Regional GNSS Position Time Series in the Presence of Missing Data by Expectation-Maximization Principal Component Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12635, https://doi.org/10.5194/egusphere-egu2020-12635, 2020.

EGU2020-3042 | Displays | G1.1

On Downward Continuing Airborne Gravity Data for Local Geoid Modeling

Xiaopeng Li, Jianliang Huang, Cornelis Slobbe, Roland Klees, Martin Willberg, and Roland Pail

The topic of downward continuation (DWC) has been studied for many decades without very conclusive answers on how different methods compare with each other. On the other hand, there are vast amounts of airborne gravity data collected by the GRAV-D project at NGS NOAA of the United States and by many other groups around the world. These airborne gravity data are collected on flight lines where the height of the aircraft actually varies significantly, and this causes challenges for users of the data. A downward continued gravity grid either on the topography or on the geoid is still needed for many applications such as improving the resolution of a local geoid model. Four downward continuation methods, i.e., Residual Least Squares Collocation (RLSC), the Inverse Poisson Integral, Truncated Spherical Harmonic Analysis, and Radial Basis Functions (RBF), are tested on both simulated data sets and real GRAV-D airborne gravity data in a previous joint study between NGS NOAA and CGS NRCan. The study group is further expanded by adding the TU Delft group on RBF and the TUM group on RLSC to incorporate more updated knowledge in the theoretical background and more in-depth discussion on the numerical results. A formal study group will be established inside IAG for providing the best answers for downward continuing airborne gravity data for local gravity field improvement. In this presentation, we review and compare the four methods theoretically and numerically. Simulated and real airborne and terrestrial data are used for the numerical comparison over block MS05 of the GRAV-D project in Colorado, USA, where the 1cm geoid experiment was performed by 15 international teams. The conclusion drawn from this study will advance the use of GRAV-D data for the new North American-Pacific Geopotential Datum of 2022 (NAPGD2022).

How to cite: Li, X., Huang, J., Slobbe, C., Klees, R., Willberg, M., and Pail, R.: On Downward Continuing Airborne Gravity Data for Local Geoid Modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3042, https://doi.org/10.5194/egusphere-egu2020-3042, 2020.

EGU2020-3403 | Displays | G1.1

Overview on the spectral combination of integral transformations

Martin Pitoňák, Michal Šprlák, Pavel Novák, and Robert Tenzer

Geodetic boundary-value problems (BVPs) and their solutions are important tools for describing and modelling the Earth’s gravitational field. Many geodetic BVPs have been formulated based on gravitational observables measured by different sensors on the ground or moving platforms (i.e. aeroplanes, satellites). Solutions to spherical geodetic BVPs lead to spherical harmonic series or surface integrals with Green’s kernel functions. When solving this problem for higher-order derivatives of the gravitational potential as boundary conditions, more than one solution is obtained. Solutions to gravimetric, gradiometric and gravitational curvature BVPs (Martinec 2003; Šprlák and Novák 2016), respectively, lead to two, three and four formulas. From a theoretical point of view, all formulas should provide the same solution, but practically, when discrete noisy observations are exploited, they do not.

In this contribution we present combinations of solutions to the above mentioned geodetic BVPs in terms of surface integrals with Green’s kernel functions by a spectral combination method. We investigate an optimal combination of different orders and directional derivatives of potential. The spectral combination method is used to combine terrestrial data with global geopotential models in order to calculate geoid/quasigeoid surface. We consider that the first-, second- and third-order directional derivatives are measured at the satellite altitude and we continue them downward to the Earth’s surface and convert them to the disturbing gravitational potential, gravity disturbances and gravity anomalies. The spectral combination method thus serves in our numerical procedures as the downward continuation technique. This requires to derive the corresponding spectral weights for the n-component estimator (n = 1, 2, … 9) and to provide a generalized formula for evaluation of spectral weights for an arbitrary N-component estimator. Properties of the corresponding combinations are investigated in both, spatial and spectral domains.

 

How to cite: Pitoňák, M., Šprlák, M., Novák, P., and Tenzer, R.: Overview on the spectral combination of integral transformations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3403, https://doi.org/10.5194/egusphere-egu2020-3403, 2020.

EGU2020-13258 | Displays | G1.1 | Highlight

Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data

Michal Šprlák, Khosro Ghobadi-Far, Shin-Chan Han, and Pavel Novák

The problem of estimating mass redistribution from temporal variations of the Earth’s gravity field, such as those observed by GRACE, is non-unique. By approximating the Earth’s surface by a sphere, surface mass change can be uniquely determined from time-variable gravity data. Conventionally, the spherical approach of Wahr et al. (1998) is employed for computing the surface mass change caused, for example, by terrestrial water and glaciers. The accuracy of the GRACE Level 2 time-variable gravity data has improved due to updated background geophysical models or enhanced data processing. Moreover, time series analysis of ∼15 years of GRACE observations allows for determining inter-annual and seasonal changes with a significantly higher accuracy than individual monthly fields. Thus, the improved time-variable gravity data might not tolerate the spherical approximation introduced by Wahr et al. (1998).

A spheroid (an ellipsoid of revolution) represents a closer approximation of the Earth than a sphere, particularly in polar regions. Motivated by this fact, we develop a rigorous method for determining surface mass change on a spheroid. Our mathematical treatment is fully ellipsoidal as we concisely use Jacobi ellipsoidal coordinates and exploit the corresponding series expansions of the gravitational potential and of the surface mass. We provide a unique one-to-one relationship between the ellipsoidal spectrum of the surface mass and the ellipsoidal spectrum of the gravitational potential. This ellipsoidal spectral formula is more general and embeds the spherical approach by Wahr et al. (1998) as a special case. We also quantify the differences between the spherical and ellipsoidal approximations numerically by calculating the surface mass change rate in Antarctica and Greenland.

 

References:

Wahr J, Molenaar M, Bryan F (1998) Time variability of the Earth’s gravity field: Hydrological and oceanic effects and their possible detection using GRACE. Journal of Geophysical Research: Solid Earth, 103(B12), 30205-30229.

How to cite: Šprlák, M., Ghobadi-Far, K., Han, S.-C., and Novák, P.: Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13258, https://doi.org/10.5194/egusphere-egu2020-13258, 2020.

EGU2020-15381 | Displays | G1.1

A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters

Hadi Amin, Lars E. Sjöberg, and Mohammad Bagherbandi

According to the classical Gauss–Listing definition, the geoid is the equipotential surface of the Earth’s gravity field that in a least-squares sense best fits the undisturbed mean sea level. This equipotential surface, except for its zero-degree harmonic, can be characterized using the Earth’s Global Gravity Models (GGM). Although nowadays, the satellite altimetry technique provides the absolute geoid height over oceans that can be used to calibrate the unknown zero-degree harmonic of the gravimetric geoid models, this technique cannot be utilized to estimate the geometric parameters of the Mean Earth Ellipsoid (MEE). In this study, we perform joint estimation of W0, which defines the zero datum of vertical coordinates, and the MEE parameters relying on a new approach and on the newest gravity field, mean sea surface, and mean dynamic topography models. As our approach utilizes both satellite altimetry observations and a GGM model, we consider different aspects of the input data to evaluate the sensitivity of our estimations to the input data. Unlike previous studies, our results show that it is not sufficient to use only the satellite-component of a quasi-stationary GGM to estimate W0. In addition, our results confirm a high sensitivity of the applied approach to the altimetry-based geoid heights, i.e. mean sea surface and mean dynamic topography models. Moreover, as W0 should be considered a quasi-stationary parameter, we quantify the effect of time-dependent Earth’s gravity field changes as well as the time-dependent sea-level changes on the estimation of W0. Our computations resulted in the geoid potential W0 = 62636848.102 ± 0.004 m2s-2 and the semi-major and –minor axes of the MEE, a = 6378137.678 ± 0.0003 m and b = 6356752.964 ± 0.0005 m, which are 0.678 and 0.650 m larger than those axes of the GRS80 reference ellipsoid, respectively. Moreover, a new estimation for the geocentric gravitational constant was obtained as GM = (398600460.55 ± 0.03) × 106 m3s-2.

How to cite: Amin, H., Sjöberg, L. E., and Bagherbandi, M.: A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15381, https://doi.org/10.5194/egusphere-egu2020-15381, 2020.

When treating geodetic boundary value problems in gravity field studies, the geometry of the physical surface of the Earth may be seen in relation to the structure of the Laplace operator. Similarly as in other branches of engineering and mathematical physics a transformation of coordinates is used that offers a possibility to solve an alternative between the boundary complexity and the complexity of the coefficients of the partial differential equation governing the solution. The Laplace operator has a relatively simple structure in terms of spherical or ellipsoidal coordinates which are frequently used in geodesy. However, the physical surface of the Earth substantially differs from a sphere or an oblate ellipsoid of revolution, even if these are optimally fitted. The situation may be more convenient in a system of general curvilinear coordinates such that the physical surface of the Earth is imbedded in the family of coordinate surfaces. The structure of the Laplace operator, however, is more complicated in this case and in a sense it represents the topography of the physical surface of the Earth. The Green’s function method together with the method of successive approximations is used for the solution of geodetic boundary value problems expressed in terms of new coordinates. The structure of iteration steps is analyzed and if useful, it is modified by means of the integration by parts. Subsequently, the individual iteration steps are discussed and interpreted.

How to cite: Holota, P. and Nesvadba, O.: Laplacian structure, solution domain geometry and successive approximations in gravity field studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12839, https://doi.org/10.5194/egusphere-egu2020-12839, 2020.

EGU2020-13411 | Displays | G1.1

The finite element method for solving the oblique derivative boundary value problems in geodesy

Marek Macák, Zuzana Minarechová, Róbert Čunderlík, and Karol Mikula

We present a novel approach to the solution of the geodetic boundary value problem with an oblique derivative boundary condition by the finite element method. Namely, we propose and analyse a finite element approximation of a Laplace equation holding on a domain with an oblique derivative boundary condition given on a part of its boundary. The oblique vector in the boundary condition is split into one normal and two tangential components and derivatives in tangential directions are approximated as in the finite difference method. Then we apply the proposed numerical scheme to local gravity field modelling. For our two-dimensional testing numerical experiments, we use four nodes bilinear quadrilateral elements and for a three-dimensional problem, we use hexahedral elements with eight nodes. Practical numerical experiments are located in area of Slovakia that is given by grid points located on the Earth's surface with uniform spacing in horizontal directions. Heights of grid points are interpolated from the SRTM30PLUS topography model. An upper boundary is in the height of 240 km above a reference ellipsoid WGS84 corresponding to an average altitude of the GOCE satellite orbits. Obtained solutions are compared to DVRM05.

How to cite: Macák, M., Minarechová, Z., Čunderlík, R., and Mikula, K.: The finite element method for solving the oblique derivative boundary value problems in geodesy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13411, https://doi.org/10.5194/egusphere-egu2020-13411, 2020.

EGU2020-13527 | Displays | G1.1

FVM approach for solving the oblique derivative BVP on unstructured meshes above the real Earth’s topography

Matej Medľa, Karol Mikula, and Róbert Čunderlík

We present local gravity field modelling based on a numerical solution of the oblique derivative bondary value problem (BVP). We have developed a finite volume method (FVM) for the Laplace equation with the Dirichlet and oblique derivative boundary condition, which is considered on a 3D unstructured mesh about the real Earth’s topography. The oblique derivative boundary condition prescribed on the Earth’s surface as a bottom boundary is split into its normal and tangential components. The normal component directly appears in the flux balance on control volumes touching the domain boundary, and tangential components are managed as an advection term on the boundary. The advection term is stabilised using a vanishing boundary diffusion term. The convergence rate, analysis and theoretical rates of the method are presented in [1].

Using proposed method we present local gravity field modelling in the area of Slovakia using terrestrial gravimetric measurements. On the upper boundary, the FVM solution is fixed to the disturbing potential generated from the GO_CONS_GCF_2_DIR_R5 model while exploiting information from the GRACE and GOCE satellite missions. Precision of the obtained local quasigeoid model is tested by the GNSS/levelling test.

 

[1] Droniou J, Medľa M, Mikula K, Design and analysis of finite volume methods for elliptic equations with oblique derivatives; application to Earth gravity field modelling. Journal of Computational Physics, s. 2019

How to cite: Medľa, M., Mikula, K., and Čunderlík, R.: FVM approach for solving the oblique derivative BVP on unstructured meshes above the real Earth’s topography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13527, https://doi.org/10.5194/egusphere-egu2020-13527, 2020.

The notion of an equipotential surface of the Earth’s gravity potential is of key importance for vertical datum definition. The aim of this contribution is to focus on differential geometry properties of equipotential surfaces and their relation to parameters of Earth’s gravity field models. The discussion mainly rests on the use of Weingarten’s theorem that has an important role in the theory of surfaces and in parallel an essential tie to Brun’s equation (for gravity gradient) well known in physical geodesy. Also Christoffel’s theorem and its use will be mentioned. These considerations are of constructive nature and their content will be demonstrated for high degree and order gravity field models. The results will be interpreted globally and also in merging segments expressing regional and local features of the gravity field of the Earth. They may contribute to the knowledge important for the realization of the World Height System.

How to cite: Holota, P. and Nesvadba, O.: Differential geometry and curvatures of equipotential surfaces in the realization of the World Height System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13418, https://doi.org/10.5194/egusphere-egu2020-13418, 2020.

We present a method for the estimation of the components ξ and η of the deflection of the vertical using several parameters of the gravitational potential. Specifically, we assume that we know the geodetic coordinates (φ, λ, h), the magnitude of gravity g, the components ξ, η and the second partial derivatives of the gravitational potential (elements of the Eötvös matrix) at a point P. Knowing only the geodetic coordinates of a neighboring point A (at a distance up to several kilometers from P), we estimate the components ξ and η at A. The proposed method is evaluated with simulated data at several points in Greece. The results show that it may be used for the densification of a given astrogeodetic net.

How to cite: Manoussakis, G. and Korakitis, R.: Local determination of the components of the deflection of the vertical using gravitational potential parameters at a neighboring point, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20090, https://doi.org/10.5194/egusphere-egu2020-20090, 2020.

EGU2020-10857 | Displays | G1.1

Heuristic Algorithm to Compute Geodetic Height (h) from Ellipse Equation

Mohamed Eleiche and Ahmed Mansi

The equation of the ellipse in a meridian plan is well known to be which can be defined in its most generic form as where the variable (s) is the indicator value of the ellipsoidal height. For (h=0), the value of  (s) equals (1) , for negative  (h), the value  is lower than (1), and vice versa, for positive (h) , the corresponding  value of (s) is greater than (1). Hence (s) and (h) are highly-correlated. The main goal of this work is to exploit the  (s-h) correlation and to represent it both statistically and mathematically. Moreover, the essential role of (s) in the transformation of the Cartesian coordinates (xp, yp, zp) of any generic point (P) into its geodetic coordinates (φ, λ, h) in reference to the geodetic ellipsoid is thoroughly studied.

How to cite: Eleiche, M. and Mansi, A.: Heuristic Algorithm to Compute Geodetic Height (h) from Ellipse Equation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10857, https://doi.org/10.5194/egusphere-egu2020-10857, 2020.

The errors-in-variables (EIV) model is applied to surveying and mapping fields such as empirical coordinate transformation, line/plane fitting and rigorous modelling of point clouds and so on as it takes the errors both in coefficient matrix and observation vector into account. In many cases, not all of the elements in coefficient matrix are random or some of the elements are functionally dependent. The partial EIV (PEIV) model is more suitable in dealing with such structured coefficient matrix. Furthermore, when some reliable prior information expressed by inequality constraints is considered, the adjustment result of inequality constrained PEIV (ICPEIV) model is expected to be improved. There are two kinds of algorithms to solve the ICPEIV model under the weighted total least squares (WTLS) criterion currently. On the one hand, one can linearize the PEIV model and transform it into a sequence of quadratic programming (QP) sub-problems. On the other hand, one can directly solve the nonlinear target function by common used programming algorithms.All the QP algorithms and nonlinear programming methods are complicated and not familiar to the geodesists, so the ICPEIV model is not widely used in geodesy.   

In this contribution, an algorithm based on standard least squares is proposed. First, the estimation of model parameters and random variables in coefficient matrix are separated according to the Karush-Kuhn-Tucker (KKT) conditions of the minimization problem. The model parameters are obtained by solving the QP sub-problems while the variables are determined by the functional relationship between them. Then the QP problem is transformed to a system of linear equations with nonnegative Lagrange multipliers which is solved by an improved Jacobi iterative algorithm. It is similar to the equality-constrained least squares problem. The algorithm is simple because the linearization process is not required and it has the same form of classical least squares adjustment. Finally, two empirical examples are presented. The linear approximation algorithm, the sequential quadratic programming algorithm and the standard least squares algorithm are used. The examples show that the new method is efficient in computation and easy to implement, so it is a beneficial extension of classical least squares theory.

How to cite: Jian, X. and Sichun, L.: Weighted total least squares problems with inequality constraints solved by standard least squares theory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6362, https://doi.org/10.5194/egusphere-egu2020-6362, 2020.

Abstract: With the rapid development of artificial intelligence, machine learning has become an high-efficient tool applied in the fields of GNSS data analysis and processing, such as troposphere, ionosphere or satellite clock modeling and prediction. In this paper, zenith troposphere delay (ZTD) prediction algorithms based on BP neural network (BPNN) and least squares support vector machine (LSSVM) are proposed in the time and space domain. The main trend terms in ZTD time series are deducted by polynomial fitting, and the remaining residuals are reconstructed and modeled by BPNN and LSSVM algorithm respectively. The test results show that the performance of LSSVM is better than that of BPNN in term of prediction stability and accuracy by using ZTD products of International GNSS Service (IGS) of 20 stations in time domain. In order to further improve LSSVM prediction accuracy, a new strategy of training samples selection based on correlation analysis is proposed. The results show that using the proposed strategy, about 80% to 90% of the 1-hour prediction deviation of LSSVM can reach millimeter level depending on the season, and the percentage of the prediction deviation value less than 5 mm is about 60% to 70%, which is 5% to 20% higher than that of the classical random selection in different month. The mean values of RMSE in all 20 stations using the new strategy are 1-3mm smaller than those of the classical one. Then different prediction span from 1 to 12 hours is conducted to show the performance of the proposed method. Finally, the ZTD predictions based on BPNN and LSSVM in space domain are also verified and compared using GNSS CORS network data of Hong Kong, China.

Keywords: ZTD, BP Neural Network, Support Vector Machine, Least Squares, GNSS

Acknowledgments: This work was supported by Natural Science Foundation of China (41874032) and the National Key Research and Development Program (2016YFB0501701)

 

How to cite: Xu, T., Li, S., and Jiang, N.: Zenith Troposphere Delay Prediction based on BP Neural Network and Least Squares Support Vector Machine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5471, https://doi.org/10.5194/egusphere-egu2020-5471, 2020.

This study presents a new method to calculate displacement and potential changes caused by an earthquake in a three-dimensional viscoelastic earth model. It is the first time to compute co- and post-seismic deformation in a spherical earth with lateral heterogeneities. Such a method is useful to investigate the 3-dimensional viscoelastic structure of the earth by interpreting precise satellite gravity and GPS data. Firstly, we concern with Maxwell’s constitutive equation, the linearized equation of momentum conservation and Poisson’s equation, and obtain the solution in the Laplace domain in a spherical symmetric viscoelastic earth model. Furthermore, we employ the perturbed method to deal with the effect of lateral heterogeneities and obtain the relation between the solutions of the spherical symmetric earth model, the three-dimension earth model with lateral inhomogeneity and the auxiliary solutions. Then, using the given surface boundary conditions to determine the auxiliary solutions, we obtain the perturbed solutions of lateral increment in the Laplace domain. Finally, taking the inverse Laplace transforms of solutions in a spherical symmetric viscoelastic earth model and perturbed solutions with respect to lateral hetergeneities, we obtain the solutions of deformation in a three-dimensional viscoelastic earth model. 

How to cite: zhang, X.: Dislocation Theory in a 3-dimensional Viscoelastic Earth Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5394, https://doi.org/10.5194/egusphere-egu2020-5394, 2020.

EGU2020-19292 | Displays | G1.1

Model-based hydrodynamic leveling; a power full tool to enhance the quality of the geodetic networks

Yosra Afrasteh, Cornelis Slobbe, Martin Verlaan, Martina Sacher, and Roland Klees

Model-based hydrodynamic leveling is an efficient and flexible alternative method to connect islands and offshore tide gauges with the height system on land. The method uses a regional, high-resolution hydrodynamic model that provides total water levels. From the model, we obtain the differences in mean water level (MWL) between tide gauges at the mainland and at the islands or offshore platforms, respectively. Adding them to the MWL relative to the national height system at the mainland’s tide gauges realizes a connection of the island and offshore platforms with the height system on the mainland. Usually, the geodetic leveling networks are based on spirit leveling. So, as we can not make the direct connections between coastal countries, due to the inability of the spirit leveling method to cross the water bodies, they are weak in these regions. In this study, we assessed the impact of using model-based hydrodynamic leveling connections among the North Sea countries on the quality at which the European Vertical Reference System can be realized. In doing so, we combined the model-based hydrodynamic leveling data with synthetic geopotential differences among the height markers of the Unified European Leveling Network (UELN) used to realize the European Vertical Reference Frame 2019. The uncertainties of the latter data set were provided by the BKG. The impact is assessed in terms of both precision and reliability. We will show that adding model-based hydrodynamic leveling connections lowers the standard deviations of the estimated heights in the North Sea countries significantly. In terms of reliability, no significant improvements are observed.

How to cite: Afrasteh, Y., Slobbe, C., Verlaan, M., Sacher, M., and Klees, R.: Model-based hydrodynamic leveling; a power full tool to enhance the quality of the geodetic networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19292, https://doi.org/10.5194/egusphere-egu2020-19292, 2020.

The coverage of the gravity data plays an important role in the geoid determination. This paper tries to answer whether different geoid determination techniques would be affected similarly by such gravity data coverage. The paper presents the determination of the gravimetric geoid in two different countries where the gravity coverage is quite different. Egypt has sparse gravity data coverage over relatively large area, while Austria has quite dense gravity coverage in a significantly smaller area. Two different geoid determination techniques are tested. They are Stokes’ integral with modified Stokes kernel, for better combination of the gravity field wavelengths, and the least-squares collocation technique. The geoid determination has been performed within the framework of the non-ambiguous window remove-restore technique (Abd-Elmotaal and Kühtreiber, 2003). For Stokes’ geoid determination technique, the Meissl (1971) modified kernel has been used with numerical tests to obtain the best cap size for both geoids in Egypt and Austria. For the least-squares collocation technique, a modelled covariance function is needed. The Tscherning-Rapp (Tscherning and Rapp, 1974) covariance function model has been used after being fitted to the empirically determined covariance function. The paper gives a smart method for such covariance function fitting. All geoid are fitted to GNSS/levelling geoids for both countries. For each country, the computed two geoids are compared and the correlation between their differences versus the gravity coverage is comprehensively discussed.

How to cite: Abd-Elmotaal, H. and Kühtreiber, N.: Effect of gravity data coverage on geoid determination: comparison between Stokes and Collocation techniques in Egypt and Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12900, https://doi.org/10.5194/egusphere-egu2020-12900, 2020.

The effect of the topographic potential difference and the gravity correction on the geoid-quasigeoid separation are usually ignored in numerical computations. Those effects are computed in a mountainous Colorado region by using the digital elevation model SRTM v4.1 and terrestrial gravity data. The effects are computed at 1′X1′ grid size in the region. The largest effect is the topographic potential difference. It reaches a maximum of 19.0 cm with a standard deviation of 1.8 cm over the whole region. The gravity correction is smaller, but it still reaches a maximum of 3.0 cm with a standard deviation 0.3 cm for the whole region. The combined (ignored) effect ranges from -12.2 to 20.0 cm, with a standard deviation of 1.8 cm for the region. This numerical computation shows that the ignored terms must be taken into account for cm-geoid computation in mountainous regions.

How to cite: Wang, Y. M.: Effect of topographic potential difference and gravity correction on the geoid-quasigeoid separation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20380, https://doi.org/10.5194/egusphere-egu2020-20380, 2020.

EGU2020-11091 | Displays | G1.1

Development and evaluation of the xGEOID20 Digital Elevation Model at NGS

Jordan Krcmaric

G1.2 – Mathematical methods for the analysis of potential field data and geodetic time series

EGU2020-3566 | Displays | G1.2

Robust Mahalanobis-distance based spatial outlier detection on discrete GNSS velocity fields

Balint Magyar, Ambrus Kenyeres, Sandor Toth, and Istvan Hajdu

The GNSS velocity field filtering topic can be identified as a multi-dimensional unsupervised spatial outlier detection problem. In the discussed case, we jointly interpreted the horizontal and vertical velocity fields and its uncertainties as a six dimensional space. To detect and classify the spatial outliers, we performed an orthogonal linear transformation technique called Principal Component Analysis (PCA) to dynamically project the data to a lower dimensional subspace, while redacting the most (~99%) of the explained variance of the input data.

Therefore, the resulting component space can be seen as an attribute function, which describes the investigated deformation patterns. Then we constructed two subspace mapping functions, respectively the k-nearest neighbor (k-NN) and median based neighbor function with Haversine metric, and the samplewise comparison function which compares the samples with the properties of its k-NN environment. Consequently, the resulting comparison function scores highlights the significantly different observations as outliers. Assuming that the data comes from Multivariate Gaussian Distribution (MVD), we evaluated the corresponding Mahalanobis-distance with the estimation of the robust covariance matrix of the investigated area. Then, as the main result of the Robust Mahalanobis-distance (RMD) based approach, we implemented the binary classification via the p-value and critical Mahalanobis-distance thresholding.

Compared to the formerly investigated and applied One-Class Support Vector machine (OCSVM) approach, the RMD based solution gives ~ 17% more accurate results of the European scaled velocity field filtering (like EPN D1933), as well as it corrects the ambiguities and non-desired features (like overfitting) of the former OCSVM approach.

The results will be also presented as an interactive web page of the velocity fields of the latest version of EPN D2050 filtered with the introduced RMD approach.

How to cite: Magyar, B., Kenyeres, A., Toth, S., and Hajdu, I.: Robust Mahalanobis-distance based spatial outlier detection on discrete GNSS velocity fields , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3566, https://doi.org/10.5194/egusphere-egu2020-3566, 2020.

EGU2020-2101 | Displays | G1.2

Accuracy of GNSS campaign site velocities with respect to ITRF14 solution

Yener Turen and Dogan Ugur Sanli

In this study, we assess the accuracy of deformation rates produced from GNSS campaign measurements sampled in different frequencies. The ideal frequency of the sampling seems to be 1 measurement per month however it is usually found to be cumbersome. Alternatively the sampling was performed 3 measurements per year and time series analyses were carried out. We used the continuous GPS time series of JPL, NASA from a global network of the IGS to decimate the data down to 4 monthly synthetic GNSS campaign time series. Minimum data period was taken to be 4 years following the suggestions from the literature. Furthermore, the effect of antenna set-up errors in campaign measurements on the estimated trend was taken into account. The accuracy of deformation rates were then determined taking the site velocities from ITRF14 solution as the truth. The RMS of monthly velocities agreed pretty well with the white noise error from global studies given previously in the literature. The RMS of four monthly deformation rates for horizontal positioning were obtained to be 0.45 and 0.50 mm/yr for north and east components respectively whereas the accuracy of vertical deformation rates was found to be 1.73 mm/yr. This is slightly greater than the average level of the white noise error from a global solution previously produced, in which antenna set up errors were out of consideration. Antenna set up errors in campaign measurements modified the above error level to 0.75 and 0.70 mm/yr for the horizontal components north and east respectively whereas the accuracy of the vertical component was slightly shifted to 1.79 mm/yr.

How to cite: Turen, Y. and Sanli, D. U.: Accuracy of GNSS campaign site velocities with respect to ITRF14 solution , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2101, https://doi.org/10.5194/egusphere-egu2020-2101, 2020.

EGU2020-7110 | Displays | G1.2

Estimation of Vertical Land Motion at the Tide Gauges in Turkey

Muharrem Hilmi Erkoç, Uğur Doğan, Seda Özarpacı, Hasan Yildiz, and Erdinç Sezen

This study aims to estimate vertical land motion (VLM) at tide gauges (TG), located in the Mediterranean, Aegean and the Marmara Sea coasts of Turkey, from differences of multimission satellite altimetry and TG sea level time series. Initially, relative sea level trends are estimated at 7 tide gauges stations operated by the Turkish General Directorate of Mapping over the period 2001-2019. Subsequently, absolute sea level trends independent from VLM are computed from multimission satellite altimetry data over the same period. We have computed estimates of linear trends of difference time series between altimetry and tide gauge sea level after removing seasonal signals by harmonic analysis from each time series to estimate the vertical land motion (VLM) at tide gauges. Traditional way of VLM determination at tide gauges is to use GPS@TG or preferably CGPS@TG data. We therefore, processed these GPS data, collected over the years by several TG-GPS campaigns and by continuous GPS stations close to the TG processed by GAMIT/GLOBK software. Subsequently, the GPS and CGPS vertical coordinate time series are used to estimate VLM. These two different VLM estimates, one from GPS and CGPS coordinate time series and other from altimetry-TG sea level time series differences are compared.

 

Keywords: Vertical land motion, Sea Level Changes, Tide gauge, Satellite altimetry, GPS, CGPS

How to cite: Erkoç, M. H., Doğan, U., Özarpacı, S., Yildiz, H., and Sezen, E.: Estimation of Vertical Land Motion at the Tide Gauges in Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7110, https://doi.org/10.5194/egusphere-egu2020-7110, 2020.

EGU2020-5915 | Displays | G1.2

Arctic Ocean Sea Ice Area Extent Cyclicity and Non-Stationarity

Reginald Muskett and Syun-Ichi Akasofu

Arctic sea ice is a key component of the Arctic hydrologic cycle. This cycle is connected to land and ocean temperature variations and Arctic snow cover variations, spatially and temporally. Arctic temperature variations from historical observations shows an early 20th century increase (i.e. warming), followed by a period of Arctic temperature decrease (i.e. cooling) since the 1940s, which was followed by another period of Arctic temperature increase since the 1970s that continues into the two decades of the 21st century. Evidence has been accumulating that Arctic sea ice extent can experience multi-decadal to centennial time scale variations as it is a component of the Arctic Geohydrological System. 


We investigate the multi-satellite and sensor daily values of area extent of Arctic sea ice since SMMR on Nimbus 7 (1978) to AMSR2 on GCOM-W1 (2019). From the daily time series we use the first year-cycle as a wave-pattern to compare to all subsequent years-cycles through April 2020 (in progress), and constitute a derivative time series. In this time series we find the emergence of a multi-decadal cycle, showing a relative minimum during the period of 2007 to 2014, and subsequently rising. This may be related to an 80-year cycle (hypothesis). The Earth’s weather system is principally driven the solar radiation and its variations. If the multi-decadal cycle in Arctic sea ice area extent that we interpret continues, it may be linked physically to the Wolf-Gleissberg cycle, a factor in the variations of terrestrial cosmogenic isotopes, ocean sediment layering and glacial varves, ENSO and Aurora.

Our hypothesis and results give more evidence that the multi-decadal variation of Arctic sea ice area extent is controlled by natural physical processes of the Sun-Earth system. 

How to cite: Muskett, R. and Akasofu, S.-I.: Arctic Ocean Sea Ice Area Extent Cyclicity and Non-Stationarity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5915, https://doi.org/10.5194/egusphere-egu2020-5915, 2020.

EGU2020-1891 | Displays | G1.2

Hidden Magnetizations and Localization Constraints

Christian Gerhards

Recovering the full underlying magnetization from geomagnetic potential field measurements is known to be highly nonunique. Localization constraints on the magnetization can improve this to a certain extent. We present some analytic background as well as some examples on what is meant by 'to a certain extent'. In particular, if no constraints other than spatial localization are imposed, only two out of three components of the vectorial magnetization can be reconstructed uniquely. If it is additionally assumed that the magnetization is induced by an (unknown) ambient dipole field, then the susceptibility and the direction of the ambient dipole can be reconstructed.

How to cite: Gerhards, C.: Hidden Magnetizations and Localization Constraints, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1891, https://doi.org/10.5194/egusphere-egu2020-1891, 2020.

EGU2020-22224 | Displays | G1.2

Eigenvector Model Descriptors for the Seismic Inverse Problem

Florian Faucher, Otmar Scherzer, and Hélène Barucq

We consider the quantitative inverse problem for the recovery of subsurface Earth's properties, which relies on an iterative minimization algorithm. Due to the scale of the domains and lack of apriori information, the problem is severely ill-posed. In this work, we reduce the ill-posedness by using the ``regularization by discretization'' approach: the wave speed is described by specific bases, which limits the number of coefficients in the representation. Those bases are associated with the eigenvectors of a diffusion equation, and we investigate several choices for the PDE, that are extracted from the field of image processing. We first compare the efficiency of these model descriptors to accurately capture the variation with a minimal number of coefficients. In the context of sub-surface reconstruction, we demonstrate that the method can be employed to overcome the lack of low-frequency contents in the data. We illustrate with two and three-dimensional acoustic experiments.

How to cite: Faucher, F., Scherzer, O., and Barucq, H.: Eigenvector Model Descriptors for the Seismic Inverse Problem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22224, https://doi.org/10.5194/egusphere-egu2020-22224, 2020.

EGU2020-430 | Displays | G1.2

Gravity inversion with depth normalization

Lev Chepigo, Lygin Ivan, and Andrey Bulychev

Actually the most common method of gravity data interpretation is a manual fitting method. In this case, the density model is divided into many polygons with constant density and each polygon is editing manually by interpreter. This approach has two main disadvantages:

- significant amount of time is needed to build a high-quality density model;

- if density isn’t constant within anomalous object or a layer, object must be divided into many blocks, which requires additional time, and editing the model during the interpretation process becomes more complicated.

 To solve these problems, we can use methods of automatic fitting of the density model (inversion). At the same time, it is convenient to divide the model into many identical cells with constant density (grid). In this case, solving the inverse problem of gravity is reduced to solving a system of linear algebraic equations. To solve the system of equations, it is necessary to construct a loss function, which includes terms responsible for the difference between the observed gravitational field and the theoretical field, as well as for the difference between the model and a priori data (regularizer). Further, the problem is solved using iterative gradient optimization methods (gradient descent method, Newton's method and etc.).

However, in this case, the problem arises – final fitted model differs from the initial by contrasting near-surface layer due to the greater influence of the near-surface cells on the loss function, and the deep sources of gravity field anomalies are not included in inversion. Such models can be used in the processing of gravity data (source-based continuation, filtering), but are useless in solving of geological problems.

To take into account the influence of the deep cells of the model, the following solution is proposed: multiplying the gradient of the loss function by a normalization depth function that increases with depth. For example, such a function can be a quadratic function (its choice is conditioned by the fact that the gravity is inversely proportional to the square of the distance).

The use of inversion with a normalizing depth function allows solving the following problems:

- taking into account both surface and deep sources of gravity anomalies;

- solving the problem of taking into account the density gradient within the layers (since the layer is divided into many cells, the densities of which can be differen);

- reliably determine singular points of anomalous objects;

- significantly reduce the time of  the density model fitting.

How to cite: Chepigo, L., Ivan, L., and Bulychev, A.: Gravity inversion with depth normalization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-430, https://doi.org/10.5194/egusphere-egu2020-430, 2020.

EGU2020-3580 | Displays | G1.2

Sea floor topography modeling by cumulating different types of gravity information

Lucia Seoane, Benjamin Beirens, and Guillaume Ramillien

We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.

How to cite: Seoane, L., Beirens, B., and Ramillien, G.: Sea floor topography modeling by cumulating different types of gravity information, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3580, https://doi.org/10.5194/egusphere-egu2020-3580, 2020.

A fundamental problem in the geosciences is the downward continuation of the gravitational potential. It enables us to learn more about the system Earth and, in particular, the climate change.

Mathematically, we can model a (downward continued) signal in a 'best basis' consisting of local and global trial functions from a dictionary. In practice, our dictionaries include spherical harmonics, Slepian functions and radial basis functions. The expansion in dictionary elements is obtained by one of the Inverse Problem Matching Pursuit (IPMP) algorithms.

However, it remains to discuss the choice of the dictionary. For this, we further developed the IPMP algorithms by introducing a learning technique. With this approach, they automatically select a finite number of optimized dictionary elements from infinitely many possible ones. We present the details of our method and give numerical examples.

See also: V. Michel and N. Schneider, A first approach to learning a best basis for gravitational field modelling, arxiv: 1901.04222v2

How to cite: Schneider, N. and Michel, V.: Dictionary learning algorithms for the downward continuation of the gravitational potential, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2367, https://doi.org/10.5194/egusphere-egu2020-2367, 2020.

EGU2020-2692 | Displays | G1.2

Fast determination of surface water mass changes using regional orthogonal functions

Guillaume Ramillien and Lucia Seoane

Approaches based on Stokes coefficient filtering and « mass concentration » representations have been proposed for recovering changes of the surface water mass density from along-track accurate GRACE K-Band Range Rate (KBRR) measurements of geopotential change. The number of parameters, i.e. surface triangular tiles of water mass, to be determined remains large and the choice of the regularization strategy as the gravimetry inverse problem is non unique. In this study, we propose to use regional sets of orthogonal surface functions to image the structure of the surface water mass density variations. Since the number of coefficients of the development is largely smaller than the number of tiles, the computation of daily GRACE solutions for continental hydrology, e.g. obtained by Extended Kalman Filtering (EKF), is greatly fastened and eased by the matrix dimensions and conditioning. The proposed scheme of decomposition is applied to the African continent where it enables to very localized sources of (sub-)monthly water mass amplitudes.

How to cite: Ramillien, G. and Seoane, L.: Fast determination of surface water mass changes using regional orthogonal functions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2692, https://doi.org/10.5194/egusphere-egu2020-2692, 2020.

The objective of this study is the combination of different types of basis functions applied separately to different kinds of gravity observations. We use two types of regional data sets: terrestrial gravity data and airborne gravity data, covering an area of about 500 km × 800 km in Colorado, USA. These data are available within the “1 cm geoid experiment” (also known as the “Colorado Experiment”). We apply an approach for regional gravity modeling based on series expansions in terms of spherical radial basis functions (SRBF). Two types of basis functions covering the same spectral domain are used, one for the terrestrial data and another one for the airborne measurements. To be more specific, the non-smoothing Shannon function is applied to the terrestrial data to avoid the loss of spectral information. The Cubic Polynomial (CuP) function is applied to the airborne data as a low-pass filter, and the smoothing features of this type of SRBF are used for filtering the high-frequency noise in the airborne data. In the parameter estimation procedure, these two modeling parts are combined to calculate the quasi-geoid.

The performance of our regional quasi-geoid model is validated by comparing the results with the mean solution of independent computations delivered by fourteen institutions from all over the world. The comparison shows that the low-pass filtering of the airborne gravity data by the CuP function improves the model accuracy by 5% compared to that using the Shannon function. This result also makes evident the advantage of combining different SRBFs covering the same spectral domain for different types of observations.

How to cite: Liu, Q., Schmidt, M., and Sánchez, L.: The use of different spherical radial basis functions to combine terrestrial and airborne measurements for regional gravity field refinement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9565, https://doi.org/10.5194/egusphere-egu2020-9565, 2020.

EGU2020-11745 | Displays | G1.2

Using spherical scaling functions in scalar and vector airborne gravimetry

Vadim Vyazmin and Yuri Bolotin

Airborne gravimetry is capable to provide Earth’s gravity data of high accuracy and spatial resolution for any area of interest, in particular for hard-to-reach areas. An airborne gravimetry measuring system consists of a stable-platform or strapdown gravimeter, and GNSS receivers. In traditional (scalar) airborne gravimetry, the vertical component of the gravity disturbance vector is measured. In actively developing vector gravimetry, all three components of the gravity disturbance vector are measured.

In this research, we aim at developing new postprocessing algorithms for estimating gravity from airborne data taking into account a priori information about spatial behavior of the gravity field in the survey area. We propose two algorithms for solving the following two problems:

1) In scalar gravimetry:  Mapping gravity at the flight height using the gravity disturbances estimated along the flight lines (via low-pass or Kalman filtering), taking into account spatial correlation of the gravity field in the survey area and statistical information on the along-line gravity estimate errors.

2) In vector gravimetry:  Simultaneous determination of three components of the gravity disturbance vector from airborne measurements at the flight path.

Both developed algorithms use an a priori spatial gravity model based on parameterizing the disturbing potential in the survey area by three-dimensional harmonic spherical scaling functions (SSFs). The algorithm developed for solving Problem 1 provides estimates of the unknown coefficients of the a priori gravity model using a least squares technique. Due to the assumption that the along-line gravity estimate errors at any two lines are not correlated, the algorithm has a recursive (line-by-line) implementation. At the last step of the recursion, regularization is applied due to ill-conditioning of the least squares problem. Numerical results of processing the GT-2A airborne gravimeter data are presented and discussed.

To solve Problem 2, one need to separate the gravity horizontal component estimates from systematic errors of the inertial navigation system (INS) of a gravimeter (attitude errors, inertial sensor bias). The standard method of gravity estimation based on gravity modelling over time is not capable to provide accurate results, and additional corrections should be applied. The developed algorithm uses a spatial gravity model based on the SSFs. The coefficients of the gravity model and the INS systematic errors are estimated simultaneously from airborne measurements at the flight path via Kalman filtering with regularization at the last time moment. Results of simulation tests show a significant increase in accuracy of gravity vector estimation compared to the standard method.

This research was supported by RFBR (grant number 19-01-00179).

How to cite: Vyazmin, V. and Bolotin, Y.: Using spherical scaling functions in scalar and vector airborne gravimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11745, https://doi.org/10.5194/egusphere-egu2020-11745, 2020.

For the quasi-geoid determination by 3-D Least Squares Collocation (LSC) in the context of Molodensky’s approach, there is no need to measured or modelled vertical gravity gradient (VGG) as the 3-D LSC takes the varying heights of the gravity observation points into account. However, the use of measured or modelled VGG instead of the thereotical value is expected to improve the quasigeoid-geoid separation term particularly in mountainous areas. The VGG measurements are found to be different from the theoretical value in the range of - % 25 and + % 39 in western Turkey. Previously there has been no study using modelled VGGs for gravimetric geoid modelling in Turkey. VGGs are modelled by 3-D Least Squares Collocation (LSC) in remove-restore approach and validated by terrestrial VGG measurements in western Turkey. The effect of using modelled VGG instead of the theoretical one in quasigeoid-to-geoid separation term is found to be significant. The quasi-geoid computed by 3-D LSC in western Turkey is converted to geoids using theoretical or modelled VGG values and compared with GPS/levelling geoid-undulations.

 

How to cite: Ahi, G., Akdoğan, Y. A., and Yıldız, H.: Vertical Gravity Gradient Modeling by 3-D Least Squares Collocation and its impact on quasigeoid-geoid separation term , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-680, https://doi.org/10.5194/egusphere-egu2020-680, 2020.

 Uncertainties usually exist in the process of acquisition of measurement data, which affect the results of the parameter estimation. The solution of the uncertainty adjustment model can effectively improve the validity and reliability of parameter estimation. When the coefficient matrix of the observation equation has a singular value close to zero, i.e., the coefficient matrix is ill-posed, the ridge estimation can effectively suppress the influence of the ill-posed problem of the observation equation on the parameter estimation. When the uncertainty adjustment model is ill-posed, it is more seriously affected by the error of the coefficient matrix and observation vector. In this paper, the ridge estimation method is applied to ill-posed uncertainty adjustment model, deriving an iterative algorithm to improve the stability and reliability of the results. The derived algorithm is verified by two examples, and the results show that the new method is effective and feasible.

How to cite: lu, T.: Ridge estimation iterative algorithm to ill-posed uncertainty adjustment model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18906, https://doi.org/10.5194/egusphere-egu2020-18906, 2020.

G1.3 – High-precision GNSS: methods, open problems and Geoscience applications

EGU2020-1810 | Displays | G1.3 | Highlight

Instantaneous Ambiguity Resolved GLONASS FDMA Attitude Determination

Peter Teunissen, Amir Khodabandeh, and Safoora Zaminpardaz

G1 – Geodetic Theory and Algorithms

G1.3 High-precision GNSS: methods, open problems and Geoscience applications

 

Instantaneous Ambiguity Resolved GLONASS FDMA Attitude Determination

 

PJG Teunissen1,2, A. Khodabandeh3, S. Zaminpardaz4

1GNSS Research Centre, Curtin University, Perth, Australia

2Geoscience and Remote Sensing, Delft University of Technology, The Netherlands

3University of Melbourne, Melbourne, Australia

4RMIT University, Melbourne, Australia

 

In [1] a new formulation of the double-differenced (DD) GLONASS FDMA model was introduced. It closely resembles that of CDMA-based systems and it guarantees the estimability of the newly defined GLONASS ambiguities. The close resemblance between the new GLONASS FDMA model and the standard CDMA-models implies that available CDMA-based GNSS software is easily modified [2] and that existing methods of integer ambiguity resolution can be directly applied. Due to its general applicability, we believe that the new model opens up a whole variety of carrier-phase based GNSS applications that have hitherto been a challenge for GLONASS ambiguity resolution [3]

We provide insight into the ambiguity resolution capabilities of the new GLONASS FDMA model, combine it with next-generation GLONASS CDMA signals [4] and demonstrate it for remote sensing platforms that require single-epoch, high-precision direction finding. This demonstration will be done with four different, instantaneous baseline estimators: (a) unconstrained, ambiguity-float baseline, (b) length-constrained, ambiguity-float baseline, (c) unconstrained, ambiguity-fixed baseline, and (d) length-constrained, ambiguity-fixed baseline. The unconstrained solutions are computed with the LAMBDA method, while the constrained ambiguity solutions with the C-LAMBDA method, thereby using the numerically efficient bounding-function formulation of [5]. The results will demonstrate that with the new model, GLONASS-only direction finding is instantaneously possible and that the model and associated method therefore holds great potential for array-based attitude determination and array-based precise point positioning.

 

[1] P.J.G. Teunissen (2019): A New GLONASS FDMA Model, GPS Solutions, 2019, Art 100.

[2] A. Khodabandeh and P.J.G. Teunissen (2019): GLONASS-L. MATLAB code archived in GPSTOOLBOX:

https://www.ngs.noaa.gov/gps-toolbox/GLONASS-L.htm

[3] R. Langley (2017): GLONASS: Past, present and future. GPS World November 2017, 44-48.

[4] S. Zaminpardaz, P.J.G. Teunissen and N. Nadarajah (2017): GLONASS CDMA L3 ambiguity resolution

and positioning, GPS Solutions, 2017, 21(2), 535-549.

[5] P.J.G. Teunissen PJG (2010): Integer least-squares theory for the GNSS compass. Journal of Geodesy, 84:433–447

 

Keywords: GNSS, GLONASS, FDMA, CDMA model, Instantaneous Attitude Determination, Integer Ambiguity Resolution

How to cite: Teunissen, P., Khodabandeh, A., and Zaminpardaz, S.: Instantaneous Ambiguity Resolved GLONASS FDMA Attitude Determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1810, https://doi.org/10.5194/egusphere-egu2020-1810, 2020.

EGU2020-18142 | Displays | G1.3

CODE IGS reference products including Galileo

Lars Prange, Arturo Villiger, Stefan Schaer, Rolf Dach, Dmitry Sidorov, Adrian Jäggi, and Gerhard Beutler

The International GNSS service (IGS) has been providing precise reference products for the Global Navigation Satellite Systems (GNSS) GPS and (starting later) GLONASS since more than 25 years. These orbit, clock correction, coordinate reference frame, troposphere, ionosphere, and bias products are freely distributed and widely used by scientific, administrative, and commercial users from all over the world. The IGS facilities needed for data collection, product generation, product combination, as well as data and product dissemination, are well established. The Center for Orbit Determination in Europe (CODE) is one of the Analysis Centers (AC) contributing to the IGS from the beginning. It generates IGS products using the Bernese GNSS Software.

 

In the last decade new GNSS (European Galileo and Chinese BeiDou) and regional complementary systems to GPS (Japanese QZSS and Indian IRNSS/NAVIC) were deployed. The existing GNSS are constantly modernized, offering - among others - more stable satellite clocks and new signals. The exploitation of the new data and their integration into the existing IGS infrastructure was the goal of the Multi-GNSS EXtension (MGEX) when it was initiated in 2012. CODE has been participating in the MGEX with its own orbit and clock solution from the beginning. Since 2014 CODE’s MGEX (COM) contribution considers five GNSS, namely GPS, GLONASS, Galileo, BeiDou2 (BDS2), and QZSS. We provide an overview of the latest developments of the COM solution with respect to processing strategy, orbit modelling, attitude modelling, antenna calibrations, handling of code and phase biases, and ambiguity resolution. The impact of these changes on the COM products will be discussed.

 

Recent assessment showed that especially the Galileo analysis within the MGEX has reached a state of maturity, which is almost comparable to GPS and GLONASS. Based on this finding the IGS decided to consider Galileo in its third reprocessing campaign, which will contribute to the next ITRF. Recognizing the demands expressed by the GNSS community, CODE decided in 2019 to go a step further and consider Galileo also in its IGS RAPID and ULTRA-RAPID reference products. We summarize our experiences from the first months of triple-system (ULTRA)-RAPID analysis including GPS, GLONASS, and Galileo. Finally we provide an outlook of CODE’s IGS analysis with the focus on the new GNSS.

How to cite: Prange, L., Villiger, A., Schaer, S., Dach, R., Sidorov, D., Jäggi, A., and Beutler, G.: CODE IGS reference products including Galileo, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18142, https://doi.org/10.5194/egusphere-egu2020-18142, 2020.

EGU2020-1000 | Displays | G1.3

Geocenter coordinates and Earth rotation parameters from GPS-only, GLONASS-only, Galileo-only, and the combined GPS+GLONASS+Galileo solutions

Krzysztof Sośnica, Radosław Zajdel, Grzegorz Bury, Dariusz Strugarek, and Kamil Kaźmierski

The European GNSS – Galileo can be considered as fully serviceable with 24 active satellites in space since late 2018. Galileo satellites have a different revolution period than that of GPS and GLONASS, and moreover, two additional Galileo satellites are orbiting in an eccentric orbit which helps to decorrelate some global geodetic parameters.

This contribution shows the results from Galileo-only, GPS-only, GLONASS-only, and the combined multi-GNSS solutions with a focus on Earth rotation parameters and geocenter coordinates based on the 3-year solution. We discuss the system-specific issues in individual GNSS-derived series and resonances between satellite revolution periods and Earth rotation. We found that the Galileo-based and GLONASS-based parameters are inherently influenced by the spurious signals at the frequencies which arise from the combination of the satellite revolution period and the Earth’s rotation, e.g. 3.4 days for Galileo and 3.9 days for GLONASS. On the other hand, we observe a systematic drift of GPS-based UT1-UTC values with a magnitude of 8.1 ms/year which is due to the revolution period of the GPS satellites which is equal to half of the sidereal day and causes a deep resonance. For Galileo, the UT1-UTC drift is sixteen times smaller than that of GPS and equals just 0.5 ms/year. GLONASS-derived pole coordinates and geocenter coordinates show large spurious offsets with respect GPS and Galileo solutions, as well as with respect to the IERS-C04-14 series and Satellite Laser Ranging data. GLONASS-specific problems can be partially reduced by applying a box-wing orbit model and by reducing the number of estimated empirical orbit parameters. The quality of Galileo-derived geocenter coordinates is comparable to the GPS-based results. The Galileo-derived polar motion is affected by systematic errors in receiver and satellite antenna offsets. The best results of geocenter coordinates and Earth rotation parameters can be obtained from the combined GPS+Galileo+GLONASS solutions, however, some system-specific issues still remain in the combination.

 

How to cite: Sośnica, K., Zajdel, R., Bury, G., Strugarek, D., and Kaźmierski, K.: Geocenter coordinates and Earth rotation parameters from GPS-only, GLONASS-only, Galileo-only, and the combined GPS+GLONASS+Galileo solutions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1000, https://doi.org/10.5194/egusphere-egu2020-1000, 2020.

EGU2020-1668 | Displays | G1.3

Resolving millimeter-level storm surge loading deformations using multi-GNSS data over the subdaily timescales

Jianghui Geng, Shaoming Xin, and Simon Williams

Storm surges often strike the southern coast of North Sea in Europe during the winter season. The largest event on December 5-6, 2013 since 1953 pushed the water level to rise by up to 4 m within a few hours, which caused a transient but appreciable loading on the crust under the southern North Sea. Consequently, GNSS stations around this oceanic area experienced considerable displacements, which were up to 30 mm in the vertical while 5 mm in the horizontal component as predicted by the Proudman Oceanographic Laboratory Storm Surge Model (POLSSM). We processed the GPS/GLONASS data at 18 coastal stations from Nov. 1 until Dec. 31, 2013. We computed station displacements using precise point positioning ambiguity resolution every three hours to track subdaily loading deformations, and compared them with POLSSM predictions. The second- and third-order delays were mitigated using IGS global ionosphere map derived corrections; orbital repeat time (ORT) filtering, which aimed at reducing multipath effects, were enabled for both GPS and GLONASS on the observation level. We found that GNSS derived displacements presented high correlations of up to 0.7 with POLSSM predictions in the vertical direction over the 61 days; higher-order ionosphere corrections reduced the north RMS between GNSS solutions and POLSSM predictions by 0.2-0.3 mm, whereas the ORT filtering decreased the RMS by more than 10% for all three components. Introducing GLONASS data to GPS-only solutions further reduced the RMS to 5.9, 2.2 and 2.7 mm in the vertical, east and north components, suggesting a 6-12% improvement. Despite this millimeter-level agreement, the peak-to-peak vertical displacement of about 10 mm over the 6–24-h timescales for the largest surge event on December 5 was only marked marginally in the subdaily wavelet power spectra. Thanks to the spatial coherence among the 18 stations, the principal component analysis could enhance dramatically the resolution capability of subdaily GNSS in discriminating the subdaily vertical loading signals of 5-10 mm amplitude over the 6–24-h wavelet timescales. We demonstrate that multi-GNSS data have the potential to improve significantly the detection of subdaily geophysical signals dwelling on the periods of tens of minutes to hours.

How to cite: Geng, J., Xin, S., and Williams, S.: Resolving millimeter-level storm surge loading deformations using multi-GNSS data over the subdaily timescales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1668, https://doi.org/10.5194/egusphere-egu2020-1668, 2020.

EGU2020-3014 | Displays | G1.3

Efficient multi-GNSS processing based on raw observations from large global station networks

Sebastian Strasser and Torsten Mayer-Gürr

The year 2020 is going to mark the first time of four global navigation satellite systems (i.e., GPS, GLONASS, Galileo, and BeiDou) in full operational capability. Utilizing the various available observation types together in global multi-GNSS processing offers new opportunities, but also poses many challenges. The raw observation approach facilitates the incorporation of any undifferenced and uncombined code and phase observation on any frequency into a combined least squares adjustment. Due to the increased number of observation equations and unknown parameters, using raw observations directly is more computationally demanding than using, for example, ionosphere-free double-differenced observations. This is especially relevant for our contribution to the third reprocessing campaign of the International GNSS Service, where we process observations from up to 800 stations per day to three GNSS constellations at a 30-second sampling. For a single day, this results in more than 200 million raw observations, from which we estimate almost 5 million parameters.

Processing such a large number of raw observations together is computationally challenging and requires a highly optimized processing chain. In this contribution, we detail the key steps that make such a processing feasible in the context of a distributed computing environment (i.e., large computer clusters). Some of these steps are the efficient setup of observation equations, a suitable normal equation structure, a sophisticated integer ambiguity resolution scheme, automatic outlier downweighting based on variance component estimation, and considerations regarding the estimability of certain parameter groups.

How to cite: Strasser, S. and Mayer-Gürr, T.: Efficient multi-GNSS processing based on raw observations from large global station networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3014, https://doi.org/10.5194/egusphere-egu2020-3014, 2020.

EGU2020-6685 | Displays | G1.3

GLONASS R720 transmit power loss

Peter Steigenberger, Steffen Thölert, Gerardo Allende-Alba, and Oliver Montenbruck

All GLONASS satellites transmit navigation signals in the L1 and L2 frequency band whereas newer generations (M+ and K1) also utilize the L3 band. Previous studies have shown that the transmit power in the individual frequency bands can significantly differ for dedicated satellites. These differences are visible in the carrier-to-noise density ratio (C/N0) of geodetic GNSS receivers and can be measured with a high-gain antenna. Whereas C/N0 allows for a continuous monitoring, high-gain antenna measurements are only performed on an irregular basis.

In April 2019, a drop in C/N0 could be observed for the GLONASS-M satellite R720. Measurements of the R720 equivalent isotropically radiated power (EIRP) with the 30 m high-gain antenna of the German Aerospace Center show a reduction by up to 9 dB for L1 and 1.5 dB for L2 compared to earlier measurements obtained in June 2017. The 2019 EIRP measurements also show an asymmetry of ascending and descending arcs that was not present before the power loss and indicate a change in the apparent gain pattern of the R720 transmit antenna. The transmit power change is accompanied by discontinuities in the estimated satellite antenna phase center offsets (PCOs) by about 15 cm in the transmit antenna plane and inter-frequency differential code biases (DCBs) by up 0.6 ns. Several GLONASS PCO and DCB changes were already reported by Dach et al. (2019) but they could not show a direct relation to transmit power changes.

This contribution analyzes the impact of the R720 transmit power loss on C/N0 and high gain antenna measurements as well as PCO and DCB estimates. The current transmit antenna gain pattern is reconstructed based on repeated high-gain antenna measurements. Differential gain pattern are obtained from C/N0 measurements of geodetic receivers and low-gain GNSS antennas before and after April 2019. Furthermore, the impact on precise orbit determination is evaluated as transmit power affects the modeling of antenna thrust.

How to cite: Steigenberger, P., Thölert, S., Allende-Alba, G., and Montenbruck, O.: GLONASS R720 transmit power loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6685, https://doi.org/10.5194/egusphere-egu2020-6685, 2020.

EGU2020-5255 | Displays | G1.3

Multi-GNSS PPP instantaneous ambiguity resolution with precise atmospheric corrections augmentation

Jiaxin Huang, Xin Li, Hongbo Lv, and Yun Xiong

The performance of precise point positioning (PPP) can be significantly improved with multi-GNSS observations, but it still needs more than ten minutes to obtain positioning results at centimeter-level accuracy. In order to shorten the initialization time and improve the positioning accuracy, we develop a multi-GNSS (GPS + GLONASS + Galileo + BDS) PPP method augmented by precise atmospheric corrections to achieve instantaneous ambiguity resolution (IAR). In the proposed method, regional augmentation corrections including precise atmospheric corrections and satellite uncalibrated phase delays (UPDs) are derived from PPP fixed solutions at reference network and provided to user stations for correcting the dual-frequency raw observations. Then the regional augmentation corrections from nearby reference stations are interpolated on the client through a modified linear combination method (MLCM). With the corrected observations, IAR can be achieved with centimeter-level accuracy. This method is validated experimentally with Hong Kong CORS network, and the results indicate that multi-GNSS fusion can improve the performance in terms of both positioning accuracy and reliability of AR. The percentage of IAR for multi-GNSS solutions is up to 99.7%, while the percentage of GPS-only solutions is 88.7% when the cut-off elevation angle is 10°. The benefit of multi-GNSS fusion is more significant with high cut-off elevation angle. The percentage of IAR can be still above 98.4% for multi-GNSS solutions while the result of GPS-only solutions is below 43.5% when the cut-off elevation angle reaches 30°.  The positioning accuracy of multi-GNSS solutions is improved by 30.0% on the horizontal direction (0.7 cm) and 17.1% on the vertical direction (2.9 cm) compared to GPS-only solutions.

How to cite: Huang, J., Li, X., Lv, H., and Xiong, Y.: Multi-GNSS PPP instantaneous ambiguity resolution with precise atmospheric corrections augmentation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5255, https://doi.org/10.5194/egusphere-egu2020-5255, 2020.

EGU2020-12206 | Displays | G1.3

Time Synchronization Method Based on Real-Time Precise Point Positioning

Daqian Lyu, Tianbao Dong, Fangling Zeng, and Xiaofeng Ouyang

Precise point positioning (PPP) technique is an effective tool for time and frequency applications. Using phase/code observations and precise products, the PPP time transfer allows an accuracy of sub-nanoseconds within a latency of several days. Although the PPP time transfer is usually implemented in the post-processing mode, using the real-time PPP (RT-PPP) technique for time transfer with the shorter latency remains attractive to time community. In 2012, the IGS (International GNSS Service) launched an open-access real-time service (RTS) project, broadcasting satellite orbit and clock corrections on the Internet, which enables PPP time transfer in the real-time mode. In this contribution, we apply the RT-PPP for high-precision time transfer and synchronization. The GNSS receiver is required to be equipped with an atomic clock as the external local clock. We use the RT-PPP technique to compute the receiver clock offset with respective to the GNSS time scale. On the basis of clock offsets, we steer the local clock by frequency adjustment method. In this way, all the local clocks are synchronized to the GNSS time scale, making local clocks synchronized with each other.

The time scales of the RTS products are evaluated at first. Six kinds of the RTS products (IGS01, CLK10, CLK53, CLK80 and CLK93) on DOY220-247, 2019 are pre-saved to compute the receiver clock offsets. The clock offset with respect to the GPST (GPS Time) obtained from the IGS final product is applied as the reference. The standard deviations (STDs) of the clock offsets with respect to the reference are 0.63, 1.76, 0.28, 0.27 and 1.28 ns for IGS01, CLK10, CLK53, CLK80 and CLK93, respectively.

Finally, we set up a hardware system to examine the validity of our time synchronization method. The baseline of the time synchronization experiment is about 5 m. The synchronization error of the 1 PPS outputs is precisely measured by the frequency counter. The STD of the 4-days results is about 0.48 ns. The peak-to-peak value of the synchronization error is about 2.5 ns.

How to cite: Lyu, D., Dong, T., Zeng, F., and Ouyang, X.: Time Synchronization Method Based on Real-Time Precise Point Positioning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12206, https://doi.org/10.5194/egusphere-egu2020-12206, 2020.

Strain rate fields within strike-slip regimes often possess complexity associated with along-strike  slip  rate  variations.  These along-strike  slip  rate  variations  produce dilatational  components  of  strain  rate  within  and  near  the  fault  zones  and  within  the adjacent block areas. These dilatation rates do not directly reflect the slip rate magnitude on the strike  slip  fault,  but  rather  the  relative  change in  along-strike  slip  rate.  Displacement rates measured  using  GPS  observations  reflect  the  full  deformation  gradient  field,  which may involve significant dilatational components and other off-fault deformation. Thus, using displacement rates  to  infer  slip  rate  and  locking  depth  of  major  strike-slip  faults  may introduce  errors  when  along-strike  slip  rate  variations  are  present.  On the  contrary,  true locking depth and slip rate can be obtained from the pure strike-slip component of shear strain rates. In this study we investigate the use of shear strain rates alone (obtained from the full displacement rate field of the SCEC 4.0 velocity field in southern California) to infer fault slip rate and locking depth parameters along the San Andreas (up to 37° N) as well as the San Jacinto fault zones. Such an  analysis is  critical  for  accurate  estimation  of  off-fault  strain  rates  outside  of  the major shear zones.

We conducted benchmarking tests to determine if accurate shear strain rates  can  be  obtained  from  a  synthetic  fault  slip  rate  field  possessing  the  same  station spacing as the SCEC 4.0 dataset. The synthetics were derived using Okada’s [1992] elastic dislocation routine (Coulomb  3.2).  These displacement  rates  were  interpolated  using  bi-cubic  Bessel  interpolation  to  infer the full  horizontal  velocity  gradient  tensor  field,  along with model uncertainties.  To test realistic conditions, along-strike slip  rates were put into the elastic dislocation model and model displacements were output at the true GPS station spacing in southern California from the SCEC 4.0 dataset. The modeled strain rate field shows negligible strain rate artifacts in most regions and both the shear strain and dilatation rates obtained  from  the  bi-cubic interpolation  were  well-resolved.  The inferred shear strain rate field was then  inverted, using a simple screw dislocation  forward model  for the best-fit  fault location,  fault locking depth,  and  fault  slip  rate.  Model parameter estimates were well resolved,  both  near  and away from fault slip rate transitions (± 1 km for fault locking depth; ± 1-2 mm/yr for fault slip rate). Test results to date show the method can resolve slip rates and locking depth within the zones of along-strike transition. Results to date from this methodology applied to southern California using the SCEC 4.0 GPS velocity field show  remarkably  well-resolved  and  prominent  shear  strain  rate  bands  that follow  both  the San Andreas and San  Jacinto  fault  systems.   The shear strain rates  reflect dramatic  along-strike  slip  rate  variations,  found  in  many  previous  studies.  However, fault locking depths are generally shallower than previously published results. Residual off-fault strain rates, not associated with the major strike-slip faults, appear to accommodate ~30% of the total Pacific-North American plate relative motion.

How to cite: Campbell, L., Holt, W., and Chen, Y.: Using GPS Derived Shear Strain Rates in Southern California to Constrain Fault Slip Rate, Locking Depth, and Residual Off-Fault Strain Rates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21179, https://doi.org/10.5194/egusphere-egu2020-21179, 2020.

EGU2020-21260 | Displays | G1.3

Spatial variations of stochastic noise properties of GNSS time series

Rui Fernandes, Xiaoxing He, Jean-Philippe Montillet, Machiel Bos, Tim Melbourne, Weiping Jiang, and Feng Zhou

The analysis of daily position Global Navigation Satellite System (GNSS) time series provides information about various geophysical processes that are shaping the Earth’s crust. The goodness of fit of a trajectory model to these observations is an indication of our understanding of these phenomena. However, the fit also depends on the noise levels in the time series and in this study we investigate for 568 GNSS stations across North America the noise properties, its relation with the choice of trajectory model and if there exists a relationship with the type of monuments. We use the time series of two processing centers, namely the Central Washington University (CWU) and the New Mexico Tech (NMT), which process the data using two different complete processing strategies.

We demonstrate that mismodelling slow slip events within the geodetic time series increases the percentage of selecting the Random-Walk + Flicker + White noise (RW+FN+WN) as the optimal noise model for the horizontal components, especially when the Akaike Information Criterion is used. Furthermore, the analysis of the spatial distribution of the RW component (in the FN+WN+RW) around North America takes place at stations mostly localised around tectonic active areas such as the Cascadia subduction zone (Pacific Northwest) or the San Andreas fault (South California) and coastal areas. It is in these areas that most shallow and drilled-braced monuments are also located. Therefore, the comparison of monument type with observed noise level should also take into account its location which mostly has been neglected in previous studies. In addition, the General Gauss-Markov (GGM) with white noise (GGM+WN) is often selected for the Concrete Pier monument especially on the Up component which indicates that the very long time series are experiencing this flattening of the power spectrum at low frequency. Finally, the amplitude of the white noise is larger for the Roof-Top/Chimney (RTC) type than for the other monument’s types. With a varying seasonal signal computed using a Wiener filter, the results show that RTC monuments have larger values in the East and North components, whereas the deep-drilled brace monuments have larger values on the vertical component.

How to cite: Fernandes, R., He, X., Montillet, J.-P., Bos, M., Melbourne, T., Jiang, W., and Zhou, F.: Spatial variations of stochastic noise properties of GNSS time series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21260, https://doi.org/10.5194/egusphere-egu2020-21260, 2020.

The VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm has been successfully applied to TIDs (Travelling ionospheric disturbances) detection in several real-time scenarios [1, 2]. VARION, thus, estimates sTEC (slant total electron content) variations starting from the single time differences of geometry-free combinations of GNSS carrier-phase measurements. This feature makes VARION suitable to also leverage GNSS observations coming from moving receivers such as ship-based GNSS receivers: the receiver motion does not affect the sTEC estimation process.

The aim of this work is to use the observations coming from two GNSS receivers installed on a ship moving near Kauai Island in the Hawaiian archipelago to detect the TIDs connected to the 2010 Maule earthquake and tsunami [3]. Indeed, this earthquake triggered a tsunami that affected all the Pacific region and that reached the Hawaiian islands after about 15 hours. All our analysis was carried out in post-processing, but simulated a real-time scenario: only the data available in real time were used.

In order to get a reference, the ship-based sTEC variations were compared with the ones coming from GNSS permanent stations situated in the Hawaiian Islands. In particular, if we considered the same satellite, the same TID is detected by both ship and ground receivers. As expected, the ship-based  sTEC variations are a little bit noisier since they are coming from a kinematic platform.

Hence, the results, although preliminary, are very encouraging: the same TIDs is detected both from the sea (ships) and land (permanent receivers).  Therefore, the VARION algorithm is also able to leverage observations coming from ship-based GNSS receivers to detect TIDs in real-time.

In conclusion, we firmly believe that the application of VARION to observation coming from ship-based GNSS receivers could really represent a real-time and cost-effective tool to enhance tsunami early warning systems, without requiring the installation of complex infrastructures in open sea.

References

[1] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, “Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, ”Scientific reports, vol. 7, pp. 46607, 2017.

[2] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, “Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,”Remote Sensing, vol. 11, no. 14, pp. 1734, 2019

[3] https://earthquake.usgs.gov/earthquakes/eventpage/official20100227063411530_30/executive

How to cite: Ravanelli, M. and Foster, J.: Detection of tsunami induced ionospheric perturbation with ship-based GNSS measurements: 2010 Maule tsunami case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11583, https://doi.org/10.5194/egusphere-egu2020-11583, 2020.

EGU2020-15474 | Displays | G1.3

Fusion applied to phase altimetry in a GNSS buoy system

Williams Kouassi, Georges Stienne, and Serge Reboul

It has been shown that the earth surface can be observed using Global Navigation Satellite System (GNSS) signals as signals of opportunity. An important advantage of GNSS in this regard is that it provides a global coverage of the earth thanks to dozens of satellites, projected to be 120 by 2030, distributed in various constellations.

GNSS signals parameters such as the carrier phase and the amplitude can be used for example for soil moisture estimation, sea ice detection or sea surface altimetry, which is an important indicator for studying climate evolution. As the sea level varies in centimeters, sea surface altimeters have to be very precise. This accuracy can be achieved using satellite altimeters, provided the availability of precise validation and calibration techniques and in-situ experiments. The objective of this study is the definition of an original GNSS buoy system for satellite altimeters calibration.

GNSS buoy systems are a cheap and light alternative solution to mareographs and can provide high rate measurements. In our approach using this system, we consider, as observable, the phase difference between incoming GPS-L1 signals at a reference, fixed antenna at ~10m height on the ground and at a buoy antenna on the sea. In an analogy with a GNSS reflectometry system, the buoy can be compared to a specular reflection point, but presents the advantage of collecting the data from all visible satellites at the same location. The signals sensed by both antennas are digitized before processing.

Assuming that the horizontal two-dimensions position of the buoy is accurately known by GNSS positioning (which is more efficient in these dimensions than for estimating the height of the buoy), a new phase observable evolving linearly in the [-π , π] interval as a function of the sine of the satellite elevation can be defined. The slope of this linear evolution is proportional to the height between the two antennas, which is the parameter to estimate. For accuracy and robustness purpose, the estimation of this slope is realized using a circular-linear regression technique that includes the fusion of the data from all visible satellites signals. Indeed, we can show that, using the full span of the sines of visible satellites elevations, centimeter accuracy can be reached for integration times as short as a few milliseconds. The GNSS buoy technique described in this work is evaluated on synthetic and real data.

How to cite: Kouassi, W., Stienne, G., and Reboul, S.: Fusion applied to phase altimetry in a GNSS buoy system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15474, https://doi.org/10.5194/egusphere-egu2020-15474, 2020.

EGU2020-18035 | Displays | G1.3

Coherent GNSS reflections over the sea surface - A classification for reflectometry

Maximilian Semmling, Sebastian Gerland, Thomas Gerber, Markus Ramatschi, Galina Dick, Jens Wickert, and Mainul Hoque

The exploitation of GNSS signals for reflectometry opens several fields of application over the ocean, land and in the cryosphere. Coherence of the reflection allows precise measurements of the carrier phase and signal amplitude for accurate sea surface altimetry and sea ice characterisation. A coherence condition can be set by a threshold of the signal-to-noise power ratio (SNR). Previous simulations suggest that an SNR > 30 dB will ensure a coherent processing of the signal.

This paper presents reflectometry measurements that provide signal coherence information. The measurements have been conducted on two research vessels: R/V Lance and R/V Polarstern. The objective is to reveal the required conditions for coherent reflectometry depending on sea state and sea ice occurrence. Three data sets from expeditions of the two research vessels to Fram Strait, the Northern Atlantic and the Arctic Ocean are analysed.

On both ships a GORS (GNSS Occultation Reflectometry Scatterometry) receiver with three antenna links has been installed. A common up-looking link is dedicated to direct signal observations. Two additional side-looking links allow sampling the reflected signal with right- and left-handed polarization (RHCP and LHCP). The respective setups have suitable positions to observe grazing sea surface reflections (< 30 deg elevation angle). The antennas are mounted on Lance and Polarstern about 24 m and 22 m above sea level, respectively.

Reflection events are recorded continuously covering more than 70 days. Each event comprises a track of the satellite signal in the grazing angle elevation range. On average 2-3 reflection events were recorded in parallel. The results of the analysis show that in coastal waters (German Bight and Svalbard fjords) up to 44%, 37% (RHCP, LHCP) of the measurements meet the coherence condition. On the high sea it is rarely met, only <0.5% of RHCP and LHCP records fulfill the coherence condition there. The rate of coherent observations increases up to 14%, 13% (RHCP, LHCP) in case of sea ice occurrence.

It can be concluded that the sea state plays an important role for coherent reflectometry. Applications of coherent reflectometry over the ocean may concentrate on the retrieval of sea ice properties and altimetry in coastal waters. For the early data set, recorded in Fram Strait 2016, the estimation of sea concentration has been demonstrated. At present the Polarstern setup continues reflectometry measurements in the MOSAiC expedition with unique opportunities for sea ice observations in the central Arctic.

The limits of coherent reflectometry at high sea became clear. However, it is worth noting that the direct signal link meets the SNR condition also at high sea with an average rate of 55%. This result motivates further investigations to exploit the direct link of shipborne GNSS for atmospheric and ionospheric soundings on the sparsely covered ocean using coherent phase delay measurements.

How to cite: Semmling, M., Gerland, S., Gerber, T., Ramatschi, M., Dick, G., Wickert, J., and Hoque, M.: Coherent GNSS reflections over the sea surface - A classification for reflectometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18035, https://doi.org/10.5194/egusphere-egu2020-18035, 2020.

EGU2020-965 | Displays | G1.3

Assessment of geodetic products from MGEX analyses for the Onsala site

Periklis-Konstantinos Diamantidis, Grzegorz Klopotek, and Rüdiger Haas
The emergence of BeiDou and Galileo as operational Global Navigation Satellite Systems (GNSS), in addition to Global Positioning System (GPS) and GLONASS which are already in use, opens up possibilities in delivering geodetic products with higher precision. Apart from ensuring the homogeneity of the derived products, multi-GNSS analysis takes the advantage of new frequencies and an improved sky coverage. This should lead to better phase ambiguity resolution and an improved estimation of target parameters such as zenith wet delays (ZWD), troposphere gradients (GRD) and station positions. The International GNSS Service (IGS) has realised this potential by initiating the Multi-GNSS Experiment (MGEX) which provides orbit, clock and observation data for all operational GNSS. Correspondingly, the multi-technique space geodetic analysis software c5++ has been augmented with a MGEX-compliant GNSS module. Based on this new module and the Precise Point Positioning (PPP) approach using six-month of data, an assessment of the derived geodetic products is carried out for several GNSS receivers located at the Onsala core site. More specifically, we perform both single- and multi-GNSS data analysis using Kalman filter and least-squares methods and assess the quality of the derived station positions, ZWD and GRD. A combined solution using all GNSS together is carried out and the improvement with respect to station position repeatabilities is assessed for each station. Inter-system biases, which homogenise the different time scale that each GNSS operates in and are necessary for the multi-GNSS combination, are estimated and presented. Finally, the applied inter-system weighting is discussed as well as its impact on the derived geodetic products.

How to cite: Diamantidis, P.-K., Klopotek, G., and Haas, R.: Assessment of geodetic products from MGEX analyses for the Onsala site, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-965, https://doi.org/10.5194/egusphere-egu2020-965, 2020.

EGU2020-263 | Displays | G1.3

Experimental Study on GNSS-R to Detect Effective Reflector Height

Cemali Altuntas and Nursu Tunalioglu

EGU2020-443 | Displays | G1.3

The Effect of the State-of-the-Art Mapping Functions on Precise Point Positioning

Faruk Can Durmus and Bahattin Erdogan

The variometric approach, based on time difference technique in which single-receiver code and carrier phase observations are processed along with available broadcast orbits and clocks, presents a high accuracy on estimating receiver velocity (at mm/s level) in real time. In order to analyze the effect of ionospheric delay on velocity estimation, we evaluate the velocity estimation accuracy of six selected stations with different latitude at approximately 120-degree longitudes during a solar cycle from 2009 to 2019. Compared with the low-solar activity year, velocity estimation RMS during the high-solar activity year will increase by 2-4 mm/s in the east, north and up direction. Velocity estimation RMS time series agree well with the sunspot number time series. The correlation coefficients of six stations between RMS values and sunspot number are 0.45-0.66, 0.39-0.52, 0.39-0.63 in the east, north and up direction respectively. The accuracy of velocity estimation is positively correlated with the sunspot number. We also reconstructed seismic velocity waveforms caused by the 2017 Mw 6.5 Jiuzhaigou earthquake using variometric approach. The results show that multi-GNSS fusion can improve the velocity accuracy by 1-2 mm/s in the horizontal component and 3-4 mm/s in vertical component, with an improvement of 47%, 54%, 41% in the east, north, up direction compared with GPS-only results.

How to cite: Geng, T. and Ding, Z.: The effect of multi-GNSS and ionospheric delay on real-time velocity estimation with the variometric approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1904, https://doi.org/10.5194/egusphere-egu2020-1904, 2020.

Commercial software are usually refered to in national surveying practice and local deformation studies. Since their working environment is user friendly and implementation is easy, they could be prefered by many surveying practitioners or even researchers. However their usage is usually limited to 20-30 km due mainly to their crude ambiguity resolution algorithms and  the fact that they usually use broadcast ephemeris and standard troposphere models.  Since usualy the tropospheric zenith delay is not estimated but obtained from a standard troposphere model, the accuracy of the vertical component would be affected as the height difference between baseline points grows. As the baseline length becomes >20-30 km the tropospheric error would be coupled with orbital errors. Results based on large height difference would affect positioning solutions as well as local geoid determination studies. Monitoring local deformation such as landslides would also be affected if there is large height difference between the crown and the toe. The level of baseline dependent error is usually well covered in surveying standards manual however the effect of large height difference is generally ignored. In this study, we made an attempt to quantify vertical positioning error levels both considering large height difference between baseline points and longer baseline lengths. We used the data of CORS stations in the western US for the simulation of the observing session duration. TOPCON’s software MAGNET (Ver 4.0.1) was used to process the GNSS data. It appears that every 10 km increase in the baseline length and every 100 m increase in the height difference would cause 2.59mm and 1.24 mm vertical positioning error respectively. 

How to cite: Erol, T. and Sanli, D. U.: Quantifying baseline length and height-difference dependent errors from commercially available software, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2089, https://doi.org/10.5194/egusphere-egu2020-2089, 2020.

EGU2020-2515 | Displays | G1.3

Real-time earthquake hazard assessment based on high-rate GNSS PPPAR

Yang Jiang, Yang Gao, and Michael Sideris

To provide hazard assessment in rapid or real-time mode, accelerations due to seismic waves have traditionally been recorded by seismometers. Another approach, based on the Global Navigation Satellite System (GNSS), known as GNSS seismology, has become increasingly accurate and reliable. In the past decade, significant improvements have been made in high-rate GNSS using precise point positioning and its ambiguity resolution (PPPAR). To reach cm-level accuracy, however, PPPAR requires specific products, including satellite orbit/clock corrections and phase/code biases generated by large GNSS networks. Therefore, the use of PPPAR in real-time seismology applications has been inhibited by the limitations in product accessibility, latency, and accuracy. To minimize the implementation barrier for ordinary global users, the Centre National D’Etudes Spatiales (CNES) in France has launched a public PPPAR correction service via real-time internet streams. Broadcasting via the real-time service (RTS) of the international GNSS service (IGS), the correction stream is freely provided. Therefore, in our work, a new approach using PPPAR assisted with the CNES product to process high-rate in-field GNSS measurements is proposed for real-time earthquake hazard assessment. A case study is presented for the Ridgecrest, California earthquake sequence in 2019. The general performance of our approach is evaluated by assessing the quality of the resulting waveforms against publicly available post-processing GNSS results from a previous study by Melgar et al. (2019), Seismol. Res. Lett. XX, 1–9, doi: 10.1785/ 0220190223. Even though the derived real-time displacements are noisy due to the accuracy limitation of the CNES product, the results show a cm-level agreement with the provided post-processed control values in terms of root-mean-square (RMS) values in time and frequency domain, as well as seismic features of peak-ground-displacement (PGD) and peak-ground-velocity (PGV). Overall, we have shown that high-rate GNSS processing based on PPPAR via a freely accessible service like CNES is a reliable approach that can be utilized for real-time seismic hazard assessment.

How to cite: Jiang, Y., Gao, Y., and Sideris, M.: Real-time earthquake hazard assessment based on high-rate GNSS PPPAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2515, https://doi.org/10.5194/egusphere-egu2020-2515, 2020.

EGU2020-3267 | Displays | G1.3

The Effect of Multiple Baseline Evalution with Commercial Software on GPS Position Accuracy

Baris Tas, Tuna Erol, and Yener Turen

The evaluation of the observation data obtained from the GPS system is performed with software. The software used today is divided into academic, web-based and commercial software. Researches generally focus on academic software and web-based services that have become widespread in recent years.Commercial software is often used by daily users, mostly in classical geodesy. These softwares differ from each other; users, their purpose of use, processing methods, accuracy, users knowledge level etc. In this study, we focused commercial software’s (Topcon Magnet version 4.0.1) accuracy of GPS positioning in single and multiple base solutions.

10 stations included in IGS network in California, USA, one base and 2, 3 and 4 network solution results in different session times (1h to 24h) positioning accuracy was achieved. In our study, it has been found that the accuracy obtained for the horizontal components North and East varies between 2 mm and 8 mm and vertical component Up varies between 3 mm and 54 mm.

In evaluations with a reference station distance of up to 100km, increasing the number of more than 2 reference stations (3 or 4) for horizontal compenents (North and East) did not make a significant contribution to accuracy. In the case of vertical component (Up) accuracy, it is determined that accuracy is affected by interstation distance and observation time more than the number of reference stations(1, 2, 3 or 4). it was found that it was meaningful to increase the accuracy of the vertical component to be observation time for as long as possible and reference base stations to be selected from the closest possible stations. Avoidance of short observation time (1 hour and less) for all three components was found to be important in terms of accuracy to be achieved.

Keywords: Commercial software, GPS, Multiple base solution.

How to cite: Tas, B., Erol, T., and Turen, Y.: The Effect of Multiple Baseline Evalution with Commercial Software on GPS Position Accuracy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3267, https://doi.org/10.5194/egusphere-egu2020-3267, 2020.

EGU2020-4808 | Displays | G1.3

Performance Evaluation of PPP-AR Method for Engineering Surveys with Embedded GNSS Chipset in a Smartphone

Caneren Gul, Taylan Ocalan, and Nursu Tunalioglu

EGU2020-7254 | Displays | G1.3

Incomplete and complete PCO/PCV chamber calibrations – impact of Galileo observations

Andrzej Araszkiewicz and Damian Kiliszek

The poster presents the impact of the use of Galileo observations on daily GNSS position solutions. Analysis were carried out at EUREF Permanent Network. For 34 EPN stations full calibration tables developed by IGG, Univ. Bonn and containing correction E01 and E05 are available. We prepared for them a daily solutions, independently for GPS and Galileo. In most analysis for GPS solutions, also here, L1 and L2 frequencies are used. For them phase centre corrections are available for long time. For Galileo solutions generally E1 and E5a frequencies are used. In this analysis we prepare two Galileo solutions. To correct the E5a signal we used E05 values and in the second case the G02 values (as it is done in most cases when there are no full PCO/PCV tables available). There is a clear bias in height between this two Galileo solutions. Analysis has shown also that we get more consistent GPS and Galileo solutions, when G02 values instead of E05 are used for E5a signal.

How to cite: Araszkiewicz, A. and Kiliszek, D.: Incomplete and complete PCO/PCV chamber calibrations – impact of Galileo observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7254, https://doi.org/10.5194/egusphere-egu2020-7254, 2020.

EGU2020-7614 | Displays | G1.3

Accuracy of PPP along with the development of GPS, GLONASS and Galileo

Damian Kiliszek, Andrzej Araszkiewicz, and Krzysztof Kroszczynski

In recent years, one can notice a significant development of the PPP, which both increases accuracy and speeds up the convergence time of the receiver position. New or improved computational algorithms have been developed. This development can also be seen in real-time measurements made possible by the IGS RTS. Other new trends are the development of PPP-AR and the use of cheap receivers such as smartphones. However, the development of the PPP method can be particularly seen in multi‑GNSS measurements. This applies to the continuous development of existing GPS and GLONASS systems and the emergence of new Galileo and BDS systems that have a significant impact on PPP. The development of multi GNSS will increase the number of satellites observed, which improves geometry and PDOP, and increases product accuracy or increases the number of available signals and frequencies. The use of multi-GNSS is possible thanks to the IGS MGEX.

This research shows how the accuracy and convergence time by the PPP changes with the development of GPS, GLONASS and Galileo systems. We used the globally distributed MGEX stations for three different weeks, each one from 2017, 2018 and 2019. The analysis was made for different constellations: GPS, GLONAS, Galileo, GPS+GLONAS, GPS+Galileo, GLONASS+Galileo and GPS+GLONASS+Galileo for different cut-off elevation angles: 0⁰, 5⁰, 10⁰, 15⁰, 20⁰, 25⁰, 30⁰, 35⁰ and 40⁰.

Based on the analysis, we show a progressive improvement of accuracy and a shortening of convergence time in recent years. This is especially visible for calculations with multi-GNSS, obtaining the best results for GPS+GLONASS+Galileo for the last analysed period. Already in 2019 on average, about 22 satellites were observed using a total of three systems together. It has also been shown that in 2019, the Galileo system already allows for positioning with high accuracy anywhere on Earth. On average, around 7 Galileo satellites were observed in 2019, where in 2017 on average, fewer than 5 satellites were observed. It has also been shown that the GPS still provides the highest accuracy and has the greatest impact on multi-GNSS positioning accuracy. Even for the GLONASS+Galileo, poorer accuracy was obtained than for GPS‑only. However, for the GLONASS+Galileo solution, a smaller error distribution and lower standard deviation values were obtained than for GPS-only. This may indicate constant bias-related error values (IFB, ISB) and poorer product quality. In addition, for higher elevation angles, it was shown that better accuracy was obtained for Galileo‑only than for GLONASS-only, but only for the third period. It was also noted that for the joint of GLONASS+Galileo, it eliminated errors that occurred in the GLONASS-only, for which, in the second period, much larger errors were obtained than for the other periods. Finally, the influence of multi-GNSS positioning for positioning in constraint conditions was demonstrated by analysing the effect of the elevation angle. It has been shown that even for elevation angle of 40⁰, the use of GPS+GLONASS+Galileo allowed obtaining about 90% of the availability of solutions with accuracy in estimation the position of individual cm.

How to cite: Kiliszek, D., Araszkiewicz, A., and Kroszczynski, K.: Accuracy of PPP along with the development of GPS, GLONASS and Galileo, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7614, https://doi.org/10.5194/egusphere-egu2020-7614, 2020.

EGU2020-7792 | Displays | G1.3

PPP-AR with GPS and Galileo: Assessing diverse approaches and satellite products to reduce convergence time

Marcus Franz Glaner, Robert Weber, and Sebastian Strasser

Precise Point Positioning (PPP) is one of the most promising processing techniques for Global Navigation Satellite System (GNSS) data. By the use of precise satellite products (orbits, clocks and biases) and sophisticated algorithms applied on the observations of a multi-frequency receiver, coordinate accuracies at the decimetre/centimetre level for a float solution and at the centimetre/millimetre level for a fixed solution can be achieved. In contrast to relative positioning methods (e.g. RTK), PPP does not require nearby reference stations or a close-by reference network. On the other hand PPP has a non-negligible convergence time. To make PPP more competitive against other high-precision GNSS positioning techniques, scientific research focuses on reducing the convergence time of PPP.

 

In this contribution, we present results of PPP with focus on integer ambiguity resolution (PPP-AR) using satellite products from different analysis centers. The resulting coordinate accuracy and convergence behaviour are evaluated in various test scenarios. In these test cases we distinguish between the use of satellite products from Graz University of Technology, which are calculated using a raw observation approach, and nowadays publicly available satellite products of different analysis centers (e.g. CNES, CODE). All those products enable PPP-AR in different approaches. To shorten the convergence time, we investigate and compare different PPP processing approaches using GPS and Galileo observations. The use of 2+ frequencies and alternatives to the classical PPP model, which is based on two frequencies and the ionosphere-free linear combination are discussed (e.g. uncombined model with ionospheric constraint). The PPP calculations are performed with the in-house software raPPPid, which has been developed at the research division Higher Geodesy of TU Vienna and is part of the Vienna VLBI and Satellite Software (VieVS PPP).

How to cite: Glaner, M. F., Weber, R., and Strasser, S.: PPP-AR with GPS and Galileo: Assessing diverse approaches and satellite products to reduce convergence time, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7792, https://doi.org/10.5194/egusphere-egu2020-7792, 2020.

EGU2020-7645 | Displays | G1.3 | Highlight

Improving PPP static and cinematic positioning by combining GPS and Galileo data.

Felix Perosanz, Georgia Katsigianni, Sylvain Loyer, Mini Gupta, Alvaro Santamaria, and Flavien Mercier

The Precise Point Positioning (PPP) technique using the GPS has become a popular alternative to the differential approach. Thanks to the MGEX pilot project of the IGS, precise orbit and clock products from other constellations like Galileo, Beidou, GLONASS are today available. This presentation focusses on GPS and Galileo systems and compares their individual performance to a combined processing.

Resolving GNSS phase observations biases to their correct integer values significantly improves the precision and the accuracy of the estimated parameters. However, PPP with ambiguity resolution (PPP-AR) requires to deal with “hardware” biases at the satellite and receiver level. Nevertheless, several Analysis Centers within the IGS community are providing these biases. Using the orbit, clock and bias products of the GPS and Galileo constellations provided by the CNES-CLS group, we were able to compare PPP and PPP-AR station coordinates repeatability from a network of around 50 stations during 6 months. For both static and cinematic solutions, the hybridized solution significantly exceeds both individual ones.

 

 

How to cite: Perosanz, F., Katsigianni, G., Loyer, S., Gupta, M., Santamaria, A., and Mercier, F.: Improving PPP static and cinematic positioning by combining GPS and Galileo data., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7645, https://doi.org/10.5194/egusphere-egu2020-7645, 2020.

EGU2020-6830 | Displays | G1.3

Precise Positioning with the Modified Ambiguity Function Approach using BDS and GPS observations

Dawid Kwaśniak and Sławomir Cellmer

For many years GPS and GLONNAS were leading navigation systems. However, recent years two new navigational systems have appeared. These systems are the European Galileo System and the Chinese BeiDou System (BDS). The full operability of both systems is foreseen for 2020. The BDS is quickly developing in last years and still increasing number of satellites allows to use this system for positioning. GPS and BDS systems share some of their signals frequencies. These shared signals frequencies allows to combine observation of both systems. The goal of this study is use the BDS along with GPS for positioning purpose.

For test purpose a self-made software was created in MatLab. It consists of three modules.  First is responsible for reading RINEX files, second for the DGPS or the DGNSS in case of combined GPS and BDS observations and the third one uses The Modified Ambiguity Function Approach (MAFA) method for precise positioning purposes. MAFA is a method of processing GNSS carrier phase observations. In this method the integer nature of  ambiguities is taken into account using appropriate form of mathematical model. The theoretical Foundations of Precise Positioning Using MAFA will be presented. For test purpose data from three different days for the same baseline was used. Test was divided on two parts. In the first part short static sessions were performed for GPS only BDS only and for GPS and BDS combination. In the second part data was tested in RTK mode for GPS only, BDS only and for GPS and BeiDou System combination.

BDS allows to obtain an accuracy on the same level as GPS. The usage of GPS and BDS combinations allows to increase the precision of the obtained result comparing to GPS only solution. Very important thing is to remember about inter system bias (ISB) - the difference between the receiver hardware delays affecting the signals from different systems, that can affect for the results.

How to cite: Kwaśniak, D. and Cellmer, S.: Precise Positioning with the Modified Ambiguity Function Approach using BDS and GPS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6830, https://doi.org/10.5194/egusphere-egu2020-6830, 2020.

EGU2020-7856 | Displays | G1.3

GNSS/IMU/Odometer based Train Positioning
not presented

Qing Li and Robert Weber

Usually train positioning is realized via counting wheel rotations (Odometer), and correcting at fixed locations known as balises. A balise is an electronic beacon or transponder placed between the rails of a railway as part of an automatic train protection (ATP) system. Balises constitute an integral part of the European Train Control System, where they serve as “beacons” giving the exact location of a train. Unfortunately, balises are expensive sensors which need to be placed over about 250 000 km of train tracks in Europe.

Therefore, recently tremendous efforts aim on the development of satellite-based techniques in combination with further sensors to ensure precise train positioning. A fusion of GNSS receiver and Inertial Navigation Unit (IMU) observations processed within a Kalman Filter proved to be one of potential optimal solutions for train traction vehicles positioning.

Today several hundreds of trains in Austria are equipped with a single-frequency GPS/GLONASS unit. However, when the GNSS signal fails (e.g. tunnels and urban areas), we expect an outage or at least a limited positioning quality. To yet ensure availability of a reliable trajectory in these areas, the GNSS sensor is complemented by a strapdown IMU platform and a wheel speed sensor (odometer).

In this study a filtering algorithm based on the fusion of three sensors GPS, IMU and odometer is presented, which enables a reliable train positioning performance in post-processing. Odometer data are counts of impulses, which relate the wheel’s circumference to the velocity and the distance traveled by the train. This odometer data provides non-holonomic constraints as one-dimensional velocity updates and complements the basic IMU/GPS navigation system. These updates improve the velocity and attitude estimates of the train at high update rates while GPS data is used to provide accurate determination in position with low rates. In case of GNSS outages, the integrated system can switch to IMU/odometer mode. Using the exponentially weighted moving average method to estimate of measurement noise for odometer velocity helps to construct measurement covariance matrices. In the presented examples an IMU device, a GPS receiver and an Odometer provide the data input for the loosely coupled Kalman Filter integration algorithm. The quality of our solution was tested against trajectories obtained with the software iXCOM-CMD (iMAR) as reference.

How to cite: Li, Q. and Weber, R.: GNSS/IMU/Odometer based Train Positioning , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7856, https://doi.org/10.5194/egusphere-egu2020-7856, 2020.

EGU2020-9715 | Displays | G1.3

Accuracy analysis of global ionospheric maps in relation to their temporal resolution and solar activity level.

Beata Milanowska, Paweł Wielgosz, Anna Krypiak-Gregorczyk, and Wojciech Jarmołowski

Since 1998 Ionosphere Associate Analysis Centers (IAAC) of the International GNSS Service (IGS) routinely provide global ionosphere maps (GIMs). They are used for a wide range of geophysical applications, including supporting precise positioning and improving space weather analysis. These GIMs are generated by different analysis centers with the use of different modelling techniques. Therefore they have different accuracy levels, which has already been evaluated in several studies. Until 2014 all GIMs were provided with 2-hour temporal resolution, and since 2015 some of the IAACs have started to provide their products with higher resolutions, up to 30 - 60 minutes. Since GIMs have different temporal resolutions, we investigated whether map interval affected their accuracies.

In this study we carried out IAAC GIM accuracy analysis for years 2014 and 2018, corresponding to high and low solar activity periods, respectively. Since in 2014 IAAC GIMs had 2-hour resolution, we also evaluated UQRG maps supplied with 15-minute interval. For low solar activity period (2018) we evaluated 4 models: CASG, CODG, EMRG and  UQRG. In addition, we studied ionosphere map performance during two selected geomagnetic storms: on 19 February 2014 and 17 March 2015. Our accuracy evaluation was based on GIM-TEC comparisons to differential STEC derived from GNSS data and VTEC derived from altimetry measurements.

The results show that temporal interval has no significant impact on the overall, annual map RMS during both high and low solar activity periods. However, during geomagnetic storms, when reducing map interval, the map accuracy improves by almost 25%.

How to cite: Milanowska, B., Wielgosz, P., Krypiak-Gregorczyk, A., and Jarmołowski, W.: Accuracy analysis of global ionospheric maps in relation to their temporal resolution and solar activity level., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9715, https://doi.org/10.5194/egusphere-egu2020-9715, 2020.

EGU2020-9818 | Displays | G1.3

An adaptive convolutional neural network model for ionosphere prediction

Maria Kaselimi, Nikolaos Doulamis, and Demitris Delikaraoglou

Knowledge of the ionospheric electron density is essential for a wide range of applications, e.g., telecommunications, satellite positioning and navigation, and Earth observation from space. Therefore, considerable efforts have been concentrated on modeling this ionospheric parameter of interest. Ionospheric electron density is characterized by high complexity and is space−and time−varying, as it is highly dependent on local time, latitude, longitude, season, solar cycle and activity, and geomagnetic conditions. Daytime disturbances cause periodic changes in total electron content (diurnal variation) and additionally, there are multi-day periodicities, seasonal variations, latitudinal variations, or even ionospheric perturbations that cause fluctuations in signal transmission.

Because of its multiple band frequencies, the current Global Navigation Satellite Systems (GNSS) offer an excellent example of how we can infer ionosphere conditions from its effect on the radiosignals from different GNSS band frequencies. Thus, GNSS techniques provide a way of directly measuring the electron density in the ionosphere. The main advantage of such techniques is the provision of the integrated electron content measurements along the satellite-to-receiver line-of-sight at a large number of sites over a large geographic area.

Deep learning techniques are essential to reveal accurate ionospheric conditions and create representations at high levels of abstraction. These methods can successfully deal with non-linearity and complexity and are capable of identifying complex data patterns, achieving accurate ionosphere modeling. One application that has recently attracted considerable attention within the geodetic community is the possibility of applying these techniques in order to model the ionosphere delays based on GNSS satellite signals.

This paper deals with a modeling approach suitable for predicting the ionosphere delay at different locations of the IGS network stations using an adaptive Convolutional Neural Network (CNN). As experimental data we used actual GNSS observations from selected stations of the global IGS network which were participating in the still-ongoing MGEX project that provides various satellite signals from the currently available multiple navigation satellite systems. Slant TEC data (STEC) were obtained using the undifferenced and unconstrained PPP technique. The STEC data were provided by GAMP software and converted to VTEC data values. The proposed CNN uses the following basic information: GNSS signal azimuth and elevation angle, GNSS satellite position (x and y). Then, the adaptive CNN utilizes these data inputs along with the predicted VTEC values of the first CNN for the previous observation epochs. Topics to be discussed in the paper include the design of the CNN network structure, training strategy, data analysis, as well as preliminary testing results of the ionospheric delays predictions as compared with the IGS ionosphere products.   

How to cite: Kaselimi, M., Doulamis, N., and Delikaraoglou, D.: An adaptive convolutional neural network model for ionosphere prediction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9818, https://doi.org/10.5194/egusphere-egu2020-9818, 2020.

EGU2020-10676 | Displays | G1.3

The detection of ionospheric trough with GNSS measurements.

Rafal Sieradzki and Jacek Paziewski

The main ionospheric trough represents a large scale depletion of plasma density elongated in longitude, which is typically observed at the boundary between high- and mid-latitude ionosphere. The trough is characterized  by a steep density gradient in a poleward direction and gradual on the equatorward site. According to the recent studies it begins in the late afternoon, moves equatorward during the night hours and rapidly retreats to higher latitudes at a dawn. Due to the dynamic of auroral oval, this ionospheric feature exhibits a high temporal variability and shifts equatorward during the geomagnetic activity. In this work we demonstrate the initial assessment of the ionospheric trough detection performed with GNSS-based relative STEC values. The basis of this indicator are time series of  geometry-free combination with removed background variations. The separation of these low-term effects is realized with a polynomial fitting applied to the particular arcs of data. Such processed data have an accuracy of phase measurements and provide an epoch-wise information on enhancement/depletion of plasma density. In order to evaluate the applicability of the proposed approach for the trough detection, we have analyzed the state of the ionosphere during different geomagnetic conditions. In our investigations we have used the data from several tens of stations located in the northern hemisphere, what makes possible to provide the comprehensive view of this ionospheric phenomenon. The results have confirmed that the network-derived relative STEC values can be successfully used for the monitoring ionospheric trough. Its signature is more pronounced for expanded auroral oval during increased geomagnetic activity and reach in such case a few TEC units.     

How to cite: Sieradzki, R. and Paziewski, J.: The detection of ionospheric trough with GNSS measurements., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10676, https://doi.org/10.5194/egusphere-egu2020-10676, 2020.

EGU2020-9846 | Displays | G1.3

Codephase center corrections for multi GNSS signals and the impact of misoriented antennas

Yannick Breva, Johannes Kröger, Tobias Kersten, and Steffen Schön

In absolute positioning approaches, e.g. Precise Point Positioning (PPP), antenna phase center corrections (PCC) have to be taking into account. Beside PCC for carrier phase measurements, also codephase center corrections (CPC) exist, which are antenna dependent delays of the code. The CPC can be split into a codephase center offset (PCO) and codephase center variations (CPV). These corrections can be applied in a Single Point Positioning (SPP) approach, to improve the accuracy in the positioning domain. The CPC vary with azimuth and elevation and are related to an antenna, which is oriented towards north. If the antenna is wrongly oriented, the effect cannot be compensated and wrong corrections will be added to the observations.

The Institut für Erdmessung (IfE) established a concept to determine CPC for multi GNSS signals, where a robot tilts and rotates an antenna under test precisely around a specific point. Afterwards time differenced single differences are calculated, which are the input to estimate the CPC by using spherical harmonics (8,8). First studies in our working group showed, that an improvement of the position in a SPP are possible, if antenna pattern for the codephase are considering and correctly applied.

In this contribution, we present the improvement of a SPP and PPP approach by considering CPC for different low cost antennas with multi GNSS signals. Beside the positioning domain, an analysis of the CPC in observation domain, by evaluating the deviations of single differences from zero mean, is performed. Furthermore, we quantify the impact of a disoriented antenna, e.g. oriented in east direction, in the positioning and observation domain by using north oriented CPC. We show, that this impact can be compensating in a post-processing by rotating the antenna pattern. Finally, we present some results of different calibrations, where the antennas are disoriented on the robot and compared to the estimated CPC pattern with the post-processing approach and discussed their impact on the positioning. 

How to cite: Breva, Y., Kröger, J., Kersten, T., and Schön, S.: Codephase center corrections for multi GNSS signals and the impact of misoriented antennas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9846, https://doi.org/10.5194/egusphere-egu2020-9846, 2020.

EGU2020-11538 | Displays | G1.3

Preliminary Positioning Results From NGS’s Upcoming Multi-GNSS Processing Software

Bryan Stressler, Jacob Heck, Andria Bilich, and Clement Ogaja

EGU2020-13973 | Displays | G1.3

GNSSpy: Python Toolkit for GNSS Data

Mustafa Serkan Işık, Volkan Özbey, Ejder Bayır, Yiğit Yüksel, Serdar Erol, and Ergin Tarı

The use of Python programming language in the academic community increased in recent years. Python is a multi-purpose language and has an easy syntax which makes it appropriate for routine computations. However, there are very few attempts to write GNSS related libraries in Python programming language.

GNSSpy is a free and open-source library for handling multi GNSS and different versions (2.X and 3.X) of RINEX files. It provides Single Point Positioning (SPP) and Precise Point Positioning (PPP) solutions by least squares adjustment using precise ephemeris, differential code biases (DCB) and clock corrections from different solutions. GNSSpy can be used for editing (slicing, decimating, merging) and quality checking (multipath, ionospheric delay, SNR) for RINEX files. It can be successfully used for visualizing GNSS data such as skyplot, azimuth-elevation, time-elevation, ground track, and visibility plot. GNSSpy can be downloaded from GitHub. The toolkit is still being improved by the authors.

How to cite: Işık, M. S., Özbey, V., Bayır, E., Yüksel, Y., Erol, S., and Tarı, E.: GNSSpy: Python Toolkit for GNSS Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13973, https://doi.org/10.5194/egusphere-egu2020-13973, 2020.

EGU2020-17792 | Displays | G1.3

High-rate GNSS positioning for tracing anthropogenic seismic activity

Iwona Kudłacik, Jan Kapłon, Grzegorz Lizurek, Mattia Crespi, and Grzegorz Kurpiński

High-rate GNSS observations are usually related to earthquake analysis and structural monitoring. The sampling frequency is in the range of 1-100 Hz and observations are processed in the kinematic mode. Most of the research on short-term dynamic deformations is limited to natural earthquakes with magnitudes exceeding 5 and amplitudes of at least several centimetres up to even meters. The high frequency GNSS stations positions monitoring is particularly important on mining areas due to the mining damages. On the underground mining areas the seismic tremors are regular and there are several hundreds of events annually of magnitude over 2 with maximum magnitudes of 4. As mining tremors are shallow and very frequent, they cause mining damages on infrastructure.

Here, we presented the application of GNSS-seismology to the analysis of anthropogenic seismic activity, where the event magnitude and amplitude of displacements significantly lower. We examined the capacity to detect mining tremors with high-rate GPS observations and demonstrated, for the first time to our knowledge that even subcentimeter ground vibrations caused by anthropogenic activity can be measured this way with a very good agreement with seismological data. One of the most-felt mining shocks in Poland in recent years occurred on January 29, 2019 (12:53:44 UTC) M3.7 event in the area of Legnica-Głogów Copper District and was successfully registered by high-rate GNSS stations co-located with seismic stations. In this mining tremor the peak ground displacements reached 2-16  mm and show the Pearson’s correlation value in range of 0.61 to 0.94 for band-pass filtered horizontal displacements.

How to cite: Kudłacik, I., Kapłon, J., Lizurek, G., Crespi, M., and Kurpiński, G.: High-rate GNSS positioning for tracing anthropogenic seismic activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17792, https://doi.org/10.5194/egusphere-egu2020-17792, 2020.

EGU2020-20898 | Displays | G1.3

Comparison of high rate GNSS and GNSS-R measurements for detecting tidal bores in the Garonne River

Pierre Zeiger, José Darrozes, Frédéric Frappart, Guillaume Ramillien, Laurent Lestarquit, Philippe Bonneton, Natalie Bonneton, and Valérie Ballu

The Reflected Global Navigation Satellite System (GNSS-R) is a bi-static radar system in which the receiver collect GNSS signals reflected from the Earth surface and compares them with corresponding direct signals. Measurements can be performed on the waveforms to determine the elevation of the free surface, leading to applications such as ocean altimetry, inland water level variations, soil moisture, snow depth and atmospheric water changes. This study presents the potential of in-situ GNSS-R for tidal bore detection and characterization, and compares it to high rate GNSS observations and other reference datasets.

The data we used were acquired on 17th and 18th October 2016 in the Garonne River, at 126 km upstream the mouth of the Gironde estuary. We processed GNSS-based elevations from data acquired on a buoy at a 20 Hz sampling rate using differential GNSS (DGNSS) technique. Acoustic Doppler Current Profiler (ADCP) measurements as well as pressure data were used for validation purposes. These techniques show good results in estimating the amplitude of the first wave, the period of the tidal bore and the oceanic tides. All of these datasets were compared to the retrieval of GNSS-R signals above the river. We have processed the changes in water height throughout the acquisition using Larson et al. (2013) and Roussel et al. (2015) techniques. We finally separate the atmospheric component from the tidal bore and the oceanic tides ones.

 

Larson, K. M., Löfgren, J. S., and Haas, R. (2013). Coastal sea level measurements using a single geodetic gps receiver. Advances in Space Research, 51(8):1301–1310.

Roussel, N., Ramillien, G., Frappart, F. et al. (2015). Sea level monitoring and sea state estimate using a single geodetic receiver. Remote Sensing of Environment, 171:261 – 277.

How to cite: Zeiger, P., Darrozes, J., Frappart, F., Ramillien, G., Lestarquit, L., Bonneton, P., Bonneton, N., and Ballu, V.: Comparison of high rate GNSS and GNSS-R measurements for detecting tidal bores in the Garonne River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20898, https://doi.org/10.5194/egusphere-egu2020-20898, 2020.

EGU2020-21092 | Displays | G1.3

PPP RAIM Algorithm of based on Fuzzy Clustering Analysis

Shouzhou Gu

With the development of various navigation systems, there is a sharp increase in the number of visible satellites. Accordingly, the probability of multiply gross measurements will increase. However, the conventional RAIM methods are difficult to meet the demands of the navigation system. In order to solve the problem of checking and identify multiple gross errors of  receiver autonomous integrity monitoring (RAIM), this paper designed full matrix of single point positioning by QR decomposition, and proposed a new RAIM algorithm based on fuzzy clustering analysis with fuzzy c-means(FCM). And on the condition of single or two gross errors, the performance of hard or fuzzy clustering analysis were compared. As the results of the experiments, the fuzzy clustering method based on FCM principle could detect multiple gross error effectively, also achieved the quality control of precision point positioning and ensured better reliability results.

How to cite: Gu, S.: PPP RAIM Algorithm of based on Fuzzy Clustering Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21092, https://doi.org/10.5194/egusphere-egu2020-21092, 2020.

By December 2019, twenty-four new-generation BeiDou (BDS-3) Medium Earth Orbit (MEO) satellites, three Inclined Geosynchronous Orbit (IGSO) satellites and one Geostationary Orbit (GEO) satellite have been launched, symbolizing its starting of global coverage.

The observations of a very limited number of 17 International GNSS (Global Navigation Satellite System) Monitoring and Assessment Service (iGMAS) stations and 80 IGS Multi-GNSS Experiment (MGEX) stations from October 2018 to October 2019 have been processed to determine the orbits of combined BDS-3 and BDS-2 satellites. All of the latest official BDS-2 and BDS-3 satellite phase center offsets (PCOs) and other satellite parameters were used in the data process. The internal consistency (daily boundary discontinuity) and satellite laser ranging (SLR) validations are conducted for the orbit validation. The average three-dimensional root-mean-square error (RMS-3D) of 24-hour overlapping arcs for BDS-2 and BDS-3 satellites is within 0.1m and 0.15m, respectively. Satellite laser ranging (SLR) validation reports that the orbit radial component for BDS-2 and BDS-3 satellites is within 0.1m. The orbit accuracy of BDS-3 is slightly lower than that of BDS-2 satellite presently.

How to cite: Tan, B.: Initial Assessment of Precise Orbit Determination for Combined BDS-2 and BDS-3 Satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22166, https://doi.org/10.5194/egusphere-egu2020-22166, 2020.

Australia and New Zealand has initiated a two-year test-bed in 2017 for the new generation of Satellite-Based Augmentation System (SBAS). In addition to the legacy L1 service, the test-bed broadcasts SBAS messages through L5 to support the dual-frequency multi-constellation (DFMC) service for GPS and Galileo. Furthermore, PPP corrections were also sent via L1 and L5 to support the PPP service for dual-frequency GPS users and GPS/Galileo users, respectively.

The positioning and integrity monitoring process are currently defined for the aeronautical DFMC SBAS service in [1]. For land applications in road transport, users may encounter problems in complicated measurement environments like urban areas, e.g., more complicated multipath effects and frequent filter initializations of the carrier-smoothed code observations. In this study, a new weighting model related to the elevation angles, the signal-to-noise ratios (SNRs) and the filter smoothing time is developed. The weighting coefficients adjusting the impacts of these factors are studied for the open-sky, the suburban and the urban scenarios. Applying the corresponding weighting models, the overbounding cumulative distribution functions (CDFs) of the weighted noise/biases are searched and proposed for these scenarios.

Using real data collected under different measurement scenarios mentioned above, the DFMC SBAS positioning errors and protection levels are computed in the horizontal direction based on the proposed weighting models and the proposed overbounding CDFs. The results are compared with the case applying only the traditional elevation-dependent weighting model. While the positioning accuracy and protection levels did not change much for the open-sky scenario, the RMS of the positioning errors and the average protection levels are found to be reduced in both the suburban and urban scenarios. 

[1] EUROCAE (2019) Minimum operational performance standard for Galileo/global positioning system/satellite-based augmentation system airborne equipment. The European Organisation for civil aviation equipment, ED-259, February 2019

How to cite: Wang, K. and El-Mowafy, A.: Positioning and integrity monitoring using the new DFMC SBAS service in the road transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-195, https://doi.org/10.5194/egusphere-egu2020-195, 2020.

EGU2020-2260 | Displays | G1.3

A Cloud Platform and Hybrid Positioning Method for Indoor Location Service

Jinzhong Mi, Dehai Li, and Xiao Liu

In order to deal with the discontinuity and deficient availability of indoor positioning, a private cloud platform of location service was built in this paper, and a hybrid positioning technology was realized. In this platform, dynamic deployment, elastic computing, and on-demand cloud computing services was implemented by the hardware resource virtualization. The limits in large users online service and data communication were overcome by utilizing microservices management and its cloud-push-service component. In the hybrid cloud positioning, a method of beacon node correction and autonomous trajectory estimation was proposed. This method could improve continuity and usability of indoor positioning, and reach a positioning accuracy of 2m approximately. At last, by integrating indoor map and hybrid indoor positioning, the cloud software and terminal application had been developed for public location service.

How to cite: Mi, J., Li, D., and Liu, X.: A Cloud Platform and Hybrid Positioning Method for Indoor Location Service, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2260, https://doi.org/10.5194/egusphere-egu2020-2260, 2020.

EGU2020-5270 | Displays | G1.3

Real-time estimation of multi-GNSS and multi-frequency integer recovery clock with undifferenced ambiguity resolution

Yun Xiong, Yongqiang Yuan, Jiaqi Wu, Xin Li, and Jiaxin Huang

Precise clock product of global navigation satellite systems (GNSS) is an important prerequisite to support real-time precise positioning service. The developments of multi-constellation and multi-frequency GNSS open new requirements for real-time clock estimation. In this contribution, the estimation model of multi-GNSS and multi-frequency integer recovery clock (IRC) is developed to improve both the accuracy and efficiency of real-time clock estimates. In the proposed method, the undifferenced ambiguities are fixed to integers, thus the integer properties of the ambiguities are recovered and the accuracy of the clock estimates is also improved. Moreover, benefitting from the removal of large quantities of ambiguity parameters, the computation time is greatly reduced which can guarantee high processing efficiency of real-time clock estimates. Multi-GNSS observations from 150 globally distributed Multi-GNSS Experiment (MGEX) tracking stations were processed with the proposed model. Compared to the float satellite clocks, the precision of the real-time IRC with respect to CODE 30 s final multi-GNSS satellite clock products were improved by 53.0%, 42.7%, 63.7% and 33.9% for GPS, BDS, Galileo and GLONASS, respectively. The average computation time per epoch with multi-GNSS observations was improved by 97.1% compared to that of standard float clock estimation. Kinematic precise point positioning (PPP) ambiguity resolution was also performed with the derived real-time IRC products. Compared to the float PPP solutions, the position accuracy of the multi-GNSS IRC-based fixed solutions was improved by 77.2%, 49.7% and 52.7% from 24.2, 13.3 and 30.7 mm to 5.5, 6.7 and 14.5 mm for the east, north and up components, respectively. The results indicate that ambiguity fixing can be successfully achieved by using the derived the IRC products. In addition, the estimation model of multi-frequency IRC products is also investigated to promote the capability and application of real-time PPP AR under multi-frequency signals.

How to cite: Xiong, Y., Yuan, Y., Wu, J., Li, X., and Huang, J.: Real-time estimation of multi-GNSS and multi-frequency integer recovery clock with undifferenced ambiguity resolution , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5270, https://doi.org/10.5194/egusphere-egu2020-5270, 2020.

The release of Android GNSS Raw Measurements API, (2016) and the growing technological development introduced by the use of multi-GNSS and multi-frequency GNSS chipsets – changed the hierarchies within the GNSS mass-market world. In this sense, Android smartphones became the new leading products. Positioning performances and quality of raw GNSS measurements have been studied extensively. Despite the greater susceptibility to multipath and cycle slip due to the low cost antenna used, a positioning up to sub-meter accuracy can be achieved. Among the improvements in positioning and navigation, the availability of GNSS measurements from Android smartphones paved new ways in geophysical applications: e.g. periodic fast movements reconstruction and ionospheric perturbances detection.  In fact, considering the number of Android smartphones compatible with the Google API, additional costless information can be used to densify the actual networks of GNSS permanent stations used to monitor atmospheric conditions. However, an extensively analysis on the reconstruction of ionospheric conditions with Android raw measurements is necessary to prove the accuracy achievable in future ionosphere monitoring networks based on both permanent GNSS station and Android smartphone.

The aim of this work is to assess the performance of multi-frequency and multi-GNSS smartphone – in particular, Xiaomi Mi 8 and Huawei Mate 20 X – in the reconstruction of real-time sTEC (slant Total Electron Content) variations meaningful of ionospheric perturbations. A 24-hour dataset of 1Hz GNSS measurements in static conditions was collected from the two smartphones in addition to data collected from M0SE, one of the EUREF/IGS permanent stations. The VARION (Variometric Approach for Real-time Ionosphere Observations) algorithm, based on the variometric approach and developed within the Geodesy and Geomatics Division of Sapienza University of Rome, was used to retrieve sTEC variations for all the observation periods.

The results, although preliminary, show that it is possible to study also from the smarthphone the trend of sTEC variations with elevation: lower elevation angles cause noisier sTEC variations. RMSE of the order of 0.02 TECU/s are found for elevation angles higher than 20 degrees as it happens for permanent stations. At the same time, the sTEC variations were compared to the overall measurements noise, due to both environmental and receiver noise, in order to statistically define the correlation between RMSE and derived sTEC variation.

Although the results obtained in this work are encouraging, still further analyses need to be carried out especially at latitudes where ionosphere conditions and perturbations play a major role. However, the possibility to perform such analyses on datasets collected worldwide is prevented from their availability. The last part of this work is therefore focused on the identification of a methodology to share with the GNSS community to collect, store and share GNSS measurements from Android smartphones to enable the researchers to enlarge the spatial and temporal boundaries of their research in the field of ionosphere modelling with mass-market devices. 

How to cite: Fortunato, M., Ravanelli, M., and Mazzoni, A.: Ionosphere Monitoring with Multi-Frequency and Multi-GNSS Android Smartphone: A Feasibility Study Towards GNSS Big Data Applications for Geosciences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9450, https://doi.org/10.5194/egusphere-egu2020-9450, 2020.

The ionospheric delay accounts for one of the major errors that the Global Navigation Satellite Systems (GNSS) suffer from. Hence, the ionosphere Vertical Total Electron Content (VTEC) map has been an important atmospheric product within the International GNSS Service (IGS) since its early establishment. In this contribution, an enhanced method has been proposed for the modeling of the ionosphere VTECs. Firstly, to cope with the rapid development of the newly-established Galileo and BeiDou constellations in recent years, we extend the current dual-system (GPS/GLONASS) solution to a quad-system (GPS/GLONASS/Galileo/BeiDou) solution. More importantly, instead of using dual-frequency observations based on the Carrier-to-Code Leveling (CCL) method, all available triple-frequency signals are utilized with a general raw-observation-based multi-frequency Precise Point Positioning (PPP) model, which can process dual-, triple- or even arbitrary-frequency observations compatibly and flexibly. Benefiting from this, quad-system slant ionospheric delays can be retrieved based on multi-frequency observations in a more flexible, accurate and reliable way. The PPP model has been applied in both post-processing global and real-time regional VTEC modeling. Results indicate that with the improved slant ionospheric delays, the corresponding VTEC models are also improved, comparing with the traditional CCL method.

How to cite: Liu, T., Zhang, B., Yuan, Y., and Zhang, X.: Ionosphere VTEC modeling with the raw-observation-based PPP model:an advantage demonstration in the multi-frequency and multi-GNSS context, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12914, https://doi.org/10.5194/egusphere-egu2020-12914, 2020.

EGU2020-15265 | Displays | G1.3

Site Characterization and Multipath Maps Using Zernike Polynomials

Andrea Gatti, Giulio Tagliaferro, and Eugenio Realini

Receiver antenna calibration plays an important role in precise point positioning (PPP). The correct management of the phase center offset and variations (PCV) and multipath effects can drastically improve the estimation of tropospheric parameters and the stability of the position over short measurement sessions. Correction parameters, to compensate for PCV, are usually computed in laboratory on all the geodetic grade antennas, but they are not available for low-cost apparatus; multipath can be partially mitigated by a robot calibration on site but this is an expensive procedure that is rarely adopted. Multipath staking maps (MPS) using carrier phase observation residuals are a cheap and powerful tool to generate site-specific corrections, effective for reducing both near-field and far-field effects. These maps can be generated by gridding multiple residuals falling in a cell of a pre-determined size. In this work, we propose to compute a set of polynomial coefficients of a Zernike expansion from the residuals of a PPP uncombined least-squares adjustment performed by the open-source goGPS processing software; these coefficients can be later used to synthesize corrections of the observations for the next processing of the target station. In contrast with gridding techniques, this approach allows a to generate smoother corrections and allows a limited automatic extrapolation of the correction values in areas of the sky that were not covered by observations in the set of data used in the calibration phase. The results show that the technique is effective in the modelling of multipath and residual phase center variations allowing a drastic reduction of the undifferenced residuals. Zernike polynomials are a sequence of polynomials orthogonal on the unit disk, vastly used in optics but, to our knowledge, never considered for GNSS applications, their symmetric properties and the circular support area makes them an interesting object of investigation for other possible usages in GNSS processing.

How to cite: Gatti, A., Tagliaferro, G., and Realini, E.: Site Characterization and Multipath Maps Using Zernike Polynomials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15265, https://doi.org/10.5194/egusphere-egu2020-15265, 2020.

EGU2020-17342 | Displays | G1.3

The INGV-RING GNSS Real-Time Services for geophysical

Gianpaolo Cecere, Antonio Avallone, Vincenzo Cardinale, Angelo Castagnozzi, Ciriaco D'Ambrosio, Giovanni De Luca, Luigi Falco, Nicola Angelo Famiglietti, Carmine Grasso, Antonino Memmolo, Felice Minichiello, Raffaele Moschillo, Giulio Selvaggi, Luigi Zarrilli, and Annamaria Vicari

In the last 15 years, INGV has built an important geodetic research infrastructure (RING - Rete Integrata Nazionale GNSS) consisting of a distributed network over the national territory of more than 200 GNSS sensors. Data are recorded in real and quasi real-time in various INGV centre of acquisition, with the aim to provide geodetic products useful to the scientific community. Presently, RING provides daily GPS 30 seconds files distributed in Rinex format. Here we introduce a prototype service for broadcasts real-time streaming GNSS/GPS data from a subset of the RING stations. We will show two use cases of the services that are streaming for raw data exchange for the estimation of the Total Electron Content (TEC), and streaming of GNSS corrections for positioning in NRTK (Network Real Time Kinematic). GNSS signals at different frequencies can be used for the estimation of the Total Electron Content (TEC) due to the dispersive characteristics of the ionosphere. Real-time kinematic (RTK) positioning, instead, has been effectively used, and we will show some examples, for various research campaigns such as the precision positioning of seismic arrays, the real-time positioning of Unmanned Aerial Vehicles (UAV) used for topographic mapping, and landslide monitoring.

How to cite: Cecere, G., Avallone, A., Cardinale, V., Castagnozzi, A., D'Ambrosio, C., De Luca, G., Falco, L., Famiglietti, N. A., Grasso, C., Memmolo, A., Minichiello, F., Moschillo, R., Selvaggi, G., Zarrilli, L., and Vicari, A.: The INGV-RING GNSS Real-Time Services for geophysical, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17342, https://doi.org/10.5194/egusphere-egu2020-17342, 2020.

Detection of the recent crustal deformation of the Upper Rhine Graben, which is part of the European Cenozoic rift system, is of interest for geoscience researcher. In April 2008 the Geodetic Institute of Karlsruhe Institute of Technology KIT and the Institut de Physique du Globe de Strasbourg (Ecole et Observatoire des Scences de laTerre) established an international joint venture called GURN (GNSS Upper Rhine Graben Network). GRUN network consists now of approximately 100 permanently operating reference stations.

The GPS observations acquired at these sites between 2002 and 2017 have been processed in different methods applying state-of-the art strategies and parameters. The resulting GPS coordinate time series have been analysed in order to extract the surface velocities for horizontal and vertical components. In this research, we will discuss the results by using different strategies of GNSS data reprocessing, PPP comparing to network solution. Advantages and disadvantages between both solutions for this kind of GNSS application, intraplate deformation, will be presented. The velocity of the height component will be also compared with the results of levelling data. One strategy or a combined solution should be selected to detect the detailed information on the present-day intraplate deformation of the Upper Rhine Graben.

How to cite: Sumaya, H.: PPP or network solution for detection of surface displacements?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19983, https://doi.org/10.5194/egusphere-egu2020-19983, 2020.

G2.1 – The Global Geodetic Observing System: Improving infrastructure for future science

EGU2020-3558 | Displays | G2.1

DORIS infrastructure: status and plans after 30 years of service

Jerome Saunier, Guilhem Moreaux, and Frank G. Lemoine

The Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system is based on a homogeneous global geodetic network. The DORIS ground network is managed and monitored by a single entity (CNES/IGN), which makes it possible to closely steer its deployment and evolution. Moreover, thanks to infrastructure and hardware improvements, the DORIS network has continuously improved over time in order to meet the performance requirements of satellite altimetry for which it is mainly dedicated.

Today, the numerous strengths of the DORIS network built up over 30 years give it an important role in contributing to the Global Geodetic Observing System (GGOS). Our extensive experience in geodetic network maintenance and long-standing commitment to international cooperation to co-locate DORIS with other space geodetic techniques and tide gauges led us to define installation requirements at co-located sites and monuments installation specifications.

After presenting an overview of the DORIS system specificities, we review the strengths and assets of the DORIS network and the continuing improvements in the DORIS technique. Then, we present examples of concrete results achieved through improved ground station configurations. Finally, we give an update on the status and plans for the DORIS network in the coming years to overcome the current limitations of DORIS to meet the GGOS goals for the Terrestrial Reference Frame.

How to cite: Saunier, J., Moreaux, G., and Lemoine, F. G.: DORIS infrastructure: status and plans after 30 years of service, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3558, https://doi.org/10.5194/egusphere-egu2020-3558, 2020.

EGU2020-12847 | Displays | G2.1

Station Infrastructure Developments of the IVS

Dirk Behrend, Axel Nothnagel, Johannes Böhm, Chet Ruszczyk, and Pedro Elosegui

The International VLBI Service for Geodesy and Astrometry (IVS) is a globally operating service that coordinates and performs Very Long Baseline Interferometry (VLBI) activities through its constituent components. The VLBI activities are associated with the creation, provision, dissemination, and archiving of relevant VLBI data and products. The operational station network of the IVS currently consists of about 40 radio telescopes worldwide, subsets of which participate in regular 24-hour and 1-hour observing sessions. This legacy S/X observing network dates back in large part to the 1970s and 1980s. Because of highly demanding new scientific requirements such as sea-level change but also due to the aging infrastructure, the larger IVS community planned and started to implement a new VLBI system called VGOS (VLBI Global Observing System) at existing and new sites over the past several years. In 2020, a fledgling network of 8 VGOS stations started to observe in operational IVS sessions. We anticipate that the VGOS network will grow over the next couple of years to a global network of 25 stations and will eventually replace the legacy S/X system as the IVS production system. We will provide an overview of the recent developments and anticipated evolution of the geodetic VLBI station infrastructure.

How to cite: Behrend, D., Nothnagel, A., Böhm, J., Ruszczyk, C., and Elosegui, P.: Station Infrastructure Developments of the IVS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12847, https://doi.org/10.5194/egusphere-egu2020-12847, 2020.

EGU2020-12593 | Displays | G2.1

Developing a highly-available GNSS reference station network

Ryan Ruddick, Amy Peterson, Richard Jacka, and Bart Thomas

Having modern and well-maintained geodetic infrastructure is critical for the development of an accurate and reliable Global Geodetic Reference Frame (GGRF). Geoscience Australia (GA) contributes to the development of the GGRF through a network of Global Navigation Satellite System (GNSS) reference stations positioned in key locations across Australia, Antarctica and the Pacific. Data from these reference stations contribute to the realisation of the GGRF, the development and maintenance of the Asia-Pacific Reference frame and the monitoring of deformation across the Australian continent. We are also seeing a rapid increase in the use of this data for location-based positioning applications, such as civil engineering, transport, agriculture and community safety. These applications bring with them a new suite of challenges for geodetic infrastructure operators, such as reduced data latency, denser networks and accessing the latest signals in the most modern formats. Through the Positioning Australia program, GA is addressing these challenges by developing a modern highly-available GNSS reference station design that will be deployed at over 200 sites across the region. This paper discusses the concept of highly-available infrastructure and presents a GNSS reference station design that is openly available for use by the global geodetic community.

How to cite: Ruddick, R., Peterson, A., Jacka, R., and Thomas, B.: Developing a highly-available GNSS reference station network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12593, https://doi.org/10.5194/egusphere-egu2020-12593, 2020.

EGU2020-7961 | Displays | G2.1

Operational infrastructure to ensure the long-term sustainability of the IHRS/IHRF

Riccardo Barzaghi, Laura Sanchez, and George Vergos

An objective of the International Height Reference System (IHRS) and its realization (the IHRF) is to support the monitoring and analysis of Earth’s system changes. The more accurate the IHRS/IHRF is, the more phenomena can be identified and modelled. Thus, the IHRS/IHRF must provide vertical coordinates and their changes with time as accurately as possible. As many global change phenomena occur at different scales, the global frame should be extended to regional and local levels to guarantee consistency in the observation, detection, and modelling of their effects. From this perspective, an operational infrastructure is needed to ensure the long-term sustainability of the IHRS/IHRF. In this contribution, we discuss the possibility of establishing such as infrastructure within the International Association of Geodesy (IAG) and its International Gravity Field Service (IGFS). Some aspects to be considered are:

  • - Improvements in the IHRS definition and realization following future developments in geodetic theory, observations and modelling.
  • - Refinement of the IHRS/IHRF standards/conventions based on the unification of the standards/conventions used by the geometric and gravity IAG Services.
  • - Development of strategies for collocation of IHRF stations with existing gravity and geometrical reference stations at different densification levels.
  • - Identification of the geodetic products associated with the IHRF and description of the elements to be considered in the corresponding metadata.
  • - Servicing the vertical datum needs of other geosciences such as, e.g., hydrography and oceanography.
  • - Implementation of a registry containing the existing local/regional height systems and their connections to the global IHRS/IHRF.

How to cite: Barzaghi, R., Sanchez, L., and Vergos, G.: Operational infrastructure to ensure the long-term sustainability of the IHRS/IHRF, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7961, https://doi.org/10.5194/egusphere-egu2020-7961, 2020.

EGU2020-10380 | Displays | G2.1

Combination Service for Time-variable Gravity Fields (COST-G) – operations

Ulrich Meyer, Adrian Jäggi, Frank Flechtner, Christoph Dahle, Torsten Mayer-Gürr, Andreas Kvas, Jean-Michel Lemoine, Stéphane Bourgogne, Andreas Groh, Annette Eicker, and Benoit Meyssignac

With the release of the combined GRACE monthly gravity field time-series COST-G RL01 the Combination Service for Time-variable Gravity fields (COST-G) of the International Association of Geodesy (IAG) became operational in July 2019. We present the COST-G RL01 time-series and provide validation in terms of orbit fit, ice mass trends, lake altimetry and sea level budget. We identify weak points in the combined monthly gravity fields and discuss possible improvements of the combination strategy for future combinations.

While COST-G RL01 is based on sets of re-processed GRACE monthly gravity fields, COST-G also provides combinations of monthly Swarm high-low satellite-to-satellite tracking (hl-SST) gravity fields on an operational basis with a latency of 3 months. Combinations of GRACE-FO monthly gravity fields are in the process of operationalization. We provide a status report and first results of GRACE-FO combinations. Combined GRACE, Swarm and GRACE-FO gravity fields complement each other to provide a long-term time-series of mass variation in the system Earth.

How to cite: Meyer, U., Jäggi, A., Flechtner, F., Dahle, C., Mayer-Gürr, T., Kvas, A., Lemoine, J.-M., Bourgogne, S., Groh, A., Eicker, A., and Meyssignac, B.: Combination Service for Time-variable Gravity Fields (COST-G) – operations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10380, https://doi.org/10.5194/egusphere-egu2020-10380, 2020.

EGU2020-16586 | Displays | G2.1

Coherent Time and Frequency for an Improved Global Geodetic Observing System

Karl Ulrich Schreiber, Jan Kodet, Thomas Klügel, and Torben Schüler

The toolbox of space geodesy contains a number of measurement techniques, which are globally distributed. In this diverse network fundamental stations are playing an important role as they are forming the backbone of the global geodetic observing system. They provide the ties for the combination of the techniques.

Until recently these ties were only considering the spatial relationship between the measurement techniques. Upon closer inspection it turns out that clocks are also playing an important role. Variable delays within the main techniques of space geodesy, namely SLR, VLBI, GNSS and DORIS are limiting the stability of the measurements and hence the entire observing system. This leads to the rather paradox situation, that each technique has to adjust the clock offsets independently. Although all main measurements systems on an observatory are usually based on the same clock, each technique provides different offsets, thus weakening the local ties. This reflects the fact that the clock adjustments are also contaminated with (variable) system specific delays. Increasing the coherence of time on these GGOS observatories disentangles erroneous system delays from local ties, thus strengthening the entire observing system. 

We have designed and built such a coherent time and frequency distribution system for the Geodetic Observatory Wettzell. It is based on a mode-locked fs- pulse laser, fed into a network of actively delay controlled two-way optical pulse transmission links. This utilizes the ultra low noise properties of optical frequency combs, both in the optical and electronic regime. Together with a common central inter- and intra- technique reference target time can provide consistency for the complex instrumentation of SLR and VLBI systems in situ, which was not possible before. This talk outlines the concept and its potential for GGOS.

How to cite: Schreiber, K. U., Kodet, J., Klügel, T., and Schüler, T.: Coherent Time and Frequency for an Improved Global Geodetic Observing System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16586, https://doi.org/10.5194/egusphere-egu2020-16586, 2020.

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Status on Chinese Space Geodesy Networks and their Applications

Xiaoya Wang, Zhongping Zhang, Fengchun Shu, Guangli Wang, and Kewei Xi

Chinese space geodetic networks were established in 1990s. The first SLR station in china was setup by Shanghai Astronomical Observatory (SHAO) in 1975 and now there are 7 SLR stations on operation in china. The observation accuracy has been improved from 1m to 8mm and the observation range has been extended from 1000km to 3600km for artificial satellites, 385000km for Lunar Range. The orbit determination accuracy has also been enhanced from several hectometer to 1-2 cm. And the products of SLR Terrestrial Reference Frame (TRF) and EOP is similar with that of other ILRS ACs and CCs. Currently 4 VLBI stations, including Seshan25, Kunming, Urumqi and Tianma65, participate in the IVS observing program. The total number of observing days was increased significantly in the past years. Shanghai VLBI correlator has been operational for the IVS data correlation since 2015. In addition to regular geodesy, we are also actively involved in the UT1 measurements and densification of the ICRF. We obtained first fringes between the two VGOS antennas at Shanghai in July 2019. A few more VGOS antennas will be built by collaborating with our partners in China or abroad. SHAO has provided the VLBI products such as POS+EOP to IVS. The first GPS station in China was setup in 1992 by JPL under the agreement between CAS and NASA, and now there are over 2000 GNSS stations running by CAS, China Earthquake Administration, Chinese Academy of Surveying & Mapping, China Meteorological Administration, Ministry of Education of the people’s Republic of China, Company and their subdivisions. From the ownership of Chinese GNSS network, we could see the comprehensive applications such as regional TRF densification, EOP measurement, meteorological service, earthquake displacement, ionospheric modelling, crustal movement monitoring, PNT and so on. The first DORIS station was set up in Wuhan in 2003 and now there are 2 DORIS sites in China. Chinese space geodetic networks and their application will be further developed in future.

How to cite: Wang, X., Zhang, Z., Shu, F., Wang, G., and Xi, K.: Status on Chinese Space Geodesy Networks and their Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4324, https://doi.org/10.5194/egusphere-egu2020-4324, 2020.

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Global Geodetic Observing System

Basara Miyahara

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) provides the basis on which future advances in geosciences can be built. By considering the Earth system as a whole (including the geosphere, hydrosphere, cryosphere, atmosphere and biosphere), monitoring Earth system components and their interactions by geodetic techniques and studying them from the geodetic point of view, the geodetic community provides the global geosciences community with a powerful tool consisting mainly of high-quality services, standards and references, and theoretical and observational innovations. The mission of GGOS is: (a) to provide the observations needed to monitor, map and understand changes in the Earth’s shape, rotation and mass distribution; (b) to provide the global frame of reference that is the fundamental backbone for measuring and consistently interpreting key global change processes and for many other scientific and societal applications; and (c) to benefit science and society by providing the foundation upon which advances in Earth and planetary system science and applications are built. The goals of GGOS are: (1) to be the primary source for all global geodetic information and expertise serving society and Earth system science; (2) to actively promote, sustain, improve, and evolve the integrated global geodetic infrastructure needed to meet Earth science and societal requirements; (3) to coordinate with the international geodetic services that are the main source of key parameters and products needed to realize a stable global frame of reference and to observe and study changes in the dynamic Earth system; (4) to communicate and advocate the benefits of GGOS to user communities, policy makers, funding organizations, and society. In order to accomplish its mission and goals, GGOS depends on the IAG Services, Commissions, and Inter-Commission Committees. The Services provide the infrastructure and products on which all contributions of GGOS are based. The IAG Commissions and Inter-Commission Committees provide expertise and support for the scientific development within GGOS. In summary, GGOS is IAG’s central interface to the scientific community and to society in general. The whole figure of GGOS and its recent focus will be presented in the presentation.

How to cite: Miyahara, B.: Global Geodetic Observing System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13390, https://doi.org/10.5194/egusphere-egu2020-13390, 2020.

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GGOS Coordinating Office – Recent Achievements and Activities

Martin Sehnal, Allison Craddock, and Kirsten Elger

The International Association of Geodesy’s (IAG) Global Geodetic Observing System (GGOS) is managed administratively by the GGOS Coordinating Office, based at the Austrian Federal Office of Metrology and Surveying (BEV). The director of GGOS Coordinating Office (CO) supports the Executive Committee, the Coordinating Board and the Science Panel as well as he ensures coordination of the activities of the various GGOS components like the Bureau of Products and Standards (BPS), the Bureau of Networks and Observations (BNO) and the three GGOS Focus Areas.

The Coordinating Office ensures information flow, maintains documentation of GGOS activities, and manages specific assistance functions that enhance the coordination across all areas of GGOS, including coordination among IAG Services and support for workshops. The Coordinating Office, in its long‐term coordination role, ensures that the GGOS components contribute to GGOS and its stakeholder community in a consistent and continuous manner. The Coordinating Office also maintains, manages, and coordinates the GGOS web- and social media presence as well as outreach and external engagement. In 2020 the current GGOS website (www.ggos.org) will be refreshed and redesigned to optimize usability and ease of navigation. The website will serve as a source of information about GGOS, geodetic data, products, and services, as well as other non-technical resources for the IAG community.

On behalf of the GGOS community, the Coordinating Office manages external relations and engagement with stakeholder organizations such as the Group on Earth Observations (GEO), the Committee on Earth Observation Satellites (CEOS) and the International Science Council (ISC) World Data System (WDS). In this capacity, the Office also identifies opportunities to link geodesy with relevant United Nations frameworks and other instruments of engagement, such as the Sendai Framework for Disaster Risk Reduction and the UN-GGIM-World Bank Integrated Geospatial Information Framework.

The Coordinating Office also works to identify opportunities for improved coordination and advocacy within the geodetic community, establishing the Working Group on “Digital Object Identifiers (DOIs) for Geodetic Data Sets” in 2019. This working group consists of more than 20 members affiliated with IAG Services, working to establish usage parameters and advocate for the consistent implementation of DOIs across all IAG Services and in the greater geodetic community.

How to cite: Sehnal, M., Craddock, A., and Elger, K.: GGOS Coordinating Office – Recent Achievements and Activities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6540, https://doi.org/10.5194/egusphere-egu2020-6540, 2020.

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The GGOS Bureau of Products and Standards

Detlef Angermann, Thomas Gruber, Michael Gerstl, Urs Hugentobler, Laura Sanchez, Robert Heinkelmann, and Peter Steigenberger

The Bureau of Products and Standards (BPS) supports GGOS in its goal to obtain consistent products describing the geometry, rotation and gravity field of the Earth. A key objective of the BPS is to keep track of adopted geodetic standards and conventions across all IAG components as a fundamental basis for the generation of consistent geometric and gravimetric products. This poster gives an overview about the organizational structure, the objectives and activities of the BPS. In its present structure, the two Committees “Earth System Modeling” and “Essential Geodetic Variables” as well as the newly established Working Group “Towards a consistent set of parameters for the definition of a new GRS” are associated to the BPS. Recently the updated 2nd version of the BPS inventory on standards and conventions used for the generation of IAG products has been compiled. Other activities of the Bureau include the integration of geometric and gravimetric observations towards the development of integrated products (e.g., GGRF, IHRF, atmosphere products) in cooperation with the IAG Services and the GGOS Focus Areas, the contribution to the re-writing of the IERS Conventions as Chapter Expert for Chapter 1 “General definitions and numerical standards”, the interaction with external stakeholders regarding standards and conventions (e.g., ISO, IAU, BIPM, CODATA) as well as contributions to the Working Group “Data Sharing and Development of Geodetic Standards” within the UN GGIM Subcommittee on Geodesy.

How to cite: Angermann, D., Gruber, T., Gerstl, M., Hugentobler, U., Sanchez, L., Heinkelmann, R., and Steigenberger, P.: The GGOS Bureau of Products and Standards, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7930, https://doi.org/10.5194/egusphere-egu2020-7930, 2020.

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GGOS Bureau of Networks and Observations: Network Infrastructure and Related Activities

Carey Noll, Michael Pearlman, Dirk Behrend, Allison Craddock, Erricos Pavlis, Jérôme Saunier, Elizabeth Bradshaw, Riccardo Barzaghi, Daniela Thaller, Benjamin Maennel, Ryan Hippenstiel, Roland Pail, and Nicholas Brown

The GGOS Bureau of Networks and Observations works with the IAG Services (IVS, ILRS, IGS, IDS, IGFS, and PSMSL) to advocate for the expansion and upgrade of space geodesy networks for the maintenance and improvement of the reference frame and other applications, as well as for the integration with other techniques, including absolute gravity and sea level measurements from tide gauges. New sites are being established following the GGOS concept of “core” and co-location sites, and new technologies are being implemented to enhance performance in data yield as well as accuracy. The Bureau continues to meet with organizations to discuss possibilities, including partnerships, for new and expanded participation. The GGOS Network continues to grow as new stations join every year.

The Bureau holds meetings frequently, providing the opportunity for representatives from the services to meet and share progress and plans, and to discuss issues of common interest. It also monitors the status and projects the evolution of the network based on information from the current and expected future participants. Of particular interest at the moment is the integration of gravity and tide gauge networks and the forthcoming establishment of the new absolute gravity reference frame. 

The IAG Committees and Joint Working Groups play an essential role in the Bureau activity. The Standing Committee on Performance Simulations and Architectural Trade-offs (PLATO) uses simulation and analysis techniques to project future network capability and to examine trade-off options. The Committee on Data and Information is working on a strategy for a GGOS metadata system for data products and a more comprehensive long-term plan for an all-inclusive system. The Committee on Satellite Missions is working to enhance communication with the space missions, to advocate for missions that support GGOS goals and to enhance ground systems support. The IERS Working Group on Site Survey and Co-location (also participating in the Bureau) is working to enhance standardization in procedures, outreach and to encourage new survey groups to participate and improve procedures to determine systems’ reference points, a crucial aid in the detection of technique-specific systematic errors.
 
We will give a brief update on the status and projection of the network infrastructure of the next several years, and the progress and plans of the Committees/Working Group in their critical role in enhancing data product quality and accessibility to the users.   

How to cite: Noll, C., Pearlman, M., Behrend, D., Craddock, A., Pavlis, E., Saunier, J., Bradshaw, E., Barzaghi, R., Thaller, D., Maennel, B., Hippenstiel, R., Pail, R., and Brown, N.: GGOS Bureau of Networks and Observations: Network Infrastructure and Related Activities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22473, https://doi.org/10.5194/egusphere-egu2020-22473, 2020.

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Recent Progress and Plans for Improvement of ILRS Infrastructure and Data Product Delivery

Michael R. Pearlman, Carey Noll, Erricos Pavlis, Toshimichi Otsubo, Jean-Marie Torre, Ulrich Schreiber, Georg Kirchner, and Michael Steindorfer Steindorfer

The International Laser Ranging Service (ILRS) is improving its services through network expansion and continuous upgrades of its modeling and analysis approaches. New ground stations are being deployed with higher repetition rate systems, more efficient detection, and increased automation; new technologies are also being adopted at some of its legacy stations. In addition, the roster of tracking missions is rapidly expanding. The top priority for the Service continues to be its contribution to the reference frame development, but of increasing importance is also the tracking of GNSS satellites, including the anticipated deployment of the new GPS III constellation over this decade. These requirements are being reflected in new system designs and updates. Stations are also being adapted to accommodate ground and space-time synchronization. A few stations continue with their lunar laser ranging activities while several others have begun testing their ability to do lunar ranging in the future. About a dozen stations are active in space-debris tracking for studies of orbital dynamics and reentry predictions. New tools and procedures have been implemented to improve the quality of SLR data and derived products, and to expedite the resolution of engineering issues. Work also continues on the design and building of improved retroreflector targets to maximize data quality and quantity.

 This paper will give an overview of activities underway within the Service, paths forward and presently envisioned, and current issues and challenges.

How to cite: Pearlman, M. R., Noll, C., Pavlis, E., Otsubo, T., Torre, J.-M., Schreiber, U., Kirchner, G., and Steindorfer, M. S.: Recent Progress and Plans for Improvement of ILRS Infrastructure and Data Product Delivery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5613, https://doi.org/10.5194/egusphere-egu2020-5613, 2020.

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Essential Geodetic Variables: Earth Orientation Parameters

Richard Gross

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) provides the basis on which future advances in geosciences can be built. By considering the Earth system as a whole (including the geosphere, hydrosphere, cryosphere, atmosphere and biosphere), monitoring Earth system components and their interactions by geodetic techniques and studying them from the geodetic point of view, the geodetic community provides the global geosciences community with a powerful tool consisting mainly of high-quality services, standards and references, and theoretical and observational innovations. A new initiative within GGOS is to define Essential Geodetic Variables. Essential Geodetic Variables (EGVs) are observed variables that are crucial (essential) to characterizing the geodetic properties of the Earth and that are key to sustainable geodetic observations. Once a list of EGVs has been determined, requirements can be assigned to them such as the accuracy with which the variables need to be determined, their spatial and temporal resolution, latency, etc. These requirements on the EGVs can then be used to assign requirements to EGV-dependent products like the terrestrial reference frame. The EGV requirements can also be used to derive requirements on the systems that are used to observe the EGVs, helping to lead to a more sustainable geodetic observing system for reference frame determination and numerous other scientific and societal applications.

For the Earth's rotation, the essential variables can be considered to be the five Earth orientation parameters (EOPs), namely, the x- and y-components of polar motion (xp, yp), the x- and y-components of nutation/precession (X, Y), and the spin parameter UT1. Related to these five Essential Earth Rotation Variables are the sub-variables of their time rates-of-change and the derived variables of the excitation functions (χx, χy, and length-of-day). The Essential Earth Rotation Variables are currently observed by the operational techniques of lunar and satellite laser ranging, very long baseline interferometry, global navigation satellite systems, and Doppler orbitography and radiopositioning integrated by satellite. In the future, the emerging techniques of ring laser gyroscopes and superfluid helium gyroscopes can be expected to routinely observe parameters related to the Essential Earth Rotation Variables. The GGOS requirements on the five Essential Earth Rotation Variables (that is, on the five EOPs) are "ERP-001-EOP: Earth Orientation Parameters will be determined with an accuracy of 1 mm, a temporal resolution of 1 hour, and a latency of 1 week; near real-time determinations of the Earth Orientation Parameters will be determined with an accuracy of 3 mm" (Plag and Pearlman, 2009, p. 223). Currently, the best-determined EOPs have an accuracy of about 1 mm, a temporal resolution of about 1 day, and a latency of about 2 weeks (Ray et al., 2017; http://www.igs.org/products). Thus, while the GGOS accuracy requirement on the Essential Earth Rotation Variables is currently being met, at least for some of the variables, the GGOS resolution and latency requirements are not being met.

How to cite: Gross, R.: Essential Geodetic Variables: Earth Orientation Parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2434, https://doi.org/10.5194/egusphere-egu2020-2434, 2020.

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Why do Geodetic Data need DOIs? First ideas of the GGOS DOI Working Group

Kirsten Elger, Glenda Coetzer, and Roelf Botha and the GGOS DOI Working Group

Only four years after the implementation of digital object identifiers (DOIs) for unambiguously identifying and linking to online articles, the first DOI for digital datasets was registered in 2004. Originally developed with the purpose of providing permanent access to (static) datasets described in scholarly literature (to allow reproducibility and scrutiny of research results), DOIs today are increasingly used for dynamic datasets (e.g. time series from observational networks, where new data values are added frequently given that the originally published data will not change), collections or networks. These DOIs (and other persistent identifiers) are mainly assigned for providing a citable and traceable reference to various types of sources (data, software, samples, equipment) and means of rewarding the originators and institutions.

As a result of international groups, like the Coalition for Publishing Data in the Earth and Space Sciences (COPDESS) and the Enabling FAIR Data project, datasets with assigned DOIs are now fully citable in scholarly literature - many journals require the data underlying a publication to be available before accepting an article. Initial metrics for data citation are available and allow data providers to demonstrate the value of the data collected by institutes and individual scientists – which makes them even more attractive.

This is especially relevant in the framework of evaluation criteria for institutions and researchers, that usually only consider scientific output in the form of scholarly literature and citation numbers. Compared to other scientific disciplines, geodesy researchers appear to be producing less “countable scientific” output. Geodesy researchers, however, are much more involved in operational aspects and data provision than researchers in other fields might be. Geodesy data and equipment therefore require a structured and well-documented mechanism which will enable citability, scientific recognition and reward that can be provided by assigning DOI to data, data products and scientific software.

To address these challenges and to identify opportunities for improved coordination and advocacy within the geodetic community, the International Association of Geodesy’s (IAG) Global Geodetic Observing System (GGOS) has established a Working Group on “Digital Object Identifiers (DOIs) for Geodetic Data Sets”. The GGOS DOI Working Group (with more than 20 members) officially started with a first meeting during December 2019, co-located to the AGU Fall Meeting. Beginning with an assessment of DOI minting strategies that are already implemented, the GGOS DOI Working Group is designated to establish best practices and advocate for the consistent implementation of DOIs across all IAG Services and in the greater geodetic community.

How to cite: Elger, K., Coetzer, G., and Botha, R. and the GGOS DOI Working Group: Why do Geodetic Data need DOIs? First ideas of the GGOS DOI Working Group, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17861, https://doi.org/10.5194/egusphere-egu2020-17861, 2020.

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GGOS Japan: Uniting Space Geodetic Activities in Japan

Toshimichi Otsubo, Basara Miyahara, Yusuke Yokota, Shinobu Kurihara, Hiroshi Munekane, Shun-ichi Watanabe, Takayuki Miyazaki, Hiroshi Takiguchi, Yuichi Aoyama, Koichiro Doi, Yoichi Fukuda, Koji Matsuo, Takaaki Jike, Takehiro Matsumoto, and Ryuichi Ichikawa

Since the establishment in 2013, GGOS Japan, formerly known as GGOS Working Group of Japan, has actively contributed to domestic and international space-geodetic activities.  Until it was established, six Japanese agencies with their own backgrounds and missions had individually conducted geodetic observations of GNSS, VLBI, SLR, DORIS and gravimetry in Japan and Antarctica.   GGOS Japan was established to strengthen the collaboration between the agencies and to get connected to international organizations such as IAG and GGOS.

Its core members consist of a chair, a secretary, a lead of the outreach working group, a lead of the DOI working group and representatives of five core techniques.  It is supported by tens of people in Japan and also by its parent entity, IAG subcommittee in Japan.

This presentation will cover our achievement such as assembling our site list, hosting various domestic/international meetings, planning a special issue in a domestic journal, producing its leaflet and website and so on.  Since 2017 it has been approved as an GGOS Affiliate and it is remarkable that Basara Miyahara was elected as GGOS President in 2019.

How to cite: Otsubo, T., Miyahara, B., Yokota, Y., Kurihara, S., Munekane, H., Watanabe, S., Miyazaki, T., Takiguchi, H., Aoyama, Y., Doi, K., Fukuda, Y., Matsuo, K., Jike, T., Matsumoto, T., and Ichikawa, R.: GGOS Japan: Uniting Space Geodetic Activities in Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3244, https://doi.org/10.5194/egusphere-egu2020-3244, 2020.

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GGOS Focus Area on Geodetic Space Weather Research – Current Status

Michael Schmidt and Ehsan Forootan

Space weather means a very up-to-date and interdisciplinary field of research. It describes physical processes in space mainly caused by the Sun’s radiation of energy. The manifestations of space weather are multiple, for instance, the variations of the Earth’s magnetic field or the changing states of the upper atmosphere, in particular the ionosphere and the thermosphere.

The main objectives of the Focus Area on Geodetic Space Weather Research (FA GSWR) are (1) the development of improved ionosphere models, (2) the development of improved thermosphere models and (3) the study of the coupled processes between magnetosphere, ionosphere and thermosphere (MIT). 

Objective (1) aims at the high-precision and the high-resolution (spatial and temporal) modelling of the electron density. This allows to compute a signal propagation delay, which will be used in many geodetic applications, in particular in positioning, navigation and timing (PNT). Moreover, it is also important for other techniques using electromagnetic waves, such as satellite- or radio-communications. Concerning objective (2), satellite geodesy will obviously benefit when working on Precise Orbit Determination (POD), but there are further technical matters like collision analysis or re-entry calculation, which will become more reliable when using high-precision and high-resolution thermospheric drag models. Objective (3) links the magnetosphere with the first two objectives by introducing physical laws and principles such as continuity, energy and momentum equations and solving partial differential equations.     

To arrive at the above described objectives of the FA GSWR one new Joint Study Groups (JSG) and three Joint Working Groups (JWG) have been installed recently. In detail, these groups are titled as JSG 1: Coupling processes between magnetosphere, thermosphere and ionosphere, JWG 1: Electron density modelling, JWG 2: Improvement of thermosphere models, and JWG 3: Improved understanding of space weather events and their monitoring by satellite missions. Other implemented IAG Study and Working Groups within the IAG programme 2019 to 2023 will provide valuable input for the FA GSWR. In this presentation we provide the latest investigations and results from the above mentioned Joint Study and Working Groups JSG 1, JWG 1, JWG 2 and JWG 3 of the FA GSWR.

How to cite: Schmidt, M. and Forootan, E.: GGOS Focus Area on Geodetic Space Weather Research – Current Status, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20304, https://doi.org/10.5194/egusphere-egu2020-20304, 2020.

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Activities and plans of the GGOS Focus Area Unified Height System

Laura Sanchez and Riccardo Barzaghi

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), providing precise geodetic infrastructure and expertise for monitoring the System Earth, promotes the standardization of height systems worldwide. The GGOS Focus Area "Unified Height System” (GGOS-FA-UHS, formerly Theme 1) was established at the 2010 GGOS Planning Meeting (February 1 - 3, Miami, Florida, USA) to lead and coordinate these efforts. Starting point was the results delivered by the IAG Inter-Commission Project 1.2 "Vertical Reference Frames" (IAG ICP1.2 VRF), which was operative from 2003 to 2011. During the 2011-2015 term, different discussions focussed on the best possible definition of a global unified vertical reference system resulted in the  IAG resolution for the "Definition and realization of an International Height Reference System (IHRS)” that was approved during the 2015 General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Prague, Czech Republic. The immediate objectives of the GGOS-FA-UHS are (1) to outline detailed standards, conventions, and guidelines to make the IAG Resolution applicable, and (2) to establish the realization of the IHRS, i.e., the International Height Reference Frame (IHRF). This contribution summarizes the main achievements of the GGOS-FA-UHS and provides a review of the open questions that need to be resolved in the near future.

How to cite: Sanchez, L. and Barzaghi, R.: Activities and plans of the GGOS Focus Area Unified Height System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8625, https://doi.org/10.5194/egusphere-egu2020-8625, 2020.

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Sea level in the Global Geodetic Observing System

Elizabeth Bradshaw, Andy Matthews, Kathy Gordon, Angela Hibbert, Sveta Jevrejeva, Lesley Rickards, Simon Williams, and Philip Woodworth

The Permanent Service for Mean Sea Level (PSMSL) is the global databank for long-term mean sea level data and is a member of the Global Geodetic Observing System (GGOS) Bureau of Networks and Observations. As well as curating long-term sea level change information from tide gauges, PSMSL is also involved in developing other products and services including the automatic quality control of near real-time sea level data, distributing Global Navigation Satellite System (GNSS) sea level data and advising on sea level metadata development.
At the GGOS Days meeting in November 2019, the GGOS Focus Area 3 on Sea Level Change, Variability and Forecasting was wrapped up, but there is still a requirement in 2020 for GGOS to integrate and support tide gauges and we will discuss how we will interact in the future. A recent paper (Ponte et al., 2019) identified that only “29% of the GLOSS [Global Sea Level Observing System] GNSS-co-located tide gauges have a geodetic tie available at SONEL [Système d'Observation du Niveau des Eaux Littorales]” and we as a community still need to improve the ties between the GNSS sensor and tide gauges. This may progress as new GNSS Interferometric Reflectometry (GNSS-IR) sensors are installed to provide an alternative method to observe sea level. As well as recording the sea level, these sensors will also provide vertical land movement information from one location. PSMSL are currently developing an online portal of uplift/subsidence land data and GNSS-IR sea level observation data. To distribute the data, we are creating/populating controlled vocabularies and generating discovery metadata.
We are working towards FAIR data management principles (data are findable, accessible, interoperable and reusable) which will improve the flow of quality controlled sea level data and in 2020 we will issue the PSMSL dataset with a Digital Object Identifier. We have been working on improving our discovery and descriptive metadata including creating a use case for the Research Data Alliance Persistent (RDA) Identification of Instruments Working Group to help improve the description of a time series where the sensor and platform may change and move many times. Representatives from PSMSL will sit on the GGOS DOIs for Data Working Group and would like to contribute help with controlled vocabularies, identifying metadata standards etc. We will also contribute to the next GGOS implementation plan.
Ponte, Rui M., et al. (2019) "Towards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level." Frontiers in Marine Science 6(437).

How to cite: Bradshaw, E., Matthews, A., Gordon, K., Hibbert, A., Jevrejeva, S., Rickards, L., Williams, S., and Woodworth, P.: Sea level in the Global Geodetic Observing System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3054, https://doi.org/10.5194/egusphere-egu2020-3054, 2020.

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Geodetic SAR for Height System Unification and Sea Level Research in the Baltics

Thomas Gruber, Jonas Ågren, Detlef Angermann, Artu Ellmann, Christoph Gisinger, Jolanta Nastula, Xanthi Oikonomidou, and Markku Poutanen

Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national levelling networks and therefore define a height system of a country. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. The project aims to make use of a new observation technique, namely SAR positioning, which can help to connect the GNSS basic network of a country to tide gauge stations and as such to link the sea level records of tide gauge stations to the geometric network. By knowing the geoid heights at the tide gauge stations in a global height reference frame with high precision, one can finally obtain absolute sea level heights of the tide gauge stations in a common reference system and can link them together. By this method, on the one hand national height systems can be connected and on the other hand the absolute sea level at the tide gauge stations can be determined. By analyzing time series of absolute sea level heights their changes can be determined in an absolute sense in a global reference frame and the impact of climate change on sea level can be quantified (e.g. by ice sheet and glacier melting, water inflow, global warming). The paper presents the main scientific questions to be addressed by the project, introduces the idea of using SAR transponders for this application and describes the observation network implemented for this feasibility study.

How to cite: Gruber, T., Ågren, J., Angermann, D., Ellmann, A., Gisinger, C., Nastula, J., Oikonomidou, X., and Poutanen, M.: Geodetic SAR for Height System Unification and Sea Level Research in the Baltics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3132, https://doi.org/10.5194/egusphere-egu2020-3132, 2020.

EGU2020-17922 | Displays | G2.1

Emerging instability in global terrestrial water storage since 2010

Shuang Yi and Nico Sneeuw

Global terrestrial water storage (TWS) is an indicator of the integrated impact of climate variability on the environment. Accurate assessments of global TWS also facilitate the understanding of disturbances in global sea level rise. Gravity satellite GRACE has proved to be an effective tool in monitoring global TWS changes. With the latest observations of GRACE and GRACE Follow-on, we estimated the global TWS from April 2002 to October 2019, and found contrasting variations in global TWS before and after 2010. Before 2010, the global TWS was almost stable with variations that contribute only a few millimeters of sea level change; while the stability is ceased after the 2010/11 La Nina and three drastic fluctuations of up to 10 millimeters sea level contribution have occurred since then. We find these TWS changes have a good linear relationship with the global precipitation trend, rather than the accumulation of net precipitation, indicating that the precipitation trend is the main driving force of the recent global TWS instability. We further investigate the sensitivities of TWS to precipitation in basins.

How to cite: Yi, S. and Sneeuw, N.: Emerging instability in global terrestrial water storage since 2010, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17922, https://doi.org/10.5194/egusphere-egu2020-17922, 2020.

EGU2020-21595 | Displays | G2.1

The International DORIS Service is preparing the future

Pascale Ferrage, Laurent Soudarin, and Frank Lemoine

The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 30 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system. Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF.
The International DORIS Service (IDS) was created in 2003 under the umbrella of the International Association of Geodesy (IAG) to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products from an expanded set of DORIS Analysis Centers. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associate Analysis Centers, and a Combination Center. Using the experience gained in the preparation of the ITRFs, many improvements were made all along both in data analysis and on technical aspects. After the IDS Retreat held in June 2018, the IDS GB worked on the development of a strategic plan for the IDS. In the coming years, IDS will focus on growing the community, extending the DORIS applications, and improving the technology, the infrastructure and the processing.
This presentation addresses the recent achievements made by IDS and how the service is preparing the future.

How to cite: Ferrage, P., Soudarin, L., and Lemoine, F.: The International DORIS Service is preparing the future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21595, https://doi.org/10.5194/egusphere-egu2020-21595, 2020.

EGU2020-5201 | Displays | G2.1

Radar Corner Reflector installation at the OCA geodetic Observatory (France)

Xavier Collilieux, Clément Courde, Bénédicte Fruneau, Mourad Aimar, Guillaume Schmidt, Isabelle Delprat, Damien Pesce, and Guy Wöppelmann

Geodetic observatories play a fundamental role in the determination of the International Terrestrial Reference System releases. They host several geodetic permanent instruments whose coordinates can be determined at the centimeter level or better. They comprise Global Navigation Satellite System (GNSS) permanent antenna/receivers, Satellite Laser Ranging (SLR) stations, Very Long Baseline Interferometry (VLBI) telescope and Doppler Orbitography Integrated by Satellite (DORIS) beacons. The Calern site of the Observatoire de la Côte d’Azur (OCA) is an example of such a multi-technique site located in the South of France. It hosts a DORIS beacon, a SLR/LLR station and two GNSS permanent stations.

 

In the process of determining coordinates of geodetic instruments in a unified reference frame, the relative positions of the instruments at co-location sites are integrated in the ITRF combination. Thanks to the additional measurements obtained from local surveys, it is possible to determine global biases between coordinates determined by individual space geodetic techniques, and express them in the same reference system. An additional fundamental assumption of the combination process is that stations located on the same site do not move with respect to each other. Spaceborne Synthetic Aperture Radar Interferometry (INSAR technique), is an interesting tool to evaluate that hypothesis as it allows measuring ground displacements in the line of sight of the satellite,  and has been used only occasionally in the past for this purpose,. Notably, the Persistent Scatterer (PS) Interferometry enables determining time series of ground displacements on particular scatterers exhibiting phase stability in a stack (or series ?) of SAR images. To ensure the existence (or presence ?) of such PS, artificial corner reflectors can be installed.

 

We present the procedure that we adapted from Parker et al. (2007) to install and validate the installation of a corner reflector at OCA observatory, close to the currently operating GNSS, SLR and DORIS stations, specifically designed for Sentinel-1 satellite. An initial local tie survey was carried out to assess the stability of the reflector through time.

How to cite: Collilieux, X., Courde, C., Fruneau, B., Aimar, M., Schmidt, G., Delprat, I., Pesce, D., and Wöppelmann, G.: Radar Corner Reflector installation at the OCA geodetic Observatory (France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5201, https://doi.org/10.5194/egusphere-egu2020-5201, 2020.

EGU2020-13687 | Displays | G2.1

VGOS Intensives Ishioka-Onsala

Rüdiger Haas, Eskil Varenius, Grzegorz Klopotek, Periklis-Konstantinos Diamantidis, Saho Matsumoto, Matthias Schartner, and Jan Tobias Nilsson

The VLBI Global Observing System (VGOS) is the VLBI contribution to GGOS. During the last years, several VGOS stations have been established, the VGOS observation program has started, and by 2020 VGOS has achieved an operational state involving eight international VGOS stations. Further VGOS stations are currently installed, so that the number of active VGOS stations will increase drastically in the near future. In the end of 2019 the International VLBI Service for Geodesy and Astrometry (IVS) decided to start a new and so-far experimental VGOS-Intensive series, called VGOS-B, involving Ishioka (Japan) and Onsala (Sweden). Both sites operate modern VGOS stations with 13.2 m diameter radio telescopes, i.e. ISHIOKA (IS) in Japan, and ONSA13NE (OE) and ONSA13SW (OW) in Sweden. In total 12 VGOS-B sessions were planned to be observed between December 2019 and February 2020, one every week, in parallel and simultaneously to legacy S/X INT1 Intensive sessions that involve the stations KOKEE (KK) on Hawaii and WETTZELL (WZ) in Germany. The 1-hour long VGOS-B sessions consist of more than fifty radio source observations, resulting in about 1.6 TB of raw data that are collected at each station. The scheduling of the VGOS-B sessions is done at Vienna University of Technology using VieSched++ and the subsequent steps (correlation, fringe-fitting, database creation) are planned to be carried out at the Onsala Space Observatory using DIFX and HOPS. The resulting VGOS databases are planned to be analysed with several VLBI analysis software packages, involving nuSolve, c5++ and ivg::ASCOT. In this presentation, we give an overview on the VGOS-B series, present our experiences, and discuss the obtained results.

How to cite: Haas, R., Varenius, E., Klopotek, G., Diamantidis, P.-K., Matsumoto, S., Schartner, M., and Nilsson, J. T.: VGOS Intensives Ishioka-Onsala, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13687, https://doi.org/10.5194/egusphere-egu2020-13687, 2020.

EGU2020-13254 | Displays | G2.1

Satellite Scheduling with VieSched++ : current status and future plans

Helene Wolf, Matthias Schartner, Johannes Böhm, and Andreas Hellerschmied

Observing extragalactic radio sources is an integral part of Very Long Baseline Interferometry (VLBI) but observing satellites also provides a variety of new possibilities. Interesting scientific applications can be found in providing space ties instead of using local ties for connecting reference frames of different space-geodetic techniques. To generate schedules including observations to satellites a dedicated module has been implemented in the new scheduling software VieSched++.


This newly developed module determines possible satellite observations considering several observation conditions, such as the visibility from the selected station network and antenna slew rates. A schedule including observations to quasars and satellites can be generated in a semi-automatic mode. The scheduling of the satellite scans is done manually by the user who can select and adjust the possible satellite observations before adding them to the schedule. The remaining part of the schedule is filled automatically by the software VieSched++ using the general optimization algorithm with observations to quasars. In this poster an overview of the current status of the satellite scheduling module in VieSched++ is given, as well as an outlook to highlight future plans. 

How to cite: Wolf, H., Schartner, M., Böhm, J., and Hellerschmied, A.: Satellite Scheduling with VieSched++ : current status and future plans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13254, https://doi.org/10.5194/egusphere-egu2020-13254, 2020.

EGU2020-18305 | Displays | G2.1

Development of novel ground-based microwave radiometer for earth science -results of the first measurements-

Ryuichi Ichikawa, Hideki Ujihara, Shinsuke Satoh, Yusaku Ohta, Basara Miyahara, Hiroshi Munekane, Taketo Nagasaki, Osamu Tajima, Kentaro Araki, Takuya Tajiri, Hiroshi Takiguchi, Takeshi Matsushima, Nobuo Matsushima, Tatsuya Momotani, and Kenji Utsunomiya

We have started to develop a next-generation microwave radiometer to be used in millimeter-wave spectroscopy for the high-resolution and high-precision monitoring of water vapor behavior. The new radiometer will be suitable for not only space geodetic techniques such as VLBI and GNSS, but also field measurements to monitor, for example, volcanic activities and cumulonimbus cloud generation. The planned front-end system for our new microwave radiometer has a wide bandwidth feed of 20–60 GHz. A signal from the feed is separated into two linear orthogonal polarized signals using an orthomode transducer (OMT); one is in the 20–30 GHz feed and the other is in the 50–60 GHz feed. We are now planning to cool the wideband feed, OMT, and LNA for each signal at 77 K using a Stirling cryocooler to improve the signal-to-noise ratio. We assembled a room-temperature 20–30 GHz receiver without the cooling system until the middle of 2019 as a first step of our development. We implemented the new receiver into the 3.7 m dish at Okinawa Electromagnetic Technology Center, National Institute of Information and Communications Technology (NICT), and carried out the first measurements using this receiver for validation tests in October 2019. Quick-look data obtained by the new receiver shows good power signals for the expected receiving band of 18–28 GHz. We are now developing another receiver for a higher band of 50–60 GHz, and we are going to implement the second one into the new prototype radiometer by the end of this fiscal year.

How to cite: Ichikawa, R., Ujihara, H., Satoh, S., Ohta, Y., Miyahara, B., Munekane, H., Nagasaki, T., Tajima, O., Araki, K., Tajiri, T., Takiguchi, H., Matsushima, T., Matsushima, N., Momotani, T., and Utsunomiya, K.: Development of novel ground-based microwave radiometer for earth science -results of the first measurements-, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18305, https://doi.org/10.5194/egusphere-egu2020-18305, 2020.

EGU2020-6153 | Displays | G2.1

Twenty-Five Years of the International GNSS Service

Allison Craddock, Gary Johnston, Felix Perosanz, Rolf Dach, Charles Meertens, Michael Moore, and Mayra Oyola

For over twenty-five years, the International Global Navigation Satellite System (GNSS) Service (IGS) has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products.

The IGS is an essential component of the IAG’s Global Geodetic Observing System (GGOS), where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF).  As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.

This poster will present an update on current IGS products and operations, as well as highlights on recent organizational developments and community activities. The impacts and benefits of global cooperation and openly available data will be emphasized, and information about the IGS stations and network, contributions to the International Terrestrial Reference Frame solutions, and product applications will be presented. A summary of IGS products, with emphasis on analysis, coordination, applications, and their availability will be described. Information about efforts to form new groups supporting product generation within IGS open data and product policies will be included. Information about the themes and topics of discussion for the upcoming 2020 IGS Workshop in Boulder, Colorado, USA will also be provided.

How to cite: Craddock, A., Johnston, G., Perosanz, F., Dach, R., Meertens, C., Moore, M., and Oyola, M.: Twenty-Five Years of the International GNSS Service, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6153, https://doi.org/10.5194/egusphere-egu2020-6153, 2020.

GEONET tracking data is analyzed applying Galileo and/or GPS satellite systems, using GAMIT/GLOBK software. We adopt ITRF2014 reference frame and CODE precise orbit obtained in the GMEX experiment. For the fiducial sites, we use 14 IGS sites in and around East Asia both Galileo and GPS analyses. At the IGS sites in this area, number of sites, whose coordinates and velocity are determined in Altamimi et al.(2016) and also tracking Galileo satellites, is very limited. In the current version of the GAMIT/GLOBK program, the solar radiation pressure model of the Galileo satellites has limited accuracy, which results in large errors in the analysis using the Galileo satellites. Preliminary results from 10-day Galileo satellites analysis of the 2018 DOY 300-309 show that the weighted rms of the N-S component of the repeatability of 1276 GEONET site coordinates is 5.5 mm, the E-W component 4.5 mm, and the U-D component 9.0 mm. On the other hand, for those from GPS satellites show that those weighted rms of the N-S component is 1.6 mm, E-W component 1.3 mm, and U-D component 3.5 mm. Therefore, the repeatability of the GEONET site coordinate solution of the composite solution of GPS and Galileo satellites has hardly improved: the weighted rms of the N-S component is 2.7 mm, E-W component 2.0 mm, and U-D component 3.7 mm. The presentation will show the results applying the new Galileo satellite solar pressure model (ECOMC model) included in the updated GAMIT/GLOBK program released in the near future, as well as the period of analysis more than one year. 

How to cite: Shimada, S.: Data analysis of GEONET network data applying Galileo Satellite System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22256, https://doi.org/10.5194/egusphere-egu2020-22256, 2020.

EGU2020-18634 | Displays | G2.1

GNSS Station Metadata Revisited in Response to Evolving Needs

Carine Bruyninx, Andras Fabian, Juliette Legrand, and Anna Miglio

The IGS (International GNSS Service) site log format is the worldwide standard for exchanging GNSS station metadata. It contains, among other things, a description of the GNSS site and its surroundings, the contact persons, and an historical overview of the GNSS equipment. This information is valuable for reliable GNSS data analysis and interpretation of the results.

This IGS site log is also used within the EUREF Permanent Network (EPN, Bruyninx et al., 2019) and the GNSS component of the European Plate Observing System (EPOS, https://www.epos-eu.org/). However, due to their specific needs, these networks collect additional GNSS metadata. For example, within the EPN, individual receiver antenna calibration values are collected, as well as the information on the data provided by the station. EPOS is collecting in addition data licences. Within the Creative Commons permitted licence scheme, two licences will be adopted by EPOS, CC:BY and CC:BY:NC. Both licenses require that the data user acknowledges (cites) the data owner. To facilitate this data citation, EPOS recommends attributing Digital Object Identifiers (DOI) to the GNSS data and therefore also includes the DOI in the collected GNSS station metadata.

Many IGS and EPN stations also contribute to EPOS and therefore it is imperative to harmonize the collection and distribution of the additional metadata. The GeodesyML (http://geodesyml.org) format already allows including more metadata compared to the IGS site log format. In this poster, we will review the challenges and propose how to tackle them. We will finish by showing the choices made within the “Metadata Management and Distribution System for Multiple GNSS networks” (M3G) which collects and disseminates GNSS station metadata within both the EPOS and EPN networks.

Bruyninx C., Legrand J., Fabian A., Pottiaux E. (2019) GNSS Metadata and Data Validation in the EUREF Permanent Network. GPS Sol., 23(4), https://doi: 10.1007/s10291-019-0880-9          

How to cite: Bruyninx, C., Fabian, A., Legrand, J., and Miglio, A.: GNSS Station Metadata Revisited in Response to Evolving Needs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18634, https://doi.org/10.5194/egusphere-egu2020-18634, 2020.

EGU2020-10126 | Displays | G2.1

The IGFS gravity field observations and products contributions to GGOS infrastructure

Georgios S. Vergos, Riccardo Barzaghi, Sylvaint Bovalot, Elmas Sinem Ince, Adrian Jäggi, Mirko Reguzzoni, Hartmut Wziontek, and Kevin Kelly

Through its structure the International Gravity Field Service (IGFS) promotes the interaction, cooperation and synergy between the Gravity Services, namely the Bureau Gravimétrique International (BGI), the International Service for the Geoid (ISG), the International Geodynamics and Earth Tides Service (IGETS), the International Center for Global Earth Models (ICGEM), the International Combination Service for Time-variable Gravity Fields (COST-G) and the International Digital Elevation Model Service (IDEMS).

Furthermore, via its Central Bureau hosted at the Aristotle University of Thessaloniki (Greece), IGFS provides a link to the Global Geodetic Observing System (GGOS) Bureaus in order to communicate their requirements and recommendations to the IGFS-Centers. Moreover, IGFS provides a coordination host for the utilization of gravity-field related products and services towards their inclusion within a GGOS consistent frame meeting the necessary precision and accuracy requirements.

In this work, an outline is given on the recent activities of IGFS, namely those related to the contributions to the implementation of: the International Height Reference System/Frame; the Global Geodetic Reference System/Frame; the new Global Absolute Gravity Reference System/Frame and rhe combination of temporal monthly global gravity field models. Particularly, the impact that these activities have and will have in improving the estimation of the Earth’s gravity field, either at global and local scale, is highlighted also in the framework of GGOS.

How to cite: Vergos, G. S., Barzaghi, R., Bovalot, S., Ince, E. S., Jäggi, A., Reguzzoni, M., Wziontek, H., and Kelly, K.: The IGFS gravity field observations and products contributions to GGOS infrastructure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10126, https://doi.org/10.5194/egusphere-egu2020-10126, 2020.

EGU2020-3511 | Displays | G2.1

The International Centre for Global Earth Models (ICGEM)

Christoph Förste, Elmas Sinem Ince, Sven Reissland, Kirsten Elger, Frank Flechtner, and Franz Barthelmes

The more than 15-year-old ICGEM is one of the five services coordinated by the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG). It is hosted by GFZ German Research Centre for Geosciences in Potsdam, Germany. The aim of the ICGEM service is to provide the scientific community with a state-of-the-art archive of static and time variable global gravity field models of the Earth in a standardized format with a possibility to assign DOI number. Furthermore, ICGEM contains an interactive calculation and visualization service of gravity field functionals. Development and maintenance of such a unique platform is crucial for the scientific community in geodesy, geophysics, oceanography and climatology and has a positive impact in governmental institutions and industrial practice. This poster covers the maintenance, recently established new features and future plans of the ICGEM Service. New features include the calculation of gravity field functionals at a list of user-defined distributed points and new topographic gravity field models, whereas the future plans aim to meet the needs of the scientific community. As an add-on, ICGEM provides also access to the gravity field models of some other celestial bodies (Mars, Venus, and Earth’s moon).

How to cite: Förste, C., Ince, E. S., Reissland, S., Elger, K., Flechtner, F., and Barthelmes, F.: The International Centre for Global Earth Models (ICGEM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3511, https://doi.org/10.5194/egusphere-egu2020-3511, 2020.

G2.2 – The International Terrestrial Reference Frame: Elaboration, Usage and Applications

EGU2020-7218 | Displays | G2.2

A Status Report on the ILRS Contribution to ITRF2020

Vincenza Luceri, Erricos C. Pavlis, Antonio Basoni, David Sarrocco, Magdalena Kuzmicz-Cieslak, Keith Evans, and Giuseppe Bianco

The International Laser Ranging Service (ILRS) Analysis Standing Committee (ASC) plans to complete the re-analysis of the SLR data since 1983 to end of this year by early 2021. This will ensure that the ILRS contribution to ITRF2020 will be available to ITRS by February 2021, as agreed by all space geodetic techniques answering its call. In preparation for the development of this contribution, the ILRS completed the re-analysis of all data (1983 to present), based on an improved modeling of the data and a novel approach that ensures the results are free of systematic errors in the underlying data. The new approach was developed after the completion of ITRF2014, the ILRS ASC devoting almost entirely its efforts on this task. A Pilot Project initially demonstrated the robust estimation of persistent systematic errors at the millimeter level, leading us to adopt a consistent set of a priori corrections for data collected in past years. The initial reanalysis used these corrections, leading to improved results for the TRF attributes, reflected in the resulting new time series of the TRF origin and scale. The ILRS ASC will now use the new approach in the development of its operational products and as a tool to monitor station performance, extending the history of systematics for each system that will be used in future re-analysis. The new operational products form a seamless extension of the re-analysis series, providing a continuous product based on our best knowledge of the ground system behavior and performance, without any dependence whatsoever on a priori knowledge of systematic errors (although information provided by the stations from their own engineering investigations are always welcome and taken into consideration). The presentation will demonstrate the level of improvement with respect to the previous ILRS product series and give a glimpse of what is to be expected from the development of a preliminary version of the ITRF2020.

How to cite: Luceri, V., Pavlis, E. C., Basoni, A., Sarrocco, D., Kuzmicz-Cieslak, M., Evans, K., and Bianco, G.: A Status Report on the ILRS Contribution to ITRF2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7218, https://doi.org/10.5194/egusphere-egu2020-7218, 2020.

EGU2020-11252 | Displays | G2.2

The IDS Contribution to the ITRF2020: Preliminary results

Guilhem Moreaux, Frank Lemoine, Hugues Capdeville, Petr Štěpánek, and Pascale Ferrage

To provide its contribution to the next realization of the International Terrestrial Reference Frame (ITRF2020), the International DORIS Service (IDS) plans to complete the re-analysis of the DORIS data from 1993.0 to 2021.0 by early 2021. In preparation for the development of its contribution, the IDS completed several pilot studies for a better modelling of the solar radiation pressure, to mitigate the effect of the South Atlantic Anomaly on the DORIS receivers, to improve the stability of the DORIS scale. The complete re-analysis is divided in several parts depending on the time evolution of the DORIS constellation and on modelling issues.

IDS Analysis Center contributions for first time period, which corresponds to the observations from the DORIS satellites with the first generation of the DORIS receivers: 1993.0-2002.3 (start of Envisat – first DORIS 2G receiver), are expected by the end of the first quarter of 2020.

After presentation of the status of the main guidelines of the DORIS contribution to the ITRF2020, we will analyze the first time period of the DORIS contribution to ITRF2020 in terms of (1) geocenter and scale solutions; (2) station positions and week-to-week repeatability; (3) EOPs. In addition, we will compare this new DORIS solution with the IDS contribution to ITRF2014. Then, we will present updated results on the latest IDS pilot studies.

How to cite: Moreaux, G., Lemoine, F., Capdeville, H., Štěpánek, P., and Ferrage, P.: The IDS Contribution to the ITRF2020: Preliminary results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11252, https://doi.org/10.5194/egusphere-egu2020-11252, 2020.

EGU2020-20320 | Displays | G2.2 | Highlight

Quality assessment of GNSS reference stations: Criteria and Thresholds

Juliette Legrand and Carine Bruyninx

When using a network approach, expressing reliably GNSS position and velocities in a given reference frame (ITRF2014, IGS14, …) requires the identification of ‘stable’ and ‘rebliable’ reference stations. The choice of these reference stations can have a non-negligible impact on the estimated positions and velocities and of course on the derived geodynamic interpretations.

This study will present the work done to address this issue within EUREF and help the users of the EUREF products (more specifically of the EPN multi-year position and velocity solution) to identify the best reference stations in the EUREF Permanent Network (EPN). To that aim, a new station classification was developed based on a set of criteria.

First, the position time series of the stations were analyzed in terms of seasonal signals and scattering.

Then, we quantified the reliability of the velocity estimation: The EPN multi-year position and velocity solution is estimated using CATREF software (Altamimi et al., 2007). We used more realistic velocity error estimates taking into account a temporal correlated noisederived from the Hector software (Bos et al., 2013) and compared the velocity estimates from Hector and CATREF.

Finding a suitable reference station is particularly difficult when dealing with a different period of observations compared to the reference solution. Therefore, finally, we looked for a criterion to assess the stability of the station over its full history. For this, we quantified the velocity variability over time of a station by comparing the velocities estimated using various time spans with velocities from the full time span of the station.

Based on those criteria, the information has been organized and thresholds have been defined in order to end up with a simple station classification, which is currently under evaluation within EUREF. Based on this classification, we also developed a web tool in order to help the user to select the best reference stations in a considered area and for a given period of observation.

How to cite: Legrand, J. and Bruyninx, C.: Quality assessment of GNSS reference stations: Criteria and Thresholds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20320, https://doi.org/10.5194/egusphere-egu2020-20320, 2020.

EGU2020-18184 | Displays | G2.2

Investigation of the relationship between sensitivity level of the sources and the internal reliability value of VLBI observations during CONT14

Pakize Kurec Nehbit, Robert Heinkelmann, Harald Schuh, and Haluk Konak

The quality of geodetic networks can be determined with the sensitivity and the internal reliability magnitudes when the mathematical model established for the network adjustment is questioned. Internal reliability is used for controlling an observation with the help of the other observations in the network and describes the magnitude of the undetectable gross errors by using hypothesis testing. The sensitivity level is explained as the minimum value of the undetectable gross error in the adjusted coordinate differences. In VLBI the observed sources are of major importance for the quality of the observations.  In this study, it is investigated how the sensitivity levels of the sources impact the internal reliability of the observations during the continuous VLBI campaign CONT14. It is aimed to detect the poor sources and their effects statistically in the VLBI data analysis. If the sources having worst sensitivity value such as 0506-612, 3C454.3, NRAO150, and 3C345  have been excluded, the internal reliability values of the observations get better. For the rest of the sources the sensitivity distributions have been obtained as better. It can be concluded that the source structure might be significant for the quality of the observations.

How to cite: Kurec Nehbit, P., Heinkelmann, R., Schuh, H., and Konak, H.: Investigation of the relationship between sensitivity level of the sources and the internal reliability value of VLBI observations during CONT14, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18184, https://doi.org/10.5194/egusphere-egu2020-18184, 2020.

EGU2020-6546 | Displays | G2.2

An Advanced Formulation of Kalman Filter Time Series Reference Frame Realization for Geophysical Applications

Xiaoping Wu, Bruce Haines, Michael Heflin, and Felix Landerer

A Kalman filter and time series approach to the International Terrestrial Reference Frame (ITRF) realization (KALREF) has been developed and used in JPL. KALREF combines weekly or daily SLR, VLBI, GNSS and DORIS data and realizes a terrestrial reference frame in the form of time-variable geocentric station coordinate time series. The origin is defined at nearly instantaneous Center-of-Mass of the Earth system (CM) sensed by weekly SLR data and the scale is implicitly defined by the weighted averages of those of weekly SLR and daily VLBI data. The standard KALREF formulation describes the state vector in terms of time variable station coordinates and other constant parameters. Such a formulation is fine for station positions and their uncertainties or covariance matrices at individual epochs. However, coordinate errors are strongly correlated over time given KALREF’s unique nature of combining different technique data with various frame strengths through local tie measurements and co-motion constraints and its use of random walk processes. For long time series and large space geodetic networks in the ITRF, KALREF cannot keep track of such correlations over time. If they are ignored when forming geocentric displacements for geophysical inverse or network shift geocenter motion studies, the covariance matrices of coordinate differences cannot adequately represent those of displacements. Consequently, significant non-uniqueness and inaccuracies would occur in the results of studies using such matrices. To overcome this difficulty, an advanced KALREF formulation is implemented that features explicit displacement parameters in the state vector that would allow the Kalman filter and smoother to compute and return covariance matrices of displacements. The use of displacement covariance matrices reduces the impact of time correlated errors and completely solves the non-uniqueness problem. However, errors in the displacements are still correlated in time. Further calibrations are needed to accurately assess covariance matrices of derivative quantities such as averages, velocities and accelerations during various time periods. We will present KALREF results of the new formulation and their use along with newly reprocessed RL06 GRACE gravity data in a new unified inversion for geocenter motion.

How to cite: Wu, X., Haines, B., Heflin, M., and Landerer, F.: An Advanced Formulation of Kalman Filter Time Series Reference Frame Realization for Geophysical Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6546, https://doi.org/10.5194/egusphere-egu2020-6546, 2020.

EGU2020-10823 | Displays | G2.2

Temporal variations in ITRF station displacements analyzed with vector spherical harmonics

Benedikt Soja, Claudio Abbondanza, T. Mike Chin, Richard Gross, Michael Heflin, Jay Parker, and Xiaoping Wu

The ITRF2014 candidate solutions DTRF2014 and JTRF2014 provide time-dependent station coordinates accounting for irregular station motions. DTRF2014 by DGFI-TUM expands the secular coordinate model via non-tidal loading corrections caused by changes in the atmosphere and continental water storage. JTRF2014 by JPL follows a time series approach to TRF determination based on Kalman filtering, providing weekly updates to station coordinates. The process noise model of the Kalman filter is derived from non-tidal loading deformations.

Global features in station displacements have been studied in the past by determining coefficients of spherical harmonics. So far, studies have mostly focused on individual coordinate components at a time. Typically, the vertical coordinate component is of most interest, since it most often contains the largest signals.

In this work, we apply the concept of vector spherical harmonics (VSH) to study temporal variations in station displacements of DTRF2014 and JTRF2014. The advantage of VSH compared to scalar spherical harmonics is that all three coordinate components can be considered at the same time. We estimate VSH coefficients up to degree-2, which includes dipole and quadrupole deformations. Degree-1 deformations represent translations and rotations of the frame, while degree-2 terms contain, inter alia, information on the oblateness of the Earth. We use VSH to analyze station displacements of DTRF2014 and JTRF2014 individually and to conduct comparisons between the two frames. Furthermore, since the temporal variations in both DTRF2014 and JTRF2014 are linked to non-tidal loading deformations, our analysis of temporal variations in VSH coefficients allows for geophysical interpretation.

 

How to cite: Soja, B., Abbondanza, C., Chin, T. M., Gross, R., Heflin, M., Parker, J., and Wu, X.: Temporal variations in ITRF station displacements analyzed with vector spherical harmonics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10823, https://doi.org/10.5194/egusphere-egu2020-10823, 2020.

The reprocessed time series (weekly from SLR, daily from GNSS, and 24h session-wise from VLBI) of co-located station position solutions spanning their full observation histories up to the end of 2014 are analyzed with the goal to detect nonlinear time-variable effects in station positions, such as periodic variations or discontinuities caused e.g. by instrumental changes or earthquakes. This information is then used to assess the reliability of the results about the nonlinear changes of all technique stations in each colocation site since they can be verified with each other. Next, the iterative adjustment is performed, i.e. jumping changes, post-seismic deformation and periodical signals are determined altogether for accurate estimation of station velocity. Finally, the information of the relative motion among the stations equipped with different technique instruments per colocation site is determined which can offer a reference for the necessary arrangement of local resurvey in the future.

How to cite: Lian, L., Huang, C., and Zhang, J.: Comparative Analysis of non-linear position variations using the time series of station coordinates in some ITRF co-location sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6812, https://doi.org/10.5194/egusphere-egu2020-6812, 2020.

EGU2020-8712 | Displays | G2.2

Preparations for the ITRF2020 at TU Wien

Anna Zessner-Spitzenberg, David Mayer, Andreas Hellerschmied, Markus Mikschi, and Sigrid Böhm

The next International Terrestrial Reference Frame (ITRF), ITRF2020, will be released in early 2021 and preparations are entering the final phase. It will be realized by using the observations of the space geodetic techniques Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).
The Vienna VLBI group is planning to contribute to the ITRF2020. This poster will present the goals, the methodology and preparations for our contribution. In order to analyse the VLBI observation sessions, the Vienna VLBI and Satellite Software (VieVS) will be used. The poster will focus on the influence of applying the gravitational deformation and the atmospheric loading on the individual solutions and the ITRF.  For this purpose, a selected list of more than 800 sessions of the last 40 years, which was released by the International VLBI Service for Geodesy and Astrometry (IVS) to verify the latest changes in the implementation, will be analysed and the results will be presented.

How to cite: Zessner-Spitzenberg, A., Mayer, D., Hellerschmied, A., Mikschi, M., and Böhm, S.: Preparations for the ITRF2020 at TU Wien, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8712, https://doi.org/10.5194/egusphere-egu2020-8712, 2020.

EGU2020-5100 | Displays | G2.2

On the impact of gravitational deformation on VLBI-derived parameters

Sahar Shoushtari, Susanne Glaser, Kyriakos Balidakis, Robert Heinkelmann, James Anderson, and Harald Schuh

On the impact of gravitational deformation on VLBI-derived parameters

Sahar Shoushtari1,2, Susanne Glaser1, Kyriakos Balidakis1, Robert Heinkelmann1,2, James M. Anderson1,2, Harald Schuh1,2

(1) GFZ German Research Centre for Geosciences, Section 1.1 Space Geodetic Techniques, Telegrafenberg, 14473 Potsdam, Germany

(2) Technische Universität Berlin, Chair of Satellite Geodesy, Strasse des 17. Juni 135, 10623 Berlin, Germany

Very Long Baseline Interferometry (VLBI) is a highly accurate space geodetic technique that observes extragalactic radio sources to measure the time delay between arrival times of a plane wavefront at two distant radio telescopes. The gravitational deformation of the VLBI telescopes as a function of pointing direction, caused by gravitational forces acting on the massive telescope structures, mainly impacts the estimated station heights and can reach centimeter-level for large antennas. Thus far, this effect has not been considered in operational VLBI data analysis. In the next realization ITRF2020, it is envisaged to model this effect in an effort to reduce the persistent scale discrepancy in ITRF2014 between VLBI and Satellite Laser Ranging. Currently, there are models for only a minority of antennas available, six in total: Effelsberg, Gilcreek, Medicina, Noto, Onsala, and Yebes, which are provided by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, the impact of the gravitational models on station positions, Earth orientation parameters and the network scale is assessed within VLBI data analysis. The standard 24-hours IVS-R1 and -R4 sessions are analyzed using the PORT (Potsdam Open-source Radio Interferometry Tool) software package. First results show that the gravitational models of the six antennas change the station heights by a few mm and the horizontal components by less than 1 mm (in case of Medicina).

How to cite: Shoushtari, S., Glaser, S., Balidakis, K., Heinkelmann, R., Anderson, J., and Schuh, H.: On the impact of gravitational deformation on VLBI-derived parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5100, https://doi.org/10.5194/egusphere-egu2020-5100, 2020.

EGU2020-8710 | Displays | G2.2

Estimation of VGOS Station Coordinates

Markus Mikschi, Johannes Böhm, and Matthias Schartner

With the number of available VGOS (VLBI Global Observing System) sessions rising, precise coordinates for the participating stations become more important. While station coordinates can be estimated during the VLBI (Very Long Baseline Interferometry) analysis, the definition of the geodetic datum via Not-Net-Rotation (NNR) and No-Net-Translation (NNT) conditions requires at least three participating stations with precise a priori coordinates. The VGOS station network is currently independent of the International Terrestrial Reference Frame (ITRF), as none of the stations have participated in a solution for the ITRF in VGOS mode. By estimating the VGOS station coordinates based on ITRF coordinates, originating from local surveying and solutions of S/X observations by now converted stations, a link to the ITRF can be established. First a global solution, which is the combination of individual sessions on the normal equation level, of the five VGOS CONT17 sessions was calculated. The datum was defined by WESTFORD, ISHIOKA and WETTZ13S whereby the coordinates of the first two stations are known from S/X observations and of the latter from local surveying. With velocities from adjacent stations, the estimated coordinates were used to calculate a global solution of the 2019 VGOS sessions. The obtained coordinates were assessed on basis of formal errors, coordinate repeatability and comparisons of estimated Earth Orientation Parameters (EOP) time series with fixed station coordinates to the 14 C04 a priori dataset.

How to cite: Mikschi, M., Böhm, J., and Schartner, M.: Estimation of VGOS Station Coordinates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8710, https://doi.org/10.5194/egusphere-egu2020-8710, 2020.

EGU2020-17532 | Displays | G2.2

Where - A Software for geodetic Analysis

Ingrid Fausk, Michael Dähnn, and Ann-Silje Kirkvik

Where is a software package developed by the Norwegian Mapping Authority (NMA). The software will provide a useful contribution to the International Terrestrial Reference Frame, by analysis of data from Very-long-baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR).

Where is written in Python, and is taking advantage of well-tested code like the SOFA and IERS libraries. The architecture is easily maintainable and extendable. Python makes it easy to write, and utilizes external libraries written in faster languages.
 
Both the NMA and the Instituto Geografico Nacional, Spain, are in a test phase of deliveries of VLBI analysis results to the IVS with the Where software. After some improvements of the software, we will also deliver analysis results to the ILRS. Our goal is to receive full status as operational analysis center for both VLBI and SLR, and to contribute to ITRF2020.
 
Sharing and cooperating with other institutions is made possible by making Where an open source project on GitHub.

How to cite: Fausk, I., Dähnn, M., and Kirkvik, A.-S.: Where - A Software for geodetic Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17532, https://doi.org/10.5194/egusphere-egu2020-17532, 2020.

The European GNSS Galileo became almost fully operational with 22 usable satellites in orbit and two testing satellites on the extended orbit. Since the introduction of the first Galileo satellite in December 2005, it became an important complement in GNSS applications to the already established GPS and GLONASS. The combination of Galileo with GPS observations allows to achieve an increased accuracy of precise parameter estimation.

GNSS-based applications are one of the most important methods to derive estimates of the pole coordinates x, y and the LOD (Length-of-Day). In previous work, the potential to improve GNSS observations for the estimation of hourly earth rotation parameters (ERP), based on a Multi-GNSS approach, has been investigated. The analysis covered a 6 month’s (August 2017 – December 2017) time period and considered a globally distributed network of approximately 160 GNSS stations. For around 75 stable stations, an NNR (No-Net-Rotation) constraint to their ITRF2014 coordinates was applied and precise GPS+Galileo ephemerides provided by ESA were used (based on an improved SRP apriori box-wing model for the Galileo satellites). On top solar radiation pressure coefficients were estimated using the empirical CODE orbit model (ECOM). Two solutions were applied, a GPS-only and a combined GPS+Galileo solution.

Meanwhile a reprocessing of the same time series was performed, based on an upgraded stable GNSS station network. Again, a GPS-only and a combined GPS+Galileo solution was carried out. The processing of the new time series has been extended for the whole year of 2017 and the first half of 2018, to provide more reliable results.

In this presentation, comparisons of 1- and 3-day arc ERP solutions with the IERS reference model IERS2010XY will be examined and discussed. Additionally, the different solution types (GPS-only and GPS+Galileo) from the first and reprocessed run were compared. From both GNSS solutions, amplitude corrections for tidal waves were estimated and analyzed w.r.t. the IERS2010XY reference model.

How to cite: Halilovic, D. and Weber, R.: Contribution of Galileo observations to improve the quality of daily and sub-daily earth rotation parameter estimates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3625, https://doi.org/10.5194/egusphere-egu2020-3625, 2020.

EGU2020-7980 | Displays | G2.2

Status of IGS repro3 activities at GFZ

Benjamin Männel, Andre Brandt, Markus Bradke, Andreas Brack, Pierre Sakic, and Thomas Nischan

Based on a large network of continuously operated GNSS tracking stations, the International GNSS Service (IGS) has a valuable contribution to the realization of the International Terrestrial Reference System. In order to provide the highest accurate and consistent solution, the IGS refined the strategy and the set of associated models for the ongoing third reprocessing campaign. Beyond updated background models, a major improvement is the combined reprocessing of three GNSS, namely GPS, GLONASS, and Galileo. Furthermore, signal-specific receiving antenna calibrations for Galileo and scale-free transmission phase center positions are applied. These modifications will allow exciting new investigations based on the delivered products. Hosting an IGS Analysis Center and an Analysis Center of the IGS Tide Gauge Benchmark Monitoring Project (TIGA), GFZ will contribute with two solutions to the IGS reprocessing efforts.

In this contribution, we will present the first outcomes of the ongoing preparations and preliminary results of the GFZ reprocessing activities. In the first part, we will present selected results of dedicated tests with a special focus on correction models and parametrization options. Secondly, we will present the initial results of the AC solution as a basis to discuss also further applications of the derived products (e.g., orbits, Earth rotation parameters). Finally, the first results of our TIGA-related reprocessing will be presented which are based on the previously discussed orbits and satellite clocks.

How to cite: Männel, B., Brandt, A., Bradke, M., Brack, A., Sakic, P., and Nischan, T.: Status of IGS repro3 activities at GFZ , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7980, https://doi.org/10.5194/egusphere-egu2020-7980, 2020.

EGU2020-21925 | Displays | G2.2

The benefits for ITRF2020 from multi-technique combination at the observation level (COOL) processing

Michiel Otten, Tim Springer, Francesco Gini, Volker Mayer, Erik Schoenemann, and Werner Enderle

For the previous ITRF calls for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with a single software package (NAPEOS), running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the techniques themselves, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models.

At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GNSS) into one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using “space ties”. Of course these space ties are not perfectly known but they still allow for a rigorous combination of the different reference frames. Furthermore, and very important for the GNSS technique, they allow for the direct estimation of the GNSS satellite transmitter phase centre offset. We solve not only for integer ambiguities of the GPS satellites but also for those of the LEO satellites, which is also providing GPS phase observations on two frequencies. 

Our poster presents an overview of this multi-technique combination approach at observation level (COOL). We have included all observations provided by the following satellites in a single parameter estimation process: GNSS, JASON, SPOT, Sentinels, GRACE, LAGEOS and Etalon satellites. We demonstrate the benefits of such a rigorous approach compared to processing the various space geodetic techniques separately.

How to cite: Otten, M., Springer, T., Gini, F., Mayer, V., Schoenemann, E., and Enderle, W.: The benefits for ITRF2020 from multi-technique combination at the observation level (COOL) processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21925, https://doi.org/10.5194/egusphere-egu2020-21925, 2020.

EGU2020-5914 | Displays | G2.2

ITRS 2020 realization: the new situation for scale realization

Manuela Seitz, Mathis Blossfeld, Matthias Glomsda, and Detlef Angermann

For the ITRS realization 2020 input data series of high quality from SLR, VLBI, GNSS and DORIS will be provided by the respective Technique Services ILRS, IVS, IGS and IDS. The observation data are currently reprocessed applying agreed state-of-the-art models. Between ITRF2014 and the ITRS realization 2020, many model changes had to be implemented for the individual techniques which nearly all have an impact on the realized scale. To mention the most important ones: (i) For SLR, estimated mean range biases will be introduced for each station and satellite. (ii) In VLBI analysis, the gravitational deformation of the telescopes will be considered for some stations. (iii) In GNSS analysis, highly-precise Galileo satellite phase center calibrations allow for the realization of the scale from Galileo observations. Calibrating GPS phase center corrections accordingly might even allow for a scale realization from the complete GNSS time series history. (iv) In case of DORIS, which was not involved in the ITRS scale realization up to now (as wasn’t GNSS), a new antenna type and changes in elevation cut-off and observation down-weighting will also have an impact on the scale.

It is a fact, that many of the model changes are not analyzed in detail with respect to their impact on the ITRF scale, and neither is the combination of model changes. The situation is even more complex since the ITRS realizations 2014, ITRF2014 on the one hand and DTRF2014 and JTRF2014 on the other hand, differ significantly with respect to the realized scale.

The poster summarizes and categorizes the various model changes and their impact on the scale. It critically discusses the new situation, which is a challenge for ITRS 2020 scale realization and will lead to significant differences between ITRF2020 and its predecessor ITRF2014.

How to cite: Seitz, M., Blossfeld, M., Glomsda, M., and Angermann, D.: ITRS 2020 realization: the new situation for scale realization , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5914, https://doi.org/10.5194/egusphere-egu2020-5914, 2020.

EGU2020-10805 | Displays | G2.2

Realization of time sequential estimation of terrestrial reference frame using square-root information filter and smoother

Toshio Mike Chin, Claudio Abbondanza, Richard Gross, Michael Heflin, Jay Parker, Benedikt Soja, and Xiaoping Wu

The JTRF2014 realization of terrestrial reference frame has adopted a weekly time series representation that can track dominant non-linear station motions including periodic and random variations.  The realization is based on the Kalman filter and smoother algorithms whose time sequential nature would also be suitable for continuous updating of an existing frame as soon as new geodetic data become available.

As a part of preparation for the next reference frame realization, we have been examining alternative filter and smoother algorithms based on the square-root information filter (SRIF), known generally for improved numerical accuracy of the covariance matrix represented by a square-root matrix.

The new algorithms offer a number of other advantages over the conventional filter/smoother algorithms used in JTRF2014.  Namely, the new approach allows us to (1) avoid using some fictitious covariance matrix to initialize the filter, (2) avoid the random-walk constraints for the Helmert parameter sequences, and (3) handle cross-temporal EOP data such as the week-long segments reported by the SLR and DORIS networks.  We have also been enhancing the stochastic models of the station position motion to be used by the filter and smoother, including models for non-tidal deformation.

How to cite: Chin, T. M., Abbondanza, C., Gross, R., Heflin, M., Parker, J., Soja, B., and Wu, X.: Realization of time sequential estimation of terrestrial reference frame using square-root information filter and smoother, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10805, https://doi.org/10.5194/egusphere-egu2020-10805, 2020.

EGU2020-17353 | Displays | G2.2

ITRF use for global applications and estimation of linear velocities of dense networks

Francesco Matonti, Adam Miller, and Nejc Krasovec

GNSS networks are required to continue meeting the ever-increasing demand for global positioning applications operating in a global reference frame. Meanwhile, the requirements of applications based in a local (regional) official reference frame must still be met. Using Bernese GNSS software (Dach, 2015), we can process GNSS networks in the ITRF2014 reference frame and, using Leica GNSS Spider, deliver GNSS corrections in ITRF2014, whilst continuing to serve those with local demands.  To maintain high precision of the GNSS network we perform a daily solution, which is computed based on precise orbits and following the guidelines of the EPN Analysis Centres. To ensure the daily solution runs with correct data, we maintain a database of all reference station equipment changes. Using the daily solution, we are estimating the linear velocity of reference stations within GNSS networks, and are also considering jumps due to equipment changes. The estimated velocities give the opportunity to monitor the long-term stability of the network as well as the quality of reference station coordinates. The daily solution and monitoring of GNSS networks are executed by the Leica Geosystems solution named Leica CrossCheck, which is based on Bernese GNSS software. Leica CrossCheck is capable to monitor GNSS networks of all scales. This includes the computation and monitoring of approximately 5000 GNSS reference stations worldwide, including those part of the HxGN SmartNet GNSS network.  

KEYWORDS: GNSS reference station network, Bernese GNSS 5.2, Leica CrossCheck, Leica GNSS Spider, HxGN SmartNet 
 

References: 
Dach, R., S. Lutz, P. Walser, P. Fridez (Eds); 2015: Bernese GNSS Software Version 5.2. User manual, Astronomical Institute, Universtiy of Bern, Bern Open Publishing. DOI: 10.7892/boris.72297; ISBN: 978-3-906813-05-9.   
 

How to cite: Matonti, F., Miller, A., and Krasovec, N.: ITRF use for global applications and estimation of linear velocities of dense networks , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17353, https://doi.org/10.5194/egusphere-egu2020-17353, 2020.

EGU2020-3364 | Displays | G2.2

Continuously operating reference stations in Russia: current state and future enhancements

Elena Mazurova, Igor Stoliarov, and Vladimir Gorobets

     At the present time the Russian  state geodetic reference frame of the new generation consists of the three hierarchical levels that include: 1. fundamental astronomical-geodetic reference frame ; 2. high-precision geodetic reference frame; 3. satellite-based geodetic reference frame of the first category.  The spatial coordinates of the networks of these three levels are determined by satellite methods.   However, only the points of the fundamental astronomical-geodetic reference frame are continuously operating reference stations.  Many surveying engineers, geodesists, map-ping specialists, as well as scientists from different backgrounds, are using RINEX files every day freely downloading them from the site //rgs.centre.ru

    At the same time, private networks of Continuously operating reference stations are developing rapidly in Russia. These networks are owned by various corporations, both private and public, as well as stations owned by private individuals.  Now,  a center is being created, the main task of which is to unite all Continuously operating reference stations located on the territory of Russia into a unified network.

    This paper addresses the current state of the Continuously operating reference stations network  in Russia and plans for enhancing it within the next few years.

Key words: Russian continuously operating reference stations network

How to cite: Mazurova, E., Stoliarov, I., and Gorobets, V.: Continuously operating reference stations in Russia: current state and future enhancements , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3364, https://doi.org/10.5194/egusphere-egu2020-3364, 2020.

EGU2020-1922 | Displays | G2.2

Taiwan Semi-kinematic Reference Frame Based on Surface Deformation Model Derived from GNSS Data, 2003 to 2019

Kwo-Hwa Chen, Kuo-En Ching, Ray Y. Chuang, Ming Yang, and He-Chin Chen

Taiwan’s current horizontal coordinate system, TWD97[2010], is a static geodetic datum located at the boundary between Eurasian and Philippine Sea plates. Due to the relative motions between different plates, the accuracy of TWD97[2010] has been constantly decreasing. To maintain the internal accuracy of a national coordinate system at a high level, establishing a semi-kinematic reference frame is a practical solution. The semi-kinematic reference frame includes a static datum and a surface deformation model that is composed of velocity grid models and displacement grid models. In this study, observations of 437 continuous GNSS stations from January 2003 to December 2019 were adopted to estimate the horizontal velocity fields in Taiwan. We also integrated twelve horizontal velocity fields between 2003 and 2018 from 785 campaign-mode GNSS sites surveyed by the Central Geological Survey to derive the horizontal grid velocity models using the Kriging spatial interpolation method. Six coseismic displacement grid models from 2010 to 2018 were constructed using the dislocation model based on published coseismic source models. Independent GNSS observations of 1400 stations collected by the National Land Surveying and Mapping Center (NLSC) between 2013 and 2018 were also used for exterior checking on the accuracy of the surface deformation model. In addition, the network-based RTK system in Taiwan established by NLSC, named e-GNSS, is proposed to be used for assessing the accuracy of the velocity model and for the decision on the timing of velocity model renewal.

How to cite: Chen, K.-H., Ching, K.-E., Chuang, R. Y., Yang, M., and Chen, H.-C.: Taiwan Semi-kinematic Reference Frame Based on Surface Deformation Model Derived from GNSS Data, 2003 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1922, https://doi.org/10.5194/egusphere-egu2020-1922, 2020.

A newly developed Converted Total Least Squares (CTLS) algorithm is introduced, which is to take the stochastic design matrix elements as virtual observations, and to transform the TLS problem into a traditional Least Squares problem. This new algorithm has the advantages that it can not only easily consider the weight of observations and the weight of stochastic design matrix, but also deal with TLS problem without complicated iteration processing, which enriches the TLS algorithm and solves the bottleneck restricting the application of TLS solutions. The notable development of the CTLS reveals also that CTLS estimator is identical to Gauss-Helmert model estimator in dealing with EIV model, especially in the case of similarity coordinate transformation. CTLS has been successfully applied to the estimation of the transformation parameters, their rates and related transformed residuals between actual ITRF realizations of ITRF2014 and ITRF2008 with obvious improvement of their accuracies.

How to cite: Cai, J., Dong, D., and Sneeuw, N.: New Total Least Squares Algorithm and Model with Applications to the Transformation among ITRF Realizations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8188, https://doi.org/10.5194/egusphere-egu2020-8188, 2020.

G2.3 – Precise Orbit Determination for Geodesy and Earth Science

EGU2020-20170 | Displays | G2.3

COSMIC-2 Precise Orbit Determination Results

Jan-Peter Weiss, Doug Hunt, William Schreiner, Teresa VanHove, Daniel Arnold, and Adrian Jaeggi

We present results for GNSS orbit estimation strategies implemented for the FORMOSAT-7/COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere, and Climate) constellation. The six COSMIC-2 satellites launched on June 25, 2019 into a 24 deg inclination, ~725 km circular orbit. Over time, all satellites will be lowered to an operational altitude of ~520 km. The primary COSMIC-2 science payload is the JPL designed Tri-GNSS Radio-occultation Receiver System (TGRS), which tracks GPS and GLONASS signals on two upward looking choke-ring precise orbit determination antennas facing the forward- and anti-velocity directions. We evaluate recently implemented post-processed orbit determination strategies. These include single antenna GPS-only and GPS+GLONASS solutions, as well as experimental dual-antenna GPS-only processing applying different approaches for the handling of receiver clock parameters (e.g. dual clocks, single clock plus bias). Evaluation metrics include data volume and tracking arc coverage, postfit residuals, internal orbit overlaps, and stability of the receiver clock estimates. We furthermore compare the performance of the six orbiters, and look for differences in quality metrics at the higher and lower orbit altitudes.

How to cite: Weiss, J.-P., Hunt, D., Schreiner, W., VanHove, T., Arnold, D., and Jaeggi, A.: COSMIC-2 Precise Orbit Determination Results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20170, https://doi.org/10.5194/egusphere-egu2020-20170, 2020.

EGU2020-3470 | Displays | G2.3

Kinematic orbit positioning applying the raw observation approach

Barbara Suesser- Rechberger, Torsten Mayer-Guerr, and Sandro Krauss

The kinematic strategy for precise orbit determination (POD) of low earth orbit (LEO) satellites uses only geometric observations to estimate the satellite orbit and does not take any forces into account. This strategy requires a large amount of observation data for one epoch to determine the three-dimensional satellite position. One possibility to get these data is the usage of the spaceborne global navigation satellite system (GNSS) technology, which provides a high number of accurate observations. Following Zehentner (2016) the kinematic orbit positioning applying the raw observation approach by using a least-squares adjustment has shown promising results with a high accuracy.

By applying this approach the kinematic orbits for several LEO satellite missions are estimated and subsequently validated by a comparison with state of the art gravity field solutions. Furthermore due to the fact that solar events causes an orbit decay, these precise determined orbit data are used to analyze solar event impacts on LEO satellites.

How to cite: Suesser- Rechberger, B., Mayer-Guerr, T., and Krauss, S.: Kinematic orbit positioning applying the raw observation approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3470, https://doi.org/10.5194/egusphere-egu2020-3470, 2020.

EGU2020-10519 | Displays | G2.3

A GNSS Payload for CubeSat Precise Orbit Determination

Kangkang Chen, Markus Rothacher, Lukas Müller, Flavio Kreiliger, and Sergio De Florio

Global Navigation Satellite Systems (GNSS) have been used as a key technology for satellite orbit determination for about 30 years. With the increasing popularity of miniaturized satellites (e.g., CubeSats that are nanosatellites based on standardized 10 cm-sized units) the need for an adapted payload for orbit determination arises. We developed a small-size versatile GNSS payload board using commercial off-the-shelf single-frequency GNSS receivers with extremely small weight (1.6 g), size (12.2 x 16.0 x 2.4 mm3) and power consumption (100 mW). The board features two separate antenna connectors and four GNSS receivers – two connected to each antenna. This redundancy lowers the risk of a total payload failure in case one receiver is malfunctioning.

Two prototypes of the GNSS positioning board have been successfully launched onboard the Astrocast-01 and -02 3-unit cube satellites with altitudes of 575 and 505 km, respectively. The multi-GNSS receivers are capable of tracking the GNSS satellites of the four major systems, i.e., GPS, GLONASS, BeiDou and Galileo. In addition, both satellites are equipped with a small array of three laser retroreflectors enabling orbit validation with Satellite Laser Ranging (SLR). After the two precursor missions, a constellation of 80 satellites is planned, allowing the formation and computation of a highly uniform polyhedron in space with cm-accuracy, relevant for geocenter, reference frame, and GNSS orbit determination.

At present, we have continuous receiver PVT solutions available. The real-time onboard orbit determination results indicate that the receivers perform very well on both satellites. The RMS of a daily orbit fitting is, after removing one or the other outlier, at the level of 2-5 meters despite errors caused by the ionosphere and the orbit model. For a few satellite arcs, the recording of GNSS raw phase and code data was enabled, allowing orbit determination in a post-processing mode. This allows a better assessment of the achievable orbit quality and an overall performance estimation. The tests performed so far include the improvement of the orbit quality by eliminating the ionospheric refraction based on a linear combination of phase and code observations, the comparison of various single-system solutions and advances in combining the different tracking systems for orbit determination. In collaboration with the Zimmerwald Observatory in Switzerland a first SLR campaign was conducted that successfully tracked both nanosatellites. The SLR measurements with their high accuracy were then analyzed to validate the orbits of the Astrocast satellites derived from GNSS measurements.

We will present details on the payload board, on the results of the orbit determination in real-time and in post-processing mode based on the low-cost single-frequency multi-GNSS receivers onboard the satellites and on the SLR orbit validation.

 

Keywords: CubeSat; GNSS payload; LEO orbit determination; low-cost; ionospheric refraction; linear combination; SLR

How to cite: Chen, K., Rothacher, M., Müller, L., Kreiliger, F., and De Florio, S.: A GNSS Payload for CubeSat Precise Orbit Determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10519, https://doi.org/10.5194/egusphere-egu2020-10519, 2020.

EGU2020-18560 | Displays | G2.3

Thermal thrust accelerations on LAGEOS satellites

David Lucchesi, Luciano Anselmo, Massimo Bassan, Marco Lucente, Carmelo Magnafico, Carmen Pardini, Roberto Peron, Giuseppe Pucacco, and Massimo Visco

Thermal thrust forces are non-conservative forces that act on the surface of a satellite as a result of temperature gradients across its surface. In the case of the older LAGEOS satellite these kinds of perturbations have been well-known since the end of 80s. The main effects are due to the thermal inertia of the corner cube retroreflectors (CCRs) of the satellites with sources the Earth’s infrared radiation and the direct solar visible radiation modulated by the eclipses. However, the solar radiation reflected by the complex Earth-atmosphere system, i.e. the albedo, is also responsible for a non-uniform heating of the satellite surface. We reconsider such perturbations by means of a new thermal model for the satellites called LATOS (LArase Thermal mOdel Solutions), which is not based on averaged equations as those previously developed in the literature. Of course, in such analyses the attitude of the satellite plays an important key role; we modeled it by means of the LASSOS (LArase Satellites Spin mOdel Solutions) model for the evolution of the spin-vector that we have already developed within the LARASE (LAser RAnged Satellites Experiment) research program. We also included the contribution of the Earth’s albedo in the determination of the overall distribution of temperature on the surface of the satellites, that was not considered in previous works. The CERES (Clouds and the Earth’s Radiant Energy System) data have been used to account for this effect. The thermal thrust accelerations have been computed together with their effects on the orbital elements by means of the Gauss equations. These effects are compared with the orbit residuals of the satellites in the same elements, obtained by an independent Precise Orbit Determination (POD), in order to highlight the signature of the unmodeled effects. The improvement in the POD that can be achieved through a better modeling of the thermal thrust perturbations is of fundamental importance for the geophysical products that are determined by means of the analysis of the orbits of the two LAGEOS satellites. Similarly, the measurements in the field of fundamental physics that are obtained with these satellites can benefit from a more precise modeling of their orbit.

How to cite: Lucchesi, D., Anselmo, L., Bassan, M., Lucente, M., Magnafico, C., Pardini, C., Peron, R., Pucacco, G., and Visco, M.: Thermal thrust accelerations on LAGEOS satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18560, https://doi.org/10.5194/egusphere-egu2020-18560, 2020.

EGU2020-340 | Displays | G2.3

Precise Galileo orbit determination using combined GNSS and SLR observations

Grzegorz Bury, Krzysztof Sośnica, Radosław Zajdel, and Dariusz Strugarek

The European navigation system Galileo is on its final stretch to become a fully operational capability (FOC) Global Navigation Satellite System (GNSS). The current constellation consists of 24 healthy satellites decomposed into three Medium Earth Orbits and since late 2016 is considered as an operational system. So far, the official Galileo orbits are provided by the European Space Agency and in the frame of the International GNSS Service (IGS) Multi-GNSS pilot project (MGEX) whose one of the goals is to develop orbit determination strategies for all new emerging navigation satellite systems.

All the Galileo satellites are equipped with Laser Retroreflector Arrays (LRA) for Satellite Laser Ranging (SLR). As a result, a number of Galileo satellites is tracked by laser stations of the International Laser Ranging Service (ILRS). SLR measurements to GNSS, such as Galileo, comprise a valuable tool for the validation of the orbit products as well as for an independent orbit solution based solely on laser ranging data. However, the SLR data may be used together along with the GNSS observations for the determination of the combined GNSS orbit using the two independent space techniques co-located onboard the Galileo satellites. The Galileo orbit determination strategies, as well as the usage of laser ranging to the navigation satellites, is crucial, especially in the light of the discussion concerning possible usability of the Galileo observation in the future realizations of the International Terrestrial Reference Frames.    

In this study, we present results from the precise Galileo orbit determination using the combined GNSS data transmitted by the Galileo satellites and the range measurements performed by the ILRS stations. We test different weighting strategies for GNSS and SLR observations. We test the formal errors of the Keplerian elements which significantly decrease when we apply the same weights for SLR  and GNSS data. However, in such a manner, we deteriorate the internal consistency of the solution, i.e., the orbit misclosures.  

For the solution with optimal weighting strategy, we present results of the quality of Galileo orbit predictions based on the combined solutions, as well as the SLR residuals. The combined GNSS+SLR solution seems to be especially favorable for the Galileo In-Orbit Validation (IOV) satellites, for which the standard deviation (STD) of the SLR residuals decreases by 13% as compared to the microwave solutions, whereas for the Galileo-FOC satellite the improvement of the STD of SLR residuals is at the level of 9%. Finally, we test the impact of adding SLR observations to the LAGEOS satellites which stabilizes the GNSS solutions, especially in terms of the realization of terrestrial reference frame origin. 

How to cite: Bury, G., Sośnica, K., Zajdel, R., and Strugarek, D.: Precise Galileo orbit determination using combined GNSS and SLR observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-340, https://doi.org/10.5194/egusphere-egu2020-340, 2020.

EGU2020-18361 | Displays | G2.3

Recent Advances in Galileo and BeiDou Precise Orbit Determination

Florian Dilssner, Erik Schönemann, Volker Mayer, Tim Springer, Francisco Gonzalez, and Werner Enderle

To produce Global Navigation Satellite System (GNSS) orbits and clocks with high accuracy and for all constellations, the ESA’s Navigation Support Office (NSO) continually strives to keep abreast and improve its precise orbit determination (POD) strategies. In this presentation, we report on NSO’s recent developments and progress in Galileo and BeiDou POD. We first discuss the approach of improving Galileo POD solutions through a prudent combination of radiometric and satellite laser ranging (SLR) measurements at the observation level. For this technique to be effective, SLR normal point (NP) data from the Galileo SUCCESS campaign are used. Launched by the European Laser Network (EUROLAS) in the middle of May 2019, this three-week tracking campaign provided over 1000 NPs for two selected Galileo spacecraft: GSAT0102 and GSAT0220. We show that the precision of the GSAT0102 and GSAT0220 orbits is more than 10 percent better than that produced by solutions without SLR data. In this performance evaluation, we also discuss the presence of station-specific SLR biases, taking advantage of near-simultaneous SLR tracking by two or three separate laser sites. Additionally, we demonstrate that the SLR full-rate data from a single kHz laser system can be used to determine the Galileo satellites’ yaw state during eclipse maneuvers. This approach takes advantage of the 1.0 m distance between a Galileo spacecraft’s laser retroreflector array (LRA) and rotation axis to estimate the yaw angle in a recursive least-squares algorithm epoch by epoch. The method may serve as an interesting alternative to reverse kinematic point positioning (RPP), particularly for LRA-equipped satellites without significant transmit antenna phase center offsets. Finally, we present the first centimeter-quality orbit solutions for BeiDou’s third-generation series of medium Earth orbit (MEO) spacecraft. We discuss the POD strategy underlying these orbits and evaluate its performance by way of several metrics including laser range residuals, day-to-day orbit overlaps, satellite clock residuals, as well as RPP estimates as measure for the attitude model accuracy. Challenges pertaining to the satellite antenna phase center and radiation force modeling are addressed. The results on the overlap and SLR residuals suggest that our BeiDou-3 MEO orbits are accurate to better than 5 cm in all three components. Therefore, the new BeiDou constellation is fully integrated into our operational multi-GNSS routine, bringing the total number of daily processed GNSS satellites to more than 110 (http://navigation-office.esa.int/products/gnss-products).

How to cite: Dilssner, F., Schönemann, E., Mayer, V., Springer, T., Gonzalez, F., and Enderle, W.: Recent Advances in Galileo and BeiDou Precise Orbit Determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18361, https://doi.org/10.5194/egusphere-egu2020-18361, 2020.

EGU2020-18550 | Displays | G2.3

Taking advantage of satellite clock stability for Galileo orbit model performance assessment.

Dmitry Sidorov, Rolf Dach, and Adrian Jäggi

Over the course of 2016 and 2017 the European GNSS Agency (GSA) made the Galileo satellite meta information publicly available. This long-awaited metadata package included details on satellite mass, dimensions, surface optical properties, attitude law as well as the antenna phase center corrections. As a result of this undertaking, the GNSS community initiated numerous studies to advance orbit models for these spacecrafts. In particular, the Center for Orbit Determination in Europe (CODE) refined the Empirical CODE Orbit Model (ECOM2) to adopt it to these lightweight satellites. This extended ECOM2 is currently used for computation of the CODE precise products involving Galileo (the Ultra-Rapid, Rapid and Multi-GNSS Extension (MGEX) products) in the frame of the International GNSS Service (IGS) activities.

The Galileo satellites carry state-of-the-art passive hydrogen maser (PHM) clocks that have been marked by high stability by many research groups. The commonly adopted procedure for the satellite clock corrections computation includes introduction of orbits estimated beforehand. This is served to fix the geometry between satellites and ground stations with a disadvantage that the estimated satellite clock corrections to a large degree depend on the quality of the introduced orbits. As a consequence, the estimated satellite clock corrections may suffer from potential radial orbital errors.

In this study we make an attempt to assess empirical orbit models used for Galileo satellites by introducing clock modelling in our precise orbit determination (POD) procedure. Thus, we take advantage of the stability of the PHM clocks operated by the Galileo satellites to introduce additional constraints to the radial orbital component already during the dynamic POD step. The obtained results suggest that introducing a satellite clock model to POD leads to improvements in solutions if the employed dynamic orbit model is correct. Also, in view of increasing number of GNSS satellites using well-performing clocks, the POD employing clock modelling appears to have high potential in further refining of orbit models.

How to cite: Sidorov, D., Dach, R., and Jäggi, A.: Taking advantage of satellite clock stability for Galileo orbit model performance assessment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18550, https://doi.org/10.5194/egusphere-egu2020-18550, 2020.

EGU2020-10780 | Displays | G2.3

ICESat-2 Precision Orbit Determination Performance

Taylor Thomas, Scott Luthcke, Teresa Pennington, Joseph Nicholas, David Rowlands, and Timothy Rebold

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission launched on September 15th, 2018, with the primary goal of measuring ice sheet topographic change. The fundamental measurement used to achieve mission science objectives is the geolocation of individual photon bounce points. Geolocation is computed as a function of three complex measurements: (1) the position of the laser altimeter instrument in inertial space, (2) the pointing of each of the six individual laser beams in inertial space, and (3) the photon event round trip travel time observation measured by the Advanced Topographic Laser Altimeter System (ATLAS) instrument. ICESat-2 Precision Orbit Determination (POD) is responsible for computing the first of these; the precise position of the laser altimeter instrument.

ICESat-2 carries two identical on-board GPS receivers, both manufactured by RUAG Space. Tracking data collected by GPS receiver #1 is used as the primary data source for generating POD solutions. POD is performed using GEODYN, NASA Goddard Space Flight Center’s state-of-the-art orbit determination and geodetic parameter estimation software, and a reduced-dynamic solution strategy is employed. The GPS-based POD solutions are calibrated and validated using independent Satellite Laser Ranging (SLR) data from ground-based tracking stations.

ICESat-2 mission requirements state that the POD solutions must have a one-sigma radial accuracy of 3 cm over a 24-hour time interval. Here we show that early mission ICESat-2 POD performance is exceeding mission requirements. We describe in-depth the ICESat-2 spacecraft macro-model, used for non-conservative force modeling, and the results from tuning of the associated parameters. Lastly, we show the iterated GPS receiver antenna phase center variation map solution and assess its impact on POD performance.

How to cite: Thomas, T., Luthcke, S., Pennington, T., Nicholas, J., Rowlands, D., and Rebold, T.: ICESat-2 Precision Orbit Determination Performance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10780, https://doi.org/10.5194/egusphere-egu2020-10780, 2020.

EGU2020-22070 | Displays | G2.3

On SENTINEL-3A and -3B DORIS, GPS and SLR precise orbit determination

Karl-Hans Neumayer, Patrick Schreiner, Rolf König, and Anna Michalak

How to cite: Neumayer, K.-H., Schreiner, P., König, R., and Michalak, A.: On SENTINEL-3A and -3B DORIS, GPS and SLR precise orbit determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22070, https://doi.org/10.5194/egusphere-egu2020-22070, 2020.

EGU2020-13184 | Displays | G2.3

Copernicus Sentinel Orbit Validation – Investigations on systematic geographical differences

Javier Berzosa, Marc Fernández Usón, Jaime Fernández Sánchez, Heike Peter, and Pierre Féménias

The Copernicus POD (Precise Orbit Determination) Service delivers, as part of the PDGS of the Copernicus Sentinel-1, -2, and -3 missions, orbital products and auxiliary data files for their use in the corresponding PDGS processing chains. The precise orbit results from the three missions are validated based on orbit comparisons to independent orbit solutions from member of the Copernicus POD Quality Working Group (QWG). In the case of Sentinel-3 a validation based on satellite laser tracking (SLR) measurements is also possible. The orbit comparisons are done based on orbit time series. Typically, only daily RMS metrics are derived, and its time-series mean and standard deviation are provided. Another possibility is to analyse the dependence of orbit differences with geographical differences; this is already done for the altimeter satellites to guarantee long-term stability of the orbit solutions.

Geographical orbit differences may reveal systematics due to, e.g., different background models or different geocenter motion models used in the orbit determination process. The geographical orbit differences of all six satellites and from all POD QWG contributions are analysed and checked for model- or satellite-specific systematics to improve the orbit quality and long-term stability.   

Additionally, it is proposed to analyse the orbit differences (with respect to other orbital solutions, either reduced-dynamic or kinematic) with Fourier transformation, in order to derive amplitude vs. frequency plots. This could provide light into the sub-daily differences. The Fourier analysis of the sub-daily differences will be assessed for all the six satellites.

How to cite: Berzosa, J., Fernández Usón, M., Fernández Sánchez, J., Peter, H., and Féménias, P.: Copernicus Sentinel Orbit Validation – Investigations on systematic geographical differences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13184, https://doi.org/10.5194/egusphere-egu2020-13184, 2020.

EGU2020-13256 | Displays | G2.3

Improved SLR orbit validation for Copernicus Sentinel-3 mission

Marc Fernández, Virginia Raposo, Jaime Fernández Sánchez, Heike Peter, and Pierre Féménias

The European Copernicus Sentinel-3 mission, a jointly operated mission by ESA and EUMETSAT, consists of two satellites equipped with GPS and DORIS receivers, and a Laser Retro Reflector (LRR) array, which allows tracking the satellites by Satellite Laser Ranging (SLR). The SLR observations are mainly used for the validation of GPS- and/or DORIS-derived precise orbit solutions. The SLR residuals are derived from the simple difference between observed and computed range between SLR station and the satellite. Only a subset of the SLR stations tracking the satellites is normally used for this purpose. The subset consists of stations delivering good quality observations on a long-term. The station selection is regularly reviewed to guarantee a continuous quality for the orbit validation.

Instead of using only a subset of the stations it would be preferable to use as many laser tracking data as possible. Long-term and highly accurate orbit time series of low Earth orbiting satellites can be used to estimate station range biases. The SLR validation is significantly improved by adding these station range biases due to additional stations and due to the removal of SLR related systematic patterns.

In the Copernicus POD Service (CPOD), the SLR station range biases are estimated based on a combined Sentinel-3A and -3B orbits computed from different orbit providers (the CPOD Quality Working Group). Performance, quality, mission dependency and stability of these SLR station range biases are analysed based on operational CPOD orbits and orbit solutions delivered by the Copernicus POD Quality Working Group.

How to cite: Fernández, M., Raposo, V., Fernández Sánchez, J., Peter, H., and Féménias, P.: Improved SLR orbit validation for Copernicus Sentinel-3 mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13256, https://doi.org/10.5194/egusphere-egu2020-13256, 2020.

EGU2020-5288 | Displays | G2.3

Long-term evaluation of estimated solar radiation pressure coefficients from Copernicus Sentinel-1, -2, -3 satellites

Heike Peter, Javier Berzosa, Jaime Fernández, and Pierre Féménias

The Copernicus POD (Precise Orbit Determination) Service is responsible for the generation of precise orbital products of the Copernicus Sentinel-1, -2, and -3 missions. In the near future, the processing setup of the Copernicus POD Service will be updated to state-of-the-art background models (geopotential, ocean tides and atmospheric gravity) and the use of single-receiver ambiguity fixing using CODE (Center for Orbit Determination in Europe) products.

In the current orbit parametrization of the six satellites, a solar radiation pressure coefficient is estimated for each daily arc. To provide long-term stability, in particular for the time series of the altimeter Sentinel-3 satellites, it would be preferable to use a constant solar radiation pressure coefficient in the processing. A reprocessing based on the updated models and set-up will be used to compute daily estimates of the solar radiation pressure coefficient for all satellites. The analysis may reveal satellite model deficiencies and might help to improve the satellite macro-models.

Mean values of the solar radiation pressure coefficients from the long-term series can be used on future operational processing. At the same time a refinement of the selection of the estimated orbit parameters might also be done if necessary, in particular the empirical accelerations. Impact on the orbit determination results and on the quality of the orbits is presented for all six satellites.

How to cite: Peter, H., Berzosa, J., Fernández, J., and Féménias, P.: Long-term evaluation of estimated solar radiation pressure coefficients from Copernicus Sentinel-1, -2, -3 satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5288, https://doi.org/10.5194/egusphere-egu2020-5288, 2020.

Sentinel-3 is an Earth observation satellite formation of the European Space Agency (ESA) devoted to oceanography and land-vegetation monitoring. It operates as a crucial segment of the Copernicus Programme coordinated by the European Union. Up until now, two identical Sentinel-3 satellites, Sentinel-3A and -3B, have been launched into a circular sun-synchronous orbit with an altitude of about 800 km. Their prime onboard payload systems, e.g. radar altimeter, necessitate high-precision orbits, particularly in the radial direction. This can be fulfilled by using the collected measurements from the onboard dual-frequency high-precision multi-channel Global Positioning System (GPS) receivers. The equipped laser retro-reflector allows for external and independent validation to the GPS-derived orbits.

This research will outline the recent Precise Orbit Determination (POD) methodology developments at the Astronomical Institute of the University of Bern (AIUB) and investigate  the POD comparison between Sentinel-3A and -3B satellites. On one hand, a refined satellite non-gravitational force modeling strategy is newly implemented into the BERNESE GNSS software. It consists of comprehensive modeling of atmospheric drag, solar radiation pressure and Earth albedo/radiation pressure based on an 8-plate satellite macromodel. Radiation pressure is modeled considering spontaneous re-emission for non-solar plates. Besides, a linear interpolation between monthly Clouds and the Earth's Radiant Energy System (CERES) S4 grid products is specifically done for the Earth albedo/radiation pressure modeling. On the other hand, use is made of the GNSS Observation-Specific Bias (OSB) products provided by the Center for Orbit Determination in Europe (CODE), allowing for the so-called single-receiver ambiguity resolution.

A test period is selected from 7/Jun/2018 to 14/Oct/2018 (Day of Year: 158-287), when Sentinel-3A and -3B satellites operated in a tandem formation maintained at a separation of about 30 s. This foresees nearly identical in-flight environment for both satellites and thereby enables direct POD performance comparison. The single-receiver (zero-difference) ambiguity-fixed orbit solutions can also be compared with the double-difference ambiguity-fixed baseline solution. Results reveal that the implemented non-gravitational force modeling in POD leads to a reduction of empirical acceleration estimates, which are designated to compensate uncertainties in the satellite dynamic models. Single-receiver ambiguity resolution further improves the reduced-dynamic orbits and significant enhancement occurs to the kinematic orbits. This research implies promising benefits to the Sentinel-3 scientific research community.

How to cite: Mao, X., Arnold, D., and Jäggi, A.: Sentinel-3A/3B orbit determination using non-gravitational force modeling and single-receiver ambiguity resolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16611, https://doi.org/10.5194/egusphere-egu2020-16611, 2020.

Space-borne accelerometers measure the sum of all non-gravitational forces, which interact with the surface of a spacecraft. For low Earth orbit satellites, the atmospheric drag is the largest non-gravitational force. With increasing satellite altitude, the acceleration due to the Earth radiation pressure becomes less relevant, whereas the effect of the Solar radiation pressure becomes prevalent. Accurately modeled non-gravitational forces are necessary for precise orbit determination, satellite gravimetry, or thermospheric density estimation.

In this study, we apply an inverse procedure with the aim to overcome remaining limitations in state-of-the-art radiation pressure force models. We estimate corrections of limiting parameters such as the satellite’s thermo-optical material properties or systematic errors in Earth radiation data sets. We define different parameterizations and analyse their estimability in terms of rank deficiency and condition numbers. Correlation analyses between estimated parameters will help to detect and overcome multicollinearity. The results are expected to improve the estimation of certain physical radiation pressure model parameters from satellite accelerometer data. Here, the inverse modeling is based on calibrated accelerometer measurements from the satellite mission Gravity Recovery and Climate Experiment (GRACE).

How to cite: Vielberg, K. and Kusche, J.: Estimation of Earth- and satellite-related parameters in radiation pressure modeling from space-borne accelerometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2587, https://doi.org/10.5194/egusphere-egu2020-2587, 2020.

EGU2020-21223 | Displays | G2.3

Impacts of solar events on atmospheric density variations as revealed by Satellite Laser Ranging orbits.

Florent Deleflie, Changyong Hé, Carine Briand, Muhammad Ali Sammuneh, and Pieter Visser

This paper is focused on precise orbitography with SLR data, using as well when they are available accelerometric data, as in the GRACE mission. The main purpose of this paper is to analyse whether low SLR satellite orbits (namely Starlette, Stella, Lares, Ajisai) are sensitive or not to variations of the atmospheric density due to solar events over the period 2003-2019, and including the ones that occurred in 2017.

The relationships between solar events and the way they modify the density of the Earth's thermosphere, as revealed by perturbations induced on artificial satellites orbits, are in fact of crucial importance for satellite operators. A wide literature focused on these issues already exists, but it appears to the authors that some improvements of thermosphere models are still expected, especially at high latitudes. This paper aims, hence, at contributing to fill a gap in that direction.  

We first select over the period 1984-2019 a list of solar events that may be representative of the conditions that may heat the terrestrial atmosphere, in terms of geometrical configurations and the intensity of solar activity. The goal is to identify whether these events have impacted or not the thermospheric density at some relevant altitudes; therefore, a post-fit residual analysis is provided, accounting for the whole set of tracking data acquired by the stations of the ILRS network. A comprehensive comparison between precise results obtained with SLR and accelerometric data, using different atmospheric drag modelling, is then provided.

How to cite: Deleflie, F., Hé, C., Briand, C., Sammuneh, M. A., and Visser, P.: Impacts of solar events on atmospheric density variations as revealed by Satellite Laser Ranging orbits. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21223, https://doi.org/10.5194/egusphere-egu2020-21223, 2020.

The processing configuration for our IDS contribution to the International Terrestrial Reference Frame (ITRF2020) realization was defined. We adopted the last standards and models recommended by IERS. We took into account the IDS recommendations to mitigate the non-conservative force model error on satellites, to mitigate the effect of the South Atlantic Anomaly on the DORIS receivers and to improve the stability of the DORIS scale.

A Precise Orbit Determination (POD) status for DORIS satellites by taking into account all these improvements will be presented for the processed time span. We will give statistical results such as one per revolution empirical acceleration amplitudes and orbit residuals. We will also give some comparisons to some external precise orbits used for altimetry. Some external validations of our orbits will be done, such as with independent SLR measurements processing as well as through the use of altimeter crossovers when available. We will also look at the impact of our new ITRF2020 configuration on the DORIS geocenter and scale.

 

How to cite: Capdeville, H.: Preliminary DORIS results on Precise Orbit Determination and on geocenter and scale solutions from CNES/CLS IDS Analysis Center contribution to the ITRF2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21245, https://doi.org/10.5194/egusphere-egu2020-21245, 2020.

EGU2020-19172 | Displays | G2.3

Impact of re-scaled macro models for GNSS orbit determination

Arturo Villiger, Rolf Dach, and Adrian Jäggi

EGU2020-8239 | Displays | G2.3

Solar radiation pressure model of GPS and GLONASS satellites considering potential surface radiator impact

Bingbing Duan, Urs Hugentobler, and Inga Selmke

Within the IGS (International GNSS Service), precise orbit and clock products of GPS and GLONASS satellites as well as Earth rotation parameters (ERPs) are routinely generated by individual analysis centers. As the dominant non-gravitational perturbation, solar radiation pressure (SRP) is modeled differently by different centers. Without surface properties, the empirical CODE orbit models (ECOM, ECOM2) are mostly used. We find that the ECOM models are not optimal for GLONASS satellites, especially during the eclipsing seasons. Also, the use of a conventional a priori box-wing (BW) model does not help much. By assessing the ECOM estimates we conclude that there are potential radiators on the –x surface of GLONASS satellites causing orbit perturbations in eclipse as well. Based on this finding, we firstly adjust optical properties of GLONASS satellites considering the potential radiator and thermal radiation effects. Then, we introduce all the adjusted parameters into a new a priori model and jointly use it together with the ECOM models. Results show that orbit misclosure between two consecutive arcs reduces by about 30 % for the ECOM model during the eclipsing seasons. In addition, the spurious pattern of the satellite laser ranging (SLR) residuals is greatly reduced. Also, we have repeated the same adjustment of optical properties for GPS satellites by using 6 years’ data (2014 - 2019). We evaluate GPS orbits, ERPs and geocenter products calculated with different SRP models (ECOM, ECOM+BW, ECOM2, ECOM2+BW, adjustable BW, GSPM) and present corresponding systematic errors of each product at harmonics of the GPS draconitic year.

How to cite: Duan, B., Hugentobler, U., and Selmke, I.: Solar radiation pressure model of GPS and GLONASS satellites considering potential surface radiator impact, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8239, https://doi.org/10.5194/egusphere-egu2020-8239, 2020.

EGU2020-9936 | Displays | G2.3

Impact of a-priori SRP models and ECOM models on GNSS precise orbit determination

Xiao Chang, Benjamin Männel, Harald Schuh, and Roman Galas

As one of the products of the International GNSS Service (IGS), precise orbits for Global Navigation Satellite Systems (GNSS) play an important role in many geoscientific applications. Currently, the precision and consistency of GNSS orbits are still limited by insufficient knowledge of spacecraft response to non-conservative perturbations, of which the solar radiation pressure (SRP) has the strongest influence. SRP modeling strategies adopted by IGS Analysis Centers (ACs) can be categorized: 1) analytical SRP model like the ROCK models (Fliegel et al. 1992), 2) empirical representation, for example by estimating ECOM parameters (Beutler et al. 1994, Springer et al. 1999a, and Arnold et al. 2015), and 3) the combination of both, hybrid empirical-physical SRP model such as adjustable box-wing model (e.g. Rodriguez-Solano et al. 2012). While empirical models fit the observations well, the loss of physical explanation may cause unexpected systematic errors. Uncertainties in the a-priori SRP models, which rely on the optical coefficients and surface structure of the satellites, can also degrade the determined orbit systematically. Using a hybrid model, i.e. estimation of empirical parameters on top of a-priori model, is expected to take the advantage of the existing satellite properties and to compensate for the inaccuracy related to the satellite properties based on observations. Thus, different hybrid models have to be tested for each constellation and block type.

 

In this study, we assess the GNSS precise orbit determination (POD) based on different setups of a-priori models and ECOM parametrization. The results will be presented as follows: 1) first, the orbits difference introduced by a-priori model is analyzed by comparing orbit with the one based on pure ECOM models. 2) Second, the effect of a-priori models will be discussed by assessing the estimated ECOM parameters. 3) Third, the derived orbit will be compared with the final orbits of selected IGS ACs. 4) The effect of the selected SRP modeling strategy on geodetic parameters will be discussed with special focus on the estimated station coordinates.

How to cite: Chang, X., Männel, B., Schuh, H., and Galas, R.: Impact of a-priori SRP models and ECOM models on GNSS precise orbit determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9936, https://doi.org/10.5194/egusphere-egu2020-9936, 2020.

EGU2020-5985 | Displays | G2.3

A new solar radiation pressure model for BDS-3 satellites

Xinghan Chen, Maorong Ge, and Harald Schuh

Currently, with the rapid development of the third generation of BeiDou satellite system (BDS-3), the corresponding solar radiation pressure (SRP) forces should be well and soon modeled in order to enhance the performance of precise orbit determination (POD) and precise clock estimation (PCE) for high-precision applications. In this contribution, the BDS-3 post-processed and ultra-rapid PODs have been realized by fully exploiting data provided by the International GNSS Service (IGS). We firstly test the Center for Orbit Determination in Europe (CODE) SRP model (ECOM1) and ECOM2 models and notice a large disagreement of overlapping orbits at the boundary of two adjacent days within an eclipse period. The reason for this could be that the ECOM2 model is over-parameterized or an extra periodic SRP term should be considered. Furthermore, our numerical analyses confirm that the cosinus terms must be excluded and the fourth- and sixth-order SRP sinus terms are significant in the Sun direction for the SRP model of BDS-3 satellites. Therefore, a new SRP model is developed herein to improve BDS-3 orbits, especially for eclipse season. Using the new SRP model, the large fluctuations of 20 cm can be reduced to below 10 cm for the radial-track component of overlapping orbits over eclipse seasons and SLR residuals are improved by a factor of 2 compared to that of ECOM1 and ECOM2. For the predicted orbits, the improvement due to the new SRP model is also demonstrated and the mean offsets of overlapping orbit differences over the eclipse periods can be reduced from -9.3 cm, -18.9 cm, and 39.9 cm to -5.5 cm, 8.3 cm, and 12.7 cm in the radial, cross, and along directions, respectively.

How to cite: Chen, X., Ge, M., and Schuh, H.: A new solar radiation pressure model for BDS-3 satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5985, https://doi.org/10.5194/egusphere-egu2020-5985, 2020.

EGU2020-9354 | Displays | G2.3

Combined Precise Orbit Determination for BDS-2 and BDS-3 Satellites

Hanbing Peng, Maorong Ge, Yuanxi Yang, Harald Schuh, and Roman Galas

Since November 2017, the 3rd generation BeiDou Navigation Satellite System (BDS-3) of China has stepped into an intensive build-up phase. Up to the end of 2019, there are 5 experimental and 28 operational BDS-3 satellites in the space. Besides that, 16 BDS-2 legacy satellites are still providing Positioning, Navigation and Timing (PNT) service for Asia-Pacific users. Unlike BDS-2 satellites, BDS-3 satellites will not transmit signal on frequency B2I which is one of the open service frequencies of BDS-2 and will be replaced by B2a of BDS-3. For legacy signals, only that on B1I and B3I will be transmitted by all BDS-3 satellites. Therefore, current routine scheme that generates precise orbit and clock products with B1I+B2I combination observations becomes infeasible for BDS-3. Observation combination used for product generation of BDS-2 could be switched to B1I+B3I combination as well. However, this might cause discontinuity in BDS-2 products as different hardware delays specific to signals are contained in them. In this study, combined processing of BDS-2 and BDS-3 satellites to generate consistent precise orbit and clock products is researched. To elaborate the impact of observation biases between BDS-2 and BDS-3, different combined Precise Orbit Determination (POD) processing schemes are examined. It shows that receiver biases between BDS-2 and BDS-3 should be considered in combined POD which is clear from the post-fit residuals of observations, especially from that of BDS-3 code observations. After estimating those biases between B1I+B2I of BDS-2 and B1I+B3I of BDS-3, Root-Mean-Square (RMS) of BDS-3 code observations decreases from 5.07 to 1.23 m. The results show that, biases of B1I+B3I between BDS-2 and BDS-3 are relatively small, less than 4 m for most receivers and around 1.2 m on average. But their estimates are stable with standard deviations (STDs) of 0.13 ~ 0.34 m depending on receiver types. Influences of these biases on the POD results are limited. However, biases between B1I+B2I of BDS-2 and B1I+B3I of BDS-3 are more significant, from -10 to 30 m for different receivers. Except for Septentrio receivers, quantities of those biases are basically related to the receiver types. Averages of biases from Trimble, JAVAD and Leica receivers are 18.5, 5.0 and 10.0 m, respectively. Those biases are also estimated with very small STDs, which ranges from 0.13 to 0.28 m. It is demonstrated that those receiver biases should be properly handle in combined POD processing of BDS-2 and BDS-3 satellites. As B1I+B2I is more appropriate for BDS-2, using different observation combinations for BDS-2 and BDS-3 in combined POD processing is more preferred over the scheme in which B1I+B3I is used for both BDS-2 and BDS-3.

How to cite: Peng, H., Ge, M., Yang, Y., Schuh, H., and Galas, R.: Combined Precise Orbit Determination for BDS-2 and BDS-3 Satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9354, https://doi.org/10.5194/egusphere-egu2020-9354, 2020.

In order to enable our new PPP processing engine and online service to work in full multi-GNSS mode, and provide high quality precise GNSS orbit and clock (POD) products to IGS and international geodetic community, Canadian Geodetic Survey (known as EMR) has started to modernize his POD system. The new system is based on GipsyX and in-house software development and will replace our current POD system in near future. When become operational, the new POD system will produce multi-GNSS precise orbit and clock corrections with ambiguity resolution along with wide-lane and phase biases using zero-differenced, dual-frequency, ionosphere-free phase and code observations in RINEX 2 and 3 formats estimated in combined solution. The new system also benefits from advanced features such as removing observations affected by ionospheric scintillation and ground stations affected by earthquake as well as real-time monitoring of estimated position time-series of ground stations, among others.

How to cite: Goudarzi, M. A.: Modernizing Canadian Geodetic Survey’s precise GNSS orbit and clock system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19612, https://doi.org/10.5194/egusphere-egu2020-19612, 2020.

This research aims at evaluation of the Variance Component Estimation (VCE) to derive a combined orbit solution from the Inter-Satellite Links (ISLs) and GNSS measurements. The ISLs provide precise range measurements between satellites in the specific GNSS constellation which is one of the key requirements for improving accuracy and reliability of the orbit determination. Our investigation based on various ISLs connectivity schemes (observation scenarios) indicates that by using ISLs measurements in addition to GNSS observations, it is possible to improve orbit estimation mainly by reducing RMS errors in cross-track and along-track directions.

This study, however, is focused on comparison of weighting methods based on presupposed measurement accuracies (described here as an empirical weighting) and four approaches to the VCE method. VCE is a method used to determine proper weighting factors for different types of measurements, e.g. of diverse nature or based on distinct techniques and thus of various accuracy. It is expected that systematic and random errors of the individual solutions could be reduced by this combination method. In this simulation-based study we assess orbit solutions using both types of weighting with a few approaches to the empirical weighting as well as to the VCE. In parallel, we evaluate properties of the simulated ISLs measurements including the connectivity schemes and observation accuracy.

This work is concluded with general advantages and disadvantages of proposed weighting methods along with the observation scenarios, that are potentially optimal for better orbit and clock estimates using ISLs and GNSS observations.

How to cite: Kur, T., Liwosz, T., and Kalarus, M.: Study on the Variance Component Estimation in relative weighting of the Inter-Satellite Links and GNSS observations for orbit determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7229, https://doi.org/10.5194/egusphere-egu2020-7229, 2020.

G2.4 – New strategies for consistent geodetic products and improved Earth system parameters

EGU2020-5922 | Displays | G2.4

Satellite geodesy with VLBI in the GGOS era: observation concepts, geodetic products and the technical feasibility

Grzegorz Klopotek, Rüdiger Haas, Thomas Hobiger, and Toshimichi Otsubo

The demanding requirements of the global geodetic observing system (GGOS) necessitate appropriate changes to be made also in the field of geodetic/astrometric very long baseline interferometry (VLBI). The VLBI global observing system (VGOS) is the milestone step towards reaching the GGOS goals. This next-generation VLBI system has already reached an operationally stable international network and it continuously evolves into a truly global infrastructure, with the aim of delivering geodetic products and frame parameters with an unprecedented quality. Thanks to the enhanced measurement precision, increased observation density and improved tracking capabilities, VGOS provides also a great opportunity for extending the current VLBI research with new applications such as observations of geodetic satellites with VLBI. This requires also that a geodetic satellite transmits signals that can be observed by VLBI telescopes, and such ideas have been proposed over the last years. Although a variety of simulation studies have already been performed with the aim of addressing the usefulness of this concept for geodesy and few interesting aspects have been discussed, this topic has not been fully exploited, especially in connection with VGOS. Observations of natural radio sources (quasars) and dedicated geodetic satellites with the same instruments (radio telescopes) bring several benefits as well as new challenges related to the observing strategy and the technical feasibility of this concept. When observing satellites, VLBI gains an access to the set of geodetic parameters that are usually out of scope for conventional VLBI, e.g., satellite orbits or geocenter motion (observed directly). Besides the co-location in space and on the ground, the combined quasar-satellite solutions could also potentially result in an enhanced quality of common geodetic products such as Earth Rotation Parameters (ERP) or station positions. Lastly, the goal of a consistent determination of the terrestrial and celestial reference frames, Earth Orientation Parameters and satellite orbits could be also met in this case.
The following contribution provides a holistic view concerning the prospective VLBI observations of geodetic satellites in the era of GGOS and their impact on various geodetic products. The aspect of VGOS-type satellite observations in the GGOS era is investigated with the use of Monte-Carlo simulations carried out with the c5++ analysis software. The basis of our study form three-day VGOS schedules, which include both quasar and satellite observations. The latter are realized with the use of several Galileo satellites, which are located on different orbital planes. Both observation types are used to derive satellite orbits and estimate common station-based and global geodetic parameters.  The impact on classical geodetic parameters (station positions, ERP), caused by additional satellite observations and the orbit determination process, is investigated with the use of different satellite observation precision levels. We also provide insights concerning the quality of the determined satellite orbits and geocenter estimates. In addition, the scheduling aspects and the technical feasibility of the presented approach are also discussed.

How to cite: Klopotek, G., Haas, R., Hobiger, T., and Otsubo, T.: Satellite geodesy with VLBI in the GGOS era: observation concepts, geodetic products and the technical feasibility, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5922, https://doi.org/10.5194/egusphere-egu2020-5922, 2020.

EGU2020-3620 | Displays | G2.4

On the prospects of a future GNSS constellation on the global terrestrial reference frame

Susanne Glaser, Grzegorz Michalak, Rolf Koenig, Benjamin Maennel, and Harald Schuh

Global terrestrial reference frames (TRFs), as one of the most important geodetic products, currently miss the imperative requirements of 1 mm accuracy and 1mm/decade long-term stability. In this study, the prospects of a future Global Navigation Satellite System (GNSS) to improve global TRFs is assessed by simulations. The future constellation, named “Kepler”, is proposed by the German Aerospace Center DLR in view of the next generation Galileo system. In addition to a contemporary Medium Earth Orbit (MEO) segment with 24 satellites in three orbital planes, Kepler consists of six Low Earth Orbit (LEO) satellites in two near polar planes, all carrying long-term stable optical clocks. The MEO satellites in one orbital plane and the LEO and MEO satellites in different planes are connected with optical two-way inter-satellite links (ISLs) as the innovative key feature. The ISLs allow very precise range measurements and time synchronization (at the picosecond-level) between the satellites. Different simulation scenarios are set up to evaluate the impact of the Kepler features on the TRF-defining parameters origin and scale as well as on the Earth rotation parameters (ERPs). The origin of a Kepler-only TRF improves considerably by factors of 8, 8, and 43 in X, Y, and Z direction, respectively, w.r.t. a Galileo-only solution. The scale realized by a Kepler-TRF shows improvements of 34% w.r.t. Galileo-only. In a combination with simulated observations of Very Long Baseline Interferometry the impact on multi-technique TRFs is assessed as well. The ERPs of both techniques are combined as global ties and benefits especially on the determination of UT1-UTC are expected.

How to cite: Glaser, S., Michalak, G., Koenig, R., Maennel, B., and Schuh, H.: On the prospects of a future GNSS constellation on the global terrestrial reference frame, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3620, https://doi.org/10.5194/egusphere-egu2020-3620, 2020.

EGU2020-7991 | Displays | G2.4

Simulation studies on single-satellite space ties and their potential to achieve the Global Geodetic Observing System goals.

Patrick Schreiner, Nicat Mammadaliyev, Susanne Glaser, Rolf Koenig, Karl Hans Neumayer, and Harald Schuh

The German Research Foundation (DFG) project GGOS-SIM-2, successor of project GGOS-SIM, is a collaboration between the Helmholtz Center Potsdam - German Research Center for Geosciences (GFZ) and the Technische Universität Berlin (TUB). The project aims at investigating the feasibility of meeting the requirements specified by the Global Geodetic Observing System (GGOS) for a global terrestrial reference frame (TRF) with the help of simulations. In GGOS-SIM-2 the potential of so-called space ties is examined in relation to the GGOS targets, 1 mm accuracy in position and 1 mm / decade long-term stability, which have not yet been achieved by the recent International Terrestrial Reference Frame (ITRF). Space ties are provided by a satellite that carries two, three or all the four main space-geodetic techniques, i.e. DORIS, GPS, SLR and VLBI. This allows for a quantification of the impact of systematic errors on the derived orbits and subsequent results of the dynamic method as the TRF. Proposed co-location in space missions such as GRASP and E-GRASP anticipate such a scenario. We therefor simulate the space-geodetic observations based on Precise Orbit Determination (POD) with real observations from various missions and evaluate their potential for determining a TRF. So far, we simulated DORIS and SLR observations to six orbit scenarios, including a GRASP-like and an E-GRASP-like one, and generated TRFs based on each scenario either technique-wise or combined via the space-ties or in combination with ground data. We quantify the effect on the TRF in terms of changes of origin and scale and of formal errors of the ground station coordinates and of the Earth rotation parameters.

How to cite: Schreiner, P., Mammadaliyev, N., Glaser, S., Koenig, R., Neumayer, K. H., and Schuh, H.: Simulation studies on single-satellite space ties and their potential to achieve the Global Geodetic Observing System goals., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7991, https://doi.org/10.5194/egusphere-egu2020-7991, 2020.

EGU2020-9193 | Displays | G2.4

A Study on Rigorous Combination of GNSS and VLBI Observations

Iván Darío Herrera Pinzón and Markus Rothacher

The ITRF is realized through the combination of the individual solutions (station coordinates and velocities) of the four space geodetic techniques. This combination features two main aspects: 1) precise local ties, to establish the link among techniques, and 2) full variance-covariance information of each solution, to account for the accuracy of each technique. Although this approach strives to obtain accurate geodetic products, this combination is not entirely "rigorous'', especially when it comes to the Earth Orientation Parameters (EOPs). In the current realization of the ITRF only polar motion (x-pole and y-pole) are combined, whereas UT1-UTC and nutation offsets and rates are taken from the solution of a single technique (VLBI). Furthermore, parameters such as troposphere delays and clock offsets are not part of the combination strategy. Thus, a rigorous estimation of the ITRF, with consistent EOPs and with appropriate tropospheric and clock ties, is still a challenge to be met.

To achieve a rigorous combination, all parameter types common to more than one space geodetic observation technique should be combined including their full variance-covariance information as well as the corresponding ties. In particular, as both, GNSS and geodetic VLBI, are based on microwave frequencies, their physical models and their parameter types are closely related. These common parameters are the site coordinates and velocities, troposphere estimates, EOPs and (possibly) clock estimates. Thus, using the data from the CONT17 campaign as a case study, we discuss the processing scheme, the challenges and initial results of a rigorous combination of VLBI and GNSS observations, in order to estimate and densify EOPs, particularly diurnal and sub-diurnal variations for polar motion and UT1-UTC, and to realize an inter-technique tropospheric tie, thus remedying the deficiencies mentioned above. The results obtained constitute an important step towards the realization of a rigorous ITRF solution that is able to improve the accuracy and consistency of all geodetic products.

How to cite: Herrera Pinzón, I. D. and Rothacher, M.: A Study on Rigorous Combination of GNSS and VLBI Observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9193, https://doi.org/10.5194/egusphere-egu2020-9193, 2020.

EGU2020-21503 | Displays | G2.4

A multi-frequency Celestial Reference Frame at S/X, K and X/Ka-band

Maria Karbon and Axel Nothnagel

We present a Celestial Reference Frame (CRF) based on the combination of independent, multi-frequency radio source position catalogs using nearly 40 years of Very Long Baseline Interferometry observations at the standard geodetic frequencies at S/X band and about 15 years of observations at higher frequencies (K and X/Ka). The final catalog contains 4617 sources.

The novelty in our approach is the combination of independent, multi-frequency radio source position catalogs through a rigorous combination by carrying over the full co-variance information of each catalog through the process of accumulation of normal equation systems instead of using only the positions themselves. Through the novel process of combination, a complete co-variance matrix of the entire set of sources across the three bands is provided. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined one.

The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8~Ghz, 824 sources being observed also at 24 GHz and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 μas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

How to cite: Karbon, M. and Nothnagel, A.: A multi-frequency Celestial Reference Frame at S/X, K and X/Ka-band, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21503, https://doi.org/10.5194/egusphere-egu2020-21503, 2020.

EGU2020-7818 | Displays | G2.4

On the multi-technique combination with atmospheric ties

Kyriakos Balidakis, Susanne Glaser, Florian Zus, Tobias Nilsson, Harald Schuh, and Richard Gross

We explore a new strategy to combine geodetic observations employing the existing and future systems. Imposing atmospheric ties on the combination at either the observation or normal equation level introduces a physical interpretation to the estimated atmospheric delay parameters, that is, zenith delays and gradients. In essence, besides combining station coordinates via local ties, we combine atmospheric delays via atmospheric ties. The purpose of this work is to assess the advantages and caveats of such a combination approach, on legacy, state-of-the-art, and next generation geodetic systems. We simulate 10 years of observations of all space geodetic techniques that currently contribute to the realization of the international terrestrial reference system; that is, very long baseline interferometry (VLBI), satellite laser ranging (SLR), global navigation satellite systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS). The noise we inject in the simulated observations is technique-specific and - besides a thermal contribution - stems from three-state clock models and ray-traced delays from the latest ECMWF reanalysis, ERA5. To make the simulations more realistic, we estimate the probability of potential observations being successful by utilizing ERA5 fields, for example cloud fields for SLR. To avoid overoptimistic uncertainty estimates, we have accounted for the correlation between observations based on ERA5 fields. In a bias-free setup, we find that the improvement of employing atmospheric ties in addition to local ties to fuse multi-sensor observations, on the combined station coordinates and atmospheric delays is statistically significant for all techniques except for GNSS. We attribute the latter to the relatively good observing geometry. We also find that employing atmospheric ties reveals unaccounted systematic errors stemming from erroneous auxiliary data that are necessary for the reduction of geodetic observations, such as pressure measurements, cable calibrations, and range biases. Performing the observation combination with atmospheric ties improves the combined solution, especially for sparse observing geometry, and facilitates the detection of unaccounted systematic errors.

How to cite: Balidakis, K., Glaser, S., Zus, F., Nilsson, T., Schuh, H., and Gross, R.: On the multi-technique combination with atmospheric ties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7818, https://doi.org/10.5194/egusphere-egu2020-7818, 2020.

EGU2020-9378 | Displays | G2.4

Recent studies on troposphere delay modeling for SLR

Mateusz Drożdżewski, Janina Boisits, Florian Zus, Kyriakos Balidakis, and Krzysztof Sośnica

Recent studies on troposphere delay in Satellite Laser Ranging (SLR) show that the compliance of horizontal gradients of troposphere delay reduces the observation residuals, as well as improves the consistency between SLR results and other space geodetic techniques, all of which are essential for the realization of the terrestrial reference frame. In this work, we examine 3 novel approaches of troposphere delay modeling in SLR, with respect to the standard Mendes-Pavlis approach. We test Potsdam Mapping Function (PMF) with mapping function coefficients and linear horizontal gradients which are based on ERA5 reanalysis provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) model with improved time and spatial resolution in comparison to ERA-Interim reanalysis. We also test a solution based on Vienna Mapping Function 3 for optical observations (VMF3o) which considers the separation of the mapping functions for hydrostatic and non-hydrostatic delays and horizontal gradients. Eventually, we test a solution based on Mendes – Pavlis model with a parameterized model for horizontal gradients based on the 16-year time series of horizontal gradients from PMF. To conduct this experiment, we use SLR observations to passive geodetic satellites LAGEOS-1 and LAGEOS-2. From differences of residual standard deviations for all proposed solutions, we observe an improvement of the SLR observation residuals, for low elevation angles above 10% and improvement of the consistency between estimated pole coordinates and the combined solution IERS-14-C04 series with respect to the currently recommended solutions that neglect the horizontal gradients in SLR solutions.

How to cite: Drożdżewski, M., Boisits, J., Zus, F., Balidakis, K., and Sośnica, K.: Recent studies on troposphere delay modeling for SLR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9378, https://doi.org/10.5194/egusphere-egu2020-9378, 2020.

EGU2020-486 | Displays | G2.4

Determination of global geodetic parameters based on integrated SLR measurements to LEO, geodetic, and Galileo satellites

Dariusz Strugarek, Krzysztof Sośnica, Daniel Arnold, Adrian Jäggi, Grzegorz Bury, and Radosław Zajdel

Numerous active low Earth orbiters (LEOs) and Global Navigation Satellite System (GNSS) satellites, including the Galileo constellation, are equipped with laser retroreflectors used for Satellite Laser Ranging (SLR). Moreover, most of LEOs are equipped with GNSS receivers for precise orbit determination. SLR measurements to LEOs, GNSS, and geodetic satellites vary in terms of the number of registered normal points (NPs) or registered satellite passes. In 2016-2018, SLR measurements to LEOs constituted 81% of all NPs and 59% of all registered satellite passes, whereas 10% of NPs and 30% of satellite passes, respectively, were assigned to GNSS. The remaining SLR measurements were completed by geodetic satellites, including LAGEOS-1/2, and LARES-1.

In this study, we show that the SLR observations to Galileo, passive geodetic and active LEO satellites together with precise GNSS-based orbits of LEOs and Galileo, can be used for the determination of global geodetic parameters, such as geocenter coordinates (GCC) and Earth rotation parameters (ERPs), i.e. pole coordinates, and length-of-day parameter.

GCC are typically determined using SLR observations to passive geodetic satellites, such as LAGEOS-1/2. Also, the SLR observations to LAGEOS-1/2 together with GNSS and Very Long Baseline Interferometry data are used for the determination of ERPs. Here, we use SLR observations to Galileo, LAGEOS-1/2, LARES-1, Sentinel-3A, SWARM-A/B/C, TerraSAR-X, Jason-2, GRACE-A/B satellites to investigate whether they can be applied for the reference frame realization and for deriving high-quality global geodetic parameters.

We present various types of solutions to investigate the best solution set-up. The studied solutions differ in terms of solution lengths, the combination of different sets of satellites and the relative weights for the variance scaling factors of technique and satellite-specific normal equations. We compare our results with the standard LAGEOS-based solutions, the combined EOP-14-C04 products and show the consistency of the results.

How to cite: Strugarek, D., Sośnica, K., Arnold, D., Jäggi, A., Bury, G., and Zajdel, R.: Determination of global geodetic parameters based on integrated SLR measurements to LEO, geodetic, and Galileo satellites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-486, https://doi.org/10.5194/egusphere-egu2020-486, 2020.

EGU2020-2504 | Displays | G2.4

The Estimation and Prediction of Geocenter Motion Based on GNSS Weekly Solutions

Chunmei Zhao, Lingna Qiao, and Tianming Ma

The development of satellite space geodesy technology makes the establishment of global terrestrial reference frame based on the Earth’s center of mass become reality. Precise and stable terrestrial reference frame is the foundation of the Earth science research, while determination and analysis of the position of the Earth's center of mass and its change is an important part to build high precision terrestrial reference frame. Based on GNSS weekly solutions provided by IGS, the geocenter motion (GM) time series between 2007 and 2017 are obtained by means of net translation method. Then the amplitude of the annual term of geocentric motion is 2.27mm, 1.84mm and 2.13mm in the direction of X, Y and Z respectively, and the amplitude of the half-year term is 0.1mm, 0.20mm and 0.15mm respectively. In addition, some other inter-annual changes with relatively small contribution rate are found. Finally, in order to get reliable GM prediction ,two kinds of methods are used, which are ARMA and SSA+ARMA. In the short-term prediction, the accuracy of the two methods is the same, both can reach the millimeter level of prediction accuracy, but SSA+ARMA is more stable. SSA+ARMA algorithm is much better in the medium and long-term scale, and it can provide 1mm medium term prediction accuracy and 1.5mm long term prediction accuracy.

How to cite: Zhao, C., Qiao, L., and Ma, T.: The Estimation and Prediction of Geocenter Motion Based on GNSS Weekly Solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2504, https://doi.org/10.5194/egusphere-egu2020-2504, 2020.

EGU2020-4722 | Displays | G2.4

Combination of GNSS and VLBI data for consistent estimation of Earth Orientation Parameters

Lisa Lengert, Hendrik Hellmers, Claudia Flohrer, Daniela Thaller, and Alexander Kehm

We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.  The main goal of the combined analyses of the two different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, as Earth Orientation Parameters (EOPs), but also station coordinates and tropospheric parameters through local ties and atmospheric ties, respectively.

The combination of GNSS data with VLBI 24-hour sessions and VLBI Intensive sessions is studied in detail w.r.t. EOPs to exploit he combination benefit to its maximum extend. We analyse the impact of the combination on the technique-specific parameters (e.g. dUT1), but also on common parameters (e.g. LOD, polar motion, station coordinates). When using GNSS data in combination with VLBI Intensive sessions, we can demonstrate an accuracy improvement of the dUT1 time series.

We also study the combination of troposphere parameters, focusing first on the validation of the technique-specific troposphere parameters at VLBI-GNSS co-located sites and on the modelling of the corresponding atmospheric ties.

BKGs primary interest is the combination of GNSS and VLBI data on the observation level. However, the current combination efforts are based on the normal equation level using technique-specific SINEX files as a starting point.

How to cite: Lengert, L., Hellmers, H., Flohrer, C., Thaller, D., and Kehm, A.: Combination of GNSS and VLBI data for consistent estimation of Earth Orientation Parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4722, https://doi.org/10.5194/egusphere-egu2020-4722, 2020.

EGU2020-10097 | Displays | G2.4

Geocenter motion determination and analysis from SLR observations to Lageos1/2

Hongjuan Yu, Krzysztof Sośnica, and Yunzhong Shen

Accurate quantification and analysis of geocenter motion are of great significance to the construction and maintenance of the international terrestrial reference frame and its geodetic and geophysical applications. Here, the time series of 13-year geocenter motion coordinates (from 2006 to 2019) is determined by using the network shift approach from Satellite Laser Ranging (SLR) observations to Lageos1 / 2. Then, the geocenter motion time series is analyzed by using singular spectrum analysis. The principal components of geocenter motion are determined with the w-correlation criterion and two principal components with large w-correlation are regarded as the periodic signals. The results show that the annual periodic terms are clearly detectable in all out of three coordinate components, whereas the semi-annual term is only detected in the X-component. Moreover, weak periodic oscillations of 3 to 4 months exist in the X- and Y-components. Besides weak periodic signals with periods of about 8 months and 1 month for the X- and Y-components, respectively, a significant periodic signal of about 2.8 years exists in the  Z-component. Compared to the geocenter motion signals derived by the Center for Space Research (CSR) and Wrocław University of Environmental and Life Sciences (WUELS), both amplitude and phase agree well, with a better consistency with those from CSR, especially for the X- and Y-components.

How to cite: Yu, H., Sośnica, K., and Shen, Y.: Geocenter motion determination and analysis from SLR observations to Lageos1/2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10097, https://doi.org/10.5194/egusphere-egu2020-10097, 2020.

EGU2020-18527 | Displays | G2.4

DORIS positioning from Sentinel-3A and Sentinel-3B data applying GPS onboard clock modeling

Petr Stepanek, Bingbing Duan, Urs Hugentobler, and Vratislav Filler

A unique architecture of Sentinel-3A and Sentinel-3B satellites includes the shared ultra stable oscillator (USO) by DORIS and GPS receiver. This concept enables to apply GPS estimates of onboard clocks in DORIS processing and to substitute DORIS polynomial clock model by GPS epochwise model.  Such an approach is particularly profitable for the mitigation of South Atlantic Anomaly effect (SAA), affecting the short-term frequency stability of USO oscillator in South America and South Atlantic region.  GPS clock modeling precisely maps the SAA effect and enables us to demonstrate a difference between Sentinel-3A and Sentinel-3B USO sensitivity to SAA. Moreover, we present an impact on 3Dpositioning, where SAA-related bias reaches in extreme cases a decimeter level.  We also determine an effect of the precise clock modeling on the Earth rotation parameters estimation. Elimination of SAA effect also gives us an opportunity to get an SAA free DORIS solution of Sentinel-3A and Sentinel-3Bsatellites. Using this solution as a reference, we estimate an SAA effect on the DORIS positioning by satellites Jason-2, Jason-3, Sentinel, Cryosat-2 and Hy-2A and the efficiency of SAA mitigation strategies for these satellites. 

How to cite: Stepanek, P., Duan, B., Hugentobler, U., and Filler, V.: DORIS positioning from Sentinel-3A and Sentinel-3B data applying GPS onboard clock modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18527, https://doi.org/10.5194/egusphere-egu2020-18527, 2020.

EGU2020-19169 | Displays | G2.4

NEW EOP, TRF and CRF determination by GNSS & VLBI COMBINATION

Jean-Yves Richard, Maria Karbon, Chrsitian Bizouard, Sebastien Lambert, and Olivier Becker

The Earth orientation parameters (EOP), the regular products of IERS Earth Orientation Centre, are computed at daily bases by combination of EOP solutions using different astro-geodetic techniques. At SYRTE we have developed a strategy of combination of the Global Navigation Satellite Systems (GNSS) and Very Long Baseline Interferometry (VLBI) techniques at normal equation level using Dynamo software maintained by CNES (France). This approach allows to produce the EOP at the daily bases, which contains polar coordinates (x,y) and their rates (xr,yr), universal time UT1 and its rate LOD, and corrections from IAU2000A/2006 precession-nutation model (dX,dY), and in the same run station coordinates constituting the terrestrial frame (TRF) and the quasar coordinates constituting the celestial frame (CRF). The recorded EOP solutions obtained from GNSS and VLBI combination at weekly bases is recently maintained by SYRTE.

The strategy applied to consistently combine  the IGS and IVS  solutions provided  in Sinex format over the time period 2000-2020 are presented and the resulting  EOP, station positions (TRF) and quasars coordinates (CRF) are analysed and evaluated, differences w.r.t. the individual solutions and the IERS time-series investigated.

How to cite: Richard, J.-Y., Karbon, M., Bizouard, C., Lambert, S., and Becker, O.: NEW EOP, TRF and CRF determination by GNSS & VLBI COMBINATION, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19169, https://doi.org/10.5194/egusphere-egu2020-19169, 2020.

In the correction for polar motion, terrestrial gravimetry and 3-D positioning follow different conventions. The 3-D positions are corrected to refer to the "mean pole" (IERS Conventions 2010) or to the "secular pole" (IERS update working version since 2018). In any case, the pole reference evolves in time and describes the track of secular or low-frequency polar wander. However, in terrestrial gravimetry the gravity values are corrected to refer to the IERS Reference Pole, a fixed quantity. This may lead to discrepancies when for instance gravity change rates from absolute gravity measurements are compared with vertical velocities from GNSS. I discuss the size and geographical distribution of the possible discrepancies.

How to cite: Mäkinen, J.: The correction for polar motion in gravimetry and in 3-D positioning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11837, https://doi.org/10.5194/egusphere-egu2020-11837, 2020.

EGU2020-21088 | Displays | G2.4

Short-Term Realization of the ITRS with GNSS/SLR/VLBI/DORIS

Changhui Xu, Yingyan Cheng, and Yamin Dang

International Terrestrial Reference Frame (ITRF) is the realization of the International Terrestrial Reference System (ITRS), which can be used for the variety applications such as earth research, surveying and mapping. 2000 National Geodetic Coordinate System (CGCS2000) has been established and widely applied as a long-term reference frame in China, however, a software for short-term reference frame establishment is also developed to provide high accuracy applications based on the fusion of GNSS/SLR/VLBI/DORIS. We analyzed the covariance from sinex format of the GNSS/SLR/VLBI/DORIS and the quality of local ties. The errors between the local ties and the ITRF2014 within 1cm was 89% in north direction and 85% east direction. We used inner constraints as the method of datum realization and Helmert variance component estimation for giving the weight of different space geodetic GNSS/SLR/VLBI/DORIS. Finaly, short-term terrestrial reference frame realization software can produce the weekly, monthly and annual frame products for high accuracy applications.

How to cite: Xu, C., Cheng, Y., and Dang, Y.: Short-Term Realization of the ITRS with GNSS/SLR/VLBI/DORIS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21088, https://doi.org/10.5194/egusphere-egu2020-21088, 2020.

EGU2020-5749 | Displays | G2.4

GNSS and VLBI integrated processing at the observation level

Jungang Wang, Kyriakos Balidakis, Maorong Ge, Robert Heinkelmann, and Harald Schuh

The terrestrial and celestial reference frames, which serve as the basis for geodesy and astronomy, are mainly determined and maintained by space geodetic techniques such as Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). These techniques are also used together to determine the Earth Orientation Parameters (EOP), which are very important for precise positioning, navigation and timing. Currently, the combination of all these techniques is done on the parameter level (ITRF) or on the normal equation level (DTRF), which are well-known and convenient methods but may suffer from some inconsistency.

Unlike the combination on the parameter or normal equation levels, the integrated processing at the observation level exploits the lengths and unique features of different techniques, and is valuable in determining homogeneous reference frames and EOP, and to connect the terrestrial, celestial, and dynamic frames. We are applying the integrated GNSS, VLBI and SLR data processing in the current Positioning And Navigation Data Analyst (PANDA) software, which aims on processing multi-geodetic techniques on the observation level. We present the strategy and current status of the integrated GNSS and VLBI processing and demonstrate the benefit of integrating GNSS for VLBI using 14 years of VLBI intensive sessions (2001-2014) and five CONT campaigns (2005-2017). We discuss the impact of applying tropospheric tie and local tie in the integrated processing.

How to cite: Wang, J., Balidakis, K., Ge, M., Heinkelmann, R., and Schuh, H.: GNSS and VLBI integrated processing at the observation level, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5749, https://doi.org/10.5194/egusphere-egu2020-5749, 2020.

EGU2020-20227 | Displays | G2.4

Simulations of VLBI observations to satellites enabling co-location in space

Nicat Mammadaliyev, Patrick Schreiner, Susanne Glaser, Karl Hans Neumayer, Rolf Koenig, Robert Heinkelmann, and Harald Schuh

The exceptional situation of simultaneously observing a dedicated near-Earth orbiting satellite via the four main space geodetic techniques opens the unique opportunity to investigate the additional benefits on the realization of global terrestrial reference frame using co-location in space. Applying co-location in space requires a precise orbit determination (POD) of dedicated satellites for all techniques. In this regard, current VLBI infrastructure is extended by the observation to satellites and the impact of such observation concept on the VLBI estimates is assessed. Thus the main geodetic products including the terrestrial reference frame are investigated within the GGOS-SIM-II project. In this study, the potential influence of orbital errors on the estimates and capability of VLBI observations to satellites within the POD are investigated for different scenarios with varying networks, observation time and measurement noise.  

How to cite: Mammadaliyev, N., Schreiner, P., Glaser, S., Neumayer, K. H., Koenig, R., Heinkelmann, R., and Schuh, H.: Simulations of VLBI observations to satellites enabling co-location in space , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20227, https://doi.org/10.5194/egusphere-egu2020-20227, 2020.

EGU2020-7787 | Displays | G2.4

On the Feasibility and Applicability of Multipath Mitigation Maps as an IGS Product

Addisu Hunegnaw, Yohannes Getachew Ejigu, Felix Norman Teferle, and Gunnar Elgered

Multipath is a largely unmodelled source of error and causes large range errors in Global Navigation Satellite System (GNSS) observations. The effects have strong site-specific characteristics and impact each receiver differently. Multipath errors can propagate and can cause in-situ position and velocity biases and are also contributing to the pervasive draconitic harmonic signals. We employ an empirical approach to reducing the effects of multipath by stacking one-way post-fit carrier phase residual observations by applying an appropriate averaging scheme. Our processing is based on static multi-GNSS observations using various scientific GNSS software packages (Bernese GNSS Software, NAPEOS, GAMIT-GLOBK, PRIDE and GINS). Our multipath stacking (MPS ) uses the stacking of individual residuals generated by variable azimuth cell size (congruent cells) by allocating carrier phase residuals in each cell, unlike fixed azimuth cell resolution in the standard MPS approaches. This reduces the binning of fewer residuals at higher elevation angles. Before stacking, we also apply rigorous statistical outlier screening tests for each one-way post-fit carrier phase residual assigned to each of the congruent cells. We thus correct the multipath effects by subtracting the stacked multipath map from the post-fit carrier phase residual. Using this technique we produce a model available in the form of the Antenna Exchange (ANTEX) file format, that can potentially be implemented in routine GNSS analysis with no or little additional overhead for individual analysis centers (ACs).

In this study, we assess the feasibility and applicability of the MPS maps as an International GNSS Service (IGS) product for routine GNSS analysis. We have selected a subset of IGS stations with and without known multipath issues in different climatic zones. We demonstrate the multipath stacking technique to result in a significant reduction of the variation in the one-way post-fit carrier phase residuals. For GPS-only solutions, the MPS technique shows a decrease of up to 30% in the RMS value of the one-way post-fit carrier phase residuals. We have also tested our MPS for other constellations such as GLONASS, Galileo and BeiDou, and combinations of these .

How to cite: Hunegnaw, A., Ejigu, Y. G., Teferle, F. N., and Elgered, G.: On the Feasibility and Applicability of Multipath Mitigation Maps as an IGS Product, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7787, https://doi.org/10.5194/egusphere-egu2020-7787, 2020.

G3.1 – Earth Rotation: Theoretical aspects, observation of temporal variations and physical interpretation

EGU2020-13484 | Displays | G3.1

Optimal VGOS telescope location for the estimation of Earth orientation parameters

Matthias Schartner, Johannes Böhm, and Axel Nothnagel

In this investigation, we identify optimal locations for VGOS radio telescopes to estimate Earth orientation parameters (EOP) with a new method based on bulk schedule generation and large-scale Monte-Carlo simulations. Thereby, we focus on a high number of simulations and a proper consideration of scheduling to minimize these undesired error sources.

The location of the telescope is varied over 477 possible locations, homogeneously distributed over land areas on the globe. The antenna is added to a fixed network of 6, 12 and 18 existing and upcoming VGOS stations. The optimal location is defined through the minimal resulting repeatabilities of the simulated EOP. In this study, a special focus was laid on the generation of high-quality observing plans to minimize the effects of scheduling combined with a high number of simulations to minimize their randomness. To remove the unintended effects caused by scheduling over 93 thousand schedules were iteratively generated. Each schedule is further simulated 1000 times leading to over 5 trillion simulated and analyzed observations. Besides showing our results for the best telescope location, we will highlight how scheduling and the number of simulations affects the repeatability of the estimated EOP. This will help further simulation studies to improve their results.

The optimal telescope location depends on the EOP of interest and the existing network. For simple network geometries, such as the 6 station network which consists of antennas in Europe and North America, the importance of east-west baselines can be seen for the determination of dUT1 while the importance of north-south baselines can be seen for the determination of polar motion and nutation. For more complex network geometries and an increasing number of VGOS stations, the lack of southern stations becomes more prominent. For the 12 and 18 station network, the location of an additional antenna in south America can significantly improve the accuracy of the EOP by up to 60%.

How to cite: Schartner, M., Böhm, J., and Nothnagel, A.: Optimal VGOS telescope location for the estimation of Earth orientation parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13484, https://doi.org/10.5194/egusphere-egu2020-13484, 2020.

EGU2020-18545 | Displays | G3.1

Constraints on the Rheology of the Earth's Deep Mantle from Decadal Observations of the Earth's Figure Axis and Rotation Pole

Alexandre Couhert, Christian Bizouard, Flavien Mercier, Kristel Chanard, Marianne Greff, and Pierre Exertier

The over four decades long record of Satellite Laser Ranging (SLR) observations to a variety of historical geodetic spherical satellites makes it possible to directly observe the long-term (seasonal to decadal time scales) displacement of the Earth’s mean axis of maximum inertia, namely its principal figure axis, with respect to the crust, through the determination of the degree-2 order-1 geopotential coefficients over the 34-year period 1984—2017.

On the other hand, the pole coordinate time series (mainly from GPS and VLBI data), yield the motion of the rotation pole with even a greater accuracy.

The time-dependent nature of the response of the Earth’s mantle to external forces, where it behaves either elastically on short time scales (seconds) or like a viscous fluid over geological time scales (millions of years), is poorly constrained at decadal periods. Here we propose to relate oscillations of the figure axis to those of the Earth’s rotation pole (through the Euler-Liouville equations) to study the mass-related excitation of polar motion and provide global constraints on the rheological properties of the deep Earth.

How to cite: Couhert, A., Bizouard, C., Mercier, F., Chanard, K., Greff, M., and Exertier, P.: Constraints on the Rheology of the Earth's Deep Mantle from Decadal Observations of the Earth's Figure Axis and Rotation Pole, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18545, https://doi.org/10.5194/egusphere-egu2020-18545, 2020.

EGU2020-16509 | Displays | G3.1

Effects of the observed Earth’s oblateness variation on precession-nutation: A first assessment

José M. Ferrándiz, Alberto Escapa, Tomás Baenas, Santiago Belda, and M. Isabel Vigo

The current IAU2000 nutation theory considers the Earth’s dynamical ellipticity as a constant, whereas the IAU2006 precession theory uses a linear model for it. Apart from the problems of consistency between the two theories, whose full solution was proposed recently, the fundamental issue, namely whether the observed time variation of the Earth’s gravity field can affect the Earth’s rotation to a non-negligible extent or not, remains untreated.

This presentation is intended to share some preliminary results concerning precession and nutation. The variation of the Earth’s dynamical ellipticity is modelled from one of the time series providing the time-varying Stokes coefficients, and its effects on the longitude are computed following a new method introduced by the authors to that purpose. The found variations are above the accuracy goals of GGOS, the Global Geodetic Observing System of the International Association of Geodesy, adopted by its Joint Working Group on Improving theories and models of the Earth rotation (JWG ITMER).

How to cite: Ferrándiz, J. M., Escapa, A., Baenas, T., Belda, S., and Vigo, M. I.: Effects of the observed Earth’s oblateness variation on precession-nutation: A first assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16509, https://doi.org/10.5194/egusphere-egu2020-16509, 2020.

EGU2020-17154 | Displays | G3.1

Status of ESA’s independent Earth Orientation Parameter products

Erik Schoenemann, Tim Springer, Michiel Otten, Volker Mayer, Sara Bruni, Werner Enderle, and René Zandbergen

The availability of highly accurate, up-to-date Earth Orientation Parameters is of major importance for all positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for ESA missions and the EU space programs, e.g. Galileo, EGNOS and Copernicus.

In the frame of its responsibility to provide the Geodetic reference for ESA missions, ESA’s Navigation Support Office at ESOC is already contributing to the realisation of the International Terrestrial Reference Frame (ITRF) and the combined Earth Orientation Parameters provided by the International Earth Rotation Service (IERS). The contribution is realised through individual contributions to international services such as the International GNSS Service (IGS), the International Laser Ranging Services (ILRS), the International DORIS Service (IDS), the International Earth Rotation Service (IERS) and in the future also to the International VLBI Service (IVS).

For the combination and the long-term predictions of the Earth orientation products ESA is still relying on the International Earth Rotation Service (IERS). Over the past years, ESA repeatedly experienced problems with outdated or missing predictions of the Earth orientation parameters (Bulletin A). Considering the importance of up-to-date Earth orientation parameters, the dependence on a single source outside Europe is considered a risk for European industry, for ESA missions and for EU programmes. For this reason, ESA initiated in 2017 a study with the target to develop independent ESA Earth Orientation parameter products. This study, executed by a consortium led by the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM), is expected to finish in the course of this year.

In this presentation we will give an overview of ESAs up-to-date reference products and discuss their quality. It will outline the combination approach and discuss the way forward to an fully operational provision of the ESA Earth Orientation Parameter products.

How to cite: Schoenemann, E., Springer, T., Otten, M., Mayer, V., Bruni, S., Enderle, W., and Zandbergen, R.: Status of ESA’s independent Earth Orientation Parameter products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17154, https://doi.org/10.5194/egusphere-egu2020-17154, 2020.

EGU2020-174 | Displays | G3.1

Preliminary hydrological polar motion excitation estimates from the GRACE Follow-On mission

Justyna Śliwińska, Małgorzata Wińska, and Jolanta Nastula

Over almost 20 last years, observations from the Gravity Recovery and Climate Experiment (GRACE) mission have become invaluable as means to examine Earth global mass change. Since 2002, the relative along track motions between two identical satellites have been used to derive Earth’s time variable gravity field. The great success and scientific sound of the mission, which ended in 2017, contributed to the launch of its successor, GRACE Follow-On (GFO) in May 2018. Until now, monthly time series of GFO-based geopotential models have been made available to the users by official GRACE data centres at Center for Space Research (CSR), Jet Propulsion Laboratory (JPL) and GeoForschungsZentrum (GFZ). This data enables the continuation of many researches which started with the beginning of the GRACE mission. Such applications included monitoring of land water storage changes, drought event identification, flood prediction, ice mass loss detection, groundwater level change analysis, and more.

In geodesy, a crucial application of GRACE/GFO mission observations is the study of polar motion (PM) changes due to mass redistribution of the Earth’s surficial fluids (atmosphere, ocean, land hydrosphere). PM represents two out of five Earth Orientation Parameters (EOP), that describe the rotation of our Planet and link the terrestrial reference frame with the corresponding celestial reference frame. The use of C21, S21 coefficients of GRACE/GFO-based geopotential models is a common method for determining polar motion excitation.

In this study, we present the first estimates of hydrological polar motion excitation functions (Hydrological Angular Momentum, HAM) computed from GFO data which were provided by CSR, JPL and GFZ teams. The HAM are calculated using (1) C21, S21 coefficients of geopotential (GFO Level-2 data) as well as (2) gridded terrestrial water storage (TWS) anomalies (GFO Level-3 data). We compare and evaluate the two methods of HAM estimation and examine the compatibility between CSR, JPL and GFZ solutions. We also validate different HAM estimations using precise geodetic measurements of the pole coordinates.

Our analyses show that the highest internal agreement between different GFO solutions can be obtained when comparing CSR and JPL. Notably, GFZ estimates differ slightly from the other GFO models. The highest agreement between different GFO-based HAM, and between GFO-based HAM and reference data is obtained when GFO Level-3 data are used. We also demonstrate that the current accuracy of HAM from GRACE Follow-On mission meets the expectations and is comparable with the accuracy of HAM from GRACE Release-6 (RL06) data.

How to cite: Śliwińska, J., Wińska, M., and Nastula, J.: Preliminary hydrological polar motion excitation estimates from the GRACE Follow-On mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-174, https://doi.org/10.5194/egusphere-egu2020-174, 2020.

EGU2020-13127 | Displays | G3.1

Length of day fluctuations at long and short timescales. Geomagnetic drivers

Crisan Demetrescu and Venera Dobrica

We decompose the well known LOD time series provided by IERS, that shows so-called decadal variations, in fluctuations at several timescales, namely: sub-centennial (60-90 years), inter-decadal (20-35 years), decennial (~11 years) and intra-decennial (~6 years). A Hodrick and Prescott (1977) type of analysis is used, followed by the decomposition of the trend and oscillatory parts at the mentioned timescales using Butterworth filtering. Comparing the results to previously (e.g. Dobrica et al., 2018) known oscillations of the geomagnetic field (dD/dt), and carrying out a similar analysis for parameters describing the evolution of the magnetospheric ring current, suggest the latter is the ultimate driver of both geomagnetic and LOD variations. The probable mechanisms are discussed as well: Alfvén torsional oscillations in the outer core, triggered by variations in the magnetospheric ring current, or a direct control of geomagnetic declination by variations in the magnetospheric ring current. While the first one is long accepted for the long-term variations in D and LOD, a similar possibility for the 6-year variation is out of question due to the implied value of the geomagnetic field within the outer core (Gillet et al., 2010); for the latter we suggest the second mechanism.       

How to cite: Demetrescu, C. and Dobrica, V.: Length of day fluctuations at long and short timescales. Geomagnetic drivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13127, https://doi.org/10.5194/egusphere-egu2020-13127, 2020.

EGU2020-4530 | Displays | G3.1

Validation of Earth rotation time series by comparison of their sub-daily to sub-monthly excitation signal with simulated geophysical fluid model excitations

Robert Dill, Henryk Dobslaw, Maik Thomas, Hellmers Hendrik, Thaller Daniela, Bloßfeld Mathis, Kehm Alexander, and Seitz Florian

Time-variations in the orientation of the solid Earth are largely governed by the exchange of angular momentum with the surface geophysical fluids of atmosphere, oceans, and the land surface. Modelled fields of atmospheric winds, atmospheric surface pressure, ocean currents, ocean bottom pressure, and terrestrial water storage allow calculating effective angular momentum (EAM) functions that can be compared to geodetic angular momentum functions (GAM) derived from observed Earth Orientation Parameters (EOP) via the Liouville equation. Especially in the high-frequency range, currently available global geophysical fluid models provide highly reliable information about angular momentum transfers that determine the orientation changes of the Earth.

In this contribution, we investigate the extent to which the modelled Earth rotation angular momentum functions processed at GFZ can be used to evaluate time series of EOP processed from different geodetic space techniques at periods between 2 and 60 days. We therefore compare the time series from various sources that are based on individual techniques (e.g., VLBI[TD1], GNSS, SLR, and DORIS) only, and also combined solutions that are processed at different institutions (e.g., JPL, GFZ, BKG[TD2], DGFI-TUM) or published by international services (e.g., IERS, IGS, IVS[TD3] ). By calculating differences from all possible pairs of EAM and GAM and by utilizing both band-pass filtering and spectral analysis techniques, we will elaborate the systematic differences between excitation functions from different sources that are expected to help identifying deficits in geodetic data processing and/or numerical modelling.

How to cite: Dill, R., Dobslaw, H., Thomas, M., Hendrik, H., Daniela, T., Mathis, B., Alexander, K., and Florian, S.: Validation of Earth rotation time series by comparison of their sub-daily to sub-monthly excitation signal with simulated geophysical fluid model excitations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4530, https://doi.org/10.5194/egusphere-egu2020-4530, 2020.

EGU2020-18882 | Displays | G3.1

The relation between the rotational and inertial modes of a triaxial planet

Jeremy Rekier, Santiago Triana, Antony Trinh, and Véronique Dehant

Inertial modes are natural oscillations in the fluid parts of planets which are caused by the restoring action of the Coriolis force. The relation between these modes, as they appear in the liquid core of planets, and the well-known rotational modes – the Free (Inner) Core Nutation (FCN & FICN) and the Chandler and Inner Core Wobble (CW & IW) – is not well understood, with the FCN often being mistakenly identified to the simplest inertial mode, the Spin-Over (SO). In this work, we clarify this relation using a new formalism to compute the rotational modes of a two-layer triaxial planet with a rigid mantle and an inviscid fluid core to all order in the eccentricity. We confirm the validity of our model through comparison with the results from direct numerical integration of the equations of motion. Using this technique, we demonstrate how the SO is the only inertial mode affecting the rotation of the planet and we show how this mode identifies with the FCN only in the limit of vanishing eccentricity.

How to cite: Rekier, J., Triana, S., Trinh, A., and Dehant, V.: The relation between the rotational and inertial modes of a triaxial planet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18882, https://doi.org/10.5194/egusphere-egu2020-18882, 2020.

EGU2020-10201 | Displays | G3.1

About the calculation of the frequencies of lunar-solar tides in the model of viscoelastic Earth

myo zaw aung and Skorobogatykh Vladimirovich

Skorobogatykh I.V., Myo Zaw Aung

About the calculation of the frequencies of lunar-solar tides

in the model of viscoelastic Earth

The problem of calculating the Earth tidal deformations under the influence of gravity of the Moon and the Sun is considered. The Earth is assumed to be a viscoelastic body that is axisymmetric in an undeformed state and has an axisymmetric absolutely solid core. The elastic displacements at the boundary of the viscoelastic part and the solid core equal to zero, and another boundary is free. Viscoelastic material is assumed to move according to the Kelvin - Voigt model. The center of mass of the Earth – Moon system moves in a slowly changing elliptical orbit around the Sun under the influence of gravitational forces from the Sun and the Moon. For this problem the Sun and the Moon are considered as material points. Previously, this problem was considered in [1], with a significant number of simplifications and assumptions. 

The equations that describe the Earth's deformations, are obtained from the d’Alembert-Lagrange variational principle [2].Also,  according to the modal approach, the displacement vector is represented as an infinite series of eigenforms of the elastic part’s free oscillations. As a result, for modal variables an infinite system of ordinary differential equations of the second order is written The system can be simplified using the physical observation, that under the influence of viscous friction in the free oscillations in the material are damped and therefore the deformations occur in a quasi-static way [2], which allows us to discard the inertial terms in the equations.  As a result, in the obtained simplified system it can be noted that only the equations for the first four forms contain the non-zero right-hand sides, which means that the deformations of the remaining forms are (under quasi-static condition) small and can be neglected. As a result, we have a system of eight equations. The right-hand sides of these equations are due to the gravitational interactions between the  Earth and the Sun and between the Earth and the Moon which means that they depend on their radius vectors. Therefore they can are expressed through the angles that determine these radius vectors, as well as the angles that determine the orientation of the Earth in space. By expanding the right-hand sides of the equations as a series in powers of a small parameter (which is taken as the ratio of the Earth's radius to the distance from the Earth to the Moon), we can represent them as series containing sines and cosines of the combinations of aforementioned angles. Since the angles can be considered as uniformly changing over not too long time periods, this allows us to approximate the frequency of the Earth tidal deformations.

 

References

  1. Skorobogatykh I.V., Do Chung Bo “On the frequencies of the lunar-solar tides of the deformed Earth” Kosmonavtika i Raketostroyeniye, 2015, issue 1 (80), pp. 106-113.
  2. Vilke V.G. “Analytical and qualitative methods in the mechanics of systems with an infinite number of degrees of freedom” M.: Moscow Publishing House. University, 1986. 192 p.

 

How to cite: zaw aung, M. and Vladimirovich, S.: About the calculation of the frequencies of lunar-solar tides in the model of viscoelastic Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10201, https://doi.org/10.5194/egusphere-egu2020-10201, 2020.

EGU2020-21410 | Displays | G3.1

On the permanent tide and the Earth dynamical ellipticity

Alberto Escapa, Tomás Baenas, and José Manuel Ferrándiz

As other relevant quantities related to the Earth dynamics, the Earth dynamical ellipticity is influenced by tidal effects. In particular, it is affected by the permanent tide due to the time independent part of the Earth redistribution tidal potential. Hence, it is necessary to distinguish between its tide-free and non tide-free values (e.g., Burša 1995) when determining it from observations (e.g., Marchenko & Lopushanskyi 2018). This question is seldom considered in Earth rotation studies. For example, neither IAU2000/AIU2006 nutation/precession model nor IERS Conventions specify explicitly whether the dynamical ellipticity is a zero-tide parameter or not. However, current accuracy goals might be sensitive to that difference.

Within the framework of a Hamiltonian approach (Baenas, Escapa, & Ferrándiz 2019), we present a consistent treatment of the influence of the permanent tide on the dynamical ellipticity. In particular, we develop an analytical expression of the redistribution tidal potential based on Andoyer canonical variables and a semi-analytical theory of the orbital motions of the Moon and the Sun, following the same procedure as that given in Kinoshita (1977).

This method allows obtaining an expression of the zero frequency term of the redistribution tidal potential that updates that of Zadro & Marussi (1973), usually employed in reporting parameters of common relevance to Astronomy, Geodesy, & Geodynamics (e.g., Burša 1995, Groten 2004). In addition, it clarifies the procedure that must be followed in order that the dynamical ellipticity, fitted to the observations, contains the effects of the permanent tide avoiding in this way potential inconsistencies.

How to cite: Escapa, A., Baenas, T., and Ferrándiz, J. M.: On the permanent tide and the Earth dynamical ellipticity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21410, https://doi.org/10.5194/egusphere-egu2020-21410, 2020.

Accounting for non-stationary effects in the model of the Earth’s pole motion

Wai Yan Soe, Rumyantsev D.S., Perepelkin V.V.

 

Nowadays the problem of constructing a model of the Earth pole motion is relevant both in theoretical and in applied aspects. The main difficulty of accurately describing the Earth pole motion is that it has non-stationary perturbations leading to the changes in both the average parameters of its motion and the motion as a whole.

The main process of the Earth pole coordinates fluctuations is the sum of the quasi periodic Chandler component and annual one. The approximation of the Earth pole motion is generally accepted to be a few parametric two-frequency model with constant coefficients. Relatively slow changes in the parameters of the Chandler and annual components make it possible to use this approximation in the time intervals of 6–7 years, that is, during the period of the Chandler and annual components modulation. This model has low algorithmic complexity and describes the main process of pole oscillations with acceptable accuracy.

However, due to the non-stationary perturbations there are effects in the Chandler and annual components that are not typical for a simple dynamical system that is described by linear differential equations with constant coefficients. Such changes can also be observed in the dissipative systems with not only with the amplitude variations but also when oscillation process is in steady-state condition [1].

In this work the effect of changing in the Earth pole oscillatory mode is revealed, which consists in a jump-like shift in the average frequency of the pole around the midpoint (the motion of the Earth pole midpoint is a pole trend of a long-period and secular nature), which leads to a change in the average speed of its motion.

A method is proposed to determine the moment when the average frequency is shifted, which is important for refining the forecast model of the Earth pole motion. Using this method a modified model of pole motion is developed and the dynamic effects in its motion are considered, caused by the change in the amplitudes ratio of the Chandler and annual harmonics.

References

[1] Barkin M.Yu., Krylov S.S., Perepelkin V.V. Modeling and analysis of the Earth pole motion with nonstationary perturbations. IOP Conf. Series: Journal of Physics: Conf. Series 1301 (2019) 012005; doi:10.1088/1742-6596/1301/1/012005

 

How to cite: Wai, Y.: Accounting for non-stationary effects in the model of the Earth’s pole motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9954, https://doi.org/10.5194/egusphere-egu2020-9954, 2020.

EGU2020-8295 | Displays | G3.1

On the time-varying characteristic of the 6-year oscillation signal in length-of-day

Pengshuo Duan, Cancan Xu, Xueqing Xu, and Chengli Huang

A significant 6-year oscillation (SYO) signal existing in the length-of-day (LOD) variations may reflect the fast dynamics of the Earth cores. The time-varying characteristic (TVC) of this signal may reveal the relevant details on the geophysical excitation process. However, it is still debate about the TVC of the SYO. Our previous works indicated that the SYO signal was showing an obviously decaying trend during 1962~2012 based on the normal Morlet wavelet transform (NMWT) method, while other works did not show the similar decaying result based on the other methods (e.g., the least square fitting- LSF). Here, in order to solve this controversial issue, we revisit the SYO and its TVC. Through a lot of numerical simulation tests, NMWT method is further confirmed to be a good approach to quantitatively recover the target damped harmonic signals from the complex background noises, but the classical LSF method can destroy the original harmonic signal. This work indicates that the unattenuated SYO result obtained by the LSF method is not reliable. In addition, this work further analyzes the LOD data during a longer span (i.e., 1840~2018) and extracts the SYO result in the time domain, the result of which  shows: 1) the amplitude modulation phenomenon of the SYO itself on the longer time span, revealing the relevant excitation information within the Earth system; 2) a decreasing trend of the SYO signal in its amplitude after 1960s, which further supports the current SYO decaying result during 1962~2019. This recovered SYO result during a longer time-span obtained by this work is significant to understand the nature of the SYO change and its excitation process.

How to cite: Duan, P., Xu, C., Xu, X., and Huang, C.: On the time-varying characteristic of the 6-year oscillation signal in length-of-day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8295, https://doi.org/10.5194/egusphere-egu2020-8295, 2020.

EGU2020-2996 | Displays | G3.1

The status of Chandler wobble

Guocheng Wang, Lintao Liu, Jinzhao Liu, and Yi Tu

The Chandler wobble (CW) and Annual wobble (AW) are the main components of the Earth’s Polar motion, which play an important role in our understanding of their excitations. The Fourier Basis Pursuit Band-Pass Filtering (FBPBPF) method, which can effectively suppress the edge effect, are applied to extract the CW and AW in Earth's polar motion during 1900-2016. Through analyze the variation of CW extracted by the FBPBPF method, we find that the amplitude of the CW has been diminishing since 1995. However, the amplitude of the CW had stopped decline in the last year, and start to increase at now.

How to cite: Wang, G., Liu, L., Liu, J., and Tu, Y.: The status of Chandler wobble, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2996, https://doi.org/10.5194/egusphere-egu2020-2996, 2020.

EGU2020-19240 | Displays | G3.1

Study of the Earth rheological properties from polar motion

Christian Bizouard, Ibnu Nurul Huda, and Sébastien Lambert

How to cite: Bizouard, C., Nurul Huda, I., and Lambert, S.: Study of the Earth rheological properties from polar motion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19240, https://doi.org/10.5194/egusphere-egu2020-19240, 2020.

EGU2020-7621 | Displays | G3.1

A multi-model assessment of sub-monthly polar motion and the associated ocean bottom pressure variability

Michael Schindelegger, Alexander Harker, David Salstein, and Henryk Dobslaw

Budgeting geophysical fluid excitations against space-geodetic observations of polar motion reveals non-negligible residuals on sub-monthly time scales, typically 1−2 cm when projected onto the Earth's surface. A possible source for these discrepancies are imperfections in the hydrodynamic models used to derive the required ocean excitation functions. To guide future model improvements, we present a systematic assessment of the oceanic component of sub-monthly polar motion based on three global time-stepping models which are forced by the same atmospheric data but considerably differ in their numerical setup and physical parameterizations. In particular, we use ocean bottom pressure output and angular momenta from (i) the finite-element 2 Dimensions Gravity Wave Model (Mog2D), (ii) the baroclinic Max-Planck-Institute Ocean Model (MPIOM) at 1° horizontal resolution, representing the current industry standard, and (iii) a more experimental, eddy-permitting setup of the MITgcm (MIT General Circulation Model). Validations of data from 2007 to 2008 are performed against observed polar motion and daily GRACE (Gravity Recovery and Climate Experiment) solutions, which resolve the broad scales of ocean bottom pressure variability relevant for angular momentum considerations. No definite quantitative results are available at the time of this writing, but a specific question we aim to answer is whether the MITgcm run outperforms the other models in our validations, given its higher resolution and partial representation of flow interactions with major topographic features.

How to cite: Schindelegger, M., Harker, A., Salstein, D., and Dobslaw, H.: A multi-model assessment of sub-monthly polar motion and the associated ocean bottom pressure variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7621, https://doi.org/10.5194/egusphere-egu2020-7621, 2020.

EGU2020-7088 | Displays | G3.1

Climate impact on Earth rotation speed from CMIP6 model simulations

Sigrid Böhm and David Salstein

The Coupled Model Intercomparison Project (CMIP) is an effort to investigate the past, present and future state of a number of Earth system variables, using a variety of models developed by research centers around the globe. This broad initiative aims at understanding climate signals due to both natural variability and in response to changing radiative forcing. One of the so-called endorsed MIPs of the CMIP phase 6, the ScenarioMIP, is dedicated to providing multi-model climate projections based on alternative scenarios of future emissions and land use changes linked to socioeconomic factors. The climate of the 21st century is simulated based on different forcings, which are defined from a combination of possible future pathways of societal development, the Shared Socioeconomic Pathways (SSPs), and the Representative Concentration Pathways (RCPs), identified by what radiative forcing level might exist in 2100.

Our study will examine the integrated effect of atmosphere and ocean variability on the Earth rotation speed, represented as changes in the length of day (LOD). Angular momentum variations due to mass and motion terms will be calculated from different models for the four most prominent scenarios as well as for historical simulations. We will also analyze spatial patterns of the respective variables in order to identify those regions in the atmosphere and oceans that contribute the most to LOD excitation. Finally, we will compare trends in the total axial angular momentum functions among each other and to trends in the global temperature to show the influence of global warming on the rotation rate.

How to cite: Böhm, S. and Salstein, D.: Climate impact on Earth rotation speed from CMIP6 model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7088, https://doi.org/10.5194/egusphere-egu2020-7088, 2020.

EGU2020-7444 | Displays | G3.1

Reducing filter effects in GRACE-derived polar motion excitations

Franziska Göttl, Michael Murböck, Michael Schmidt, and Florian Seitz

Polar motion is caused by mass redistribution and motion within the Earth system. The GRACE satellite mission observed variations of the Earth’s gravity field which are caused by mass redistribution. Therefore GRACE time variable gravity field models are a valuable source to estimate individual geophysical mass-related excitations of polar motion. Since GRACE observations contain erroneous meridional stripes, filtering is essential in order to retrieve meaningful information about mass redistribution within the Earth system. However filtering reduces not only the noise but also smooths the signal and induces leakage of neighboring subsystems into each other.

We present a novel approach to reduce these filter effects in GRACE-derived equivalent water heights and polar motion excitation functions which is based on once and twice filtered gravity field solutions. The advantages of this method are that it is independent from geophysical model information, works on global grid point scale and can therefore be used for mass variation estimations of several subsystems of the Earth (e.g. continental hydrosphere, oceans, Antarctica and Greenland). In order to validate this new method, we perform a closed-loop simulation based on a realistic orbit scenario and error assumptions for instruments and background models, apply it to real GRACE data (GFZ RL06) and show comparisons with ocean model results from ECCO and MPIOM.

How to cite: Göttl, F., Murböck, M., Schmidt, M., and Seitz, F.: Reducing filter effects in GRACE-derived polar motion excitations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7444, https://doi.org/10.5194/egusphere-egu2020-7444, 2020.

EGU2020-1908 | Displays | G3.1

Excitations of the Earth and Mars’ Variable Rotations by Surficial Fluids

Yonghong Zhou, Xueqing Xu, Cancan Xu, Jianli Chen, and David Salstein

The dynamic interactions that occur between the solid Earth and surficial fluids are related globally by conservation of angular momentum in the Earth system. Owing to this condition, the surficial fluids have shown to be main excitation sources of the Earth’s variable rotation on timescales between a few days and several years. Likewise, the Mars’ rotation changes due to variations of atmospheric circulation and surface pressure, and the variable Martian polar ice caps associated with the CO2 sublimation/condensation effects. Investigations of the Earth and Mars’ rotations by surficial fluids may further our understandings of the Earth and planetary global dynamics. Here, we present our recent progresses on excitations of the Earth and Mars’ rotational variations on multiple time scales: (1) differences between the NCEP/NCAR and ECMWF atmospheric excitation functions of the Earth’s rotation, and (2) the Mars’ rotational variations and the dust cycles during the Mars Years 24-31.

How to cite: Zhou, Y., Xu, X., Xu, C., Chen, J., and Salstein, D.: Excitations of the Earth and Mars’ Variable Rotations by Surficial Fluids, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1908, https://doi.org/10.5194/egusphere-egu2020-1908, 2020.

EGU2020-13749 | Displays | G3.1

The rotation and interior of Ganymede

Tim Van Hoolst, Rose-Marie Baland, Alexis Coyette, and Marie Yseboodt

The rotation rate of Ganymede, the largest satellite of Jupiter, is on average equal to its orbital mean motion but cannot be constant on orbital time scale as a result of the gravitational torque exerted by Jupiter on the moon. Here we discuss small deviations from the average rotation rate, evaluate polar motion, and discuss Ganymede's obliquity. We examine different time scales, from diurnal to long-period, and assess the potential of using rotation as probes of the interior structure.

The ESA JUICE (JUpiter ICy moons Explorer) mission will accurately measure the rotation of Ganymede during its orbital phase around the satellite starting in 2032. We report on different theoretical aspects of the rotation for realistic models of the interior of Ganymede, include tidal deformations and take into account the low-degree gravity field and topography of Ganymede. We assess the advantages of a joint use of rotation and tides to constrain the satellite's interior structure, in particular its ice shell and ocean.

How to cite: Van Hoolst, T., Baland, R.-M., Coyette, A., and Yseboodt, M.: The rotation and interior of Ganymede, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13749, https://doi.org/10.5194/egusphere-egu2020-13749, 2020.

EGU2020-3738 | Displays | G3.1

IERS Rapid Service/Prediction Center Use of Atmospheric and Ocean Angular Momentum for Earth Orientation

Nicholas Stamatakos, David Salstein, and Dennis McCarthy

The accuracy of near real-time estimates and short-term predictions of Earth orientation parameters (EOPs) can be enhanced by the use of Atmospheric Angular Momentum (AAM) and Ocean Angular Momentum (OAM) information, by accounting for the global conservation of angular momentum in the Earth system. The US Navy analysis and forecast scheme is named the Navy Earth System Prediction Capability (NAVY ESPC)  and is comprised of the Navy Global Environmental Model (NAVGEM) atmospheric and Hybrid Coordinate Ocean Model (HYCOM) ocean systems (along with ice forecasts). GOFS is being improved continually, and the resultant motion and mass fields are potentially useful for operational Earth orientation applications.  Consistency between the NAVGEM and HYCOM fields is required for calculations of the total angular momentum of the combined system of geophysical fluids. However, they might not include land-based Hydrological Angular Momentum functions (HAM) and the additional amount due to sea-level variability, the Sea-Level Angular Momentum (SLAM), both of which may be accounted for separately. We investigate various combination and optimal estimation processes using these data series, in conjunction with existing EOP observations to improve accuracy and robustness of short-term EOP predictions. Results are compared with those from other fluid models, particularly from those of the GeoForschungsZentrum (GFZ), the German Research Center for Geosciences. We also estimate power spectral density as a measure of error, for NAVGEM and HYCOM-based AAM/OAM series and similar series from other centers, comparing them to equivalent measures calculated from Earth orientation parameters.

How to cite: Stamatakos, N., Salstein, D., and McCarthy, D.: IERS Rapid Service/Prediction Center Use of Atmospheric and Ocean Angular Momentum for Earth Orientation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3738, https://doi.org/10.5194/egusphere-egu2020-3738, 2020.

EGU2020-21959 | Displays | G3.1

GINGERINO and the GINGER Project

Angela D. V. Di Virgilio

GINGER (Gyroscopes IN General Relativity) is a proposal aiming at measuring the Lense-Thirring effect with an experiment based on Earth. It is based on an array of ring lasers, at present the most sensitive inertial sensors to measure the rotation rate of the Earth.

Rotation and angular measurements are of great importance for various fields of science: General Relativity predicts rotation terms originated from the kinetic term, Earth Science studies the Earth's angular velocity with its variations, the tides and related perturbations, the normal modes of the Earth, the angular perturbations associated to the movement of the plates, the deformations of hydrological nature, without neglecting the rotational signals produced by the earthquakes. A ring laser integral to the Earth's surface is sensitive not only to the angular rotation of the planet, but also to global and local rotational signals. For this reason GINGER is relevant for geophysics.

GINGERINO is a ring laser prototype installed inside the underground laboratory of the Gran Sasso. Its typical sensitivity is well below 0.1 nrad/s in 1 second measurement, and it is acquiring data on a continuous basis since several years. The most recent data of GINGERINO and the results relevant for geoscience are discussed.

How to cite: Di Virgilio, A. D. V.: GINGERINO and the GINGER Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21959, https://doi.org/10.5194/egusphere-egu2020-21959, 2020.

G3.2 – Observing geophysical signals in the Climate and Earth System through Geodesy

The establishment of the Inter-Commission Committee on "Geodesy for Climate Research" (ICCC) of the International Association of Geodesy (IAG) emphasizes on the usefulness of geodetic sensors for estimating high-resolution water mass variation, which is due to broad applications of geodetic tools ranging from water cycle studies to water resources management. As such, data from both GRACE missions continue to provide insight into the alarming rates of groundwater depletion in large aquifers worldwide. Observations of vertical land motion (VLM) from GPS and InSAR may reflect elastic responses of the Earth's crust to changes in mass load, including those in aquifers. However, above confined aquifers, VLM observations are dominated by poroelastic deformation processes. In previous works, Ojha et al. 2018 and 2019 show that GRACE-based estimates of groundwater storage change in the Central Valley, California, are consistent with those obtained by utilizing measurements of surface deformation. These studies also show that annual variations in VLM correlate well in time with groundwater levels.

Here, we investigate seasonal variations in groundwater storage by identifying how their effect is manifested in geodetic and hydrological datasets. Groundwater well observations in the Central Valley indicate maximum groundwater levels at the beginning of the year between February to April and lowest water levels in the middle of the year about July to October. Meanwhile, GRACE groundwater storage estimates peak about four months later. To get insight into the mechanisms leading to this discrepancy, we perform a Wavelet multi-resolution analysis of GRACE TWS variations and complementary groundwater, snowcap, soil moisture, and reservoir level variations. We show that the majority of the differences between wavelet spectrums at seasonal frequencies occur during drought periods when there is no supply of precipitation in the high elevations. We employ a 1D diffusion model to demonstrate that the variations in groundwater levels across the Central Valley are due to the propagation of the pressure front at recharge sites due to gradual snowmelt. Such a model could explain the different timing of peaks in groundwater time series based on satellite gravimetry compared to deformation and well observations. We also discuss that winter rains are not able to directly contribute to recharging deep aquifers in the Central Valley, whereas most of the recharge must source from lateral flow caused by differential pressure at the sites of snow-melt in the Sierra Nevada as well as from agricultural return flows.

This analysis addresses the question of how well the different geodetic signals that reflect groundwater discharge and recharge processes agree with one another and what are the possible causes of disagreements. We emphasize the need for interdisciplinary efforts for the successful integration of available geodetic and hydrological datasets to improve our ability to utilizing geodetic sensors for climate research and water resources management.

References:

Ojha, C., Werth, S., & Shirzaei, M. (2019). JGR, https://doi.org/10.1029/2018JB016083.

Ojha, C., M. Shirzaei, S. Werth, D. F. Argus, and T. G. Farr (2018), WRR, https://doi.org/10.1029/2017WR022250.

How to cite: Werth, S. and Shirzaei, M.: Seasonal variation in water storage, vertical land motion and well levels: Implications for groundwater storage change in Central Valley, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10555, https://doi.org/10.5194/egusphere-egu2020-10555, 2020.

EGU2020-19070 | Displays | G3.2

Exploring meso-scale soil water and groundwater storage changes within the USA through a Bayesian combination of GRACE data with monthly 12.5 km model simulations

Nooshin Mehrnegar, Owen Jones, Michael B. Singer, Maike Schumacher, Thomas Jagdhuber, Bridget. R Scanlon, and Ehsan Forootan

Climatic changes in precipitation intensity across the United States (USA) may also affect the frequency and magnitude of drought and flooding events, with potentially serious consequences for water supply across this country. Reliable estimation of water storage changes in the soil root zone and groundwater aquifers is important for predicting future water availability, drought and flood monitoring and weather prediction. In this study, we assimilate Terrestrial Water Storage (TWS) derived from Gravity Recovery and Climate Experiment (GRACE) satellite observations into a water balance model with 12.5-km spatial resolution. Our goal is to explore meso-scale surface and deep-level soil water storage, as well as groundwater changes within the USA covering the period 2003-2017. A new Bayesian approach is formulated and implemented in this study, which provides a dynamic solution for a state-space equation between hydrological model outputs and TWS observations, while considering their error structures. The unknown state parameters and temporal dependency between them are estimated through a combination of forward/backward Kalman Filtering and Markov Chain Monto Carlo (MCMC) methods.

The outputs of this methodological approach are evaluated using in situ data from historical USGS groundwater data (over 6600 wells) and the ESA CCI surface soil moisture data. The results indicate that our GRACE data assimilation generally improves the simulation of groundwater and soil moisture across the USA. For example, the long-term linear trend fitted to the Bayesian-derived groundwater and soil water storage are in a same direction as those of in situ data in 63% and 58% of regions studied across the USA, respectively. However, this vale is estimated less than 51% for both water storage estimates derived from the original water balance model, which suggesting that the data assimilation modulates the hydrological models to perform more realistically. The biggest improvements are observed in the southeast USA with considerably large inter-annual variability in precipitation, where modelled groundwater apparently responded too strongly to the changes in atmospheric forcing. The Bayesian data assimilation method also improves the temporal correlation coefficients between the in situ USGS and ESA CCI data and model outputs after merging with GRACE TWS estimates. For instance, the correlation coefficient between groundwater storage and USGS observation increased from -0.52 to 0.48 and from -0.28 to 0.25 in southeast and southwest of USA, respectively. Finally, we will explore changes in Bayesian-derived groundwater and soil water storage within the Florida, California and South of Mississippi regions and interpret their relations with climate-induced factors such as precipitation and ENSO index.

Keywords: USA; Data Assimilation; Bayesian Method; Kalman Filtering; MCMC; GRACE; W3RA; groundwater storage; soil water storage; USGS; ESA CCI.

 

How to cite: Mehrnegar, N., Jones, O., Singer, M. B., Schumacher, M., Jagdhuber, T., Scanlon, B. R., and Forootan, E.: Exploring meso-scale soil water and groundwater storage changes within the USA through a Bayesian combination of GRACE data with monthly 12.5 km model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19070, https://doi.org/10.5194/egusphere-egu2020-19070, 2020.

EGU2020-6550 | Displays | G3.2

The Central European droughts of 2018 and 2019 observed with GRACE-Follow-On

Eva Boergens, Andreas Güntner, Henryk Dobslaw, and Christoph Dahle

In this study we investigate the ability of GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) to quantify the two consecutive summer droughts of 2018 and 2019 in Central Europe. The GRACE-FO mission was launched in May 2018 as the successor of GRACE (2002-2017) and thus, allows us to relate the droughts of the last two years to former droughts in 2003 and 2015.

The water mass deficit in 2018 was 90±18.5 Gt and in 2019 even 116±18 Gt compared to the long term climatology. These deficits are 60% and 76% of the annual mean variations which is so severe that a fast recovery of the water storage cannot be expected within one year. The drought of summer 2019 was more severe than the European-wide drought of 2003 with a water deficit of 85±16 Gt and had the largest water deficit in the whole GRACE and GRACE-FO time span.

GRACE-FO total water storage data also allows the analysis of the spatio-temporal drought patterns. The largest water mass deficit in 2018 was detected in October and centred in South-Western Germany and neighbouring countries. However, the exact onset of the 2018 drought is not determinable due to missing data between July and October. The drought 2019 reached its largest deficit in July and was more evenly spread across Central Europe than the 2018 drought.

From the GRACE and GRACE-FO mass anomalies, we derive a drought index which is compared to an external soil-moisture drought index. Over the whole time series between 2002 and 2019 both indices show a high congruence. However, as the two indices do not describe the same hydrological compartments a time lag and a memory effect of TWS relative to soil-moisture is visible in the comparison.

Overall, the presented study proves the successful continuation of GRACE with GRACE-FO and thus the reliability of the observed Central European summer drought of 2019 as the most extreme water scarcity event since 2002.

How to cite: Boergens, E., Güntner, A., Dobslaw, H., and Dahle, C.: The Central European droughts of 2018 and 2019 observed with GRACE-Follow-On, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6550, https://doi.org/10.5194/egusphere-egu2020-6550, 2020.

EGU2020-20224 | Displays | G3.2

Monitoring climate-driven and anthropogenic impacts on hydrology and agriculture in South-Eastern Australia in the 21st century

Maike Schumacher, Ehsan Forootan, Russell Crosbie, Theresa Mallschützke, and Jonas Rothermel

With the climate change, drought events likely become more frequent and severe in Australia, where the worst droughts were recorded during the 21st century. Particularly, in the South-East of the country, the so called "Millennium Drought" showed below average annual precipitation for an entire decade. The precipitation record was then increased by extreme precipitation events generated from the La Niña events in 2010 and 2011. Afterwards, dry conditions began again to develop. The climate-driven events and anthropogenic adaptions to the circumstances resulted in strong impacts on the hydrological resources and agricultural production. In fact, simulating hydrological processes within the (semi-)arid region of South-East Australia is very challenging especially during extreme events. In previous studies, we found a strong underestimation of the decline of total terrestrial water storage (TWS) and of groundwater in comparison to remote sensing data and in-situ station networks. Thus, we successfully calibrated the W3RA water balance model and simultaneously assimilated TWS anomalies obtained from the Gravity Recovery And Climate Experiment (GRACE) satellite mission to improve the model's skill during extreme meteorological conditions. In this presentation, we focus on the comparison of remote sensing observations and W3RA simulations after implementing the calibration and data assimilation with existing data records on anthropogenic intervention into the water cycle, as well as on agricultural production. Our results indicate high correlations between meteorological, hydrological and agricultural variables, and we observe strong similarities in the long-term trends and break points.

How to cite: Schumacher, M., Forootan, E., Crosbie, R., Mallschützke, T., and Rothermel, J.: Monitoring climate-driven and anthropogenic impacts on hydrology and agriculture in South-Eastern Australia in the 21st century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20224, https://doi.org/10.5194/egusphere-egu2020-20224, 2020.

EGU2020-20937 | Displays | G3.2

The water storage change anomaly and its causes in the middle-lower reaches of Yangtze River basin

Taoyong Jin, Xiaolong Li, and Zuansi Cai

The three gorges dam (TGD) is always thought to have a significant impact on hydrological and climatic change in the middle-lower reaches of the Yangtze River basin (MLYRB), which can be regarded as human driven factor. The El Nino/Southern Oscillation (ENSO) events are also considered have large effect in the MLYRB, which can be regarded as climate driven factor. In the study, using terrestrial water storage change anomalies (TWSA) from Gravity Recovery and Climate Experiment (GRACE) mission and hydrological data, we investigate the effect of TGD and ENSO on the TWSA in MLYRB and its sub-basins. From the routinely impoundment of TGD since October 2010, the TWSA and ENSO show high correlation greater than 0.75 with a 5-month time lag, except for the upper Han River basin which is large affected by the Danjiangkou reservoir, and during two extreme flood and drought events, the TWSA and ENSO are almost consistent. It is concluded that the TWSA in the MLYRB is mainly affected by the climate driven factor, but the impoundment of TGD has limited effect. Since the relationship between TWSA and ENSO is stable during the routinely impoundment of TGD, the extreme events occurred in the MLYRB can be early warned by the ENSO index. 

How to cite: Jin, T., Li, X., and Cai, Z.: The water storage change anomaly and its causes in the middle-lower reaches of Yangtze River basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20937, https://doi.org/10.5194/egusphere-egu2020-20937, 2020.

EGU2020-21456 | Displays | G3.2

Multi-Mission GNSS Radio Occultation Climate Data Records at the Jet Propulsion Laboratory

Mayra Oyola, Chi Ao, Olga Verkhoglyadova, and Anthony Mannucci

Both the IPCC and the 2017 US Decadal Survey for Earth Science and Applications have recognized atmospheric profiling as an immediate priority, as proper representation of the Earth’s vertical atmosphere is imperative to close gaps in our understanding of processes that impact severe weather, air quality, and climate change. Radio Occultation (RO) techniques have been recognized for their uniqueness to provide reference datasets, triggering a growing interest in using RO for Climate and Weather applications.

 At the NASA Jet Propulsion Laboratory (JPL), physical parameters such as refractivity and derived atmospheric products (temperature, pressure, moisture) are obtained by applying inversion methodologies on the atmospheric delay induced on the occulted signal. Such multi-mission retrieval system has generated nearly two decades of observations and allowed the generation of Global Navigation Satellite Systems Radio Occultation (GNSS-RO) monthly gridded data for climate model evaluation and other applications (Obs4MIPS). 

We present an overview of data and methodology involved in producing Obs4MIPS GNSS-RO data, and show current improvements in the legacy products by comparison against the next generation of JPL’s monthly gridded data (Level 3) products.  Also, we evaluate the performance of the products against reanalysis datasets, and demonstrate its capability to detect climate signals and to improve our understanding of weather processes. Additionally, we will discuss ongoing activities associated with the incorporation of the recently launched COSMIC-2 data into our system.

How to cite: Oyola, M., Ao, C., Verkhoglyadova, O., and Mannucci, A.: Multi-Mission GNSS Radio Occultation Climate Data Records at the Jet Propulsion Laboratory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21456, https://doi.org/10.5194/egusphere-egu2020-21456, 2020.

EGU2020-6329 | Displays | G3.2

Applying the ICA method to extract the potential signals in GNSS timeseries

Weijie Tan, Junping Chen, and Weijing Qu

Spatial filtering is an effective way to identify and reduce the so-called common mode error (CME) from the regional GPS networks measurements, which could improve GPS positioning accuracy and precision for detection of subtle crustal deformation signals. In this work, we decompose GPS coordinate time series into a set of temporally varying modes with the widely used principal component analysis (PCA) on minizine the misfit calculated using a L2 norm(x2). The results show that the decomposed components from PCA are not statically independent to each other. It is difficult to reveal the original geophysical mechanisms for the related signals only on the PCA results. To work around the problems, we reanalysis the output from PCA to recovery and separate the original signals from mixed observations with the independent component analysis (ICA). Here, we firstly apply the PCA methods on the GPS position time series in Sichuan_Yunnan region of China to evaluate the ability in discerning and charactering different source of crust deformation in the space and time domains. Using the PCA decomposed first 6 PCs, we find that the spatially and temporally correlated CME can be decomposed into two independent components by ICA, the second IC shows obvious variations in the beginning of each year, the same characters are also seen in the atmosphere press variations. Then we compare the two timeseries and demonstrated that atmosphere high frequency pressure mass loading is one of the main contributors to the CME.

How to cite: Tan, W., Chen, J., and Qu, W.: Applying the ICA method to extract the potential signals in GNSS timeseries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6329, https://doi.org/10.5194/egusphere-egu2020-6329, 2020.

EGU2020-4643 | Displays | G3.2

The rate and acceleration of the global mean sea level revisited

Lorena Moreira, Anny Cazenave, Denise Cáceres, Hindumathi Palanisamy, and Habib Dieng

Since nearly 3 decades, high-precision satellite altimetry allows us to precisely measure the mean sea level evolution at global and regional scales. In terms of global mean, sea level is rising at a mean rate of 3.2 mm/yr. The altimetry record is also suggesting that the global mean sea level rise is accelerating. However, the exact value of the acceleration and even its mere existence are still debated. Determination of the global warming-related sea level rate and acceleration are somewhat hindered by the interannual signal caused by natural climate variability. During the recent years, several studies have shown that at interannual time scale, the global mean sea level is mostly due to ENSO-driven land water storage variations. But thermal expansion fluctuations may also contribute. Thus, to isolate the global warming signal in the global mean sea level, we need to remove the ENSO-related interannual variability. For that purpose we use the Water Gap Global Hydrological model developed by the University of Frankfurt for land water storage as well as GRACE space gravimetry data on land and empirical models based on ENSO indices. We also extract the ENSO-related signal in thermal expansion. After removing the total interannual variability signal due to both mass and steric components, we compute the evolution with time of the ‘residual’ rate of sea level rise over successive 5-year moving windows, as well as the associated acceleration. Using time series of thermal expansion and ice sheet mass balances, we also estimate the respective contributions of each component to the global mean sea level acceleration.

How to cite: Moreira, L., Cazenave, A., Cáceres, D., Palanisamy, H., and Dieng, H.: The rate and acceleration of the global mean sea level revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4643, https://doi.org/10.5194/egusphere-egu2020-4643, 2020.

EGU2020-193 | Displays | G3.2

GRACE observing a small scale ocean mass increase in the Bohai Sea

Dapeng Mu and Tianhe Xu

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has profoundly advanced our knowledge of contemporary sea level change. Owing to the coarse spatial resolution and leakage issue across the land-ocean boundary, it is challenged for GRACE to detect mass changes over a region smaller than its spatial resolution, especially a semi-enclosed basin that is adjacent to land with significant mass variation. In this contribution, we find that GRACE is capable of recovering mass increase in the Bohai Sea, which is adjacent to the North China Plain that has been experiencing significant groundwater depletion. This water mass increase, only amounting to 0.45 Gt/yr, is demonstrated by a reconstruction that is implemented with multisource data, including altimeter observations, steric estimates, and hydrology model. The reconstructed mass signal rejects the detection of sediment accumulation by GRACE, but it does not exclude the possibility that sediment accumulation may occur at local scale. Compared with the “true” mass increase, the mass increase observed by GRACE spherical harmonic coefficients (SHCs) is seriously compromised (i.e., signal magnitudes are substantially reduced) due to leakage issue. Our reconstruction results exemplify that elaborate data-processing is necessary for specific cases. On the other hand, the recently released mascons, which are resolved with constraints and require no further processing, suggest improved seasonal cycles in the Bohai Sea that are in agreement with altimeter observations. However, the rates derived from the mascons cannot properly represent the real ocean mass increase for the Bohai Sea, because the mascons underestimate the rates or contain some artificial effect. Nevertheless, the mascons provide new insights into regional sea level change relative to the traditional SHCs.

How to cite: Mu, D. and Xu, T.: GRACE observing a small scale ocean mass increase in the Bohai Sea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-193, https://doi.org/10.5194/egusphere-egu2020-193, 2020.

EGU2020-3468 | Displays | G3.2

Monitoring the AMOC with GRACE/GRACE-FO - How far can we push the spatial resolution?

Andreas Kvas, Katrin Bentel, Saniya Behzadpour, and Torsten Mayer-Gürr

The Atlantic Meridional Overturning Circulation (AMOC) plays a key role in our global climate system and is the main mechanism of northward heat transport for a warm climate in Northern Europe. Despite its crucial role, the AMOC is only scarcely observed, as observations covering all of the Atlantic Ocean for extended time are difficult to obtain. Satellite gravimetry offers key advantages compared to existing in-situ data sources by providing ocean bottom pressure anomalies with global coverage, thus allowing the monitoring of the AMOC in the complete Atlantic Ocean basin. The Gravity Recovery And Climate Experiment (GRACE) satellite mission and its successor GRACE Follow-On have provided a nearly continuous time series of monthly gravity field snapshots since 2002. In contrast to in-situ measurements of ocean bottom pressure, which suffer from inherent drift problems, the temporally stable satellite observations allow investigations of the long-term AMOC behavior.

Preliminary studies have shown that monitoring changes in the AMOC is possible with observations from GRACE and GRACE Follow-On, however, it is pushing the limits of the current data products in resolution and accuracy. To fully exploit the information content in the gravity observations, we implemented a processing chain tailored to the Atlantic Ocean basin. Compared to existing approaches, we perform signal separation, that is the reduction of continental hydrology and glacial isostatic adjustment, on the satellite sensor data level. This has the key advantage that all background models are treated the same, thus are spectrally coherent. Geocenter motion is estimated in combination with an ocean model, as is the state-of-the-art for GRACE/GRACE-FO processing. Ocean bottom pressure anomalies are then computed through least squares collocation, which allows for point distributions tailored to the bathymetry. This consistently processed data record is then used to gauge the performance of satellite gravimetry for monitoring the AMOC.

How to cite: Kvas, A., Bentel, K., Behzadpour, S., and Mayer-Gürr, T.: Monitoring the AMOC with GRACE/GRACE-FO - How far can we push the spatial resolution?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3468, https://doi.org/10.5194/egusphere-egu2020-3468, 2020.

It is already well known that intra-seasonal oscillations in the Earth’s global temperature are driven by ENSO (El Niño Southern Oscillation) events. ENSO signal is also present in length of day and global sea level rise, because during El Niño the increase of the length of day and global sea level rise can be noticed. To detect common oscillations in length of day, global sea level rise, global temperature data and ENSO indices the wavelet-based semblance filtering method was used. This method, however, seeks the signals with a good phase agreement of oscillations in two time series thus, no phase agreement results in very small amplitudes of the common signals. The spectra-temporal semblance functions allow detecting the similarity of two time series in spectral bands in which the amplitudes and phases of the oscillations are consistent with each other. The amplitudes of oscillations in the considered data vary in time and in order to detect the signals with similar amplitude variations between pairs of time series the normalized Morlet wavelet transform (NMWT) and the combination of the Fourier transform bandpass filter with the Hilbert transform (FTBPF+HT) were used. These two methods enable computation of the instantaneous amplitudes and phases of oscillations in two real-valued time series. In order to detect oscillations with similar amplitude variations in two time series correlation coefficients between the amplitude variations as a function of oscillation frequencies were computed.

How to cite: Kosek, W.: Application of spectra-temporal analysis methods to detect common signals in length of day, global sea level rise, global temperature data, and ENSO indices, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8196, https://doi.org/10.5194/egusphere-egu2020-8196, 2020.

EGU2020-7733 | Displays | G3.2

Surface deformations of a 3D elastic self-gravitating Earth

PingPing Huang, Yoshiyuki Tanaka, Volker Klemann, Zdenek Martinec, and Maik Thomas

Surface geology and seismic tomography show that the properties of Earth’s internal structure vary laterally. Lateral heterogeneity has been demonstrated to have considerable effect on the observables of Glacial Isostatic Adjustment (GIA) such as surface deformation, geoid and sea-level change. A number of models have been developed to consider a complex viscous structure of the Earth by implementing 3D viscosity for linear or nonlinear creep laws. However, there are only few studies addressing lateral heterogeneity in the (an-)elastic structure.

Due to the increased accuracy of global observation systems like GNSS and an integrated interpretation of earth system processes, the demand for improved global deformation models for instantaneous to annual loading is rising. To analyse the effect of lateral heterogeneity on a global scale, we extend the spectral–finite element method suggested by Martinec for a viscoelastic body to compute the deformations and gravitational potential changes of an elastic spherical self-gravitating Earth. The effect of 3D elastic structure is studied by varying the elastic moduli in the crust and mantle. We present a sensitivity study in order to quantify its effect on solid-earth deformations on a regional to global scale.

How to cite: Huang, P., Tanaka, Y., Klemann, V., Martinec, Z., and Thomas, M.: Surface deformations of a 3D elastic self-gravitating Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7733, https://doi.org/10.5194/egusphere-egu2020-7733, 2020.

EGU2020-19815 | Displays | G3.2

A novel theoretical framework to estimate GIA from GPS and GRACE

Yann Ziegler, Bramha Dutt Vishwakarma, Sam Royston, Aoibheann Brady, Stephen Chuter, Richard Westaway, and Jonathan Bamber

Glacial Isostatic Adjustment (GIA) is the visco-elastic response of the Solid Earth to changes in the ice sheet load during past glacial cycles. GIA produces vertical land motion and mantle mass redistribution, both of which are important to include when studying surface deformations, sea level rise, present day mass changes from satellite data and changes in the geoid. Estimates of GIA are typically obtained from forward numerical models that are driven by varying assumptions about Earth rheology and ice load history, leading to a range of GIA estimates. As a consequence, many studies are trying to move away from forward modelling and co-estimate GIA from contemporary observations. We present a novel theoretical framework that uses GPS vertical land motion and GRACE data to provide a data-driven estimate of GIA. Assuming that all other significant processes are correctly identified and accounted for, we show that GRACE and GPS data can successfully be used together to isolate GIA. We compare our results to outputs from various GIA forward models.

How to cite: Ziegler, Y., Vishwakarma, B. D., Royston, S., Brady, A., Chuter, S., Westaway, R., and Bamber, J.: A novel theoretical framework to estimate GIA from GPS and GRACE, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19815, https://doi.org/10.5194/egusphere-egu2020-19815, 2020.

EGU2020-17390 | Displays | G3.2

Significant temporal changes in glacio isostatic adjustment in Iceland during the 1950s to present

Halldór Geirsson, Gudmundur Valsson, Benedikt G. Ófeigsson, Erik Sturkell, Thora Arnadottir, Peter C. LaFemina, Sigrun Hreinsdottir, Vincent Drouin, Peter Schmidt, Björn Lund, and Finnur Palsson

The two most widespread geodynamic signals in Iceland are caused by glacio isostatic adjustment (GIA; up to 4.5 cm/yr vertical motion) and tectonic plate spreading (approximately 1.9 cm/yr horizontal motion). GPS measurements of crustal deformation started in Iceland in 1986 and annually tens to hundreds of benchmarks are re-measured. Many of these surveys are on local scales, but the ISNET campaigns in 1993, 2004, and 2016 are the only island-wide efforts. Continuous GPS (cGPS) measurements started in 1995 and now over 100 cGPS stations are running. The cGPS allows for excellent quantification of seasonal variations in position with amplitude up to several cm closest to the glaciers, driven mainly by seasonal snowload. Frequent observations also help to observe temporal changes in uplift rates and correlate to glacier mass balance. In recent years InSAR has been applied to obtain both local signals (e.g., due to glacial surges) and island-wide estimates of GIA and plate motion. However, InSAR does not work under the glaciers where we expect the largest uplift. Regular GPS measurements at several nunataks on Vatnajökull started in 2008 and provide the only intra-glacier GIA observations in Iceland. Going further backwards in time is a challenge and relies on local levelling where relative uplift rates can be compared to current relative uplift rates to infer the temporal evolution.

During 1993-2004 the average observed uplift rates reached at most around 2 cm/yr and were likely at its lowest in the early 1990s, lower than during 1959-1991. During 2004-2010 the uplift rates increased on average by 70% compared to the previous time period. A thin layer of ash from the 2010 Eyjafjallajökull eruption enhanced the melting rates and is clearly seen as enhanced uplift rates during 2010-2012. Until 2014 the uplift rates remained high. In 2014 the average uplift rates lowered by around 20%. Comparable changes are observed in the horizontal deformation field. Overall, recent changes in GIA broadly follow changes in climate and mass balance. The first part of the 90s was cold and glaciers in Iceland were overall in equilibrium or gaining a bit of mass. After 1995 the glaciers started losing considerable mass every year. From 2011 the mass loss decreased; in 2015 there was a net mass gain, and in 2017 and 2018 the mass balance was close to equilibrium. The highly variable deformation rates call for a re-evaluation of the current GIA models, working towards a time-dependent response that can be applied to regional deformation studies.

How to cite: Geirsson, H., Valsson, G., Ófeigsson, B. G., Sturkell, E., Arnadottir, T., LaFemina, P. C., Hreinsdottir, S., Drouin, V., Schmidt, P., Lund, B., and Palsson, F.: Significant temporal changes in glacio isostatic adjustment in Iceland during the 1950s to present, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17390, https://doi.org/10.5194/egusphere-egu2020-17390, 2020.

EGU2020-15816 | Displays | G3.2

Global geodetic parameters obtained from 14 years Lageos 1 Satellite Laser Ranging

Nikolay Dimitrov, Ivan Georgiev, and Anton Ivanov

Satellite Laser Ranging (SLR) data of the geodynamic satellite Lageos-1 (LAser GEOdynamics Satellite) for the period January 2000 - June 2013 are processed and analysed through sequential estimation to obtain multiyear solution for global geodetic parameters - coordinates and velocities of 37 stations located on the main tectonic plates. The analysis is carried out with the Satellite Laser Ranging Processor (SLRP) software, version 4.3, developed in the Department Geodesy of the National Institute of Geophysics, Geodesy and Geography at Bulgarian Academy of Sciences. The software consists of two main programs – orbit determination and parameter estimation modules. Total number of 202 447 measurements are processed and analyzed by monthly batches. Arc dependent parameters, geogravitational parameter - GM, Earth Orientation Parameters (pole coordinates and length of the day - LOD), along track and solar radiation pressure coefficients are obtained from monthly solutions. The weighted root mean squares of the monthly station coordinates solution are between 2 and 16 mm. The analysis of monthly GM time series reveal value of the secular trend Ġ/G = -3.31. 10-13yr-1. The results obtained contribute to the monitoring of recent tectonics of the major continental plates and global geodynamic parameters.

How to cite: Dimitrov, N., Georgiev, I., and Ivanov, A.: Global geodetic parameters obtained from 14 years Lageos 1 Satellite Laser Ranging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15816, https://doi.org/10.5194/egusphere-egu2020-15816, 2020.

We studied front-type heavy rain and typhoon-type heavy rain in 2019 in Japan, using tropospheric delay data from the dense Global Satellite Navigation System (GNSS) network GEONET. In 2019, based on data from Japan Meteorological Agency (JMA), that front type heavy rain occurred on 26-29 August 2019, and typhoon type heavy rain occurred on 10-13 October 2019.

In this study, we analyzed the behavior of water vapor during heavy rainfall, using tropospheric parameters obtained from a database at the University of Nevada, Reno (UNR). Data sets, including delays in gradient vectors in the troposphere (G), as well as delays in the zenith troposphere (ZTD), are estimated every 5 minutes. Initially, we interpolated G to get grid points. We removed the hydrostatic delay from ZTD to get zenith wet delay (ZWD). In the inversion scheme, we use G at all GEONET stations and ZWD data at low altitude GEONET stations (<100 m) as input. Then we assume that the spatial change in ZWD is proportional to G (Gx = H δZWD /δx, where H is the height of the water vapor scale) and the estimated height of sea-level ZWD at grid points throughout Japan.

We try to justify our working hypothesis that heavy rains occur when the convergence of G and ZWD sea levels is high by analyzing the hourly water vapor distribution on all days in August 2019 and October 2019. We found that both values ​​show a maximum in the period studied when two events heavy rain occurred, i.e., August 27, 2019, and October 12, 2019. Furthermore, we studied the analysis of high time resolution (every 5 minutes) on heavy rain days. The results show that the convergence of G and ZWD sea level rises before rain occurs, and ZWD shows a rapid decline once heavy rain begins.

How to cite: Arief, S. and Heki, K.: A new approach that utilizes the GNSS atmospheric delay gradient to monitor front-type heavy rain and typhoon-type heavy rain in 2019 in Japan., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2646, https://doi.org/10.5194/egusphere-egu2020-2646, 2020.

EGU2020-4502 | Displays | G3.2

Evaluating short-term hydro-meteorological fluxes in global atmospheric reanalyses using daily GRACE data

Viviana Wöhnke, Annette Eicker, Laura Jensen, Andreas Kvas, Torsten Mayer-Gürr, and Henryk Dobslaw

Changes in terrestrial water storage as observed by the satellite gravity mission GRACE represent a new and completely independent data set for constraining the net flux deficit of precipitation (P), evapotranspiration (E), and lateral runoff (R) in atmospheric reanalyses.

In this study we use daily GRACE gravity field changes to investigate high-frequency hydro-meteorological fluxes over the continents. Band-pass filtered water fluxes are derived from GRACE water storage time series by first applying a numerical differentiation filter and subsequent high-pass filtering to isolate fluxes at periods between 5 and 30 days.

We can show that on these time scales GRACE is able to identify quality differences between different reanalyses, e.g. the improvements in the latest reanalysis ERA5 of the European Centre for Medium-Range Weather Forecasts (ECWMF) over its direct predecessor ERA-Interim. We will therefore use GRACE as an evaluation tool to compare hydro-meteorological fluxes in various global atmospheric reanalyses, such as ERA5(-Land), ERA-Interim, Merra2, JRA-55, or NCEP.

How to cite: Wöhnke, V., Eicker, A., Jensen, L., Kvas, A., Mayer-Gürr, T., and Dobslaw, H.: Evaluating short-term hydro-meteorological fluxes in global atmospheric reanalyses using daily GRACE data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4502, https://doi.org/10.5194/egusphere-egu2020-4502, 2020.

EGU2020-5802 | Displays | G3.2

How uncertain is the hydrological contribution to global sea level based on hydrological modelling compared to observational data?

Christian Mielke, Olga Engels, Bernd Uebbing, Helena Gerdener, Lara Börger, Kerstin Schulze, Petra Döll, and Jürgen Kusche

Quantifying individual contributors to global and regional mean sea level along with corresponding uncertainties is crucial for future projections. However, the contribution of terrestrial hydrology seems to be the least known, but is particularly important, since in addition to the climate-driven changes human activities (such as groundwater pumping, irrigation, deforestation) have a large impact on global sea level changes. Under the common assumption that atmospheric water storage change is negligible, (total) terrestrial water storage anomalies (TWSA) represents a proxy for the hydrologic contribution. Generally, TWSA can be derived using models, observations or a combination of both. Each of the methods has its pros and cons.

In this study, we estimate the contribution of terrestrial hydrological cycle changes to global mean sea level along with corresponding uncertainties for 2003 - 2016 based on land TWSA time series derived (i) from WaterGAP Global Hydrological Model WGHM that also simulates anthropogenic effects and provides a partitioning of TWSA into global river discharge and evapotranspiration minus precipitation, (ii) satellite gravimetry data from GRACE, and (iii) from a joint inversion using GRACE and altimetry data. To realistically describe uncertainties in forcing data, model parameters, initial water states, and errors in the model structure, an ensemble of 30 runs is generated and analyzed. Because of well-known large inter-annual and decadal hydrological variations, we estimate time-varying trends using a Kalman filter framework in addition to the usually estimated linear trends. This approach provides more reliable trend and corresponding uncertainty estimates. Moreover, it naturally enables detecting any changes in rates, which is acceleration.

How to cite: Mielke, C., Engels, O., Uebbing, B., Gerdener, H., Börger, L., Schulze, K., Döll, P., and Kusche, J.: How uncertain is the hydrological contribution to global sea level based on hydrological modelling compared to observational data?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5802, https://doi.org/10.5194/egusphere-egu2020-5802, 2020.

EGU2020-6125 | Displays | G3.2

Anthropogenic water depletion in the Indo-Gangetic Plain

Bingshi Liu, Xiancai Zou, and Jiancheng Li

The Indo-Gangetic Plain, feeding more than 9 billion people, are facing serious water scarcity due to expanding populations and development in agriculture and industry. Rainfall concentrated in monsoon season, about 70% of precipitation falls between June and September, causes the imbalance between water supply and demand. A large amount of groundwater is extracted for irrigation during dry season, causes the groundwater to decline. Increasing glacier meltwater under the ongoing warming of global climate from upstream high mountainous also modulates the variation of terrestrial water storage (TWS) in this region. Thus, estimating and evaluating anthropogenic water depletion are beneficial to water resources protection and management in the Indo-Gangetic Plain.

Here, we propose a method to remove the influence of climate variability and obtain human-driven TWS variability. Atmosphere-driven TWS variability is estimated by a relationship between change in TWS (GRACE data) and precipitation and temperature, which has been confirmed that these two variables (precipitation and temperature) already explain a substantial fraction of continental-scale run off dynamics in previous studies. Glacier melting recharge from upstream high mountainous is calculated by the proportion with the temperature.

Results show that the rate of anthropogenic depletion of water in Indus Plain increased from -5.5 km3/yr to -25.0 km3/yr during 2003 - 2011 due to the deficient precipitation, and remained stable from 2011 to 2016 at the rate of ~-26.0 km3/yr with increasing precipitation and enhancing glacier meltwater recharge. The rate of anthropogenic depletion of water in Ganges Plain (including the Brahmaputra River) slowed from -37.7 km3/yr to -12.0 km3/yr during 2003 -2011due to the increased glacier meltwater recharge, which reduced the pressure of irrigation water in northwest of the Plain. However, with the increasing temperature since 2014, The rate of anthropogenic depletion of water increased to -20.0 km3/yr in 2016.

How to cite: Liu, B., Zou, X., and Li, J.: Anthropogenic water depletion in the Indo-Gangetic Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6125, https://doi.org/10.5194/egusphere-egu2020-6125, 2020.

EGU2020-7196 | Displays | G3.2

Analyzing different ways of assimilating volume change estimates for surface water bodies into a hydrological model

Olga Engels, Kerstin Schulze, Jürgen Kusche, Simon Deggim, Annette Eicker, Stefan Mayr, Igor Klein, Laura Ellenbeck, Denise Dettmering, Christian Schwatke, Omid Elmi, Mohammad Tourian, and Petra Döll

To better understand global freshwater resources, we combine the state-of-the-art global hydrological model WGHM with Total Water Storage Anomalies (TWSA) derived from the Gravity Recovery and Climate Experiment (GRACE) satellite mission in an ensemble-based calibration and data assimilation (CDA) framework. However, when dealing with GRACE data, their limited horizontal resolution represents a major challenge. Filtering and/or ’destriping’ is the usual approach for suppressing GRACE-specific spatial noise, which causes spatial leakage and in turn attenuation of signal and reduction of spatial resolution. In GlobalCDA project, we derive altimetry-based storage variations along with corresponding uncertainties of surface water bodies, such as lakes and reservoirs, that feature significantly higher spatial resolution compared to GRACE-based TWSA. These can, additionally, be incorporated into the CDA framework.

In this study, we investigate several possibilities on how to use the additional remote sensing observations within the CDA over the Mississippi basin for the time span 2003 - 2016. For this, we run the CDA (i) using GRACE-based TWSA only, (ii) removing altimetry-based storage variations of surface water bodies from GRACE-TWSA, (iii) removing and restoring altimetry-based storage variations for GRACE-TWSA, and (iv) directly using altimetry-based storage variations. New observation operators are constructed for (ii) and (iv). The results are validated against independent discharge observations.

How to cite: Engels, O., Schulze, K., Kusche, J., Deggim, S., Eicker, A., Mayr, S., Klein, I., Ellenbeck, L., Dettmering, D., Schwatke, C., Elmi, O., Tourian, M., and Döll, P.: Analyzing different ways of assimilating volume change estimates for surface water bodies into a hydrological model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7196, https://doi.org/10.5194/egusphere-egu2020-7196, 2020.

EGU2020-7999 | Displays | G3.2

Improving the representation of ice-sheet mass changes in the global inversion for sea-level contributions

Matthias O. Willen, Bernd Uebbing, Martin Horwath, Jürgen Kusche, Roelof Rietbroek, Undine Strößenreuther, and Ludwig Schröder

Global-mean sea level rises (GMSLR) by 3.1-3.5 mm a-1 (1993-2017) and of which about 50 % can be attributed to changes in global-mean ocean mass due to hydrological variations, mass changes of land glaciers, and mass changes of the major ice sheets in Greenland and Antarctica. The ice-sheet contributions account for more than the half of the contemporary ocean mass change and can be observed with time-variable gravimetry by the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). In addition, geometric surface changes due to the volume change of ice sheets is also observed by polar altimetry missions. Of particular importance here is the signal of glacial isostatic adjustment (GIA) which is superimposed with ice mass change.

Conventionally, the gravimetry and ice-altimetry observations are processed independently. For ocean applications, a global fingerprint inversion (Rietbroek et al., 2016) allows to estimate individual mass and steric contributors to the sea-level budget by combining GRACE and ocean-altimetry data in a joint approach. To improve the estimates of the ice-sheet contributions to GMSLR, we present first results from additionally incorporating independent ice-altimetry data over Greenland and Antarctica into the fingerprint inversion. We examine the sensitivity of the sea-level contributions to the additional ice-altimetry data (from ERS-2, Envisat, ICESat, CryoSat-2 missions) and provide validation against independent estimates. In our standard runs, GIA is accounted for as an a-priori correction during the inversion. However, we demonstrate the potential and limitations of a regional inverse approach in which GIA is separated from ice mass change over Antarctica using GRACE and ice altimetry. In our future work, we aim to parametrise and co-estimate GIA within the global inversion framework.

How to cite: Willen, M. O., Uebbing, B., Horwath, M., Kusche, J., Rietbroek, R., Strößenreuther, U., and Schröder, L.: Improving the representation of ice-sheet mass changes in the global inversion for sea-level contributions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7999, https://doi.org/10.5194/egusphere-egu2020-7999, 2020.

EGU2020-8162 | Displays | G3.2

Developing geodetic tools for early warning and monitoring of tectonic activity at the Gulf of Cadiz

Jorge Garate, Javier Ramirez Zelaya, Belen Rosado, Manuel Berrocoso, Amos de Gil, Alberto Fernandez Ros, Gonçalo Prates, and Luis Miguel Peci

Gulf of Cadiz from the Strait of Gibraltar to the Western Coast of the Iberian Peninsula is a natural hazard risky region due to the existence  of several active faults related to the Eurasian and Nubian Plate interaction. The 1755 Lisbon Earthquake was remarkable example. With the epicenter located SW of Cape San Viente, and a Richter scale magnitude around 8.3, the earthquake triggered a devastating tsunami hitting the Portuguese, Moroccan and Southern Spain coasts, resulting in thousands of casualties. More recently, in 1969 a 7.8 magnitude earthquake with its epicenter located in the same region, originated another tsunami but smaller than the previous one, resulting nineteen casualties.

To prevent natural hazards like these, the Astronomy, Geodesy and Cartography Laboratory at the Universidad de Cadiz, is drawing and implementing early warning systems, trying to detect and evaluate tectonic activity in near real time at the Gulf of Cadiz. The system includes the GNSS network SPINA  receivers together with MEMS acelerometers, meteo equipments, and ancillary instrumentation for data adquistion, monitoring, quality control and results display at a dedicated control center.

How to cite: Garate, J., Ramirez Zelaya, J., Rosado, B., Berrocoso, M., de Gil, A., Fernandez Ros, A., Prates, G., and Peci, L. M.: Developing geodetic tools for early warning and monitoring of tectonic activity at the Gulf of Cadiz, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8162, https://doi.org/10.5194/egusphere-egu2020-8162, 2020.

EGU2020-7652 | Displays | G3.2

Mitigating Spatial Leakage in Monthly GRACE/GRACE-FO Gravity Fields for the Separation of Barystatic Sea-Level Variations and Residual Ocean Circulation Effects

Volker Klemann, Henryk Dobslaw, Meike Bagge, Robert Dill, Maik Thomas, Christoph Dahle, and Frank Flechtner

Temporal variations in the total ocean mass representing the barystatic part of present-day global mean sea-level rise can be unambiguously inferred from time-series of global gravity fields as provided by the GRACE and GRACE-FO missions. A spatial integration over all ocean regions, however, largely underestimates present-day rates as long as the effects of spatial leakage along the coasts of in particular Antarctica, Greenland, and the various islands of the Canadian Archipelago are not properly considered.

Based on the recent release 06 of monthly gravity fields processed at GFZ, we quantify (and subsequently correct) the contribution of spatial leakage to the post-processed mass anomalies of continental water storage and ocean bottom pressure. Utilising the sea level equation allows to predict spatially variable ocean mass trends out of the (leakage-corrected) terrestrial mass distributions from GRACE and GRACE-FO. Consistent results for the global mean barystatic sea-level rise are obtained also from spatial integrations over ocean masks with different coastal buffer zones ranging from 400 to 1000 km, thereby confirming the robustness of our method. Residual month-to-month variations in ocean bottom pressure are indicative for errors in the monthly-mean estimates of the applied de-aliasing model AOD1B RL06 and will be thus contrasted against very recent MPIOM experiments considered for AOD1B RL07. The in this way improved leakage correction will be implemented in future GravIS versions (http://gravis.gfz-potsdam.de).

How to cite: Klemann, V., Dobslaw, H., Bagge, M., Dill, R., Thomas, M., Dahle, C., and Flechtner, F.: Mitigating Spatial Leakage in Monthly GRACE/GRACE-FO Gravity Fields for the Separation of Barystatic Sea-Level Variations and Residual Ocean Circulation Effects, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7652, https://doi.org/10.5194/egusphere-egu2020-7652, 2020.

EGU2020-12944 | Displays | G3.2

On the separation of co- and post-seismic signals due to large earthquakes from GRACE observations

Jin Li, Jianli Chen, Song-Yun Wang, Lu Tang, and Xiaogong Hu

Satellite gravimetry observations from GRACE (Gravity Recovery and Climate Experiment) and GRACE Follow-On are widely used to study the co-seismic and post-seismic deformations caused by large earthquakes. Temporal gravity changes from GRACE provide good constraints to investigate the fault slips of large earthquakes especially for oceanic areas. However, reliable retrieval of seismic signals is still challenging due to large uncertainties and limited spatial and temporal resolutions of GRACE observations. To extract the co- and post-seismic signals from GRACE, the time series fitting method based on least squares is commonly used. In the time series fitting, the earthquake occurrence time parameter (t0) is usually set at the mid-month point, since most available GRACE time-variable data are monthly solutions. Nevertheless, a lot of large earthquakes did not occur exactly at mid-month. By simulative tests, we demonstrate that the commonly used mid-month approximation for the fitting parameter t0 can cause noticeable bias for the seismic signal extraction. The several-days deviation in the parameter t0 leads to obvious difference for the time series fitting of seismic signals, since the post-seismic changes are rapid and significant within a short period after the earthquake. With the case study of the 2004 Mw9.1 Sumatra-Andaman earthquake (which occurred on December 26), we indicate that the bias due to the commonly used mid-month t0 approximation reaches above 10 percent amplitude of the extracted co-seismic signals. Thus the exact date for the fitting parameter t0 should be used for more reliable separation of the co- and post-seismic signals from GRACE observations.

How to cite: Li, J., Chen, J., Wang, S.-Y., Tang, L., and Hu, X.: On the separation of co- and post-seismic signals due to large earthquakes from GRACE observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12944, https://doi.org/10.5194/egusphere-egu2020-12944, 2020.

High correlations between length-of-day (LOD) and climate variables (sea-surface temperature, surface air temperature) have been pointed out in numerous studies (e.g., Lambeck and Cazenave 1976, Dickey et al. 2011, Marcus 2016) in the recent years at both decadal and multidecadal time scales. Moreover, the multidecal LOD variations (that reach several milliseconds) have been shown to have their origin in variations in the core angular momentum and are associated with variations of the Earth magnetic field now modeled back to the middle of the 19th century. Though the climate variations unlikely arise from the core, some authors suggested that they could result from modulation of incoming cosmic ray flux by Earth's magnetic field through cloud formation. In this study, we propose to check correlations between LOD, Earth dipolar magnetic field, and climate variables as taken from a century reanalysis (gridded air temperature and cloud coverage from NCEP 20th Century Reanalysis V2 and V3) in order to (i) confirm results of previous studies about a possible causality between geomagnetism, LOD, and climate, and (ii) locate the hot spots where the link between geomagnetism and cloud formation could be significant.

How to cite: Lambert, S.: The Intriguing Relation Between Earth's Rotation, Geomagnetic Field, and Climate at Multidecadal Time Scales: Insights from NCEP 20th Century Reanalysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10437, https://doi.org/10.5194/egusphere-egu2020-10437, 2020.

Originating from econometrics, the concept of Granger causality (GC) has been widely used in a variety of fields, including climate sciences, to infer directional dependencies between stochastic variables.  Going one step further than the simple detection of lag-correlations, GC evaluates the directed interaction of a variable Y on a variable X by quantifying the improvement of prediction of future values of X when past values of Y are considered or omitted. Although not prescribed initially as such, GC is routinely computed from an estimated vector autoregressive model of the data of interest X, with and without the exogenous variable Y. However, such a modelling is somewhat restrictive and not suitable for filtered, sampled and noisy time series which may contain a moving-average component, impairing at the same time the quality of the GC estimator. Conversely, state-space representation offers a much more general framework for linear time series modelling.

In this study, we use Granger causality in the framework of a state-space modelling of time series to infer the presence of causal influences of the sea surface temperature (SST) and the 500hPa geopotential height on the Terrestrial Water Storage Anomaly (TWSA) over Australia[PS1] . A first and critical step is to reduce the high-dimension of the spatio-temporal data to a size compatible with classical state-space modelling algorithms. To do that we extract a limited number of leading modes of variability from the geophysical fields. Next, the state-space models of the extracted modes are identified using subspace-based methods. Then, the Granger causality of every mode of SST (resp. 500hPa geopotential height) on TWSA is estimated. Finally, we discuss the capability of the presented method to detect real directional dependencies in the light of current knowledge on Australia’s rainfall climatology and compare it to the results obtained with the classical vector autoregressive models.

How to cite: Douch, K., Saemian, P., and Sneeuw, N.: Investigating Granger causality with state-space representation of time series: a case study of the total water storage anomaly over Australia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10684, https://doi.org/10.5194/egusphere-egu2020-10684, 2020.

EGU2020-13554 | Displays | G3.2

Analysis of groundwater storage changes in main Polish river basins using GRACE observations, in-situ data, and hydrological and climate models

Jolanta Nastula, Justyna Śliwińska, Zofia Rzepecka, and Monika Birylo

The Gravity Recovery and Climate Experiment (GRACE) measurements have provided global observations of total water storage (TWS) changes at monthly intervals for almost 20 years. They are useful for estimating changes in groundwater storage (GWS) after extracting other water storage components like soil water or snow water.

In this study, we analyse the GWS variations of two main Polish basins, the Vistula and the Odra, using GRACE observations, in-situ wells measurements, GLDAS (Global Land Data Assimilation System) hydrological models, and CMIP5 (the World Climate Research Programme’s Coupled Model Intercomparison Project Phase 5) climate data. The research is conducted for the period between September 2006 and October 2015.

Here, TWS is taken directly from GRACE measurements and also computed from all considered models. GWS is obtained by subtracting the modelled sum of soil moisture and snow water from the GRACE-based TWS. The resultant GWS series are validated by comparing with appropriately calibrated in-situ wells measurements. For each GWS time series, the trends, spectra, amplitudes, and seasonal components were computed and analysed. The results suggest that in Poland there has been generally no major GWS depletion. The results can contribute toward selection of an appropriate model that, in combination with GRACE observations, would provide information on groundwater changes in regions with limited or inaccurate in-situ groundwater storage measurements.

How to cite: Nastula, J., Śliwińska, J., Rzepecka, Z., and Birylo, M.: Analysis of groundwater storage changes in main Polish river basins using GRACE observations, in-situ data, and hydrological and climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13554, https://doi.org/10.5194/egusphere-egu2020-13554, 2020.

EGU2020-21943 | Displays | G3.2

Data pre-processing for ionosphere TEC retrieval based on DORIS observations

Shaocheng Zhang, Wei Li, Fei Yin, and Hongfei Gou

 DORIS system aims to provide precise orbit determination of low earth orbit satellites, and the dual-frequencies on S1=2036.25 MHz and U2=401.25 MHz were used on DORIS signals. The ionosphere TEC retrieval on the signal path is possible based on DORIS dual-frequency observations.

Analysis results show that DORIS pseudo-ranges had noise with several kilometers level, hence only the carrier-phase observations could be utilized on TEC retrieval. Moreover, as the DORIS ground stations were thousands kilometers separated with each other, station differential cannot be guaranteed and the data preprocessing can only be done base on the un-difference observations before the TEC could be precisely determined.

In this research, a polynomial function was applied to model the DORIS phase observations, and minimal detectable biases (MDB) of less than one cycle wavelength was used as the index on the cycle-slip detection. And then the geometry free combination of S1 and U2 phase measurements were calculated for each DORIS LEO satellite passing arc. Finally, the unknown ambiguities bias on S1 and U2 geometry free observables were shifted to coincide with STEC calculated from the IGS GIM products.

Both the Jason-2 & 3 based DORIS observations were used for the validation, several simulated +5 and -1 cycle-slip events on both DORIS observation could be clearly detected and correctly repaired. And the calculated STEC on one satellite passing arc from the LEO satellite to station show well agreement with IGS STEC on continent area, and the differences on ocean areas could be used to prove that the IGS GIM products were less precise on those areas.

How to cite: Zhang, S., Li, W., Yin, F., and Gou, H.: Data pre-processing for ionosphere TEC retrieval based on DORIS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21943, https://doi.org/10.5194/egusphere-egu2020-21943, 2020.

EGU2020-3512 | Displays | G3.2

Small-Scale Signal in Mean Dynamic Topographies Applying Combined Geoid Models

Frank Siegismund, Xanthi Oikonomidou, and Philipp Zingerle

The Dynamic ocean Topography (DT) describes the deviation of the true ocean surface from a hypothetical equilibrium state ocean at rest forced by gravity alone. With the geostrophic surface currents obtained from its gradients the DT is an essential parameter for describing the ocean dynamics. Observation-based global temporal Mean geodetic DTs (MDTs) are obtained from the difference of altimetric Mean Sea Surface (MSS) and the geoid height, that equipotential surface of gravity closest to the ocean surface.

The geoid is provided either as a satellite-only, or a combined model including in addition gravity anomalies derived from satellite altimetry and ground data. In recent years the focus was on satellite-only models, produced from new space-born observations obtained from the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and Ocean Circulation Explorer (GOCE) satellite missions. Moreover, combined geoid models are only cautiously used for MDT calculation, since it is still in question to what extent the gravity information obtained from altimetry is distorted by the MDT information included therein and how this translates into errors of the MDT.

Here we want to concentrate on MDT models based on recent combined geoid models. An assessment is provided based on comparisons to near-surface drifter data from the Global Drifter Program (GDP). Besides providing a general, global assessment, we focus on signal content on small scales, addressing mainly two questions: 1) Do MDTs obtained from combined geoid models contain signal for scales smaller than resolvable by the
satellite-only models? 2) Is there a maximum resolution beyond which no signal is detectable?

Until recently, these questions couldn't be answered since low resolution MDTs usually contained strong wavy-structured errors and thus needed a strong spatial filtering thereby killing the smallest scales resolved in the MDT. These errors, which worsen with lower resolution, are caused by Gibbs effects provoked by imperfections in bringing the high resolution ocean-only MSS models into spectral consistency with the much lower resolved global geoid model. A new methodology, however, improves the necessary globalization of the MSS. After subtraction of the geoid model, subsequent cutting-off the signal beyond a specific spherical harmonic degree and order (d/o) results in an MDT without any Gibbs effects, also for low resolution models.

To answer the questions posed above applying the new methodology, the scale-dependent signal in MDTs for different geoid models is presented for a list of cut off d/os. To minimize the influence of noise on the results we concentrate on strong signal Western Boundary Currents like the Gulf Stream and the Kuroshio. For the Gulf Stream results of a high resolution hydrodynamic model are available and presented as an independent method to estimate the scale dependent signal.

How to cite: Siegismund, F., Oikonomidou, X., and Zingerle, P.: Small-Scale Signal in Mean Dynamic Topographies Applying Combined Geoid Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3512, https://doi.org/10.5194/egusphere-egu2020-3512, 2020.

EGU2020-931 | Displays | G3.2

What is the relationship between water storage change and NDVI?

Vedashree Mankar, Ajayraj Singh Jhaj, Samyak Jain, and Balaji Devaraju

The fluctuation in vegetation is affected by water availability, while on the same hand vegetation also influences regional water balance. A better understanding of the relationship between variation in vegetation state and water storage change would help explain the complicated interactions between vegetation dynamics and regional water balance. We use total water storage change from the Gravity Recovery and Climate Experiment (GRACE) and its successor mission GRACE Follow-On (GRACE-FO) and Normalised Difference Vegetation Index (NDVI) data from Advanced Very High Resolution Radiometer (AVHRR). First, we bring the two datasets to a comparable resolution and then we aggregate the two datasets over the 37 sub-catchments of the Ganga basin. The Pearson correlation coefficient was very high (R > 0.5) for 35 of the 37 sub-catchments when the full signals were used, indicating that the seasonality signals have a high correlation. Once the seasonal signal was removed, the Pearson correlation coefficient became insignificant. We will look into the causes of the lack of correlation between the two residual signals and also perform an autocorrelation analysis to identify the lag between the two variables.

How to cite: Mankar, V., Jhaj, A. S., Jain, S., and Devaraju, B.: What is the relationship between water storage change and NDVI?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-931, https://doi.org/10.5194/egusphere-egu2020-931, 2020.

EGU2020-10369 | Displays | G3.2

Geocenter Motion from a Combination of GRACE Mascon and SLR Data

Claudio Abbondanza, Toshio M Chin, Richard S Gross, Michael B Heflin, Jay W Parker, Benedikt S Soja, David N Wiese, and Xiaoping Wu

GRACE and GRACE Follow-On (FO) Level 2 data provide quasi-monthly, band-limited estimates of Stokes (geopotential, spherical harmonic) coefficients mostly reflecting surface mass variability due to non-tidal atmosphere, ocean, and continental hydrology.    
Although space gravimetry does not directly provide CM-related degree-1 Stokes coefficients, GRACE data have been successfully used over the years to complement time series of station positions from global space-geodetic (SG) network when inverting for Center-of-Mass to Center-of-Network (CM-CN) displacements (Wu et al, 2006).

Surficial mass variability observed through GRACE/GRACE-FO can be conveniently converted into load-induced (ENU) deformations at SG observing sites by adopting a spectral (i.e. load Love-number based) formalism and assuming Earth’s response is fully elastic and isotropic. GRACE-derived elastic displacements at observing sites would represent, if accurate, band-limited (degree 2 to 96, or higher if Mascon solutions are adopted) load-induced deformations that can be removed from SG-derived station displacements  in order to more accurately recover degree-1 surface deformation signature (and therefore geocenter motion). 

In this study, we adopt GRACE JPL Mascon RL06 data in conjunction with Preliminary Reference Earth Model-derived load Love numbers to infer elastic displacement at SG sites and remove them from SLR inherently geocentric time series of station positions.
In so doing, the residual SLR station displacements, consistently expressed in a geocentric frame, would in principle reflect a degree-1 deformation signature that can be recovered via either surface deformation (Chanard et al, 2018) or translational approach.

We will compare the SLR/GRACE (CM-CN) determined in this study to standard estimates of geocenter motion such as ILRS’s and JTRF2014’s estimated via translational approach and spectrally inverted solutions (CM-CF).

References
Chanard K et al, (2018). JGR-Sol Ea doi:10.1002/2017JB015245 
Wu X et al, (2006). JGR-Sol Ea doi:10.1029/2005JB004100. 

How to cite: Abbondanza, C., Chin, T. M., Gross, R. S., Heflin, M. B., Parker, J. W., Soja, B. S., Wiese, D. N., and Wu, X.: Geocenter Motion from a Combination of GRACE Mascon and SLR Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10369, https://doi.org/10.5194/egusphere-egu2020-10369, 2020.

G3.3 – Advances in methods and applications for satellite altimetry

The future international Surface Water and Ocean Topography (SWOT) Mission, planned for launch in late 2021, will make high-resolution 2D observations of sea-surface height using SAR radar interferometric techniques. SWOT will map the global and coastal oceans up to 77.6° latitude every 21 days over a swath of 120 km (20 km nadir gap). Today’s 2D mapped altimeter data can resolve ocean scales of 150 km wavelength whereas the SWOT measurement will extend our 2D observations down to 15-30 km, depending on sea state. SWOT will offer new opportunities to observe the oceanic dynamic processes at these smaller scales, that are important in the generation and dissipation of ocean kinetic energy, and are one of the main gateways connecting the surface to the ocean interior. Active vertical exchanges linked to these scales have impacts on the local and global budgets of heat and carbon, and on nutrients for biogeochemical cycles.

SWOT’s unprecedented 2D ocean SSH observations include “balanced” geostrophic eddy motions and high-frequency internal tides and internal waves. SWOT will provide global observations of the 2D structure of these phenomena, enabling us to learn more about their interactions, and helping us to interpret what is currently observed in 1D with conventional altimetry. Yet this mix of balanced and unbalanced motions is a challenge for calculating geostrophic currents directly from SSH or for reconstructing the 4D upper ocean circulation. At these small scales, the ocean dynamics evolve rapidly, and even with SWOT’s 2D SSH images, one satellite cannot observe the temporal evolution of these processes. SWOT data will need to be combined with other satellite and in-situ data and models to better understand the upper ocean 4D circulation (x,y,z,t) over the next decade. SWOT’s new technology will be a forerunner for the future altimetric observing system.

We will present recent progress in understanding the ocean dynamics contributing to fine-scale sea-surface height, including high-frequency processes such as internal tides, from 1D alongtrack altimetry, SAR data, in-situ data and models. We will also discuss the specific problems of validating the SWOT 2D small, rapid dynamics with in-situ data and other satellite data. 

How to cite: Morrow, R. and Fu, L.-L.: Preparing for fine-scale ocean surface topography observations with the Surface Water and Ocean Topography (SWOT) Mission , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7535, https://doi.org/10.5194/egusphere-egu2020-7535, 2020.

EGU2020-6773 | Displays | G3.3

Using the Baltic Sea to advance algorithms to extract altimetry-derived sea-level data from complex coastal areas, featuring seasonal sea-ice

Marcello Passaro, Felix L. Müller, Adili Abulaitijiang, Ole B. Andersen, Denise Dettmering, Jacob L. Høyer, Milla Johansson, Julius Oelsmann, Laura Rautiainen, Ida M. Ringgaard, Eero Rinne, Jani Särkkä, Rory Scarrott, Christian Schwatke, Florian Seitz, Kristine Skovgaard Madsen, Laura Tuomi, Americo Ambrozio, Marco Restano, and Jérôme Benveniste

The use of satellite altimetry at high latitudes and coastal regions is currently limited by the presence of seasonal sea ice coverage, and the proximity to the coast. The semi-enclosed Baltic Sea features seasonal coverage of sea-ice in the northern and coastal regions, and complex jagged coastlines with a huge number of small islands. However, as a semi-enclosed sea with a considerable extent, the Baltic Sea features a much-reduced tidal signal, both open- and coastal- waters, and an extensive multi-national network of tide-gauges. These factors maximise opportunities to drive improvements in sea-level estimations for coastal, and seasonal-ice regions.

The ESA Baltic SEAL project, launched in April 2019, aims to exploit these opportunities. It is generating and validating a suite of enhanced multi-mission sea level products. Processing is developed specifically for coastal regions, with the objective of achieving a consistent description of the sea-level variability in terms of long-term trends, seasonal variations and a mean sea-surface. These will advance knowledge on adapting processing algorithms, to account for seasonal ice, and complex coastlines. Best practice approaches will be available to update current state-of-the-art datasets.

In order to fulfill these goals, a novel altimeter re-tracking strategy has been developed. This enables the homogeneous determination of sea-surface heights for open-ocean, coastal and sea-ice conditions (ALES+). An unsupervised classification algorithm based on artificial intelligence routines has been developed and tailored to ingest data from all current and past satellite altimetry missions. This identifies radar echoes, reflected by narrow cracks within the sea-ice domain. Finally, the improved altimetry observations are gridded onto a triangulated surface mesh, featuring a spatial resolution greater than 1/4 degree. This is more suitable for utility for coastal areas, and use by coastal stakeholders.

In addition to utilizing a wide range of altimetry data (Delay-Doppler and Pulse-Limited systems), the Baltic SEAL initiative harnesses the Baltic Seas unique characteristics to test novel geophysical corrections (e.g. wet troposphere correction), use the latest generation of regional altimetry datasets, and evaluate the benefits of the newest satellite altimetry missions. This presentation outlines the methodology and results achieved to date. These include estimations of a new regional mean sea surface, and insights into the trends of the sea level along the altimetry tracks with the longest records. The transfer of advances to other regions and sea-level initiatives are also highlighted.

How to cite: Passaro, M., Müller, F. L., Abulaitijiang, A., Andersen, O. B., Dettmering, D., Høyer, J. L., Johansson, M., Oelsmann, J., Rautiainen, L., Ringgaard, I. M., Rinne, E., Särkkä, J., Scarrott, R., Schwatke, C., Seitz, F., Skovgaard Madsen, K., Tuomi, L., Ambrozio, A., Restano, M., and Benveniste, J.: Using the Baltic Sea to advance algorithms to extract altimetry-derived sea-level data from complex coastal areas, featuring seasonal sea-ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6773, https://doi.org/10.5194/egusphere-egu2020-6773, 2020.

Single-waveform retracking for satellite altimetry applications over coastal zones has reached its limits, obtaining decimeter-level accuracy. The existing retracking methods find a retracker offset in a waveform by analyzing the variation in backscattered power along the bin coordinate. This makes the retracking procedure strongly dependent on noise in backscattered power. Moreover, the success of such methods is only guaranteed for certain waveform types requiring cumbersome pre-processing steps including waveform classification. 

With the launch of the operational Sentinel-3 series of the European Copernicus programme, the algorithms to obtain highly precise water level estimates over inland waters and coastal seas need to become more robust, efficient and fit for automated use. Therefore, the main objective of this study is to demonstrate the potential of developing a next-level retracking algorithm and, consequently, improve altimetric water level determination over coastal regions. To this end, neighboring waveforms are collected into a (single-pass) radargram and, then, such radargrams are stacked over time. These so-called (multi-pass) radargram stacks contain, unlike single waveforms, the full information on spatio-temporal variation of backscattered power over water surfaces.

The radargram stack eases the recognition of patterns like retracking gate, shoreline, tides, etc. Instead of a retracking gate as a point in the 1D waveform, in a 3D radargram stack a surface referred to as retracking manifold is to be determined.

The potential of our new approach will be demonstrated using Sentinel 3B data, pass number 655, over the Cuxhaven tide gauge station at the Wadden Sea.

The idea of waveform retracking by analyzing its spatio-temporal behavior in a 3D data structure opens new pathways for achieving robust and more accurate water level estimates from operational missions, e.g. Sentinel 3, and from future missions, e.g. SWOT, over inland waters and coastal seas.

How to cite: Sneeuw, N., Elmi, O., Eitel, M., and Tourian, M.: Defining a retracking manifold within a radargram stack to improve satellite altimetric water level over coastal seas: A feasibility study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9547, https://doi.org/10.5194/egusphere-egu2020-9547, 2020.

EGU2020-19534 | Displays | G3.3

Multi-Peak Retracking of CryoSat-2 SARIn Waveforms: Potential for Sea Ice Applications

Alessandro Di Bella, Ron Kwok, Thomas Armitage, Henriette Skourup, and René Forsberg

For the last 25+ years, satellite altimetry has proven to be a powerful tool to estimate sea ice thickness from space, by measuring directly the sea ice freeboard. Nevertheless, available thickness estimates from satellite altimetry are affected by a relatively high uncertainty, with the largest contributions originating from the poor knowledge of both the Arctic snow cover and the sea surface height (SSH) in ice-covered regions. The ESA’s CryoSat-2 (CS2) radar altimetry mission is the first mission carrying on board an altimeter instrument able to operate in Synthetic Aperture Radar Interferometric (SARIn) mode. Previous studies showed how the phase information available in the SARIn mode can be used to reduce the random uncertainty of the SSH in ice-covered regions [1] and, consequently, the average uncertainty of along-track freeboard retrievals [2].

This work shows that it is possible to extract even more information from level 1b SARIn data. In fact, while it is not possible to perform full swath processing [3] over sea ice, the contribution from sea ice reflections originating close to the satellite nadir is successfully separated from the specular returns from off-nadir leads for some SARIn waveforms. We find that retracking multiple peaks, in combination with the respective phase information, enables to obtain more than one valid height estimate from single SARIn waveforms over sea ice. The resulting larger amount of freeboard estimates, together with the more precise SSH, is found to contribute to an average reduction of the gridded random and total sea ice thickness uncertainties of ~40% and ~25%, respectively, compared to a regular SAR processing scheme. This study also investigates how the CS2 SARIn phase information can aid thickness estimation in coastal areas, using ESA Sentinel-1 SAR images and airborne data from NASA Operation IceBridge campaigns as a mean of validation.

The more precise and, potentially, more accurate freeboard retrievals, as well as the potential for coastal freeboard and thickness estimation shown in this work, support the design of future satellite altimetry missions, e.g. Sentinel-9, operating in SARIn mode over the entire Arctic Ocean.

 

References

[1] Armitage, T. W. K., & Davidson, M. W. J. (2014). Using the interferometric capabilities of the ESA CryoSat-2 mission to improve the accuracy of sea ice freeboard retrievals. IEEE Transactions on Geoscience and Remote Sensing, 52(1), 529–536. http://doi.org/10.1109/TGRS.2013.2242082

[2] Di Bella, A., Skourup, H., Bouffard, J., & Parrinello, T. (2018). Uncertainty reduction of Arctic sea ice freeboard from CryoSat-2 interferometric mode. Advances in Space Research, 62(6), 1251–1264. http://doi.org/10.1016/j.asr.2018.03.018

[3] Gray, L., Burgess, D., Copland, L., Cullen, R., Galin, N., Hawley, R., & Helm, V. (2013). Interferometric swath processing of Cryosat data for glacial ice topography. Cryosphere, 7 (6), 1857–1867.

How to cite: Di Bella, A., Kwok, R., Armitage, T., Skourup, H., and Forsberg, R.: Multi-Peak Retracking of CryoSat-2 SARIn Waveforms: Potential for Sea Ice Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19534, https://doi.org/10.5194/egusphere-egu2020-19534, 2020.

EGU2020-13288 | Displays | G3.3 | Highlight

Seasonal elevation changes in the Greenland Ice Sheet from CryoSat-2 altimetry

Thomas Slater, Andrew Shepherd, Malcolm McMillan, Amber Leeson, Lin Gilbert, and Kate Briggs

Seasonal changes in the elevation of the Greenland Ice Sheet below the equilibrium line altitude are driven by ice dynamics and fluctuations in surface melting and snowfall accumulation. Here, we use CryoSat-2 altimetry to estimate summer and winter elevation changes in the ablation area of the Greenland Ice Sheet between 2011 and 2019. During this period, we find average summer and winter elevation trends of -2.52 ± 0.68 m/yr and 0.90 ± 0.39 m/yr, respectively. While the rate at which the ablation zone thickens in winter due to snowfall has remained relatively stable, variability in ice thinning in the summer due to surface melting has followed recent changes in atmospheric circulation. In combination with a regional climate model, we examine patterns of change associated with ice sheet dynamics on both multi-annual and seasonal timescales. At the ice sheet scale, we find our altimeter record of height change within the ablation zone strongly agrees with regional climate model reconstructions of elevation change due to surface processes alone. Between 2011 and 2019, we estimate that the ablation zone of the Greenland Ice Sheet has thinned by 3.86 ± 0.30 m from CryoSat-2 altimetry.

How to cite: Slater, T., Shepherd, A., McMillan, M., Leeson, A., Gilbert, L., and Briggs, K.: Seasonal elevation changes in the Greenland Ice Sheet from CryoSat-2 altimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13288, https://doi.org/10.5194/egusphere-egu2020-13288, 2020.

EGU2020-20434 | Displays | G3.3

Correlated Fluctuations in Surface Melting and Ku-band Radar Penetration in West Central Greenland

Inès Otosaka, Andrew Shepherd, Tânia Casal, Alex Coccia, Alessandro di Bella, Malcolm Davidson, Xavier Fettweis, René Forsberg, Veit Helm, Anna Hogg, Sine Hvidegaard, Peter Kuipers Munneke, Adriano Lemos, Karlus Macedo, Tommaso Parinello, Louise Sandberg Sørensen, Henriette Skourup, and Sebastian Simonsen

Melting at the surface of the Greenland ice sheet has significantly increased since the early 1990s and this affects the degree to which radar sensors can penetrate beyond the snow surface. Indeed, radars are sensitive to changes in the surface and subsurface properties, up to ~15 m below the snow surface for instruments using the Ku-band (13.5 GHz). When melting occurs, meltwater can percolate in the snowpack or refreeze at the surface and in turn, the degree of radar penetration is sharply reduced. Here we use measurements of near-surface density from firn cores and models and airborne radar and laser data collected during the European Space Agency of ESA’s CRYOsat Validation EXperiment (CRYOVEX) campaigns along a 675 km transect in West Central Greenland between 2006 and 2017 to examine spatial and temporal fluctuations in the near-surface properties and how this affects radar measurements. From airborne data acquired with ASIRAS at Ku-band, we identify internal layers corresponding to melt layers in the snowpack down to 15 m, in good agreement with a firn densification model. We examine the spatial and temporal distribution of these melt layers and we find that the abundance of melt layers is increasing with elevation and depicts a strong inter-annual variability and that these fluctuations are correlated with fluctuations in the degree of the radar penetration depth. For instance, in 2012, the Greenland ice sheet experienced unprecedented melting and this is seen in the radar data by a reduction of 70% of the penetration in the snowpack following this event. The 2012 melt layer is still visible in data recorded 5 years after the melt event at a depth of 5.1 m.  As the frequency and extent of extreme melt events is likely to increase in the coming decades, the effects of fluctuations in Ku-band radar penetration are an important consideration for satellite radar altimetry studies.  However, we show that despite large fluctuations in volume scattering, there is a good agreement between Ku-band retracked heights and coincident laser measurements of 13.9 ± 19.9 cm using a threshold retracker. Finally, we also investigate the potential of using higher-frequency KAREN Ka-band (34.5 GHz) airborne radar data to limit the impact of temporal variations in the snowpack properties on backscattered power. We show that surface scattering dominates the Ka-band radar echoes and, overall, they penetrate to significantly lower distances into the near-surface firn by comparison to those acquired at Ku-band. This suggests that Ka-band data are less sensitive to extreme melt events and that the impact of such events on Ka-band data are likely to last for a shorter period of time compared to Ku-band data.

How to cite: Otosaka, I., Shepherd, A., Casal, T., Coccia, A., di Bella, A., Davidson, M., Fettweis, X., Forsberg, R., Helm, V., Hogg, A., Hvidegaard, S., Kuipers Munneke, P., Lemos, A., Macedo, K., Parinello, T., Sandberg Sørensen, L., Skourup, H., and Simonsen, S.: Correlated Fluctuations in Surface Melting and Ku-band Radar Penetration in West Central Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20434, https://doi.org/10.5194/egusphere-egu2020-20434, 2020.

EGU2020-445 | Displays | G3.3

High-resolution bathymetry mapping of shallow and ephemeral desert lakes using satellite imagery and altimetry

Moshe Armon, Elad Dente, Yuval Shmilovitz, Amit Mushkin, Efrat Morin, Tim J. Choen, and Yehouda Enzel

Many of the world’s drylands are characterized by interior drainage systems that terminate at shallow desert lakes or playas. Except for episodic flooding these largely ephemeral water bodies, remain mostly dry. Surveying and mapping their respective floor topography in a suitable resolution for calculating water balance is a difficult and laborious task. As this is crucial for water resources management and reconstructing paleoenvironmental conditions, diverse methods and efforts were applied. However, detailed, high-quality bathymetric surveys in such environments are rare and have only been conducted in a few such lakes. This is primarily due to their shallow, low-relief, large areas, and often remote characteristics, which complicate application of conventional topographic surveying techniques.  Therefore, satellite-based remote sensing is an essential complementary approach for deriving bathymetry of such lakes.

Global digital elevation models, such as NASA’s Shuttle Radar Topography Mission (SRTM) or ASTER’s GDEM, are unsuitable for accurate measurements of these ephemeral lakes, mainly because of their impenetrability to water and their high signal-to-noise ratio in the low-relief environments. Recent studies addressed these complications by combining remote sensing data with local calibrations of in-situ measurements, or alternatively, by relating shoreline altitudes with precise altimetry. This approach requires a spatial interpolation of individual measurements. Therefore, it is prone to errors that demand intensive efforts to be reduced; even then the errors may remain larger than the actual depth of a flooded lake. Moreover, such methods are hard to apply in complex lakes with multiple sub-basins.

To tackle these problems, we developed a simple methodology to derive a high-resolution (30 m per pixel) bathymetry of shallow desert lakes. In this new method we combine two sources of data: a >30-yr record of Landsat-derived surface water occurrence data; and accurate high-resolution elevation data, acquired by the NASA’s recently launched ICESat-2 satellite (Ice, Cloud, and Land Elevation Satellite-2). We test the proposed new method over three ephemeral lakes around the world: Lake Eyre, Australia, with its complex shallow lake system, consisting of a few sub-basins; Sabkhat Al-Mellah, Algeria; Lago Coipasa, Bolivia. The accuracy of the resulted bathymetric maps was evaluated using cross-validation of ICESat-2 scans, yielding low RMSD values of ~0.3 m, versus ~2.5 m of the SRTM data (validated through other ICESat-2 scans). At Lago Coipasa, we show that bathymetry was effectively determined even when the lake was full of water (up to a few meters depth). This high-resolution, low-error bathymetry mapping complement other globally available topographic data.

How to cite: Armon, M., Dente, E., Shmilovitz, Y., Mushkin, A., Morin, E., Choen, T. J., and Enzel, Y.: High-resolution bathymetry mapping of shallow and ephemeral desert lakes using satellite imagery and altimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-445, https://doi.org/10.5194/egusphere-egu2020-445, 2020.

EGU2020-12239 | Displays | G3.3

Analysis on the Accuracy of Marine Gravity Inversion from the Wide-swath Altimeter Mission

Mao Zhou, Taoyong Jin, Jiancheng Li, Shengjun Zhang, and Minzhang Hu

Marine gravity is mainly inversed by the nadir satellite altimetry observations. However, the accuracy of the east-west component of vertical deflection is significantly lower than the north-south component. The wide-swath altimeter is one of the main altimetry missions in the future. Its two-dimensional design is expected to obtain high-precision and high-resolution sea surface height simultaneously, and to improve the accuracy of the marine gravity inversion. Taking the SWOT (Surface Water and Ocean Topography) wide-swath altimeter mission as an example, based on the parameters including the ground track and the width of swath, the static sea surface height observations of SWOT, as well as the nadir altimeter missions Jason-1/GM, Cryosat-2/LRM, and SARAL/GM were simulated. Then, the vertical deflections were calculated from above observations to analyze the ability of marine gravity inversion in the South China Sea and part of the Indian Ocean. Compared with EGM2008 model, the vertical deflections determined by one cycle of SWOT are better than the result determined by combining Jason-1/GM, Cryosat-2/LRM, and SARAL/GM. And the results determined by SWOT improve the accuracy of the east-west component of vertical deflection significantly. And then, several specific errors of SWOT satellite were simulated, and their influence on the determination of the vertical deflection was analyzed. It is noted that these errors have certain influence on the accuracy, but can be weakened by using a simple Gaussian filter. In addition, the influence of SWOT sea surface height resolution on the gravity field inversion was analyzed. As a result, under the premise of the designed accuracy and resolution of the SWOT mission, its observations can improve the quality of marine gravity inversion effectively.

How to cite: Zhou, M., Jin, T., Li, J., Zhang, S., and Hu, M.: Analysis on the Accuracy of Marine Gravity Inversion from the Wide-swath Altimeter Mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12239, https://doi.org/10.5194/egusphere-egu2020-12239, 2020.

EGU2020-312 | Displays | G3.3

Regional Mean Sea Surface Model over the Eastern Mediterranean Sea

Milaa Murshan, Balaji Devaraju, Nagarajan Balasubramanium, and Onkar Dikshit

The Mean Sea Level is not an equipotential surface because it is subject to several variations, e.g., the tides, currents, winds, etc. Mean Sea Level can be measured either by tide gauges near to coastlines relative to local datum or by satellite altimeter above the reference ellipsoid. From this observable quantity, one can derive a non-observable quantity at which the potential is constant called geoid and differs from mean sea surface by amount of ±1 m. This separation is called Sea Surface Topography. In this research, the data of nine altimetric Exact Repeat Missions (Envisat, ERS_1 of 35 days (phase C and G), ERS_2, GFO, Jason_1, Jason_2, Jason_3, Topex/Poseidon and SARAL) were used for computing the regional mean sea surface model over the eastern Mediterranean Sea. The data of all missions together span approximately 25 years from September -1992 to January-2017 and referenced to Topex ellipsoid.  Which is later transformed to WGS84 ellipsoid, as it is chosen to be a unified datum in this study. Prior to computing the altimetric MSS,  altimetric sea surface height measurements were validated  by comparing  time series of altimetric-MSL with mean sea level time series calculated from three in-situ tide gauge measurements.  The sea surface heights values of the derived MSS model is between 15.6 and 26.7 m. And the linear trend slope is between -3.02 to 6.53 mm/year.

Keywords: Mean Sea Level, Satellite Altimetry, Tide Gauge, Exact Repeat Missions

How to cite: Murshan, M., Devaraju, B., Balasubramanium, N., and Dikshit, O.: Regional Mean Sea Surface Model over the Eastern Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-312, https://doi.org/10.5194/egusphere-egu2020-312, 2020.

EGU2020-777 | Displays | G3.3

Waveguide for Rossby waves in the Antarctic Circumpolar current based on the altimetry data

Anastasiia Frolova and Tatyana Belonenko

Rossby waves in the ocean play a crucial role in large-scale ocean circulation and global climate. However, the interaction of Rossby waves with large-scale currents in the ocean is still a relatively little studied issue. The Antarctic Circumpolar Current (ACC) is the largest ocean current in the World Ocean. The ACC is a waveguide for Rossby waves where wave kinetic energy is captured by jets, and where Rossby waves interact with the flow. The purpose of this research is to analyze a manifestation of Rossby waves in the ACC based on satellite altimetry data. We propose a new approach to determining the boundaries of the waveguide. We analyze the variability of sea level anomalies and examine the latitude where the zonal velocity of Rossby waves is zero. For calculating Rossby waves velocities we use Radon and cross-correlation methods. We detect the Northern and the Southern Waveguide Boundaries for the ACC and compare them to the climatological fronts in the ACC. The linear theory of Rossby waves doesn’t work within the waveguide due to that we should consider nonlinear in the long-wave approximation. It follows from the theory of shallow water that nonlinearity in the long-wave approximation compensates exactly for the Doppler shift. The nonlinear dispersion equation agrees well with altimetry data.

The investigation is supported by the Russian Foundation for Basic Research grant (17-05-00034).

How to cite: Frolova, A. and Belonenko, T.: Waveguide for Rossby waves in the Antarctic Circumpolar current based on the altimetry data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-777, https://doi.org/10.5194/egusphere-egu2020-777, 2020.

EGU2020-15814 | Displays | G3.3

The BRAT and GUT Couple: Broadview Radar Altimetry and GOCE User Toolboxes

Américo Ambrózio, Marco Restano, and Jérôme Benveniste

The scope of this work is to showcase the BRAT (Broadview Radar Altimetry Toolbox) and GUT (GOCE User Toolbox) toolboxes.

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from all previous and current altimetry missions, including Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases on Geodesy & Geophysics, Oceanography, Coastal Zone, Atmosphere, Wind & Waves, Hydrology, Land, Ice and Climate, which can also be consulted in  http://www.altimetry.info/radar-altimetry-tutorial/.

BRAT's last version (4.2.1) was released in June 2018. Based on the community feedback, the front-end has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images.

The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions.

In the current version (3.2), GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's Variance/Covariance Matrix (VCM) tool, which enables non-experts to compute and study, with relative ease, the formal errors of quantities – such as geoid height, gravity anomaly/disturbance, radial gravity gradient, vertical deflections – that may be derived from the GOCE gravity models.

On our continuous endeavour to provide better and more useful tools, we intend to integrate BRAT into SNAP (Sentinel Application Platform). This will allow our users to easily explore the synergies between both toolboxes. During 2020 we will start going from separate toolboxes to a single one.

BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.

How to cite: Ambrózio, A., Restano, M., and Benveniste, J.: The BRAT and GUT Couple: Broadview Radar Altimetry and GOCE User Toolboxes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15814, https://doi.org/10.5194/egusphere-egu2020-15814, 2020.

EGU2020-13608 | Displays | G3.3

High-resolution numerical modelling of the altimetry-derived gravity disturbances and disturbing gradients

Róbert Čunderlík, Marek Macák, Michal Kollár, and Karol Mikula

Recent high-resolution mean sea surface models obtained from satellite altimetry in a combination with the GRACE/GOCE-based global geopotential models provide valuable information for detailed modelling of the altimetry-derived gravity data. Our approach is based on a numerical solution of the altimetry-gravimetry boundary-value problem using the finite volume method (FVM). FVM discretizes the 3D computational domain between an ellipsoidal approximation of the Earth's surface and an upper boundary chosen at a mean altitude of the GOCE satellite orbits. A parallel implementation of the finite volume numerical scheme and large-scale parallel computations on clusters with distributed memory allow to get a high-resolution numerical solution in the whole 3D computational domain. Our numerical experiment presents the altimetry-derived gravity disturbances and disturbing gradients determined with the high-resolution 1 x 1 arc min at two altitude levels; on the reference ellipsoid and at the altitude of 10 km above the ellipsoid. As input data, the Dirichlet boundary conditions over oceans/seas are considered in the form of the disturbing potential. It is obtained from the geopotential evaluated on the DTU18 mean sea surface model from the GO_CONS_GCF_2_TIM_R5 geopotential model and then filtered using the nonlinear diffusion filtering. On the upper boundary, the FVM solution is fixed to the disturbing potential generated from the GO_CONS_GCF_2_DIR_R5 model while exploiting information from the GRACE and GOCE satellite missions.

How to cite: Čunderlík, R., Macák, M., Kollár, M., and Mikula, K.: High-resolution numerical modelling of the altimetry-derived gravity disturbances and disturbing gradients, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13608, https://doi.org/10.5194/egusphere-egu2020-13608, 2020.

EGU2020-2215 | Displays | G3.3

Improved Retrieval Methods for Sentinel-3 SAR Altimetry over Coastal and Open Ocean and recommendations for implementation: ESA SCOOP Project Results

David Cotton, Thomas Moreau, Mònica Roca, Christine Gommenginger, Mathilde Cancet, Luciana Fenoglio-Marc, Marc Naeije, M Joana Fernandes, Andrew Shaw, Marco Restano, Americo Ambrosio, and Jérôme Benveniste

SCOOP (SAR Altimetry Coastal & Open Ocean Performance) is a project funded under the ESA SEOM (Scientific Exploitation of Operational Missions) Programme Element, to characterise the expected performance of Sentinel-3 SRAL SAR mode altimeter products, and then to develop and evaluate enhancements to the baseline processing scheme in terms of improvements to ocean measurements. Another objective is to develop and evaluate an improved Wet Troposphere correction for Sentinel-3.

The SCOOP studies are based on two 2-year test data sets derived from CryoSat-2 FBR data, produced for 10 regions. The first Test Data Set was processed with algorithms equivalent to the Sentinel-3 baseline, and the second with algorithms expected to provide an improved performance.

We present results from the SCOOP project that demonstrate the excellent performance of SRAL at the coast in terms of measurement precision, with noise in Sea Surface Height 20Hz measurements of less than 5cm to within 5km of the coast.

We then report the development and testing of new processing approaches designed to improve performance, including, for L1B to L2:

  • Application of zero-padding
  • Application of intra-burst Hamming windowing
  • Exact beam forming in the azimuthal direction
  • Restriction of stack processing to within a specified range of look angles.
  • Along-track antenna compensation

 

And for L1B to L2

  • Application of alternative re-trackers for SAR and RDSAR.

 

Based on the results of this assessment, a second test data set was generated and we present an assessment of the performance of this second Test Data Set generated, and compare it to that of the original Test Data Set.

Regarding the WTC for Sentinel-3A, the correction from the on-board MWR has been assessed by means of comparison with independent data sets such as the GPM Microwave Imager (GMI), Jason-2, Jason-3 and Global Navigation Satellite Systems (GNSS) derived WTC at coastal stations. GNSS-derived path Delay Plus (GPD+) corrections have been derived for S3A. Results indicate good overall performance of S3A MWR and GPD+ WTC improvements over MWR-derived WTC, particularly in coastal and polar regions.

 

Based on the outcomes of this study we provide recommendations for improving SAR mode altimeter processing and priorities for future research.

How to cite: Cotton, D., Moreau, T., Roca, M., Gommenginger, C., Cancet, M., Fenoglio-Marc, L., Naeije, M., Fernandes, M. J., Shaw, A., Restano, M., Ambrosio, A., and Benveniste, J.: Improved Retrieval Methods for Sentinel-3 SAR Altimetry over Coastal and Open Ocean and recommendations for implementation: ESA SCOOP Project Results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2215, https://doi.org/10.5194/egusphere-egu2020-2215, 2020.

EGU2020-8012 | Displays | G3.3

Evaluation of Sentinel-3 SRAL SAR Altimetry over Recently Constructed Global Reservoirs

Xingxing Zhang, Liguang jiang, Zhijun Yao, Zhaofei Liu, Rui Wang, Jun Liu, and Peter Bauer-Gottwein

Satellite radar altimetry is increasingly being used for hydrological studies. However, it is still challenging to deliver high quality data over inland water bodies, i.e. lakes, rivers and reservoirs. One of the reasons is that the positioning of the range window is difficult due to highly variable topography and water surface elevation. To address this issue, Sentinel-3, the first SAR altimeter operating at global scale, is configured with a new on-board tracking system, i.e. open-loop mode. An open-loop tracking system can position the range window very efficiently based on a priori surface elevation stored on-board. In this context, a suitable a priori surface elevation of inland water bodies is very important.

Sentinel-3 is operating based on a pseudo-DEM controlled through the Open-Loop Tracking Command (OLTC).  The current OLTC V5 (operated after March 2019) is generated based on an inland water mask and Altimeter corrected Elevations (ACE-2), which is created using multi-mission Satellite Radar Altimetry from 1994-2005 in combination with the Shuttle Radar Topography Mission (SRTM). However, OLTC V5 still misses some inland water bodies and contains some incorrect surface elevations, especially over newly built reservoirs, where the difference between water surface elevation and ACE-2 can exceed 100m.

In this study, a comprehensive evaluation of Sentinel-3A (S3A) is conducted at 26 globally-distributed recently constructed large reservoirs. The results show that S3A fails to deliver useful data over most new reservoirs in open loop due to the incorrect a priori elevations stored in OLTC V5. On the contrary, S3A closed-loop (operated before March 2019) can deliver useful data in many cases.

To improve the OLTC table, we propose two approaches. The first one is to use dam height to correct the a priori surface elevation, which is relevant for very recently completed dams or dams under construction. The other is to use water surface elevation from Cryosat-2 to update the OLTC table. The approaches are demonstrated for reservoirs located on the Lancang and Nu rivers in the Southwest of China. The updated OLTC table will help exploit the Sentinel-3 radar altimetry mission to its full potential, enabling it to correctly track water surface elevation in a larger number of water bodies.

How to cite: Zhang, X., jiang, L., Yao, Z., Liu, Z., Wang, R., Liu, J., and Bauer-Gottwein, P.: Evaluation of Sentinel-3 SRAL SAR Altimetry over Recently Constructed Global Reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8012, https://doi.org/10.5194/egusphere-egu2020-8012, 2020.

EGU2020-19345 | Displays | G3.3

Coastal Sea Level Change from in the North Eastern Atlantic

Luciana Fenoglio-Marc, Bernd Uebbing, Jürgen Kusche, and Salvatore Dinardo

A significant part of the World population lives in the coastal zone, which is affected by coastal sea level rise and extreme events. Our hypothesis is that the most accurate sea level height measurements are derived from the Synthetic Aperture Altimetry (SAR) mode. This study analyses the output of dedicated processing and assesses their impacts on the sea level change of the North-Eastern Atlantic. 

It will be shown that SAR altimetry reduces the minimum usable distance from five to three kilometres when the dedicated coastal retrackers SAMOSA+ and SAMOSA++ are applied to data processed in SAR mode. A similar performance is achieved with altimeter data processed in pseudo low resolution mode (PLRM) when the Spatio-Temporal Altimeter sub-waveform Retracker (STAR) is used. Instead the Adaptive Leading Edge Sub-waveform retracker (TALES) applied to PLRM is less performant. SAR processed altimetry can recover the sea level heights with 4 cm accuracy up to 3-4 km distance to coast. Thanks to the low noise of SAR mode data, the instantaneous SAR and in-situ data have the highest agreement, with the smallest standard deviation of differences and the highest correlation. A co-location of the altimeter data near the tide gauge is the best choice for merging in-situ and altimeter data. The r.m.s. (root mean squared) differences between altimetry and in-situ heights remain large in estuaries and in coastal zone with high tidal regimes, which are still challenging regions. The geophysical parameters derived from CryoSat-2 and Sentinel-3A measurements have similar accuracy, but the different repeat cycle of the two missions locally affects the constructed time-series.

The impact of these new SAR observations in climate change studies is assessed by evaluating regional and local time series of sea level. At distances to coast smaller than 10 Kilometers the sea level change derived from SAR and LRM data is in good agreement. The long-term sea level variability derived from monthly time-series of LRM altimetry and of land motion-corrected tide gauges agrees within 1 mm/yr for half of in-situ German stations. The long-term sea level variability derived from SAR data show a similar behaviour with increasing length of the time series.

 

How to cite: Fenoglio-Marc, L., Uebbing, B., Kusche, J., and Dinardo, S.: Coastal Sea Level Change from in the North Eastern Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19345, https://doi.org/10.5194/egusphere-egu2020-19345, 2020.

EGU2020-12691 | Displays | G3.3

Validation of ICESat-2 Data along CHINARE Route in East Antarctica

Tong Hao, Rongxing Li, Gang Qiao, Hongwei Li, Gang Hai, Haotian Cui, Youquan He, Hong Tang, Huan Xie, and Bo Sun

NASA launched the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) satellite on September 15, 2018. The photon counting altimeter of ICESat-2 is designed to provide centimeter-level accuracy surface elevation observations and is expected to reduce the uncertainty of the estimated sea level rise contribution from Antarctica. The ICESat-2 mission team has conducted a validation campaign and stated that the data released in the first year met the design requirements. In this study we designed and implemented an independent validation scheme along the 36th CHINARE (Chinese Antarctic Research Expedition) route in East Antarctica as a different validation site. 1) GNSS data collected during a week in December 2019 along the 500-km traverse from the Zhongshan Station to the Taishan Station are compared with the crossover ICESat-2 points. The GNSS receiver (CHC i70) was fixed on the roof of the Pisten Bully Polar 300 and cooperated with 5 GNSS base stations spaced every ~100 km. 2) To investigate photons reflectivity we used a rectangular area target for each site at three Chinese stations, with considerations of the reflectivity and satellite tracks. 22 upward-looking optical prisms were installed to capture photons with known ground elevations. 3) Finally, we utilized DJI Phantom 4 unmanned aerial vehicles (UAVs) to obtain centimeter-level DEMs of ice sheet surface and compare with the ICESat-2 points. The results are analyzed for several applications and compared against the published validation results of the mission team.

How to cite: Hao, T., Li, R., Qiao, G., Li, H., Hai, G., Cui, H., He, Y., Tang, H., Xie, H., and Sun, B.: Validation of ICESat-2 Data along CHINARE Route in East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12691, https://doi.org/10.5194/egusphere-egu2020-12691, 2020.

EGU2020-10571 | Displays | G3.3

A new elevation change time series of the Antarctic Ice Sheet from Envisat and CryoSat-2 radar altimetry

Baojun Zhang, Quanming Yang, Zemin Wang, Hong Geng, Jiachun An, and Shengjun Zhang

Satellite altimetry is an important data source for ice sheet change observation. The long-term time series of ice sheet changes can be obtained by combining satellite altimetry missions with similar sensor characteristics. Then, how to correct the inter-mission offsets becomes an important scientific issue. Review of previous studies, we found that the observations of satellite ascending and descending orbits also have an important influence on the estimation of inter-mission offsets. On this basis, have created a new least-square fitting mathematical model to estimate and correct the errors of ascending and descending orbits and inter-mission offsets by introducing the inter-mission offsets terms related to the observations of ascending and descending orbits. Utilizing this model, we developed a time series of monthly Antarctic ice sheet elevation changes of 5 km grid from May 2002 to April 2019. A validation with surface elevation from airborne observations and a comparison with surface elevation changes from ICESat proved that the proposed model can successfully estimate and correct the errors and be used to construct multi-mission surface elevation time series. Without a doubt, the temporal and spatial changes of Antarctic ice sheet elevation can be obtained from our monthly grid time series. From the time series, we find that over the period May 2002 to April 2019 the loss of ice and snow in the Antarctic ice sheet mainly occurred in the glaciers along the Amundsen coast in the West Antarctic and the Totten glacier in the East Antarctic, while the accumulation took place in Queen Maud of the East Antarctic. In May 2002, the Antarctic ice sheet experienced a volume loss of -71.4 ± 11.7 km3/yr, with an acceleration of –5.8 ± 1.2 km3/yr2 over the period May 2002 to April 2019, including 45.0 ± 9.6 km3/yr and 0.1 ±1.0 km3/yr2 for the East Antarctic ice sheet, -97.0 ± 4.4 km3/yr and -7.6 ±0.5 km3/yr2 for the West Antarctic ice sheet and -19.5 ± 5.3 km3/yr and 1.7 ±0.5 km3/yr2 for the Antarctic Peninsula ice sheet.

How to cite: Zhang, B., Yang, Q., Wang, Z., Geng, H., An, J., and Zhang, S.: A new elevation change time series of the Antarctic Ice Sheet from Envisat and CryoSat-2 radar altimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10571, https://doi.org/10.5194/egusphere-egu2020-10571, 2020.

EGU2020-21772 | Displays | G3.3

Investigation of the added value of a varying coherence threshold for CryoSat-2 swath processing

Natalia Havelund, Louise S. Sørensen, and Sebastian B. Simonsen

In a changing climate it is important to continuously monitor the Greenland Ice Sheet (GrIS) in relation to global sea level rise (Gardner et al., 2013). The margin of the GrIS is the most sensitive to climate changes and responds quickly.

Here, we study how to improve the sensing capabilities of the marginal areas by applying the novel swath processing technique of interferometric SAR radar data, which is only available from the SIRAL altimeter onboard the Cryosat-2 satellite. In contrast to traditional Point-of-closest-approach (POCA) processing of radar altimeter data, the swath processing delivers a band of data far from nadir and beyond the POCA point. Despite the swath processing, in comparison with POCA, delivers millions of extra data points (Foresta et al., 2018) the new estimates come with a lower signal-to-noise ratio and the method can be optimized further. Here, we investigate the added value of, under suitable surface conditions, to lower the coherence limit to derive the optimal number of observation points and still keep an acceptable signal-to-noise ratio. This will allow us to get the most out of each Cryosat-2 waveform. The validation is further aided by the inter-comparison to airborne data collected during the ESA CryoVEx campaigns.

 

How to cite: Havelund, N., S. Sørensen, L., and B. Simonsen, S.: Investigation of the added value of a varying coherence threshold for CryoSat-2 swath processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21772, https://doi.org/10.5194/egusphere-egu2020-21772, 2020.

EGU2020-712 | Displays | G3.3

Satellite altimetry for hydraulic model calibration: potential of single and multi-mission series

Giada Molari, Alessio Domeneghetti, Mohammad Tourian, Angelica Tarpanelli, Tommaso Moramarco, and Nicolaas Sneeuw

The recent improvement of satellite products has provided an increasing data availability with an unprecedented coverage, stimulating their usage in hydraulic and hydrological fields. Notwithstanding, regarding the satellite water level monitoring, the limited temporal resolution (i.e. revisit time varying from 10 to 35 days) and decimeter accuracy of  altimetry satellites strongly restrict their applications. Recently proposed multi-mission (MM) densified time series might represent a possible alternative to ensure higher spatial and temporal coverage. However, an assessment of the potential of different altimetry products, including MM series, for hydrodynamic model calibration is still missing. The goal of this study is the assessment of remotely sensed water surface elevations usefulness for the calibration of a hydraulic model implemented for a 140-km stretch of the Po River (Italy). In particular this study presents: i) a comparison of altimetry satellite data collected from different missions (ENVISAT (E), ENVISAT extended (EX), TOPEX/Poseidon (TP), SARAL/AltiKa (SA), Jason-2 (J2) and Jason-3 (J3); ii) insights to the effects of satellite series length on hydraulic model calibration; iii) the analysis of how data uncertainty influences model accuracy; iv) the potential of multi-mission (MM) densified time series as possible alternative to overcome spatial and temporal limitations of single mission. The results highlight a good agreement among satellite and in-situ observations for all the series, excluding EX series. J2 provides the best outcome in terms of calibration error (about 30 cm) and number of measurements required to achieve a reliable calibration (less than 1 year of data). In case of frequent and accurate satellite data (i.e. J2 and TP), the MM series seem unable to provide additional benefits in calibrating the hydraulic model. On the other hand, MM series outperform low frequency products (i.e. E and SA) when the latter are available only for short period. This research offers a wide overview of the potential of altimetry products, providing a general comparison of different satellite missions series and showing the potential, as well as limitations, offered by multi-mission series.

How to cite: Molari, G., Domeneghetti, A., Tourian, M., Tarpanelli, A., Moramarco, T., and Sneeuw, N.: Satellite altimetry for hydraulic model calibration: potential of single and multi-mission series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-712, https://doi.org/10.5194/egusphere-egu2020-712, 2020.

EGU2020-12039 | Displays | G3.3

Evaluation of Sentinel-3A SAR Altimetry Observations over the Taiwan coastal region

Huan Chin Kao, Chung Yen Kuo, Ck Shum, and Yuchan Yi

Pulse-limited radar altimeters have been proven to be an excellent data source in oceanography for monitoring sea surface heights and inland water surface elevations since the 1990s. However, the measurements of conventional altimetry missions in coastal areas present the principal problems related to the inherent limitations of this technique such as wider footprint resulting in contaminated waveforms and relatively unreliable media and geophysical corrections. The European Space Agency (ESA) and the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) joint mission Sentinel-3A, launched in February 2016, is the first altimetry mission to provide 100% global coverage of ocean observations in Synthetic Aperture Radar (SAR) mode. The Sentinel-3A carries a dual-frequency (Ku- and C-band) Synthetic Aperture Radar Altimeter (SRAL) with a new on-board tracking system (open-loop tracking mode) to employ SAR altimetry technologies providing finer along-track spatial resolution up to ~300 m. Compared with the similar mission Cryosat-2, Sentinel-3A has a better ability to observe the global monitoring of ocean dynamics with a shorter repeat cycle of 27 days and less affected by topography in contaminated waveforms from coastal regions due to open-loop tracking mode with a good prior surface elevation estimate on-board. In this study, the SAR altimetry observations of Sentinel-3A over the Taiwan coastal region were reprocessed by a proposed retracking strategy to obtain more accurately retrieved sea level observations. The main objective of this study is to evaluate the performance of Sentinel-3A in coastal observation by using a near-by tide gauge measurements or other altimetry mission like SARAL/Altika and Jason-3.

How to cite: Kao, H. C., Kuo, C. Y., Shum, C., and Yi, Y.: Evaluation of Sentinel-3A SAR Altimetry Observations over the Taiwan coastal region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12039, https://doi.org/10.5194/egusphere-egu2020-12039, 2020.

G3.4 – Coastal Subsidence: Natural versus anthropogenic drivers

EGU2020-9778 | Displays | G3.4 | Highlight

Unravelling and quantifying natural and anthropogenic subsidence drivers in a mega delta

Philip S.J. Minderhoud, Gilles Erkens, Henk Kooi, Claudia Zoccarato, Pietro Teatini, and Esther Stouthamer

Unraveling the contribution of different natural and anthropogenic drivers to total subsidence can be a main challenge when studying changes of land elevation in a coastal-deltaic area. In fact, the contribution of a single driver often varies both in time and space and segmented land subsidence measurements only provide part of the solution. However, it is a crucial step required to facilitate the development of effective mitigation and adaptation strategies for sinking coastal-deltaic areas. This presentation highlights recent and future advances towards unravelling the contribution of different subsidence drivers for one of the largest deltas on the planet, the Mekong delta.

The multidisciplinary approach combined estimates of subsidence rates, both remotely-sensed (PS INSAR) and from field observations, with spatial data analysis and two complementary numerical modelling approaches, which bring together information and expertise from amongst others geology, hydrogeology and geomechanics. This multi-year effort provides insights in several significant natural (i.e. natural compaction) and anthropogenic subsidence (i.e. aquifer systems compaction due to groundwater extraction) processes that play a role in the Mekong delta system. Combining various advances enabled the creation of future elevation projections following groundwater-extraction scenarios, which provides valuable insights for Mekong delta’s policymakers but also shows the dire situation of the low-lying delta. Efforts towards further unraveling and quantification different subsidence drivers in the Mekong delta are ongoing and new Sentinel’s PS INSAR data provide exciting opportunities for detailed quantification of depth-depending sinking rates.

Present results make clear that the effectiveness of mitigation measures to reduce groundwater extraction-induced sinking rates will predominantly determine elevation evolution and thereby faith of the low-lying Mekong delta in the coming decades.

How to cite: Minderhoud, P. S. J., Erkens, G., Kooi, H., Zoccarato, C., Teatini, P., and Stouthamer, E.: Unravelling and quantifying natural and anthropogenic subsidence drivers in a mega delta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9778, https://doi.org/10.5194/egusphere-egu2020-9778, 2020.

City level coastal subsidence can be caused by a number of factors, both natural (e.g. compaction) and anthropogenic (e.g. ground water extraction). Past observations in cities indicates that the rate of subsidence can be altered through policy intervention (e.g. Tokyo's ban on ground water pumping in 1970's). Given vertical land motion is a key component in local sea level projections where subsidence amplifies the onset of future damages, we test the extent to which intervention could reduce risk with a simple city level coastal damage model. We adjust water levels to embed different time dependent subsidence scenarios over the 21st century. We contend that local policy intervention to slow anthropogenic subsidence where possible will slow the onset of damaging sea level rise thus reducing potential coastal damages, and reduce the required increases in future flood protection heights. Performed in tandem with global mitigation efforts, cities currently under major threat may yet survive the climate crisis.

How to cite: Jackson, L.: Using subsidence scenarios to assess flood risk to delta cities under future sea level rise., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19378, https://doi.org/10.5194/egusphere-egu2020-19378, 2020.

EGU2020-12838 | Displays | G3.4

Multi-temporal Spaceborne InSAR technique to compensate Vertical Land Motion in Sea Level Change records: A case study of Tide gauges in Korean Peninsula

Suresh Krishnan Palanisamy Vadivel, Duk-jin Kim, Jungkyo Jung, and Yang-Ki Cho

Relative sea-level changes observed by tide gauges are commonly corrected for several components including crustal displacement, ocean dynamics, and vertical land motion. Vertical Land Motion (VLM) due to local land hydrology is a crucial component that observed as localized ground motion and varies with each tide gauges. Permanent GNSS stations are used to measure the VLM trend at tide gauges, however, only few tide gauges are equipped with collocated GNSS stations. Multi-temporal InSAR analysis provides ground displacements in both the spatial and temporal domains. Therefore, in our study, we applied the spaceborne Interferometric SAR technique to measure the local ground motion using Sentinel-1 SAR data. The Korean peninsula is surrounded by the East Sea/Sea of Japan, the Yellow Sea and the East China Sea have continuously monitoring tide gauges with a record length of more than 30 years. We acquire C-band Sentinel-1 SAR data (both ascending and descending mode) over the Korean Peninsula during 2014/11 and 2019/04. We estimate the high-resolution (~ 10 m) land motion at tide gauges (mm-level accuracy) over these 21 tide gauges and, compared with available collocated GNSS observations. 2D displacements (vertical and horizontal) are derived from ascending and descending mode InSAR displacements. The linear trend of VLM observed from our InSAR estimates is used to compensate for the relative velocity of sea-level changes observed from tide gauges.

How to cite: Palanisamy Vadivel, S. K., Kim, D., Jung, J., and Cho, Y.-K.: Multi-temporal Spaceborne InSAR technique to compensate Vertical Land Motion in Sea Level Change records: A case study of Tide gauges in Korean Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12838, https://doi.org/10.5194/egusphere-egu2020-12838, 2020.

EGU2020-19876 | Displays | G3.4

Importance of Northern Hemisphere Vertical Land Motion for Geodesy and Coastal Sea Levels

Carsten Ankjær Ludwigsen, Ole Baltazar Andersen, Shfaqat Abbas Khan, and Ben Marzeion

Vertical Land Motion (VLM) is a composite of several earth dynamics caused by changes of earth’s surface load or tectonics. In most of the Northern Hemisphere mainly two dynamics are causing large scale vertical land motion – Glacial Isostatic Adjustment (GIA), which is the rebound from the loading of the latest glacial cycle (10-30 kyr ago) and elastic rebound from contemporary land ice changes, that happens immediately when loading is removed from the surface.

With glacial mass balance data and observations of the Greenland Ice Sheet we have created an Northern Hemisphere ice history from 1996-2015 that is used to make a model for elastic VLM caused by ice mass loss that varies in time.

It shows that, in most cases, the elastic VLM model is able to close gaps between GIA induced VLM and GNSS-measured VLM, giving confidence that the combined GIA + elastic VLM-model is a better alternative to adjust relative sea level measurements from tide-gauges (where no (reliable) GNSS-data is available) to absolute sea level than 'just' a GIA-model. In particular for Arctic Sea Level, where elastic uplifts are prominent and large coastal regions have limited in-situ data available, the VLM-model is useful for correcting Tide Gauge measurements and thereby validate satellite altimetry observed sea levels, which is challenged by sea ice in the coastal Arctic.

Furthermore, our elastic VLM-model shows, that the uplift caused by the melt of the Greenland Ice Sheet (GIS) is far-reaching and even in the North Sea region or along the North American coast show uplift rates in the order of 0.4-0.7 mm/yr from 1996-2015. Interestingly, this is roughly equivalent to Greenland’s sea level contribution in the same period, thereby 'neutralizing' the melt of GIS. As GIS ice mass loss continues to accelerate, the elastic uplift will have increased importance for coastal regions and future relative sea level projections. Unfortunately, the opposite effect is true for the southern hemisphere or vice versa if Antarctic ice sheet mass loss would increase.

How to cite: Ludwigsen, C. A., Andersen, O. B., Khan, S. A., and Marzeion, B.: Importance of Northern Hemisphere Vertical Land Motion for Geodesy and Coastal Sea Levels, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19876, https://doi.org/10.5194/egusphere-egu2020-19876, 2020.

EGU2020-20314 | Displays | G3.4 | Highlight

Investigating land subsidence of transitional environments

Claudia Zoccarato and Eugenia Parrella

Lagoons and deltas are characterized by the presence of transitional environments, such as low-lying plains or islands, salt marshes, and tidal flats with fundamental value in terms of biodiversity, recreational activities, and protection of inland territories from storms. The fate of these morphological landforms is severely threatened by the ongoing rise of the mean sea level (SLR) and land subsidence (LS). The loss of elevation relative to mean sea level, i.e. SLR plus LS, must be counterbalanced by accretion of inorganic sediments and biodegradation of organic matter. A large contribution to LS of transitional landforms is due to auto-compaction of the Holocene sediments. In fact, the large porosity and compressibility of these recent deposits, especially when the organic fraction is high, are responsible for a significant thickness reduction because of consolidation when new deposition occurs on the surface. SAR interferometry on deep-founded and surface radar scatterers, ground-based monitoring equipment (deep levelling benchmarks, SET, accretion traps), and a novel in-situ loading test have been used in the Venice Lagoon to distinguish between deep and shallow LS contributions, i.e. LS occurring below and above the Pleistocene / Holocene bound. After a review of the available dataset, the present contribution describes the modelling activities that are ongoing to understand the collected measurements. In particular, an advance coupled mixed finite-element poromechanical model is used to reproduce the loading test carried out on the Lazzaretto Nuovo marshland on summer 2019. With the aim of reliably characterize the geomechanical properties of the Holocene sediments of the tidal-marsh, a number of plastic tanks were filled with seawater, reaching a cumulative load of 40 kN applied on a 2.5´1.8 m2 surface. Specific instrumentations were deployed before positioning the tanks to measure soil vertical displacement and pore overpressure at various depths below the load and distances from the load center. The numerical model uses linear piecewise polynomials and the lowest order Raviart–Thomas mixed space to represent the three-dimensional porous medium motion and the groundwater flow rate, respectively. The model is applied to the various loading and unloading phases that superpose to the tidal fluctuation of the lagoon level recorded over the 4-day test duration. The geomechanical properties thus derived constitute a significant advancement to understand the LS drivers in transitional environments and predict their resilience to SLR.    

How to cite: Zoccarato, C. and Parrella, E.: Investigating land subsidence of transitional environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20314, https://doi.org/10.5194/egusphere-egu2020-20314, 2020.

 Transparent soils are developed as a physical modelling of macroscopic soil behaviors in geotechnical engineering aspect. Transparent surrogates with its index-matching fluid, called as transparent porous media or transparent soils, have been used for simulating geotechnical properties of natural soils. Visualization technique itself have been applied to microscopic level of soil deformation and soil flow problems such as X-ray, Computerized Tomography (CT), and Magnetic Resonance Imaging (MRI) cameras by very expensive apparatuses with highly operating skills. Geotechnical researches need rather understanding of macroscopic scale of larger test models with inexpensive experimental industrial substances. Transparent soils have been developed to achieve these needs with easy handling performance. 
 The authors demonstrated a pumping test in a glass tank of 30mm width by 80mm length by 70mm height filled with transparent hydrated superabsorbent polymer to represent aquitard (clay layer) over aquifer (saturated silica sand). The subsidence within the synthetic clay layer due to pumping of pore water from silica sand was constantly monitored by target racking method using four 8mm-diameter particles immersed in the synthetic clay layer. The test successfully visualized deformation due to vertical propagation of pore water pressure during subsidence event within the transparent synthetic clay layer. It was also found that this experiment result and the results from three-dimensional numerical simulation of poroelastic deformation were consistent with each other.

How to cite: Tabe, K. and Aichi, M.: Experimental technique for visualization of aquitard compaction over aquifer caused by excess pumping, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3265, https://doi.org/10.5194/egusphere-egu2020-3265, 2020.

EGU2020-3279 | Displays | G3.4

Integration of geodetic observations and geological models for investigating the permanent component of land subsidence in the Po Delta (northern Italy)

Eleonora Vitagliano, Rosa Di Maio, Chiara D'Ambrogi, Domenico Calcaterra, Simone Fiaschi, and Mario Floris

Defining land subsidence causes is not an easy task, because ground lowering is a complex phenomenon due to the contribution of different physical processes related to natural contest and to anthropic actions. Indeed, such processes, which are characterized by a specific origin and may act in different spatial and temporal intervals, can overlap giving rise to a single surface land deformation, observable through conventional and innovative monitoring techniques (i.e. high-precision levelling, InSAR and GNSS). Of course, discriminating the individual causes is fundamental for reducing environmental and social harms, especially in deltas and coastal areas, where land sinking, coupled with climatic effects, can induce massive flooding. The present work concerns an application of a multi-component and multi-source approach, recently proposed by some of the authors for studying land subsidence in deltas. Such a methodology is aimed at understanding the processes causing both periodic and permanent components of the vertical land movement and at retrieving more accurate subsidence rates. It consists of three steps, respectively involving: a component recognition phase, based on statistical and spectral analyses of geodetic time series; a source (or physical process) selection phase, based on the comparison with data of different nature; a source validation step, where the selected sources are validated through physically-based models. The proposed procedure has been applied to the permanent component of subsidence in the Po Delta (northern Italy), an area historically affected by land subsidence and influenced by climatic changes, where continuous GNSS data and differential InSAR-derived time series were simultaneously acquired from 2012 to 2017. In particular, the exponential relation found between the mean SAR-derived LOS velocity and the thickness of the Late Holocene prograding deposits, pointed out the key role of the sedimentary compaction process with respect to the spatial distribution of the subsidence rates and confirmed the importance, already highlighted by other authors, of the consolidation of the shallower strata. In order to validate the consolidation process and to quantify also the deeper contributions of tectonics- and isostasy-depending mechanisms, 2D geological models have been constructed along two west-east sections across the central part of the Delta. Finally, the computed subsidence rates have been compared with the geodetic velocities estimated in Taglio di Po and Porto Tolle villages (Rovigo, northern Italy), clarifying the contribution of each geological mechanism to the observed delta subsidence.

How to cite: Vitagliano, E., Di Maio, R., D'Ambrogi, C., Calcaterra, D., Fiaschi, S., and Floris, M.: Integration of geodetic observations and geological models for investigating the permanent component of land subsidence in the Po Delta (northern Italy) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3279, https://doi.org/10.5194/egusphere-egu2020-3279, 2020.

EGU2020-4509 | Displays | G3.4

Millennial scale land subsidence history along the southern China coast

Haixian Xiong and Yongqiang Zong

Estimation of coastal land subsidence rates due to GIA and tectonic factors on millennial scale has become an urgent task for the hazard assessment of future rising sea level. Whilst geophysical simulation is a promising approach, the modeling uncertainty is still difficult to constrain due to the lack of accurate sea-level data. Another practical approach is based on the present elevations of paleo indicative landforms of known ages, such as coastal terraces and MIS5e marine sediments. However, this method also suffers from uncertainties associated with the measurements of landform relicts. In order to obtain a robust estimation of long-term coastal subsidence rates along the southern China coast, an active economic zone vulnerable to future sea-level rise, this study applies a statistical method to determining the high-probability land subsidence histories of six coastal sectors (the Yangtze Delta, Fujian & Taiwan Strait, Han River Delta, East Guangdong, Pearl River Delta, and West Guangdong & Hainan Island) over the past six millennia. The land subsidence histories of the six sites are produced by comparing their RSL histories reconstructed from qualified sea-level index points (SLIPs) with those of the Malay Peninsula, based on the assumption that the Malay Peninsula has been tectonically stable. Therefore, the RSL history at each site is considered as a function of eustatic sea-level change, global GIA (e.g. ocean siphoning), local GIA (e.g. coastal levering) and tectonic movement. Therefore, a subtraction of RSL histories between the China sites and the Malay Peninsula will result in land vertical movement trends consisting of both the local GIA and tectonic components. The result shows that the coast of southern China has been undergoing linear land subsidence over the past 6000 years. The subsidence rates of the six sites average at about 1.2±0.1 mm/yr, with the highest rate of 2.1±0.1 mm/yr in the Han River Delta and the lowest rate of 0.5±0.1 mm/yr in West Guangdong & Hainan Island. In order to separate the tectonic subsidence rate from the local GIA rate for each site, outputs of GIA models (a 3D Earth model HetM-LHL140 coupled with ICE-6G_C) for China and the Malay Peninsula were obtained. The result suggests that the local GIA component (mainly coastal levering) might have accounted for half of the land subsidence along the China coast over the past 6000 years. This estimation of long-term land subsidence rates should form an integral part of the hazard assessment for the coastal communities in China.

How to cite: Xiong, H. and Zong, Y.: Millennial scale land subsidence history along the southern China coast, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4509, https://doi.org/10.5194/egusphere-egu2020-4509, 2020.

EGU2020-18912 | Displays | G3.4

Recent Subsidence Rates in the Mekong Delta derived from Sentinel-1 SAR-Interferometry

Nils Dörr, Andreas Schenk, Kim de Wit, Bente R. Lexmond, Philip S.J. Minderhoud, Olaf Neussner, Diem K. Nguyen, and T. Loi Nguyen

Coastal subsidence increases the vulnerability to flooding risk, salinization of water resources and permanent inundation. For the Mekong Delta, whose mean elevation is less than 2 m above sea level, subsidence rates of up to several centimeters per year have been reported recently. This leads to a growing risk for the resident population, infrastructure and economy, increased by the accelerating sea level rise. Land subsidence in Mekong Delta has different causes, most prominently natural compaction of young deltaic sediments, but also overexploitation of groundwater aquifers with accompanying head decline. Precise monitoring of the subsidence rate is necessary for analyses of cause and hazard as well as planning and assessment of countermeasures. Here, we present and discuss recent land subsidence rates in the Mekong Delta derived from satellite-based SAR-Interferometry.

We use Sentinel-1 scenes acquired between 2015 and 2019 to analyze recent land subsidence in the lower Mekong Delta. The Persistent Scatterer Interferometry technique (PS-InSAR) is applied, which allows for the estimation of displacement rates of coherent backscatter targets with mm-accuracy. Separate analyses of time series from ascending and descending observations and comparison with other studies based on data of the same sensor give insight into the accuracy of the parameter estimation and the error budget.

The observed subsidence rates of up to 6 cm/yr feature mainly three different spatial characteristics: (i) interconnected areas of little to no subsidence, (ii) isolated urban hot-spots with high subsidence rates and (iii) larger regions with increased subsidence rates covering urban as well as rural areas. Points on deeply founded infrastructure frequently exhibit lower subsidence rates than adjacent ground surface points. We study this phenomenon at different buildings since subsidence rates with respect to different foundation depths can be used as a proxy to constrain the effective depths of sediment compaction. Further, the correlation of observed subsidence rates and spatial distribution of lithostratigraphic units from quaternary sedimentary depositions is investigated. Finally, we show changes and commons in the spatial distribution of the subsidence rates compared to a previously published study on subsidence in the Mekong Delta covering data from 2006 to 2010.

How to cite: Dörr, N., Schenk, A., de Wit, K., Lexmond, B. R., Minderhoud, P. S. J., Neussner, O., Nguyen, D. K., and Nguyen, T. L.: Recent Subsidence Rates in the Mekong Delta derived from Sentinel-1 SAR-Interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18912, https://doi.org/10.5194/egusphere-egu2020-18912, 2020.

Land subsidence caused by seasonal fluctuation of groundwater level caused by agricultural groundwater use was numerically simulated in this study. In the study area, Kawajima, Saitama prefecture, Japan, the hydraulic head has been gradually increasing over time with seasonal fluctuations and the subsurface formations have repeated expansion and compaction. However, the land subsidence progressed because the compaction included the plastic deformation. In this study, vertically one-dimensional model to numerically simulate coupled groundwater flow and soil deformation in Kawajima was developed with modified cam-clay model. Because of the lack of subsurface information, it was difficult to set the physical properties such that the simulated subsidence and the observed subsidence are satisfactorily close to each other. This study applied a genetic algorithm in order to search the set of underground physical properties. The improved set of underground physical properties succeeded to reproduce the observed land subsidence in Kawajima.

How to cite: Akitaya, K. and Aichi, M.: One dimensional numerical modeling of land subsidence caused by seasonal groundwater level fluctuations in Kawajima, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6592, https://doi.org/10.5194/egusphere-egu2020-6592, 2020.

Predicting the future land subsidence caused by groundwater abstraction is necessary for the planning and decision-making of groundwater usage in coastal area. Although numerical modeling is expected to quantitatively predict land subsidence, a single calibrated model cannot provide a reliable prediction because of the uncertainty on properties and conditions in the subsurface. In addition, applying ensemble Kalman filter or ensemble smoother to land subsidence modeling is not straightforward because of the highly nonlinear and hysteric characteristics in clay compaction process.

This study developed a smoother algorithm with a multiple calibration-constrained null-space Monte Carlo method for a numerical simulator of groundwater mass balance with modified Cam-clay model. The developed algorithm calibrates a model ensemble using a newly obtained observed value in each observation step. Based on the calibration-constrained null-space Monte Carlo method, a new model ensemble in the null-space is produced in each observation step. In this step, both the current and past state as well as parameters in the model are updated like ensemble smoother in order to follow the hysteretic behavior in the soil compaction. The produced ensemble can be used not only for prediction uncertainty analysis at that step but also as initial estimates of a multiple calibration-constrained null-space Monte Carlo method in the next observation step.

The proposed method was applied to the land subsidence modeling in the Tokyo lowland area, Japan. The proposed method could make model ensemble with satisfactory good reproducibility and show the range of uncertainty of future prediction for several scenarios of future groundwater level change.

How to cite: Aichi, M.: Land subsidence prediction with uncertainty analysis by a smoother algorithm with a multiple calibration-constrained null-space Monte Carlo method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16906, https://doi.org/10.5194/egusphere-egu2020-16906, 2020.

EGU2020-21525 | Displays | G3.4

A critical examination of the flooding and its impact on the Munro Island in Southwest India

Sheela Nair L, Swathy Krishna P. S., Prasad Ravindran, and Tiju I Varghese

Munro Thuruth (Island) is an island group comprising of 8 medium size and a few tiny islands located in the backwaters of the famous Ashtamudi lake in Kerala, South India. The Munro Island with an area of 13.4 sq.km is situated at the confluence of the Ashtamudi Lake and the Kallada river (9oN Latitude and 76o 37’ E Longitude). It is an artificial island built during the 18th Century by reclamation of the Kallada river delta on the downstream side, where it debouches into the Arabian Sea. The individual islands of the Munro group, with an elevation of 3.3m (approx.) above MSL, remained more or less stable till 1965. However, during the last two decades media reports on sinking/subsidence of the individual islands have drawn attention of scientists, politicians, administrators as well as the government.  As per the reports, the subsidence or rise in surrounding water level has been rather alarming and this is quite evident from the perennial inundation observed at certain critical low-lying areas in the island. Speculations on the causative factors responsible for the permanent/alarming rates of inundation witnessed in the island are linked to both local and global changes in the environmental conditions. According to one school of thought it is land subsidence due to tectonic activity combined with sea level rise due to global warming that has contributed to the sinking of the Munroe Island.  But there is another group that advocates that the flooding/inundation reached the critical level after the 26 December, 2004 Tsunami which struck the Kerala coast.  In this study, the various causative factors and their respective roles in the rise in water level/ subsidence reported at various locations is being critically reviewed and the salient conclusions that emanated from the analysis are presented. The analysis reveals that the flooding in the Munro Island can be attributed to a multitude of factors like rise in sea level linked to climate change, wave setup and wind setup which act individually or in combination under favourable conditions;  changes in morphology (post Tsunami) of the Ashtamudi estuary and changes in the inlet geometry over a period of time; land subsidence due to primary and secondary (creep) consolidation as well as the impact of ground vibration due to the movement of high speed trains ; groundwater drawdown due to excessive water extraction and reduction in fresh water flow from the Kallada river; sand mining from the river and reduced sediment inflow to the system because of the Kallada dam construction. The importance of carrying out numerical model studies to understand the tidal dynamics as well as the combined effect of tides, wind and waves on the water surrounding the islands which are located at varying distances of 8-10km from the Ashtamudi tidal inlet is also emphasized.

How to cite: Nair L, S., Krishna P. S., S., Ravindran, P., and I Varghese, T.: A critical examination of the flooding and its impact on the Munro Island in Southwest India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21525, https://doi.org/10.5194/egusphere-egu2020-21525, 2020.

G3.5 – Linking the Solid Earth and Glacial Isostatic Adjustment

EGU2020-7699 | Displays | G3.5

Dependence of late glacial sea-level predictions on 3D Earth structure

Meike Bagge, Volker Klemann, Bernhard Steinberger, Milena Latinovic, and Maik Thomas

Glacial isostatic adjustment is dominated by Earth rheology resulting in a variability of relative sea-level (RSL) predictions of more than 100 meters during the last glacial cycle. Seismic tomography models reveal significant lateral variations in seismic wavespeed, most likely corresponding to variations in temperature and hence viscosity. Therefore, the replacement of 1D Earth structures by a 3D Earth structure is an essential part of recent research to reveal the impact of lateral viscosity contrasts and to achieve a more consistent view on solid-Earth dynamics. Here, we apply the VIscoelastic Lithosphere and MAntle model VILMA to predict RSL during the last deglaciation. We create an ensemble of geodynamically constrained 3D Earth structures which is based on seismic tomography models while considering a range of conversion factors to transfer seismic velocity variations into viscosity variations. For a number of globally distributed sites, we discuss the resulting variability in RSL predictions, compare this with regionally optimized 1D Earth structures, and validate the model results with relative sea-level data (sea-level indicators). This study is part of the German Climate Modeling initiative PalMod aiming the modeling of the last glacial cycle under consideration of a coupled Earth system model, i.e. including feedbacks between ice-sheets and the solid Earth.

How to cite: Bagge, M., Klemann, V., Steinberger, B., Latinovic, M., and Thomas, M.: Dependence of late glacial sea-level predictions on 3D Earth structure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7699, https://doi.org/10.5194/egusphere-egu2020-7699, 2020.

EGU2020-2685 | Displays | G3.5

Unraveling the upper mantle heterogeneity from integrated multi-observable inversions

Javier Fullea, Sergei Lebedev, Zdenek Martinec, and Nicolas Celli

The lateral and vertical thermochemical heterogeneity in the mantle is a long standing question in geodynamics. The forces that control mantle flow and therefore Plate Tectonics arise from the density and viscosity lateral and vertical variations. A common approach to estimate the density field for geodynamical purposes is to simply convert seismic tomography anomalies sometimes assuming constraints from mineral physics. Such converted density field does not match in general with the observed gravity field, typically predicting anomalies the amplitudes of which are too large. Knowledge on the lateral variations in lithospheric density is essential to understand the dynamic/residual isostatic components of the Earth’s topography linking deep and surface processes. The cooling of oceanic lithosphere, the bathymetry of mid oceanic ridges, the buoyancy and stability of continental cratons or the thermochemical structure of mantle plumes are all features central to Plate Tectonics that are dramatically related to mantle temperature and composition.


Conventional methods of seismic tomography, topography and gravity data analysis constrain distributions of seismic velocity and density at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. In fact, global Earth models based on different observables often lead to rather different, even contradictory images of the Earth.


 Here we present a new global thermochemical model of the lithosphere-upper mantle (WINTERC-grav) constrained by state-of-the-art global waveform tomography, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data. WINTERC-grav is based upon an integrated geophysical-petrological approach where all relevant rock physical properties modelled (seismic velocities and density) are computed within a thermodynamically self-consistent framework allowing for a direct parameterization of the temperature and composition variables.

How to cite: Fullea, J., Lebedev, S., Martinec, Z., and Celli, N.: Unraveling the upper mantle heterogeneity from integrated multi-observable inversions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2685, https://doi.org/10.5194/egusphere-egu2020-2685, 2020.

EGU2020-5189 | Displays | G3.5

Glacial Isostatic Adjustment with 3D Earth models: A comparison of case studies of deglacial relative sea level records of North America and Russian Arctic

Tanghua Li, Nicole Khan, Simon Engelhart, Alisa Baranskaya, Peltier William, Patrick Wu, and Benjamin Horton

The Canadian landmass of North America and the Russian Arctic were covered by large ice sheets during the Last Glacial Maximum, and have been key areas for Glacial Isostatic Adjustment (GIA) studies. Previous GIA studies have applied 1D models of Earth’s interior viscoelastic structure; however, seismic tomography, field geology and recent studies reveal the potential importance of 3D models of this structure. Here, using the latest quality-controlled deglacial sea-level databases from North America and the Russian Arctic, we investigate the effects of 3D structure on GIA predictions. We explore scaling factors in the upper mantle (βUM) and lower mantle (βLM) and the 1D background viscosity model (ηo) with predictions of of the ICE-6G_C (VM5a) glaciation/deglaciation model of Peltier et al (2015, JGR) in these two regions, and compare with the best fit 3D viscosity structures.

We compute gravitationally self-consistent relative sea-level histories with time dependent coastlines and rotational feedback using both the Normal Mode Method and Coupled Laplace-Finite Element Method. A subset of 3D GIA models is found that can fit the deglacial sea-level databases for both regions. These databases cover both the near and intermediate field regions. However, North America and Russian Arctic prefer different 3D structures (i.e., combinations of (ηo, βUM, βLM)) to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (ηo), but larger scaling factors (βUM, βLM) than those preferred by the North America database.

Outstanding issues include the uncertainty of the history of local glaciation history. For example, preliminary modifications of the ice model in Russian Arctic reveal that the misfits of 1D models can be significantly reduced, but still fit less well than the best fit 3D GIA model.An additional issue concerns the extent to which the 3D models are able to improve both fits in North America and Russian Arctic when compared with 1D internal structure (ICE-6G_C VM5a & ICE-7G VM7), will be assessed in a preliminary fashion.

How to cite: Li, T., Khan, N., Engelhart, S., Baranskaya, A., William, P., Wu, P., and Horton, B.: Glacial Isostatic Adjustment with 3D Earth models: A comparison of case studies of deglacial relative sea level records of North America and Russian Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5189, https://doi.org/10.5194/egusphere-egu2020-5189, 2020.

EGU2020-6964 | Displays | G3.5

Constraining dynamic models in North America using the static gravity field

Jesse Reusen, Bart Root, Javier Fullea, Zdenek Martinec, and Wouter van der Wal

The negative anomaly present in the static gravity field near Hudson Bay bears striking resemblance to the area depressed by the Laurentide ice sheet during the Last Glacial Maximum, suggesting that it is at least partly due to Glacial Isostatic Adjustment (GIA), but mantle convection and density anomalies in the crust and the upper mantle are also expected to contribute. At the moment, the contribution of GIA to this anomaly is still disputed. Estimates, which strongly depend on the viscosity of the mantle, range from 25 percent to more than 80 percent. Our objective is to find the contributions from GIA and mantle convection, after correcting for density anomalies in the topography, crust and upper mantle. The static gravity field has the potential to constrain the viscosity profile which is the most uncertain parameter in GIA and mantle convection models. A spectral method is used to transform 3D spherical density models of the crust into gravity anomalies. Density anomalies in the lithosphere are estimated so that isostatic compensation is reached at a depth of 300 km. The dynamic processes of mantle flow are corrected for before isostasy is assumed. Upper and lower mantle viscosities are varied so that the gravity anomaly predicted from the dynamic models matches the residual gravity anomaly. We consider uncertainties due to the crustal model, the lithosphere-asthenosphere boundary (LAB), the conversion from seismic velocities to density and the ice history used in the GIA model. The best fit is found for lower mantle viscosities >1022 Pa s.

How to cite: Reusen, J., Root, B., Fullea, J., Martinec, Z., and van der Wal, W.: Constraining dynamic models in North America using the static gravity field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6964, https://doi.org/10.5194/egusphere-egu2020-6964, 2020.

EGU2020-12280 | Displays | G3.5

Upper mantle viscosity structure and lithospheric thickness of Antarctica inferred from recent seismic models

Douglas Wiens, Andrew Lloyd, Weisen Shen, Andrew Nyblade, Richard Aster, and Terry Wilson

Upper mantle viscosity structure and lithospheric thickness control the solid Earth response to variations in ice sheet loading. These parameters vary significantly across Antarctica, leading to strong regional differences in the timescale of glacial isostatic adjustment (GIA), with important implications for ice sheet models.  We estimate upper mantle viscosity structure and lithospheric thickness using two new seismic models for Antarctica, which take advantage of temporary broadband seismic stations deployed across Antarctica over the past 18 years. Shen et al. [2018] use receiver functions and Rayleigh wave velocities from earthquakes and ambient noise to develop a higher resolution model for the upper 200 km beneath Central and West Antarctica, where most of the seismic stations have been deployed. Lloyd et al [2019] use full waveform adjoint tomography to invert three-component earthquake seismograms for a radially anisotropic model covering Antarctica and adjacent oceanic regions to 800 km depth. We estimate the mantle viscosity structure from seismic structure using laboratory-derived relationships between seismic velocity, temperature, and rheology. Choice of parameters for this mapping is guided in part by recent regional estimates of mantle viscosity from geodetic measurements. We also describe and compare several different methods of estimating lithospheric thickness from seismic constraints.

The mantle viscosity estimates indicate regional variations of several orders of magnitude, with extremely low viscosity (< 1019 Pa s) beneath the Amundsen Sea Embayment (ASE) and the Antarctic Peninsula, consistent with estimates from GIA models constrained by GPS data.  Lithospheric thickness is also highly variable, ranging from around 60 km in parts of West Antarctica to greater than 200 km beneath central East Antarctica. In East Antarctica, several prominent regions such as Dronning Maude Land and the Lambert Graben show much thinner lithosphere, consistent with Phanerozoic tectonic activity and lithospheric disruption. Thin lithosphere and low viscosity between the ASE and the Antarctic Peninsula likely result from the thermal effects of the slab window as the Phoenix-Antarctic plate boundary migrated northward during the Cenozoic. Low viscosity regions beneath the ASE and Marie Byrd Land coast connect to an offshore anomaly at depths of ~ 250 km, suggesting larger-scale thermal and geodynamic processes that may be linked to the initial Cretaceous rifting of New Zealand and Antarctica. Low mantle viscosity results in a characteristic GIA time scale on the order of several hundred years, such that isostatic adjustment occurs on the same time scale as grounding line retreat.  Thus the associated rebound may lessen the effect of the marine ice sheet instability proposed for the ASE region. 

How to cite: Wiens, D., Lloyd, A., Shen, W., Nyblade, A., Aster, R., and Wilson, T.: Upper mantle viscosity structure and lithospheric thickness of Antarctica inferred from recent seismic models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12280, https://doi.org/10.5194/egusphere-egu2020-12280, 2020.

EGU2020-7035 | Displays | G3.5

Antarctica crustal model by means of the Bayesian gravity inversion

Martina Capponi and Daniele Sampietro

The Antarctica crustal structure is still not completely unveiled due to the presence of thick ice shields all over the continent which prevent direct in situ measurements. In the last decades, various geophysical methods have been used to retrieve information of the upper crust and sediments distribution however there are still regions, especially in central Antarctica, where our knowledge is limited. For these kind of situations, in which the indirect investigation of the subsurface is the only valuable solution, the gravity data are an important source of information. After the recent dedicated satellite missions, like GRACE and GOCE, it has been possible to obtain global gravity field data with spatial resolution and accuracy almost comparable to those of local/regional gravity acquisitions, paving the way to new geophysical applications. The new challenge today is the capability to invert such gravity data on large areas with the aim to obtain a 3D density model of the Earth crust. This is in fact a problem characterized by intrinsic instability and non-uniqueness of the solution that to be solved requires the definition of strong constrains and numerical regularization.

In this work the authors propose the application of a Bayesian inversion algorithm to the Antarctica continent to infer a model of mass density distribution. The first operation is the definition of an initial geological model in terms of geological horizons and density. These two variables are considered as random variables and, within the iterative procedure based on Markov Chain Monte Carlo methods, they are adjusted in such a way to fit the gravity field on the surface. The test performed show that the method is capable of retrieving an estimated model consistent with the prior information and fitting the gravity observations according to their accuracy.

How to cite: Capponi, M. and Sampietro, D.: Antarctica crustal model by means of the Bayesian gravity inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7035, https://doi.org/10.5194/egusphere-egu2020-7035, 2020.

EGU2020-1808 | Displays | G3.5

Tidal Forcing as a Trigger of Arctic Ice Stream Deglaciation

Jesse Velay-Vitow and Richard Peltier

It has been established recently (Velay-Vitow, Peltier and Stuhne JGR-Oceans 2019) that a high amplitude M2 tide may have triggered and contributed to the forcing of the rapid deglaciations of the Hudson Strait ice stream, commonly referred to as Heinrich events, during the last glacial period. The required conditions for a tidally triggered marine terminating ice stream instability are an ice stream with a retrograde slope of the ice stream bed at the edge of an ice sheet and high amplitude tides coincidental with the grounding line. Two paleo ice streams in the Arctic, the Amundsen Gulf ice stream and the McClure ice stream may have been amenable to rapid deglaciation prior to and during Younger Dryas time, as these locations may have been characterized by the required bathymetric conditions. Additionally, it has been shown in Griffiths and Peltier (GRL 2008) that the Arctic was megatidal at last glacial maximum. We investigate the possibility that some combination of the previously mentioned ice streams were rendered unstable by high amplitude polar tides, and proceeded to rapidly deglaciate, disgorging icebergs and ice rafted debris into the Arctic ocean. We further examine the effect that these proposed ice stream instabilities would have had on the tidal regime in the Arctic, and, by the mechanism of glacial isostatic adjustment, upon the underlying Arctic bathymetry.

How to cite: Velay-Vitow, J. and Peltier, R.: Tidal Forcing as a Trigger of Arctic Ice Stream Deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1808, https://doi.org/10.5194/egusphere-egu2020-1808, 2020.

The pseudo-spectral form of the sea level equation (SLE) requires the approximation of a radially-symmetric visco-elastic Earth. Thus, the resulting predictions of sea level change (SLC) and glacial isostatic adjustment (GIA) often ignore lateral variations in the Earth structure. Here, we assess the capabilities of a Multiple 1D Earth Approach (M1DEA) applied to large-scale ice load components with different Earth structures to account for these variations. In this approach the total SLC and GIA responses result from the superposition of individual responses from each load component, each computed globally assuming locally-appropriate 1D Earth structures. We apply the M1DEA to three separate regions (East Antarctica, West Antarctica, and outside Antarctica) to analyze uplift rates for a range of Earth structures and different ice loads at various distances. We find that the uplift response is mostly sensitive to the local Earth structure, which supports the usefulness of the M1DEA. However, stresses transmitted across rheological boundaries (e.g., producing peripheral bulges) present challenges for the M1DEA, but can be minimized under two conditions: (1) If the considered time period of ice loading for each component is consistent with the relaxation time of the local Earth structure. (2) If the load components can be subdivided according to the scale of the lateral variations in Earth structure. Overall, our results indicate that M1DEA could be a computationally much cheaper alternative to 3D finite element models, but further work is needed to quantify the relative accuracy of both methods for different resolutions, loads, and Earth structure variations.

How to cite: Hartmann, R., Ebbing, J., and Conrad, C. P.: A Multiple 1D Earth Approach (M1DEA) to account for lateral viscosity variations in solutions of the sea level equation: An application for glacial isostatic adjustment by Antarctic deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10466, https://doi.org/10.5194/egusphere-egu2020-10466, 2020.

EGU2020-8542 | Displays | G3.5

Modelling Antarctica’s lithospheric structure and testing the West Antarctic mantle plume hypothesis

Folker Pappa, Eva Bredow, Jörg Ebbing, and Fausto Ferraccioli

Numerous unresolved issues exist regarding the lithosphere of Antarctica, especially in terms of its fundamental density, temperature, and compositional structure. Estimates of total lithospheric thickness typically involve assumptions on the depth of the Moho discontinuity, which remains ill-constrained in several parts of Antarctica. Recent estimates of the Moho depth from different geophysical methods show significant discrepancies of 10-20 km in large sectors of the continent. While seismological methods suffer from a limited station coverage and ice reverberation, potential field methods, such as gravity studies, are inherently non-unique. By modelling multiple geophysical parameters in a consistent way and accounting for thermodynamically stable mineral phases of rocks as a function of pressure and temperature conditions, we were able to mitigate the detrimental effects of data sparseness while also reducing geophysical inconsistencies and ambiguities. Gravity gradient data from ESA’s satellite mission ‘GOCE’ are used here to constrain the density distribution within the lithosphere in an integrated 3D model of the Antarctic continent. Independent seismic estimates serve as a benchmark for the robustness of our results. Our model derives new estimates of the crustal and the total lithospheric thickness of Antarctica.
Based on our new 3D lithospheric model, we investigate the feasibility of a mantle plume beneath parts of West Antarctica, which has been inferred from previous geochemistry, seismology, and glacial isostatic adjustment studies. The impact of thermal anomalies, simulating ponded plume material, on different geophysical parameters, such as geothermal heat flux, seismic velocities, mineral phase transition changes, gravity, and topographic elevation are modelled for both Marie Byrd Land and Ross Island, two key candidate sites for putative plumes. Combined interpretation of the results is performed together with current understanding of geodynamic processes, such as locations of the LLVPs at the core-mantle boundary, representing potential ‘cradles’ for plumes.
Our results suggest that a deep-rooted mantle plume is unlikely beneath West Antarctica. However, the observed low seismic velocity zones could still correspond to proposed hot upper mantle zones characterised by lower viscosity. Alternative/additional explanations, such compositional effects and water content as causes for the seismic anomalies must also be further evaluated to better assess their effects on mantle viscosities. This is particularly important beneath regions of recent ice mass loss and recently observed remarkably high rates of GIA-induced bedrock uplift, such as the Amundsen Sea Embayment.

How to cite: Pappa, F., Bredow, E., Ebbing, J., and Ferraccioli, F.: Modelling Antarctica’s lithospheric structure and testing the West Antarctic mantle plume hypothesis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8542, https://doi.org/10.5194/egusphere-egu2020-8542, 2020.

EGU2020-7014 | Displays | G3.5

New Heat Flux Model for Antarctica with a Machine Learning Approach

Mareen Lösing, Jörg Ebbing, and Wolfgang Szwillus

Improving the understanding of geothermal heat flux in Antarctica is crucial for ice-sheet modelling and glacial isostatic adjustment. It affects the ice rheology and can lead to basal melting, thereby promoting ice flow. Direct measurements are sparse and models inferred from e.g. magnetic or seismological data differ immensely. By Bayesian inversion, we evaluated the uncertainties of some of these models and studied the interdependencies of the thermal parameters. In contrast to previous studies, our method allows the parameters to vary laterally, which leads to a heterogeneous West- and a slightly more homogeneous East Antarctica with overall lower surface heat flux. The Curie isotherm depth and radiogenic heat production have the strongest impact on our results but both parameters have a high uncertainty.

To overcome such shortcomings, we adopt a machine learning approach, more specifically a Gradient Boosted Regression Tree model, in order to find an optimal predictor for locations with sparse measurements. However, this approach largely relies on global data sets, which are notoriously unreliable in Antarctica. Therefore, validity and quality of the data sets is reviewed and discussed. Using regional and more detailed data sets of Antarctica’s Gondwana neighbors might improve the predictions due to their similar tectonic history. The performance of the machine learning algorithm can then be examined by comparing the predictions to the existing measurements. From our study, we expect to get new insights in the geothermal structure of Antarctica, which will help with future studies on the coupling of Solid Earth and Cryosphere.

How to cite: Lösing, M., Ebbing, J., and Szwillus, W.: New Heat Flux Model for Antarctica with a Machine Learning Approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7014, https://doi.org/10.5194/egusphere-egu2020-7014, 2020.

EGU2020-10664 | Displays | G3.5

Magnetic and gravity views of crust and lithosphere heterogeneity in the Wilkes Subglacial Basin of East Antarctica

Egidio Armadillo, Fausto Ferraccioli, Alessandro Ghirotto, Duncan Young, Donald Blankenship, and Martin Siegert

The Wilkes Subglacial Basin (WSB) is a major intraplate tectonic feature in East Antarctica. It stretches for ca 1400 km from the edge of the Southern Ocean, where it is up to 600 km wide towards South Pole, where it is less than 100 km wide. Recent modelling of its subice topography (Paxman et al., 2019, JGR) lends support to a long-standing hypothesis predicting that the wide basin is linked to flexure of more rigid and mostly Precambrian cratonic lithosphere induced by the Cenozoic uplift of the adjacent Trasantarctic Mountains,. However, there is also mounting evidence from potential field and radar exploration that its narrower structurally controlled sub-basins may have formed in response to more localised Mesozoic to Cenozoic extension and transtension that preferentially steered glacial erosion (Paxman et al., 2018, GRL).  

Here we exploit recent advancements in regional aerogeophysical data compilations and continental scale satellite gravity gradient imaging with the overarching aim of helping unveil the degree of 4D heterogeneity in the crust and lithosphere beneath the WSB. New views of crustal and lithosphere thickness stem from 3D satellite gravity modelling (Pappa et al., 2019, JGR) and these can be compared with predictions from previous flexural modelling and seismological results. By stripping out the computed effects of crustal and lithosphere thickness variations we then obtain residual intra-crustal gravity anomalies. These are in turn compared with a suite of enhanced aeromagnetic anomaly images. We then calculate depth to magnetic and gravity source estimates and use these results to help constrain the first combined 2D magnetic and gravity models for two selected regions within the WSB.

One first model reveals a major lithospheric scale boundary along the eastern margin of the northern WSB. It separates the Cambro-Ordovician Ross Orogen from a newly defined composite Precambrian Wilkes Terrane that forms the unexposed crustal basement buried beneath partially exposed early Cambrian metasediments and more recent Devonian to Jurassic sediments.

Our second model investigates a sector of the WSB further south, where the proposed Precambrian basement is modelled as being both shallower and of more felsic bulk composition. Although the lack of drilling precludes direct sampling of this cryptic basement, aeromagnetic anomaly patterns suggest that it may be akin to late Paleoproterozoic to Mesoproterozoic igneous basement exposed in part of the Gawler and Curnamona cratons in South Australia. We conclude that these first order differences in basement depth, bulk composition and thickness of metasediment/sediment cover are a key and previously un-appreciated intra-crustal boundary condition, which is likely to affect geothermal heat flux variability beneath different sectors of the WSB, with potential cascading effects on subglacial hydrology and the flow of the overlying East Antarctic Ice Sheet.

How to cite: Armadillo, E., Ferraccioli, F., Ghirotto, A., Young, D., Blankenship, D., and Siegert, M.: Magnetic and gravity views of crust and lithosphere heterogeneity in the Wilkes Subglacial Basin of East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10664, https://doi.org/10.5194/egusphere-egu2020-10664, 2020.

EGU2020-10542 | Displays | G3.5

Magnetotelluric Constraints on Upper Mantle Viscosity Structure and Basal Melt Beneath the Greenland Ice Sheet

Clinton Conrad, Kate Selway, Maaike Weerdesteijn, Silje Smith-Johnsen, Kerim Nisancioglu, and Nanna Karlsson

Mass loss from the Greenland Ice Sheet has accelerated during the past decade due to climate warming. This deglaciation is now considered a major contributor to global sea level rise, and a serious threat to future coastlines. It is therefore vital to measure patterns and volumes of ice sheet mass loss. However, measurements of the ice sheet’s mass and elevation, both of which decrease as the ice melts, are also sensitive to ground deformation associated with glacial isostatic adjustment (GIA), which is the solid Earth’s response to ice loss since the last ice age. For Greenland, GIA is poorly constrained in part because Greenland’s complex geologic history, with a passage over the Iceland Plume, probably created large lateral viscosity variations beneath Greenland that complicate the GIA response.

The Norwegian MAGPIE project (Magnetotelluric Analysis for Greenland and Postglacial Isostatic Evolution) seeks to develop new constraints on mantle viscosity beneath Greenland by collecting magnetotelluric (MT) data on the ice sheet. MT images the Earth’s electrical conductivity, which is sensitive to three of the major controls on mantle viscosity: temperature, partial melt content and water content of solid-state mantle minerals. We therefore plan to use MT data, together with existing seismic data, to map viscosity variations beneath Greenland. During the summer of 2019 we deployed 13 MT stations in a 200 km grid centered on EastGRIP camp on the North-East Greenland Ice Stream. Good quality data were recorded at periods up to 10,000 s, providing good resolution of upper mantle conductivity structure. We also collected a broadband MT traverse across the NE Greenland Ice Stream, which allows us to directly compare MT and radar data to investigate the role of basal melt on ice flow dynamics. During the 2020 summer season we will be collecting additional data over the south-western and central parts of the ice sheet. Here we show preliminary constraints on the conductivity of the asthenosphere, lithosphere, and crust beneath Greenland, which will be used to investigate the upper mantle viscosity structure, including the present-day signature of the Iceland Plume.

How to cite: Conrad, C., Selway, K., Weerdesteijn, M., Smith-Johnsen, S., Nisancioglu, K., and Karlsson, N.: Magnetotelluric Constraints on Upper Mantle Viscosity Structure and Basal Melt Beneath the Greenland Ice Sheet , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10542, https://doi.org/10.5194/egusphere-egu2020-10542, 2020.

EGU2020-11093 | Displays | G3.5

Impact of the Icelandic hotspot on GPS time series in southeast Greenland

Valentina R. Barletta, Andrea Bordoni, and Shfaqat Abbas Khan

The mass lost from Greenland ice sheet is one of the most important contribution to the global sea level rise, and it is under constant monitoring. However, still little is known about the heat flux at the glacier bedrock, and how it affects dynamics of the major outlet glaciers in Greenland. Recent studies suggest that the hotspot currently under Iceland have been under eastern Greenland at ~40 Ma BP and that the upwelling of hot material from the Iceland plume towards Greenland is ongoing. A warm upper mantle has a low viscosity, which in turn causes the solid Earth to rebound much faster to deglaciation. We have good reasons to believe that mantle beneath SE-Greenland has very low viscosity (Khan, et al. 2016), as also suggested by the discrepancy between the GPS velocities and the predicted purely elastic deformations caused by present-day ice loss. Here we present a preliminary computation of the Earth deformation driven by a low viscosity mantle excited by the deglatiation since the little ice age (LIA) to the present day. We produce the time series of such deformation and compare it with GPS time series, the oldest dating back to 1992.

How to cite: Barletta, V. R., Bordoni, A., and Khan, S. A.: Impact of the Icelandic hotspot on GPS time series in southeast Greenland , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11093, https://doi.org/10.5194/egusphere-egu2020-11093, 2020.

EGU2020-3531 | Displays | G3.5

Developing an open-source 3D glacial isostatic adjustment modeling code using ASPECT

Maaike Weerdesteijn, Clinton Conrad, John Naliboff, and Kate Selway

Models of Glacial Isostatic Adjustment (GIA) processes are useful because they help us understand landscape evolution in past and current glaciated regions. Such models are sensitive to ice and ocean loading as well as to Earth material properties, such as viscosity. Many current GIA models assume radially-symmetric (layered) viscosity structures, but viscosity may vary laterally and these variations can have large effects on GIA modeling outputs. Here we present the potential of using ASPECT, an open-source finite element mantle-convection code that can handle lateral viscosity variations, for GIA modeling applications. ASPECT has the advantage of adaptive mesh refinement, making it computationally efficient, especially for problems such as GIA with large variations in strain rates. Furthermore, ASPECT is open-source, as will be the GIA extension, making it a valuable future tool for the GIA community.

 

Our GIA extension is benchmarked using a similar case as in Martinec et al. (GJI, 2018), such that the performance of our GIA code can be compared to other GIA codes. In this case, a spherically symmetric, five-layer, incompressible, self-gravitating viscoelastic Earth model is used (Spada et al, GJI 2011). The surface load consists of a spherical ice cap centered at the North pole, and is applied as a Heaviside loading. The ice load remains constant with time, and thus we have not yet implemented the full sea level equation (SLE). Beyond this benchmark, we have incorporated lateral viscosity variations underneath the ice cap, to demonstrate the ability of efficiently implementing laterally-varying material properties in ASPECT.

 

We show the possibilities, capabilities, and potential of ASPECT for GIA modeling. In the near future we will further develop the code with the sea level equation and an ocean basin, and will explore ASPECT’s current capability of using time-varying distributed surface loads. These functions will allow for modeling of GIA for realistic ice load scenarios imposed above potentially complex earth structures.

How to cite: Weerdesteijn, M., Conrad, C., Naliboff, J., and Selway, K.: Developing an open-source 3D glacial isostatic adjustment modeling code using ASPECT, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3531, https://doi.org/10.5194/egusphere-egu2020-3531, 2020.

EGU2020-19774 | Displays | G3.5

Constraint of GIA in Northern Europe with Geological RSL and VLM Data

Karen Simon and Riccardo Riva

In this study, we focus on better constraint of the long term glacial isostatic adjustment (GIA) signal at present-day, and its role as a contributor to total present-day rates of change. The main study area extends from the coastal regions of northern Europe to Scandinavia. Both Holocene relative sea level (RSL) data as well as vertical land motion (VLM) data are incorporated as constraints in a semi-empirical GIA model. Specifically, 70 geological rates of GIA-driven RSL change are inferred from Holocene data; peak RSL fall is indicated in central Scandinavia and the northern British Isles where past ice sheets were thickest, RSL rise is indicated in the southern British Isles and along the northern European coastline. Rates of vertical land motion from GPS at 108 sites provide an additional measure of regional GIA deformation. Within the study area, the geological RSL data complement the spatial gaps of the VLM data and vice versa; both datasets are inverted in a semi-empirical GIA model to yield updated estimates of regional present-day GIA deformations. A regional validation is presented for the North Sea, where the GIA signal may be complicated by lateral variations in Earth structure and existing predictions of regional and global GIA models are discrepant. The model validation in the North Sea region indicates that geological data are needed to fit independent estimates of GIA-related RSL change inferred from tide gauge rates, suggesting that the geological rates provide an important additional constraint of present-day GIA.

How to cite: Simon, K. and Riva, R.: Constraint of GIA in Northern Europe with Geological RSL and VLM Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19774, https://doi.org/10.5194/egusphere-egu2020-19774, 2020.

Crustal density is a fundamental physical parameter that helps to reveal its composition and structure, and is also significantly related to the tectonic evolution and geodynamics. Based on the latest Bouguer gravity anomalies and the constrains of 3-D shear velocity model and surface heat flow data, the 3-D gravity inversion method, incorporating deep weight function, has been used to obtain the refined density structure over the Antarctic continent. Our results show that the density anomalies changes from -0.25 g/cm3 to 0.20 g/cm3. Due to the multi-phase extensional tectonics in Mesozoic and Cenozoic, the low density anomalies dominates in the West Antarctica, while the East Antarctica is characterized by high values of density anomalies. By comparing with the variations of effective elastic thickness, the inverted density structure correlates well with the lithospheric integrated strength. According to the mechanical strength and inverted density structure in the West Antarctic Rift System (WARS), our analysis found that except for the local area affected by the Cenozoic extension and magmatic activity, the crustal thermal structure in the WARS tends to be normal under the effect of heat dissipation. Finally, the low density anomalies features in West Antarctica extend to beneath the Transantarcitc Mountains (TAMs), however, we hypothesize that a single rift mechanism seems not be used to explain the entire TAMs range.

How to cite: Ji, F. and Zhang, Q.: Crustal density structure of the Antarctic continent from constrained 3-D gravity inversion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4427, https://doi.org/10.5194/egusphere-egu2020-4427, 2020.

G3.6 – Monitoring and modelling of geodynamics and crustal deformation: progress during 39 years of the WEGENER initiative

High-rate GNSS receivers, sampling satellite signals at over 1-Hz rate, can record strong ground motions and directly in the form of displacements instead of velocities or accelerations. In this case, broadband displacement waveforms down to 0 Hz can be obtained nominally; the benefit is that static offsets can be identified accurately from high-rate displacements with minimal contamination by the very early postseismic signals. The drawback of high-rate GNSS, however, consists in its orders of magnitude higher noise than that of seismometers, almost on all frequency bands concerning seismic studies. Combining collocated high-rate GNSS and accelerometers can be a remedy and produces broadband seismogeodetic displacements. However, accelerometer data must be heavily downweighted due to their baseline errors originating primarily in instrument rotations, and therefore their contribution to seismogeodetic displacements is seriously underestimated. We further introduced a gyroscope into this classic seismogeodesy to mitigate baseline errors and formulated advanced six-degree-of-freedom (6-DOF) seismogeodesy without undervaluing accelerometer data. A shake table holding one GNSS antenna, four accelerometers, and one gyroscope was used to simulate waveforms from the 2010 Mw 7.2 El Mayor-Cucapah earthquake. We found that the displacements derived from the 6-DOF seismogeodesy were up to 68% more accurate than those from the classic seismogeodesy over 0.04–0.4 Hz. Moreover, broadband rotations containing the permanent components were also generated, which were unachievable by integrating gyroscope data. We believe that the 6-DOF seismogeodesy is capable of improving both source rupture studies of large earthquakes and high-rise monitoring under strong seismic waves.

How to cite: Geng, J., Wen, Q., and Chen, Q.: Six-degree-of-freedom seismogeodesy by combining collocated high-rate GNSS, accelerometers and gyroscopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1568, https://doi.org/10.5194/egusphere-egu2020-1568, 2020.

EGU2020-19808 | Displays | G3.6 | Highlight

Toward the Development of Earthquake Recurrence Models from 3D GNSS Velocity Field in Europe

Jesus Piña-Valdés, Anne Socquet, Céline Beauval, Pierre-Yves Bard, Marie-Pierre Doin, and Zhengkang Shen

Probabilistic Seismic Hazard Assessment demands the development of reliable earthquake recurrence models, which are usually based on time and spatial distribution of the past seismicity contained on earthquake catalogs. This usually generate models rather well constrained on seismically active regions where large historical catalogs are available. But in low to moderate seismicity regions, where data is scarce, establishing earthquake recurrence from past events is a major challenge. On those regions, geodetic measurements can provide useful information for deriving alternative recurrence models based on strain rate.

The impact of the crust deformation on the processes that control the seismic activity is still controversial. The seismic activity is usually thought to be associated to the active tectonic deformation as estimated from the horizontal displacements field. But in regions with low horizontal deformation, getting the horizontal strain rates is difficult since the displacements field can be dominated by the noise of the geodetic data. Additionally, non-tectonic processes such as the Glacial Isostatic Adjustment (GIA) can exist, and may impact the seismicity rate of those regions. Then seismicity rates derived from the horizontal velocity fields might not adjust the observed seismicity rates on such regions.

We propose a methodology to build a combined GNSS velocity field dataset for Europe, that could be used for the development of earthquake recurrence models. For this, 5 different GNSS velocity field solution for Europe are considered. Using the velocity solutions of common stations, the different datasets are converted to a common reference frame. Based on the comparison of the velocity values, a methodology is established to generate a combined velocity field, considering the uncertainty of each independent solution. A criterion for automatic identification and outliers removal is implemented, as well an adaptive smoothing scheme that depends on the station density, the noise and the local tectonic deformation rate.

We propose a methodology to obtain strain rate maps from GNSS data based on the VISR software [Shen et al., 2015], not only considering the horizontal velocity field, but including also the vertical velocity field for Europe, considering the effects of flexure of the crust on regions where important GIA signals are observed.

Finally, earthquake recurrence models are derived and compared with catalog-based models in Europe to evaluate their mutual agreement, comparing also the results obtained on regions with significant tectonic deformation versus regions where important GIA signals are observed.

How to cite: Piña-Valdés, J., Socquet, A., Beauval, C., Bard, P.-Y., Doin, M.-P., and Shen, Z.: Toward the Development of Earthquake Recurrence Models from 3D GNSS Velocity Field in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19808, https://doi.org/10.5194/egusphere-egu2020-19808, 2020.

EGU2020-4835 | Displays | G3.6

Constraint of active deformation and transpression tectonics along the plate boundary in North Africa

Mustapha Meghraoui, Frederic Masson, Nejib Bahrouni, Abdelilah Tahayt, Mohamed Saleh, and Salem Kahlouche

The Maghrebian tectonic domain in North Africa is here examined in the light of the recent GPS and seismotectonic results. The region includes the plate boundary in the western Mediterranean previously characterized by transpression and block rotation. The crustal deformation is documented along the Atlas Mountains in terms of the displacement field, with strain partitioning largely controlled by plate motions. The tectonic and seismotectonic analysis is based on our published data on shortening directions of Quaternary faulting and folding compared with present-day seismotectonic characteristics (earthquake moment tensors) of significant seismic events that allow an estimate of local and regional deformation rates in North Africa. Shortening directions oriented NE-SW to NW-SE for the Pliocene and Quaternary, respectively, and the S shape of the Quaternary anticline axes are in agreement with the 2°/Myr to 4°/Myr clockwise rotation obtained from paleomagnetic results on small tectonic blocks in the Tell Atlas. The continuous GPS data and results are obtained from the network in Morocco operative 1999 to 2006, the REGAT network in Algeria since 2007, and the network in Tunisia with data collected from 2014 to 2018. In addition, we add the most recent GPS results in southern Spain and southern Italy. The NW-SE to NNW-SSE 5 ±1.5 mm/yr convergence velocity and strain distribution of the Maghrebian tectonic domain is controlled by crustal block tectonics driven by E-W trending right-lateral faulting and NE-SW thrust-related folding. The correlation between the active transpression tectonic structures and velocity field shows a geodynamic framework consistent with the oblique plate convergence of Africa towards Eurasia. 

How to cite: Meghraoui, M., Masson, F., Bahrouni, N., Tahayt, A., Saleh, M., and Kahlouche, S.: Constraint of active deformation and transpression tectonics along the plate boundary in North Africa , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4835, https://doi.org/10.5194/egusphere-egu2020-4835, 2020.

EGU2020-13278 | Displays | G3.6

GPS Imaging of Mantle Driven Uplift of the Apennines, Italy

Nicola D'Agostino and William C. Hammond

One way for the continental lithosphere to extend is to increase its regional elevation, yet the mechanism for the formation of high-topography in actively extending continental settings (e.g., Tibet, Basin and Range, southwestern Balkans, Apennines) is still uncertain. It has been suggested that active extension in the Apennines Mountain chain in Italy is intimately related with regional topographic elevation. We use a newly updated GPS dataset and the GPS Imaging technique to show that the dynamic relief of the Apennines is currently increasing along its entire length by ~1 mm/yr. We image positive uplift along the entire length of the Apennine crest including the northern Apennines, Calabria and northern Sicily. The maximum rate is geographically aligned with the highest elevations and the topographic drainage divide. Relief is increasing in a ~120 km wide zone with a profile similar to the long wavelength topography, but not similar to the shorter wavelength topography generated by active faulting and erosion. A zone of minor active uplift is aligned with areas having restive volcanic fields and high geothermal potential west of the Apennines: e.g., Campi Flegrei, Alban Hills, and Lago Bolsena. However, the primary uplift axis aligns with the topography and zone of extension accommodating east-northeast translation of the Adriatic microplate relative to the Tyrrhenian Basin. Broad uplift occurs despite that the expected consequence of extension is crustal thinning and subsidence.   Anomalies in free-air gravity and deep seismic wavespeed suggest that elevation gain is driven by forces originating in the mantle. We use these results to address the hypothesis that these forces result from upward flow of asthenospheric mantle beneath the Apennines, possibly related to a sinking and detached slab previously attached to the Adriatic microplate, or from extensional flank flexure across the axis of the Apennine rift.

How to cite: D'Agostino, N. and Hammond, W. C.: GPS Imaging of Mantle Driven Uplift of the Apennines, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13278, https://doi.org/10.5194/egusphere-egu2020-13278, 2020.

EGU2020-11110 | Displays | G3.6

How to reveal the present-day mechanism of the 600 km long Doruneh fault in eastern Iran ?

Fateme Khorrami, Andrea Walpersdorf, Zahra Mousavi, Erwan Pathier, Hamid Nankali, Reza Sa'adat, Richard Walker, Marie-Pierre Doin, Farokh Tavakoli, and Yahya Djamour

The enigmatic 600 km long E-W trending left-lateral Doruneh fault in eastern Iran is certified to be active by its well preserved geomorphological features all along its trace, but it is lacking recent seismic activity that could be attributed to its motion. Instead, the high seismogenic potential of the study zone is highlighted by the two M=7 earthquakes on the left-lateral E-W trending Dasht-e-Bayaz fault just south of Doruneh, in 1968 and 1979. Therefore, it remains important to understand the role of the Doruneh fault in the kinematics of the Arabia-Eurasia collision that takes place inside Iran’s political boundaries.

Many different slip-rates have been estimated for the left-lateral motion of the Doruneh fault: 2.5 mm/yr by geomorphological marker offset dating, 1 mm/yr from preliminary GNSS measurements, and 5 mm/yr from a local InSAR study.  These rather local estimates on the 600 km long fault highlight either temporal or spatial variability of the Doruneh present-day behavior. The spatial variability of the fault slip is still badly constraint as the western half of the fault is located in the Great Kavir desert. The analysis of satellite radar images was supposed to provide good constraints on the inter-seismic deformation with a full spatial coverage of the fault, especially thanks to the favorable E-W orientation of the Doruneh fault and the arid Iranian climate. However, decorrelation due to sand dunes and unexpected large tropospheric noise prohibited precise results from a first large-scale ENVISAT study, yielding an upper limit of the slip rate of 4 mm/yr. The high resolution SENTINEL-1 constellation (operational since 2014) is predicted to provide constraints on inter-seismic velocities down to 2 mm/yr from 2020 on. In complement, a dense GNSS survey has been conducted in 2012 and 2018 on a temporary network of 18 sites around a large part of the fault. This network densifies and completes the 17 permanent GNSS stations in up to 200 km distance to the fault trace situated mostly in the eastern, more populated part of the fault.

In this work, we will point out our recent GNSS, InSAR and tectonic studies on the present-day characteristics of the Doruneh fault, to better understand the mechanism of this major fault in the kinematics of the Arabia-Eurasia collision, and to contribute to a better assessment of the seismic hazard in eastern Iran.

How to cite: Khorrami, F., Walpersdorf, A., Mousavi, Z., Pathier, E., Nankali, H., Sa'adat, R., Walker, R., Doin, M.-P., Tavakoli, F., and Djamour, Y.: How to reveal the present-day mechanism of the 600 km long Doruneh fault in eastern Iran ?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11110, https://doi.org/10.5194/egusphere-egu2020-11110, 2020.

EGU2020-12803 | Displays | G3.6

Detection of Plastic Strain Using GNSS Data of Pre- and Post-Seismic Deformation of the 2011 Tohoku-oki Earthquake

Yukitoshi Fukahata, Angela Meneses-Gutierrez, and Takeshi Sagiya

In general, there are three mechanisms causing crustal deformation: elastic, viscous, and plastic deformation. The separation of observed crustal deformation to each component has been a challenging problem. Meneses-Gutierrez and Sagiya (2016, EPSL) have successfully separated inelastic deformation from observed geodetic data from the comparison of GNSS data before and after the 2011 Tohoku-oki earthquake in the northern Niigata-Kobe tectonic zone (NKTZ), central Japan. In this study, we further succeed in separating plastic deformation as well as viscous deformation in the northern NKTZ using GNSS data before and after the 2011 Tohoku-oki earthquake, under the assumptions that elastic deformation is principally caused by the plate coupling along the Japan trench and that plastic deformation ceased after the Tohoku-oki earthquake due to the stress drop caused by the earthquake. The cease of plastic deformation can be understood with the concept of stress shadow used in the field of seismic activity. The separated strain rates are about 30 nanostrain/yr both for the plastic deformation in the preseismic period and for the viscous deformation in both the pre- and post-seismic periods, which means that the inelastic strain rate in the northern NKTZ is about 60 and 30 nanostrain/yr in the pre- and post-seismic periods, respectively. This result requires the revision of the strain rate paradox in Japan. The strain rate was exceptionally faster before the Tohoku-oki earthquake due to the effect of plastic strain, and the discrepancy between the geodetic and geologic strain rates is much smaller in usual time, when the plastic strain is off. In oder to understand the onset timing of plastic deformation, the information on stress history is essentially important.

 

How to cite: Fukahata, Y., Meneses-Gutierrez, A., and Sagiya, T.: Detection of Plastic Strain Using GNSS Data of Pre- and Post-Seismic Deformation of the 2011 Tohoku-oki Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12803, https://doi.org/10.5194/egusphere-egu2020-12803, 2020.

California’s Central Valley is the site of a complex heterogeneous aquifer system composed of alternating layers of coarse sediments and fine-grained confining material. Confined and semi-confined aquifer systems experience groundwater fluctuations coupled with elastic and inelastic land surface deformation. Data from the UAVSAR L-band synthetic aperture radar acquired between May 29, 2013 and November 27, 2018 were used to generate a high resolution deformation time series, and identify and track the development of a small subsidence feature that developed immediately adjacent to the California Aqueduct. By the end of the time series, the feature surface area that subsided 10 cm or more was 4452 hectares. The California Aqueduct supports Central Valley agriculture and large urban populations in Southern California, and a 10.5+ km segment of the aqueduct subsided 10 cm or more due to this one subsidence feature.  The Central Valley experienced a persistent drought starting in 2012, followed abruptly by a wet period from December 2016 to February 2018. The data were analyzed for the drought period in conjunction with hydraulic head level data from nearby wells to solve for aquifer storage parameters and volume storage loss.  We found the inelastic volume storage loss was 7.1x106 m3, or an average rate of 7x103 m3/day.

Compared to satellite SARs, UAVSAR has a higher spatial resolution (<2 m ground resolution) and signal-to-noise ratio. Because of these factors along with spatial averaging to reduce phase noise, accuracy is increased and temporal decorrelation is reduced, so a greater proportion of the scene produces useful measurements while maintaining a spatial resolution of 7mx7m. The resolution achieved with UAVSAR time series processing allows for modeling and monitoring localized subsidence features affecting the aqueduct that were not previously observed by satellite. The data, analysis, model, and results are described in this presentation.  It is notable that UAVSAR is a prototype for the L-band SAR to be launched on the NASA-ISRO SAR Mission (NISAR) in 2022.  In that context, we also discuss and compare the expected performance of the two instruments and highlight how these technologies can be used to study aquifer properties in areas where water level data are sparse in both space and time.

How to cite: Miller, M. and Jones, C.: Drought-induced rapid subsidence in the Central Valley and its impact on the California Aqueduct, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10733, https://doi.org/10.5194/egusphere-egu2020-10733, 2020.

EGU2020-1158 | Displays | G3.6

Study of Intra-plate Movement in the Indian Subcontinent along Narmada Son Lineament by Baseline Processing

Sujata Dhar, Nagarajan Balasubramanian, and Onkar Dikshit

India extends from 8° 4’ N to 37° 6’ N latitude and 68° 7’ E to 97° 25’ E longitude. It lies largely on the Indian plate. Major earthquakes generally happen along tectonic plate boundaries. But, Indian subcontinent has experienced some of the largest earthquakes, with magnitude more than 7, within it. This directs the possibility of significant intraplate movement in the Indian plate. Narmada river flows through the central part of India and is considered as the boundary between northern and southern India. It is tectonically active, which is not found in other river basins. Geophysical studies in the Son Narmada Fault (SNF) zone reveal that this is a zone of intense deep-seated faulting which has been reactivated and hence, this is the cause of major earthquakes and various tectonically induced landforms in that region recently. Estimates of intraplate strain across Narmada Son Lineament (NSL) from early campaign-mode GPS data and geological studies suggested movement of 2-3 mm per year. The Indian Plate is currently moving northeast at 5 cm/year, while the Eurasian Plate is moving northeast at only 2 cm/yr. Most of the research has been done with geological studies to determine the rate of the movement along NSL. We are considering Global Navigation Satellite System (GNSS) data for around 16 continuously operating and well distributed sites in India. We are using BERNESE and GAMIT software’s for GNSS data processing. Both are scientific GNSS processing software with single differencing for ambiguity resolution. This is the first time in India that movement across NSL, with ITRF14 reference frame, will be determined from any space geodetic technique dominantly. In this study, several continuous GNSS stations in India along with nearby IGS sites from 2013 to 2018 are used to examine the distribution and magnitude of intraplate movement across the active SNF.

Keywords: Indian plate, Son Narmada Fault, GNSS, BERNESE, GAMIT, ITRF14

How to cite: Dhar, S., Balasubramanian, N., and Dikshit, O.: Study of Intra-plate Movement in the Indian Subcontinent along Narmada Son Lineament by Baseline Processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1158, https://doi.org/10.5194/egusphere-egu2020-1158, 2020.

EGU2020-1625 | Displays | G3.6

A new 3D approach to automated outliers rejection in GNSS time series

Luca Tavasci, Miriana Di Donato, Maddalena Errico, Stefano Gandolfi, and Susanna Zerbini

Permanent GNSS stations have become fundamental for geodynamic studies thanks to their capability of providing consistent coordinate time series. The time series analysis is becoming more and more sophisticated and there are several approaches, fully automated or not, helping the users to derive the main parameters of interest such as: trends, periodical signals, discontinuities, types of noises, blunders. Typically, however, the analysis of the time series is still performed considering separately each of the three coordinate components. Actually, this neglects the three-dimensional nature of the GNSS position solutions, which are computed simultaneously, and may have some impact on the analysis. We should also bear in mind that the values of the coordinates time series depend on the reference system orientation. For instance, the time series values expressed in geocentric coordinates (X, Y, Z) are usually different from the same ones represented in a topocentric (E, N, V) reference. Therefore, if the analysis is performed separately on the three coordinate components, results will be different depending on the adopted reference system.
The aim of this work is to address the issue concerning the automated rejection of outliers potentially present in the GNSS time series. This is a fundamental aspect considering the large amount of data that nowadays shall be continuously processed and analyzed, thus requiring procedures as automated as possible. A viable approach is to search for outliers by analyzing the error distribution of the coordinates after having removed trends and signals, assuming that these behave like casual errors and follow a normal density distribution. It is then possible to set a statistical threshold in order to reject iteratively all the solutions with higher residual values. This approach is usually implemented by considering mono-dimensional time series in which the three coordinate components are processed separately. Nevertheless, from a statistical point of view, each GNSS position solution should be considered to be a 3D variable, thus characterized by a probability density function defined in a 3D space. In particular, by considering a chi-square distribution with three degrees of freedom it is possible to consider an ellipsoidal density function that well fit the error distribution of a 3D casual variable such as the GNSS coordinates.
In this work, numerical results obtained from the analysis of real dataset will be presented. In particular, six years of daily position solutions obtained from 12 GNSS permanent stations have been considered. The time series have been analyzed starting from both geocentric and topocentric coordinates using alternatively two different approaches: a classical one, in which the three coordinate components have been processed separately, and the 3D approach that allowed to consider the three coordinates at once. Results show that the second approach is mostly independent from the starting reference system, whereas the classical approach is affected by the orientation of the Cartesian axes used to project the same positions.

How to cite: Tavasci, L., Di Donato, M., Errico, M., Gandolfi, S., and Zerbini, S.: A new 3D approach to automated outliers rejection in GNSS time series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1625, https://doi.org/10.5194/egusphere-egu2020-1625, 2020.

EGU2020-2061 | Displays | G3.6

GPS Constraints on the Active Deformation in Tunisia: Implications on the Geodynamics of the Western Mediterranean

Frédéric Masson, Mustapha Meghraoui, Najib Bahrouni, Mohammed Saleh, Maamri Ridha, Dhaha Faouzi, Patrice Ulrich, and Jean-Daniel Bernard

The plate boundary in the western Mediterranean includes the Tunisian Atlas Mountains. We study the active deformation of this area using GPS data collected from 2014 to 2018. WNW to NNW trending velocities express the crustal motion and geodetic strain field from the Sahara platform to the Tell Atlas, consistent with the African plate convergence. To the south, the velocities indicate a nearly WNW-ESE trending right-lateral motion of the Sahara fault-related fold belt with respect to the Sahara Platform. Further north and northeast, the significant decrease in velocities between the Eastern Platform and Central – Tell Atlas marks the NNW trending shortening deformation associated with local ENE – WSW extension visible in the Quaternary grabens. The velocity field and strain distribution associated with the active E-W trending right-lateral faulting and NE-SW fault-related folds sustain the existence of three main tectonic blocks and related transpression tectonics. The velocity field and pattern of active deformation in Tunisia document the oblique plate convergence of Africa towards Eurasia. 

How to cite: Masson, F., Meghraoui, M., Bahrouni, N., Saleh, M., Ridha, M., Faouzi, D., Ulrich, P., and Bernard, J.-D.: GPS Constraints on the Active Deformation in Tunisia: Implications on the Geodynamics of the Western Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2061, https://doi.org/10.5194/egusphere-egu2020-2061, 2020.

On April 25, 2015, the Nepal MS 8.1 earthquake took place in the Himalayan seismic belt on the southern margin of Tibetan Plateau. After the earthquake, the China Earthquake Administration established Immediately 13 GPS continuous stations in the southern Tibetan region. In this study, such data, the data of China’s crustal movement observation network in the southern Tibet region and the data of GPS continuous stations in Nepal are used to estimate the postseismic deformation of the GPS station. Three postseismic deformation models, i.e., a logarithmic model, an exponential model and an integrated combination, are used for fitting GPS postseismic deformation. The Markov Chain Monte Carlo algorithm, based on a Bayesian framework, is applied to invert model parameters. The results show that the integrated model for the logarithmic model and exponential model can accurately fit the postseismic deformation observed by GPS, indicating that the postseismic deformation observed by GPS may involve two different deformation mechanisms with multi-scale characteristics. Based on the analysis of the spatial-temporal distribution of the postseismic deformation field and its comparison with the coseismic deformation field, it is considered that the afterslip mainly occurs in the deep area where the coseismic rupture extends northward, while the seismic risk in the shallow area where the coseismic rupture is not broken still deserves further attention.

How to cite: Su, X. and Meng, G.: Postseismic deformation of the Ms 8.1 Nepal earthquake in 2015 from GPS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2503, https://doi.org/10.5194/egusphere-egu2020-2503, 2020.

EGU2020-2616 | Displays | G3.6

PCA study of the interannual variability of GPS heights and environmental parameters

Letizia Elia, Susanna Zerbini, and Fabio Raicich

Time series of GPS coordinates longer than two decades are now available at many stations around the world. The objective of our study is to investigate large networks of GPS stations to identify and analyze spatially coherent signals present in the coordinate time series and, at the same locations, to identify and analyze common patterns in the series of environmental parameters and climate indexes. The study is confined to Europe and the Mediterranean area, where 107 GPS stations were selected from the Nevada Geodetic Laboratory (NGL) archive on the basis of the completeness and length of the data series. The parameters of interest for this study are the stations height (H), the atmospheric surface pressure (AP), the terrestrial water storage (TWS) and the various climate indexes, such as NAO (North Atlantic Oscillation), AO (Artic Oscillation), SCAND (Scandinavian Index) and MEI (Multivariate ENSO Index). The Empirical Orthogonal Function (EOF) is the methodology adopted to extract the main patterns of space/time variability of these parameters. We also focus on the coupled modes of space/time interannual variability between pairs of variables using the singular value decomposition (SVD) methodology. The coupled variability between all the afore mentioned parameters is investigated. It shall be pointed out that EOF and SVD are mathematical tools providing common modes on the one hand, and statistical correlations between pairs of parameters on the other. Therefore, these methodologies do not allow to directly infer the physical mechanisms responsible for the observed behaviors which should be explained through appropriate modelling. Our study has identified, over Europe and the Mediterranean, main modes of variability in the time series of GPS heights, atmospheric pressure and terrestrial water storage. For example, regarding the station heights, the EOF1 explains about 30% of the variance and the spatial pattern is coherent over the entire study area. The SVD analysis of coupled parameters, namely H-AP, TWS-AP and H-TWS, showed that most of the common variability is explained by the first 3 modes. In particular, 70% for the H-AP, 67% for the TWS-AP and 49% for the H-TWS pair. Moreover, we correlated the stations heights with the NAO, AO, SCAND and MEI indexes to investigate the possible influence of climate variability on the height behavior. To do so, the stations heights were represented using the first three EOFs to reduce the potential effect of local anomalies. More than 30 stations, over the total of 107, show significant correlations up to about 0.3 with the AO and SCAND indexes. The correlation coefficients with MEI turn out to be significant and up to 0.5 for about half of the stations.

How to cite: Elia, L., Zerbini, S., and Raicich, F.: PCA study of the interannual variability of GPS heights and environmental parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2616, https://doi.org/10.5194/egusphere-egu2020-2616, 2020.

EGU2020-4142 | Displays | G3.6

A new Moho depth model for Fennoscandia and surroundings

Majid Abrehdary and Lars Sjöberg

Seismic data are the preliminary information for investigating Earth’s interior structure. Since large parts of the world are not yet sufficiently covered by such data, products from Earth satellite gravity and altimetry missions can be used as complimentary for this purpose. This is particularly the case in most of the ocean areas, where seismic data are sparse. One important information of Earth’s interior is the crustal/Moho depth, which is widely mapped from seismic surveys. In this study, we aim at presenting a new Moho depth model from satellite altimetry derived gravity and seismic data in Fennoscandia and its surroundings using the Vening Meinesz-Moritz (VMM) model based on isostatic theory. To that end, the refined Bouguer gravity disturbance (reduced for gravity of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components by applying so-called stripping gravity corrections) is corrected for so-called non-isostatic effects (NIEs) of nuisance gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA) and plate flexure. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and Moho depth determination from gravity in this area. To do so, the DGIA effect is removed and restored from the NIEs prior to the application of the VMM formula. The numerical results show that the RMS difference of the Moho depth from the (mostly) seismic CRUST1.0 model is 3.6/4.3 km when the above strategy for removing the DGIA effect is/is not applied, respectively. Also, the mean value differences are 0.9 and 1.5 km, respectively. Hence, our study shows that our method of correcting for the DGIA effect on gravity disturbance is significant, resulting in individual changes in Moho depth up to several kilometres.

How to cite: Abrehdary, M. and Sjöberg, L.: A new Moho depth model for Fennoscandia and surroundings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4142, https://doi.org/10.5194/egusphere-egu2020-4142, 2020.

EGU2020-6011 | Displays | G3.6

Contemporary uplift of the Kunlun Shan, Northern Tibetan Plateau

Shaozhuo Liu, jean-Mathieu Nocquet, Yann Klinger, Xiwei Xu, Guihua Chen, Guihua Yu, and Sigurjón Jónsson

GPS observations across active mountain ranges provide essential constraints on uplift rates, which sheds light on the underlying physical processes contributing to the development of topography. The Kunlun Shan (KLS) mountain range bounds the topographic high of the northern Tibetan Plateau. The elevation across the range sharply decreases from >4000 m in the interior of the plateau to ~2700 m in the Qaidam Basin. The mechanism responsible for its formation is debated with several models proposed on the basis of seismological and geological data. Here we consider data constraints from a cGPS profile that runs across the KLS and was installed in 2007. Our GPS time series reveal direct mechanical response to the crustal thickening across the KLS and therefore provide a promising dataset against which some geodynamical models can be tested.  Based on the GPS time series, we estimate rates of tectonic uplift and evaluate the impacts originating from reference frame drifts, common mode errors, some non-tectonic signals (e.g., hydrological loading), time-correlated noise, and postseismic transients of recent large earthquake. The GPS-derived uplift rate is ~1 mm/yr at the KLS. We find that ~2 mm/yr deep slip on a low- or intermediate-angle south-dipping thrust fault can explain the GPS-derived uplift rate. The possibility of a high-angle thrust fault, as has been proposed for the Longmen Shan (southeastern Tibetan Plateau), does not appear to be likely in the KLS case.

How to cite: Liu, S., Nocquet, J.-M., Klinger, Y., Xu, X., Chen, G., Yu, G., and Jónsson, S.: Contemporary uplift of the Kunlun Shan, Northern Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6011, https://doi.org/10.5194/egusphere-egu2020-6011, 2020.

The Kanto region, central Japan situated in the complex tectonic region where two oceanic plates subducts from the Japan trench and Sagami trough. Although many previous studies clarified repeated Mw~6.6 Slow Slip Events (SSEs) with a duration of a week in an offshore region of the Boso Peninsula along the Sagami trough, the number of the detected SSEs are limited and overall activity of SSEs have not been fully understood in these regions. We, here, applied our SSE detection in these regions to the whole available GNSS dataset for a quarter century spanning from 1994 to 2019 and clarify the relation between SSE and tremor distribution.

We use daily coordinates at 291 GNSS stations using a precise point positioning strategy of the GIPSY 6.4 software. We apply the method of Nishimura et al. (2013) and Nishimura (2014) to detect a jump associated with short-term SSEs in GNSS time-series and estimate their fault models from observed displacements. A rectangular fault on the Philippine Sea or the Pacific plates is assumed for each SSE. The stacking of GNSS time-series based on the displacement predicted by the fault model [Miyaoka and Yokota, 2012] enable us to estimate duration of SSEs.

  We detected ≥ 150 possible SSEs along both the Japan trench and Sagami trough but we here focus on SSEs along the southernmost part of the Japan trench. Total slip distribution of the detected possible SSEs shows that large slip (≥ 0.3 m) is limited near the trench. A comparison with low-frequency tremors (LFTs) along the Japan trench (Nishikawa et al., 2019) suggests SSEs occur in the same depth range (10-20 km) of LFTs but their distribution is rather complimentary whereas a minor tremor activity exists at the edge of the SSE total slip. This complimentary distribution is contrast to overlapping distribution of SSEs and LFTs observed in a deep episodic and tremor region in the other subduction zones including southwest Japan. Another distinctive feature is that SSEs continuously occur from the trench to a depth of ~60 km only at ~ 35.5ºN. Because the subducted seamounts locate at this latitude, geometry of plate interface may control a genesis of SSEs in these regions.

How to cite: Nishimura, T.: Short-term SSEs in the Kanto region, central Japan using GNSS data for a quarter century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8182, https://doi.org/10.5194/egusphere-egu2020-8182, 2020.

EGU2020-8952 | Displays | G3.6

Revealing of surface deformations induced by geodynamic processes in the Kuril island arc from GNSS data

Yurii Gabsatarov, Irina Vladimirova, Grigory Steblov, Leopold Lobkovsky, and Ksenia Muravieva

Kuril subduction zone is one of the most active continental margins due to the high plate convergence rate. Latest oceanographical, seismological and geological studies show a block structure of the Kuril island arc. In 2006-2008 Kuril GNSS network was installed along the island arc to provide information on the dynamics of the continental margin. Proper geodetic characterization of surface deformations in Kuril region is necessary for studies of regional geodynamical processes associated with seismic cycles and the evolution of the subduction zone. Since Kuril network has some disadvantages such as small amount of continuous stations (cGNSS) and its near-linear arrangement, special attention must be paid to correct processing of the GNSS data to exclude miscalculations that can affect further modeling of regional geodynamical processes.

We use regression analysis of time series of cGNSS stations displacements to distinguish components which are related to: 1) long-term accumulation of elastic stresses (secular velocity); 2) almost instant release of substantial part of accumulated stresses during main shock (coseismic offsets); 3) transient processes following large subduction eartquakes. The main advantages of the proposed regression analysis algorithm are: 1) an automatic process for detecting coseismic displacements, based on direct modeling of surface deformations using a dislocation model, 2) an automatic process for identifying transient processes; 3) taking into account the realistic GNSS noise model in calculating errors.

Since most of the GNSS stations were deployed only after large 2006-2007 Simushir earthquakes their time series were affected by intense and long-term postseismic transient processes such as afterslip and viscoelastic relaxation in the upper mantle. We use our direct models of these postseismic processes to construct residual time series, which allows us to estimate magnitudes of seasonal periodic signal and to calculate realistic errors.

We use correlation-based clustering algorithm to identify the influence of block structure of island arc on observed deformation patterns during interseismic, coseismic and postseismic stages of the seismic cycle. We also check our processing of GNSS data by constructing model of slip distribution in the source of 2006 Simushir earthquake on the basis of our estimates of coseismic offsets and by comparing our model with previous ones obtained on the basis of satellite geodetic data. The performed analysis of continuous GNSS observations shows that different parts of Kuril island arc are at different stages of seismic cycle.

How to cite: Gabsatarov, Y., Vladimirova, I., Steblov, G., Lobkovsky, L., and Muravieva, K.: Revealing of surface deformations induced by geodynamic processes in the Kuril island arc from GNSS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8952, https://doi.org/10.5194/egusphere-egu2020-8952, 2020.

EGU2020-11112 | Displays | G3.6

A new joint IAG-IASPEI sub-commission for Seismogeodesy

Jean-Mathieu Nocquet, Takuya Nishimura, Sara Bruni, Susanna Zerbini, and Haluk Ozener

Thanks to both technological evolution and analysis improvement in the past decades, space geodesy can now monitor crustal movements of a few millimeters over time opening new prospects for the study of earthquakes. However, fully exploiting the potential of geodetic measurements is subject to their further integration with seismological analysis and requires the development of a multidisciplinary approach. The new joint IAG-IASPEI sub-commission on Seismogeodesy aims to facilitate the cooperation between the geodetic and the seismological communities in order to improve our current understanding of the different processes leading to earthquakes.

The new Seismogeodesy sub-commission will focus on both observational challenges and theoretical aspects. Particular effort will be dedicated to identifying gaps of knowledge and opportunity for progress. Specifically, the sub-commission will:
* actively encourage the cooperation between all geoscientists studying the plate boundary deformation zones, by promoting the exploitation of synergies between different fields;
*  work to reinforce collocated and integrated geodetic and seismological monitoring of seismically active areas, inland and off-shore by increasing and/or developing infrastructures dedicated to broadband observations from the seismic wave band to the permanent displacement;
* be a reference group for the integration of the most advanced geodetic and seismological techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;
* act as a forum for discussion and scientific support for international geoscientists investigating the kinematics and mechanics of the plate boundary deformation zone;
* promote the use of standard procedures for geodetic data acquisition, quality evaluation, and processing, particularly GNSS data and InSAR data;
* promote earthquake geodesy, the study of seismically active regions with large earthquake potential, and geodetic application to early warning system of earthquakes and tsunamis for hazard mitigation;
* promote the role of geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on faults.
* facilitate and stimulate the integrated exploitation of large data sets, using Machine Learning and Data Mining
* support the organization of periodic workshops, meetings, summer schools with special emphasis on interdisciplinary research and interpretation and modeling issues
* help to the emergence of a new generation of researchers in Seismogeodesy worldwide

We invite any researcher interested in Seismogeodesy to join us and have a fruitful discussion in front of our poster.  

How to cite: Nocquet, J.-M., Nishimura, T., Bruni, S., Zerbini, S., and Ozener, H.: A new joint IAG-IASPEI sub-commission for Seismogeodesy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11112, https://doi.org/10.5194/egusphere-egu2020-11112, 2020.

EGU2020-12015 | Displays | G3.6

Cortical deformation in the Aguacaliente-Navarro fault system (Central Valley, Costa Rica) from Geodetic data (GNSS and InSAR)

Juan José Portela Fernández, Alejandra Staller Vázquez, and Marta Béjar Pizarro

The Central Valley, Costa Rica, is subject to moderate seismicity, related to the Central Costa Rica Deformation Belt: a region with diffuse deformation, where Caribbean, Cocos and Nazca Plates, as well as the Panama Micro-plate, interact.  The Eastern part of the valley is dominated by the Aguacaliente-Navarro fault system. The city of Cartago was destroyed by an earthquake Ms 6.4 in 1910, associated with the rupture of the Aguacaliente fault. Volcanic unrest –mainly in Turrialba Volcano, with recent activity reported- is present in the area, thus resulting in a very complex interaction zone, where seismic hazard studies are crucial.

In this context, we process GNSS observations from five different campaigns -2012, 2014, 2016, 2018 and 2020- in 13 stations in the area, in order to estimate their Caribbean-fixed velocities, hence the regional cumulative strain. Additionally, we use both InSAR and GNSS data to measure volcanic deformation, aiming to refine the computed velocities by removing volcanic deformation from the tectonic signal.

The refined velocities allow us to asses a more precise cumulative strain for the Aguacaliente-Navarro fault system, which is useful to improve seismic hazard assessment in Cartago, one of the most important cities in the region.

How to cite: Portela Fernández, J. J., Staller Vázquez, A., and Béjar Pizarro, M.: Cortical deformation in the Aguacaliente-Navarro fault system (Central Valley, Costa Rica) from Geodetic data (GNSS and InSAR) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12015, https://doi.org/10.5194/egusphere-egu2020-12015, 2020.

EGU2020-13627 | Displays | G3.6

Linking the Anatolian microplate rigid motions to the 1999 Mw = 7.5 Izmit earthquake rupture

Juan Ignacio Martin de Blas, Giampiero Iaffaldano, and Eric Calais

It is typically assumed that the occurrence of large earthquakes along the margins of tectonic plates does not impact on their rigid motions. However, for tectonic units of small size (i.e. for microplates), the viscous resistance at the plate base, and thus the torques needed to change their rigid motions, are significantly smaller than those needed for medium/large-size plates. In fact, a recent study that makes use of numerical simulations of synthetic microplates indicates that it is theoretically possible to link the temporal evolution of geodetically-observed microplate motions to the buildup and release of stresses associated with the earthquake cycle.

Here, we focus on the motion of the Anatolian microplate. We extract its rigid motion from GPS time series spanning the time around the 1999 MW = 7.5 Izmit earthquake. We select those GPS stations that are sufficiently away from plate boundaries, such as the North Anatolian Fault, the East Anatolian Fault and the Western Anatolia Extensional Province. Then, we attempt linking the temporal evolution of the Anatolian microplate rigid motion to the stresses associated with the 1999 MW = 7.5 Izmit earthquake rupture. The novelty of our approach lies in the fact that, in contrast to current models of the earthquake cycle, we connect earthquake stresses to changes in plate rigid motions and not to the crustal deformation in the vicinity of earthquake-prone faults.

How to cite: Martin de Blas, J. I., Iaffaldano, G., and Calais, E.: Linking the Anatolian microplate rigid motions to the 1999 Mw = 7.5 Izmit earthquake rupture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13627, https://doi.org/10.5194/egusphere-egu2020-13627, 2020.

EGU2020-19570 | Displays | G3.6

INTEGRATION OF GNSS-GPS NETWORKS (cGPS) FOR OBTAINING STRESS AND STRAIN MODELS FOR THE SPINA REGION (SOUTH OF THE IBERIAN PENINSULA AND NORTH AFRICA)

Alejandro Pérez-Peña, Alberto Fernández-Ros, Belen Rosado, Amós De Gil, Gonzalo Prates, Jorge Garate, and Manuel Berrocoso

Nowadays, both, the number of observations and the accuracy of satellite-based geodesic measurements, like GNSS, have increased. Therefore, GNSS provides more data as displacement values and velocities. This paper demonstrates that GNSS data analysis is a powerful tool to study geodynamic processes.

In this study, the analyzed GNSS data correspond to continuously recorded GPS (CGPS) stations, what we call the SPINA network. These stations are located in a region called Ibero-Maghrebian which includes the southern areas of the Iberian Peninsula and northern Africa.

The CGPS stations are included in the following organizations: RENEP (National Network of Permanent Stations), RAP (Andalusian Positioning Network), the Murcia Region CGPS Networks, ERVA (Valencian Reference Stations Network), IGN (National Geographic Institute) and the network TOPOIBERIA. The velocity was obtained in two steps: (1) preprocessing position time-series data of daily GPS measurements and (2) applying a combined model using the weighted least-squares method.

The prior knowledge of the crustal strain rate tensor provides a description of geodynamic processes such as the fault strain accumulation.

Based on the distribution of the GNSS stations, several grid sizes were tested to identify the best resolution. A Python script was used to compute the full two-dimensional velocity gradient tensor by means of inverting the GNSS velocities. The tensorial analysis provides different aspects of deformation, such as the maximum shear strain rate, including its direction, and the dilatation strain rate. These parameters can be used to characterize the mechanism of the current deformation.

Based on the computations from the GNSS-data model of components of horizontal deformations, the rates of both principal, values and axes, of the Earth’s crust deformation were found. Deformations measured in the Ibero-Maghrebian region with GPS could be interpreted in terms of either elastic loading or ductile deformation.

How to cite: Pérez-Peña, A., Fernández-Ros, A., Rosado, B., De Gil, A., Prates, G., Garate, J., and Berrocoso, M.: INTEGRATION OF GNSS-GPS NETWORKS (cGPS) FOR OBTAINING STRESS AND STRAIN MODELS FOR THE SPINA REGION (SOUTH OF THE IBERIAN PENINSULA AND NORTH AFRICA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19570, https://doi.org/10.5194/egusphere-egu2020-19570, 2020.

EGU2020-21362 | Displays | G3.6

Geodynamic study of the north of the Andes block (Colombia, Panama, Ecuador and Venezuela) through gnss-gps: models of displacements, models of deformation and definition of local and regional geodynamic structures.

Berrocoso Manuel, Del Valle Arroyo Pablo Emilio, Colorado Jaramillo David Julián, Gárate Jorge, Fernández-Ros Alberto, Pérez-Peña Alejandro, Rosado Moscoso Belén, and Ramírez Zelaya Javier Antonio

The northwest of South America is conformed by the territories of Ecuador, Colombia and Venezuela. Great part of these territories make up the Northern Andes Block (BAN). The tectonic and volcanic activity in the northwest of South America is directly related to the interaction of the South American plate, and the Nazca and Caribbean plates, with the Maracaibo and Panama-Chocó micro plates. The high seismic activity and the high magnitude of the recorded earthquakes make any study necessary to define this complex geodynamic region more precisely. This work presents the velocity models obtained through GNSS-GPS observations obtained in public continuous monitoring stations in the region. The observations of the Magna-eco network (Agustín Codazzi Geographic Institute) are integrated with models already obtained by other authors from the observations of the GEORED network (Colombian Geological Service). The observations have been processed using Bernese software v.52 using the PPP technique; obtaining topocentric time series. To obtain the speeds, a process of filtering and adjustment of the topocentric series has been carried out. Based on this velocity model, regional structures have been defined within the Northern Andes Block through a differentiation process based on the corresponding speeds of the South American, Nazca and Caribbean tectonic plates. Local geodynamic structures within the BAN itself have been established through cluster analysis based on both the direction and the magnitude of each of the vectors obtained. Finally, these structures have been correlated with the most significant geodynamic elements (fractures, faults, subduction processes, etc.) and with the associated seismic activity.

How to cite: Manuel, B., Pablo Emilio, D. V. A., David Julián, C. J., Jorge, G., Alberto, F.-R., Alejandro, P.-P., Belén, R. M., and Javier Antonio, R. Z.: Geodynamic study of the north of the Andes block (Colombia, Panama, Ecuador and Venezuela) through gnss-gps: models of displacements, models of deformation and definition of local and regional geodynamic structures. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21362, https://doi.org/10.5194/egusphere-egu2020-21362, 2020.

EGU2020-21829 | Displays | G3.6

Investigating the Earthquake Cycle along Marmara Sea Region of North Anatolian Fault by means of seismo-geodetic observations

Haluk Ozener, Bahadir Aktug, Onur Yilmaz, Asli Sabuncu, Bengisu Gelin, Kaan Alper Uçan, Bulent Turgut, and Maryna Batur

Since 1766, the North Anatolian Fault Zone in the Marmara Sea has not generated a Mw=7.0 earthquake. In the Marmara Sea, three different segments are located having ~25 mm slip rates and ~10 mm slip deficit per year. The faulting mechanism within the Marmara Sea has capability of generating earthquakes larger than Mw7.0. We are continuously monitoring this critical region with more than 30 seismo-geodetic stations equipped with 100 Hz sampling seismographs and 1 Hz sampling GPS receivers, in order to detect fast and slow tectonic motions in and around the Marmara Sea at temporal and spatial scale from milliseconds to years and from centimeters to tens of kilometers.

The data obtained during this study provides us to identify the slip deficit along the fault, the segmentation of fault, the interaction between slip-deficit and background seismicity. Besides, these data also contribute to identify the pre-seismic seismo-geodetic behavior and co-seismic slip when Mw=7.0 type of earthquakes occurs.

How to cite: Ozener, H., Aktug, B., Yilmaz, O., Sabuncu, A., Gelin, B., Uçan, K. A., Turgut, B., and Batur, M.: Investigating the Earthquake Cycle along Marmara Sea Region of North Anatolian Fault by means of seismo-geodetic observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21829, https://doi.org/10.5194/egusphere-egu2020-21829, 2020.

G4.1 – Satellite Gravimetry: Data Analysis, Results and Future Mission Concepts

EGU2020-3077 | Displays | G4.1 | Highlight

NASA and GFZ GRACE Follow-On Mission: Status, Science, Advances

Frank Flechtner, Felix Landerer, Himanshu Save, Christoph Dahle, Srinivas Bettadbur, Mike Watkins, and Frank Webb

The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission were successfully launched in May-2018. The primary objective of the mission is to continue the 15-year GRACE (2002-2017) global data record of Earth’s monthly mass changes. These measurements have become an indispensable tool to quantify and track Earth’s water movement and surface mass changes across the planet. Monitoring changes in ice sheets and glaciers, near-surface and underground water storage, the amount of water in large lakes and rivers, as well as changes in sea level and ocean currents provides an integrated global view of how Earth’s water cycle and energy balance are evolving.

In this presentation we will present the current mission status, including instrument and flight system performance, discuss science data quality and performance as well as recent science results from the first two years of observations, and address data continuity from GRACE to GRACE Follow-On.

How to cite: Flechtner, F., Landerer, F., Save, H., Dahle, C., Bettadbur, S., Watkins, M., and Webb, F.: NASA and GFZ GRACE Follow-On Mission: Status, Science, Advances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3077, https://doi.org/10.5194/egusphere-egu2020-3077, 2020.

EGU2020-7707 | Displays | G4.1

Preliminary GRACE-FO gravity field solutions from Tongji University

Qiujie Chen, Yunzhong Shen, Xingfu Zhang, and Jürgen Kusche

Due to the battery issue, the Gravity Recovery and Climate Experiment (GRACE) mission unfortunately came to an end in October 2017 after providing more than 15 years of mass transport information of our changing planet. To continue to monitoring the mass transport in the Earth system, the GRACE Follow-On (GRACE-FO) was launched in May 2018. As a new feature of GRACE-FO, a Laser Ranging Interferometer (LRI) was equipped to measure the inter-satellite range at a nanometer level. Since May 2019, GRACE-FO Level-1B observations have been made available to our community. Using the GRACE-FO Level-1B observations without laser ranging information, preliminary GRACE-FO gravity field solutions from Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL) and Graz University of Technology have been released. Incorporating laser ranging observations into gravity field determination, a preliminary time series of GRACE-FO gravity field solutions has been derived from Tongji University in collaboration with University of Bonn. In this paper, the signal and noise of our gravity field solutions are analyzed and compared to those from other research groups. Our results show that the laser ranging observations with a sampling rate of 2s are able to improve gravity field solutions by about 7% in terms of geoid degree variances up to degree and order 96 as compared to the K-Band ranging data with a sampling rate of 5s.

How to cite: Chen, Q., Shen, Y., Zhang, X., and Kusche, J.: Preliminary GRACE-FO gravity field solutions from Tongji University, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7707, https://doi.org/10.5194/egusphere-egu2020-7707, 2020.

EGU2020-11664 | Displays | G4.1

Comparing GRACE-FO Mascon Solutions Computed Using Range-Rate vs Range-Acceleration Data from K-Band Ranging (KBR) and Laser Ranging Interferometer (LRI)

Himanshu Save, Srinivas Bettadpur, Steven Poole, Nadege Pie, and Peter Nagel

The GRACE Follow-On (GRACE-FO) mission, launched on May 22, 2018, is continuing the unprecedented mass anomaly time-series started by the GRACE mission. The 18 year record of global mass change fields have become indispensable to track the movement of water in the Earth System and monitor changes in the ice sheets, glaciers, surface water, ground water, sea level, ocean currents etc.

The traditional GRACE and GRACE-FO mascon solutions produced at the Center for Space Research uses the range-rate measurement from the intersatellite K-band ranging (KBR) data. In this paper we present techniques for computing alternate mascon solutions using range-acceleration measurements from the K-band ranging system. We discuss the comparison in techniques used and the results produced using SST range-rate vs range-acceleration data. GRACE-FO carries a technology demonstration of Laser Ranging Interferometer (LRI) system which offers a 10x improvement in the ranging measurement system. We discuss the comparison of the technique, parameterization and the resulting mascon solution derived using range-acceleration data from the KBR and LRI system.

How to cite: Save, H., Bettadpur, S., Poole, S., Pie, N., and Nagel, P.: Comparing GRACE-FO Mascon Solutions Computed Using Range-Rate vs Range-Acceleration Data from K-Band Ranging (KBR) and Laser Ranging Interferometer (LRI) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11664, https://doi.org/10.5194/egusphere-egu2020-11664, 2020.

EGU2020-6368 | Displays | G4.1

Comparison between Laser Ranging Interferometer and K/Ka band Ranging instruments.

Sebastien Allgeyer, Herbert McQueen, and Paul Tregoning

The GRACE Follow-On mission is the first twin-satellite mission equipped with a laser ranging interferometer (LRI) to measure the inter-satellite distance between the pair of satellites. The LRI operates independently of the K/Ka-band interferometer (KBR) and uses wavelengths 104 times shorter than the K-band system.  Released at the end of July 2019, the LRI range data is therefore expected to be of higher accuracy than the KBR and offers the possibility of a better spatial resolution. We compare the LRI and KBR observations of the GRACE-FO mission, from launch to December 2019, to assess the quality of the new LRI system. Spectral analysis of the level1B data shows that the noise level of the LRI is 3 orders of magnitude smaller than the KBR and that the gravity signal can be detected in the spectral band up to 30mHz in the LRI data compared to 20mHz in the KBR data.  We compare gravity fields estimated using LRI and KBR and show which parts of the spherical harmonic spectrum are affected by the improved accuracy of the LRI observations.

How to cite: Allgeyer, S., McQueen, H., and Tregoning, P.: Comparison between Laser Ranging Interferometer and K/Ka band Ranging instruments. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6368, https://doi.org/10.5194/egusphere-egu2020-6368, 2020.

EGU2020-3017 | Displays | G4.1

GRACE-FO accelerometer data recovery within ITSG-Grace2018 data processing

Saniya Behzadpour, Torsten Mayer-Gürr, Andreas Kvas, Sandro Krauss, Sebastian Strasser, and Barbara Süsser-Rechberger

In GRACE-FO (Gravity Recovery and Climate Experiment Follow-on) mission, similar to its predecessor GRACE, the twin satellites are equipped with three-axis accelerometers, measuring the non-gravitational forces. After one month in orbit, the GRACE-D accelerometer data degraded and its measurements were replaced by synthetic accelerometer data, the so-called transplant data, officially generated by the Jet Propulsion Laboratory (JPL). The transplant data was derived from the GRACE-C accelerometer measurements, by applying a time and attitude corrections and adding model-based residual accelerations due to thruster firings on GRACE-D.

For the ITSG-Grace2018 GRACE-FO release, the gravity field recovery is based on the use of in-house Level-1B accelerometer data (ACT1B) using the provided Level-1A data products. In this work, we present a novel approach to recover the ACT1B data by (a) implementing the state-of-the-art non-gravitational force models and (b) applying additional force model corrections.

The preliminary results show the improved ACT1B data not only contributed to a noise reduction but also improved the estimates of the C20 and C30 coefficients. We show that the offset between SLR (Satellite Laser Ranging) and GRACE-FO derived C20 and C30 time series can be reduced remarkably by the use of the new accelerometer product, demonstrating the merit of this new approach.

How to cite: Behzadpour, S., Mayer-Gürr, T., Kvas, A., Krauss, S., Strasser, S., and Süsser-Rechberger, B.: GRACE-FO accelerometer data recovery within ITSG-Grace2018 data processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3017, https://doi.org/10.5194/egusphere-egu2020-3017, 2020.

EGU2020-15173 | Displays | G4.1

Bridging the gap – linking GRACE and GRACE-Follow On by hlSST and SLR

Matthias Weigelt, Adrian Jäggi, and Ulrich Meyer

GRACE and GRACE-Follow On are the standard tools for observing the time variable gravity field. Unfortunately, there is no overlap of the two time series of monthly gravity field solutions due to the ending of the GRACE mission in 2017 before the first monthly solutions of GRACE-Follow On became available in June 2018. Thus, there is a need for an intermediate technique that will bridge the gap between the two missions and will allow 1) for a continued and uninterrupted time series of mass observations and 2) to compare, cross-validate and link the two time series. As a bridging technology hlSST/SLR combinations are arguably the most promising candidate. We presented earlier combinations of those based on 41 kinematic orbit products of 27 satellites and 9 SLR satellites. Here, we progress to the next step and present results where we use the combined hlSST/SLR solution within a Kalman environment to link GRACE to GRACE-Follow On via the hlSST/SLR time series. The combination is conducted on coefficient level: after reducing the climatology derived from GRACE, a modified continuous Wiener process acceleration (CWPA) model is employed as the driving dynamic model of the Kalman filter for the prediction step. Subsequently the predicted time step is updated by (residual) observations when available. The resulting time series is thus complete for all months starting from April 2002 till today. We will discuss the benefit and limitations of the approach. The research is conducted within the framework of the International Gravity Field Service (IGFS) product center (COST-G) which is dedicated to the combination of monthly global gravity field models.

How to cite: Weigelt, M., Jäggi, A., and Meyer, U.: Bridging the gap – linking GRACE and GRACE-Follow On by hlSST and SLR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15173, https://doi.org/10.5194/egusphere-egu2020-15173, 2020.

EGU2020-21426 | Displays | G4.1

Along-track analysis of GRACE and GRACE Follow-On KBR and LRI data for new science applications

Shin-Chan Han, Khosro Ghobadi Far, Jeanne Sauber, Christopher Mccullough, David Wiese, and Felix Landerer

We present a method of analysing inter-satellite tracking data for detecting short-term (sub-monthly) gravitational changes from GRACE and GRACE Follow-On.  The method is based on the residual range-rate data with respect to the reference range-rate computed with dynamic orbital state vectors.  Then, we apply a numerical differentiation to compute range-acceleration residuals.  We found that the range-acceleration residuals are near-perfectly correlated with the line-of-sight gravity difference (LGD) between two spacecrafts and the transfer (admittance) function between them can be determined regardless of time and space (Ghobadi-Far et al., 2018, JGR-Solid Earth, https://doi.org/10.1029/2018JB016088).  The transfer function, to be applied directly to range-acceleration residuals, enables accurate LGD determination with the error of 0.15 nm/s^2 over the frequency band higher than 1 mHz (5 cycles-per-revolution), whereas the actual GRACE measurement error is several times larger.

In this presentation, we present two new geophysical applications to examine high-frequency gravitational changes at times scales of significantly less than one month; Gravitational observation of tsunamis triggered by the 2004 Sumatra, 2010 Maule, and 2011 Tohoku earthquakes and transient gravitational changes due to Earth’s free oscillation excited by the 2004 earthquake.  Lastly, we present new results from GRACE Follow-On KBR and LRI inter-satellite ranging data. 

How to cite: Han, S.-C., Ghobadi Far, K., Sauber, J., Mccullough, C., Wiese, D., and Landerer, F.: Along-track analysis of GRACE and GRACE Follow-On KBR and LRI data for new science applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21426, https://doi.org/10.5194/egusphere-egu2020-21426, 2020.

EGU2020-18050 | Displays | G4.1 | Highlight

Can daily GRACE gravity field models be used to evaluate short-term hydro-meteorological signals over the continents?

Annette Eicker, Laura Jensen, Viviana Wöhnke, Andreas Kvas, Henryk Dobslaw, Torsten Mayer-Gürr, and Robert Dill

Over the recent years, the computation of temporally high-resolution (daily) GRACE gravity field solutions has advanced as an alternative to the processing of monthly models. In this presentation we will show that recent processing improvements incorporated in the latest version of daily gravity field models (ITSG-Grace2018) now allow for the investigation of water flux signals on the continents down to time scales of a few days.

Time variations in terrestrial water storage derived from GRACE can be related to atmospheric net-fluxes of precipitation (P), evapotranspiration (E) and lateral runoff (R) via the terrestrial water balance equation, which makes GRACE a new and completely independent data set for constraining hydro-meteorological observations and the output of atmospheric reanalyses.

In our study, band-pass filtered water fluxes are derived from the daily GRACE water storage time series by first applying a numerical differentiation filter and subsequent high-pass filtering to isolate fluxes at periods between 5 and 30 days. We can show that on these time scales GRACE is able to identify quality differences between different global reanalyses, e.g. the improvements in the latest reanalysis ERA5 of the European Centre for Medium-Range Weather Forecasts (ECWMF) over its direct predecessor ERA-Interim.

We can further demonstrate that only the very recent progress in GRACE data processing has enabled the use of daily GRACE time series for such an evaluation of high-frequency atmospheric fluxes. The accuracy of the previous daily GRACE time series ITSG-Grace2016 would not have been sufficient to carry out such an assessment.

How to cite: Eicker, A., Jensen, L., Wöhnke, V., Kvas, A., Dobslaw, H., Mayer-Gürr, T., and Dill, R.: Can daily GRACE gravity field models be used to evaluate short-term hydro-meteorological signals over the continents?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18050, https://doi.org/10.5194/egusphere-egu2020-18050, 2020.

EGU2020-18038 | Displays | G4.1

Assessing Global Ocean and Continental Mass Change from 17 years of GRACE/-FO: the role of coastal buffer zones

Benjamin D. Gutknecht, Andreas Groh, Denise Cáceres, and Martin Horwath

Following the ESA CCI Sea Level Budget Closure (SLBC) project's work of 2017–2019, we present updated time-series of

  • Global Ocean Mass Change (OMC) and
  • Continental Mass Change (CMC),

both including continuous measurements by GRACE-FO. By least-squares adjusting a multi-parameter fit to monthly resolved OMC, we estimate the linear trend of Global Ocean mass change over all presently available GRACE/-FO months since April 2002 to be 2.41 ± 0.22 mm/a, with an acceleration of 0.10 mm a-2 over the same period.

A systematic analysis of the computed ocean response ("monthly fingerprints") to on-shore mass changes by means of solving the sea level equation implies that the common method of re-scaling the 'inner' buffered ocean may lead to OMC overestimations up to 10 per cent. We present this effect as a function of coastal buffer width for a global and for a 'truncated' global ocean (Lat ≤ ±65°), since the latter case, as seen e.g. in conjunction with radar altimetry, can lead to more than five per cent overestimated OMC. Furthermore, the use of coastal buffers seems to induce phase bias in the annual oscillation, which may explain the observed phase shift in the monthly budget between GRACE OMC and the sum of contributing continental components (i.e. ice sheets, glaciers, land water storage).

As a supplementary product of the SLBC project, we present GRACE/-FO derived mass change series 2002-04/present for continents (excluding Greenland and Antarctica). Consistent integration of out-leaking signal over coastal buffer zones, and subtraction of GAD-corrected mean OMC therein, leads to agreement with independently-assessed joint land water and glacier mass change data, well within uncertainty bounds.

How to cite: Gutknecht, B. D., Groh, A., Cáceres, D., and Horwath, M.: Assessing Global Ocean and Continental Mass Change from 17 years of GRACE/-FO: the role of coastal buffer zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18038, https://doi.org/10.5194/egusphere-egu2020-18038, 2020.

EGU2020-2229 | Displays | G4.1

GRACE-like gridded reconstructions of total water storage change from SLR and statistical techniques

Juergen Kusche, Anno Löcher, Li Fupeng, and Roelof Rietbroek

The total water storage change (TWSC) data record from the GRACE mission has found numerous applications in hydrology, oceanography, cryosphere, solid Earth and sea level research, and climate sciences. However, GRACE was only launched in 2002 and it lasted until 2017 with an increasing number of missing data, while GRACE-FO continued in May 2018. There will be no TWSC data within a gap of at least 11 months, and no GRACE-like data exists prior to 2002. As a result the current data record is not sufficiently long to for validating climate model predictions even for the long-term mean of TWSC, let alone for the probability of extreme events.

In this contribution we will discuss ways to reconstruct terrestrial TWSC from either geodetic or hydrometeorological data, or possibly from a combination. We will present new reconstructions of TWSC from 1992 onwards from satellite laser ranging (SLR) and from statistical learning methods, discuss various approaches, and compare to conventional SLR solutions, the Humphrey (2019) statistical reconstruction, and to GRACE in the more recent time frame. We show that both geodetic SLR analysis and/or multilinear regression or machine learning approaches can be successfully applied in a regularized framework where spatial modes from a GRACE-era TWSC decomposition inform the reconstructions. We show that these reconstructions reproduce many phenomena seen in modelling studies beyond the seasonal cycle; e.g. the suspected gradual onset of Greenland mass loss around 1998-2000, increase ocean mass rate since about 2011, or the presence of ENSO events.

How to cite: Kusche, J., Löcher, A., Fupeng, L., and Rietbroek, R.: GRACE-like gridded reconstructions of total water storage change from SLR and statistical techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2229, https://doi.org/10.5194/egusphere-egu2020-2229, 2020.

EGU2020-12077 | Displays | G4.1 | Highlight

The NASA Mass Change Designated Observable Study: Progress and Future Plans

David Wiese, Carmen Boening, Victor Zlotnicki, Scott Luthcke, Bryant Loomis, Matthew Rodell, Jeanne Sauber, David Bearden, Jonathan Chrone, Scott Horner, Frank Webb, Bernard Bienstock, and Lucia Tsaoussi

The 2017-2027 US National Academy of Sciences Decadal Survey for Earth Science and Applications from Space classified mass change as one of five designated observables having the highest priority in terms of Earth observations required to better understand the Earth system over the next decade.  In response to this designation, NASA initiated multi-center studies with an overarching goal of defining observing system architectures for each designated observable.  Here, we discuss the progress made and future plans for the Mass Change Designated Observable study. Progress includes the development of a Science and Applications Traceability Matrix, a tool that links science objectives to measurement techniques and accuracies,  for the 15 science and applications objectives listed in the Decadal Survey, as well as the definition of as many as three different architectural classes for which to achieve those objectives.  We will describe the Value Framework that is under way to assess and evaluate each observing system architectural option.  Preliminary results assessing the science value versus cost/risk of observing system architectures will be presented. In addition, future plans for the Mass Change Designated Observable Study will be discussed.

How to cite: Wiese, D., Boening, C., Zlotnicki, V., Luthcke, S., Loomis, B., Rodell, M., Sauber, J., Bearden, D., Chrone, J., Horner, S., Webb, F., Bienstock, B., and Tsaoussi, L.: The NASA Mass Change Designated Observable Study: Progress and Future Plans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12077, https://doi.org/10.5194/egusphere-egu2020-12077, 2020.

EGU2020-21085 | Displays | G4.1

Signal contribution of the polar and the inclined pairs in a Bender configuration

Balaji Devaraju, Anshul Yadav, and Matthias Weigelt

The Bender configuration comprises of two GRACE-like pairs, one in a polar orbit and the other in an inclined orbit. While the polar pair covers the entire globe, the inclined pair does not cover the higher latitudes. Similarly, the polar orbit due to its north-south orientation is able to capture features that are predominantly oriented in the east-west direction, but the inclined pair does not have any such issues. In this scenario, we would like to know the signal contribution of the polar and inclined pairs to the different spherical harmonic coefficients. Furthermore, this contribution analysis will enable us to understand the strengths and weaknesses of the GRACE(-FO) mission. In this study we use simulated data for analysing the signal contribution of the two pairs of satellites.

How to cite: Devaraju, B., Yadav, A., and Weigelt, M.: Signal contribution of the polar and the inclined pairs in a Bender configuration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21085, https://doi.org/10.5194/egusphere-egu2020-21085, 2020.

EGU2020-8304 | Displays | G4.1

GRAVL: a new satellite mission concept aiming to detect earthquakes with a magnitude of 6.5 Mw and higher

Jerome Woodwark and Marcel Stefko and the GRAVL development team

Data from the US and German Gravity Recovery And Climate Experiment (GRACE) showed indications of pre-, co-, and post-seismic mass redistributions associated with earthquakes down to a magnitude of 8.3 Mw. These demonstrated state-of-the-art capabilities in obtaining high spatial resolution space-based gravimetry, and helped to improve understanding of mantle rheology, potentially even providing a route to developing early warning capabilities for future seismic events. We describe a new mission concept, GRAvity observations by Vertical Laser ranging (GRAVL), which aims to extend the earthquake detection limit down to magnitude 6.5 Mw, significantly increasing the number of observable events.

GRAVL directly measures the radial component of the acceleration vector via “high-low” inter-satellite laser ranging, increasing gravity field sensitivity. A constellation of Low-Earth Orbit (LEO) satellites act as test masses, equipped with reflectors and high precision accelerometers to account for non-gravitational forces. Two or more larger satellites are placed above these, in Geostationary or Medium Earth Orbit (GEO / MEO), and measure the distance to the LEO satellites via time-of-flight measurement of a laser pulse. To do this, the GEO/MEO spacecraft are each equipped with a laser, telescope and detector, and additionally require highly  accurate timing systems to enable ranging accuracy down to sub-micron precision. To detect co-seismic mass redistribution events of the desired magnitude, we determine a gravity field measurement requirement of order 0.1 µGal at a spatial resolution of approximately 100 km over a 3-day revisit interval. These are challenging requirements, and we will discuss possible approaches to achieving them.

The GRAVL mission concept was developed during the FFG/ESA Alpbach Summer School 2019 by a team of science and engineering students, and further refined using the Concurrent Engineering approach during the Post-Alpbach Summer School Event at ESA Academy's Training and Learning Facility at ESEC-Galaxia in Belgium.

How to cite: Woodwark, J. and Stefko, M. and the GRAVL development team: GRAVL: a new satellite mission concept aiming to detect earthquakes with a magnitude of 6.5 Mw and higher, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8304, https://doi.org/10.5194/egusphere-egu2020-8304, 2020.

EGU2020-10103 | Displays | G4.1

Simulation study on future gravity missions with constellations and formations of small satellites

Nikolas Pfaffenzeller, Roland Pail, and Tom Yunck

In the context of an increased public interest in climate-relevant processes, a number of studies on Next Generation Gravity Missions (NGGMs) have been commissioned to better map mass transport processes on Earth. On the basis of the successfully completed gravity field missions CHAMP, GOCE and GRACE as well as the current satellite mission GRACE-FO, different concepts were examined for their feasibility and economic efficiency. The focus is on increasing the spatiotemporal resolution while simultaneously reducing the known error effects such as the aliasing of temporal gravity fields due to under-sampling of signals and uncertainties in ocean tide models. An additional inclined pair to a GRACE-like satellite pair (Bender constellation) is the most promising solution. Since the costs for a realization of the Bender constellation are very high, this contribution focuses on alternative concepts in the form of different constellations and formations of small satellites. The latter includes both satellite pairs and chains consisting of trailing satellites. The aim is to provide a cost-effective alternative to the previous gravity field satellites while simultaneously increasing the spatiotemporal resolution and minimizing the above mentioned error effects. In numerical closed-loop simulations, different scenarios will be performed which differ in orbit parameters like shape and number of orbits, the number of satellites per orbit and their distance to each other as well as the number of inter-satellite links. Additionally, the impacts from the co-parametrization of non-tidal temporal gravity field signal and ocean tides on the gravity field solutions, obtained by the different concepts, will be investigated. 

How to cite: Pfaffenzeller, N., Pail, R., and Yunck, T.: Simulation study on future gravity missions with constellations and formations of small satellites , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10103, https://doi.org/10.5194/egusphere-egu2020-10103, 2020.

EGU2020-2596 | Displays | G4.1

Towards AOD1B RL07

Linus Shihora, Lea Poropat, and Henryk Dobslaw

The Atmosphere and Ocean non-tidal De-aliasing Level-1B (AOD1B) product is widely used internationally to correct for transient effects of atmosphere-ocean mass variability on Earth satellites at in particular low altitudes. The most recent release 06 is given every 3 hours in Stokes coefficients expanded up to degree and order 180. It is based on ERA-Interim and ECMWF operational data for the atmosphere, and simulations with the global general ocean circulation model MPIOM consistently forced with fields from the same atmospheric data-set. RL06 was introduced in the year 2016 and is routinely updated every 24 hours with all data-sets for the previous calendar day.

Based on a stationary error assessment for AOD1B RL06 that might be also used to explicitly characterize uncertainties of AOD1B in the gravity field estimation process, we present preliminary numerical experiments with the TP10 configuration of MPIOM in preparation of a new AOD1B version 07 which is planned to be released in the year 2021. Those experiments test effects of (i) the new hourly atmospheric forcing data-set from the latest reanalysis ERA-5 of ECMWF; (ii) a revised bathymetry in particular around Antarctica that also includes cavities underneath the ice-shelves; and the consideration of shielding effects of the ice cover; and (iii) the consequences of self-attraction and loading feedbacks on the ocean dynamics. Results will be discussed in terms of differences with respect to RL06, in situ ocean observations, and alternative model data-sets.

How to cite: Shihora, L., Poropat, L., and Dobslaw, H.: Towards AOD1B RL07, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2596, https://doi.org/10.5194/egusphere-egu2020-2596, 2020.

EGU2020-8032 | Displays | G4.1

A spatial covariance model for GRACE and GRACE-FO terrestrial water storage data

Maik Thomas, Eva Boergens, Henryk Dobslaw, Robert Dill, Christoph Dahle, and Frank Flechtner

Gridded terrestrial water storage (TWS) observed by GRACE or GRACE-FO typically show a spatial error structure that is anisotropic (direction depending), non-homogeneous (latitude depending), and non-stationary (time depending).

We will introduce a new covariance model characterizing this error behavior analytically with a direction depending Bessel function of the first kind. The anisotropy of this function is governed by a shape parameter allowing for longer correlation lengths in longitudinal than in latitudinal direction. The wave-effect of the Bessel function allows us to account for the residuals of the GRACE striping errors. Both size as well as shape parameters of the Bessel function vary smoothly with latitude. These variations are implemented via even Legendre polynomials. The non-stationarity of the covariance is modeled with time-varying point variances. The validity of this covariance model on the sphere was thoroughly tested with a Monte-Carlo approach.

First, we apply this covariance model to 5 years of simulated GRACE data (Flechtner et al., 2016) where true errors are readily available from the differences of the synthetic input and the finally recovered gravity fields. For the 50 largest discharge basins, we obtain more realistic time series uncertainties than from propagating the formal errors associated with the Stokes coefficients. For smaller basins, however, the covariance model tends to provide overly pessimistic uncertainty estimates.

Second, the model is adapted to real GRACE and GRACE-FO data to obtain realistic error covariance information for arbitrarily shaped basins from globally gridded error information. We will show the current plans to update GFZ’s GravIS portal (http://gravis.gfz-potsdam.de/home) so that area- and time-dependent error information which is critically important for the assimilation of GRACE-based TWS data into numerical models will become readily available to the user community.

How to cite: Thomas, M., Boergens, E., Dobslaw, H., Dill, R., Dahle, C., and Flechtner, F.: A spatial covariance model for GRACE and GRACE-FO terrestrial water storage data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8032, https://doi.org/10.5194/egusphere-egu2020-8032, 2020.

EGU2020-10273 | Displays | G4.1

Status of GFZ's GRACE/GRACE-FO RL06 Level-2 and Level-3 Data Products

Christoph Dahle, Michael Murböck, Frank Flechtner, Rolf König, Henryk Dobslaw, Eva Boergens, Ingo Sasgen, and Andreas Groh

The GRACE Follow-On (GRACE-FO) mission was successfully launched on May 22nd, 2018 and continues the 15-year data record of monthly global mass changes from the GRACE mission (2002-2017). The German Research Centre for Geosciences (GFZ) as part of the GRACE/GRACE-FO Science Data System (SDS) has recently reprocessed the complete GRACE mission data (RL06 in the SDS nomenclature). These RL06 processing standards serve as common baseline for the continuation with GRACE-FO data.

This presentation provides an overview of the current processing status and the validation of the GFZ GRACE/GRACE-FO RL06 gravity field products. Besides its Level-2 products (monthly sets of spherical harmonic coefficients representing the Earth's gravity potential), GFZ additionally generates user-friendly Level-3 products in collaboration with the Alfred-Wegener-Institut (AWI) and TU Dresden. These Level-3 data products comprise dedicated mass anomaly products of terrestrial water storage over non-glaciated regions, bottom pressure variations in the oceans and ice mass changes in Antarctica and Greenland, available via GFZ's Gravity Information Service (GravIS) portal (http://gravis.gfz-potsdam.de/).

How to cite: Dahle, C., Murböck, M., Flechtner, F., König, R., Dobslaw, H., Boergens, E., Sasgen, I., and Groh, A.: Status of GFZ's GRACE/GRACE-FO RL06 Level-2 and Level-3 Data Products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10273, https://doi.org/10.5194/egusphere-egu2020-10273, 2020.

EGU2020-19563 | Displays | G4.1

On the determination of low degree harmonics by combining SLR with GRACE / GRACE-FO

Rolf Koenig, Patrick Schreiner, and Christoph Dahle

Today's state-of-the-art gravity missions GRACE and GRACE-FO monitor the Earth's gravitational field in high temporal and spatial resolution. The resulting time series of gravitational fields serves various geophysical applications. It is however recommended to replace the C(2,0) coefficients, which describe the change of the Earth's oblateness, by those determined by Satellite Laser Ranging (SLR) to geodetic satellites. There are also discussions ongoing on the C(2,1), S(2,1) and C(3,0) coefficients. Current research shows that a combination of GRACE and GRACE-FO with SLR can lead to an improvement of the determination of the low degree coefficients in view of certain geophysical applications. This contribution gives an insight into the recent research at the Helmholtz Center Potsdam - German Research Center for Geosciences (GFZ) on various methods for the multi-technique combination on normal equation level and discusses the effects on the low degree spherical harmonics.

How to cite: Koenig, R., Schreiner, P., and Dahle, C.: On the determination of low degree harmonics by combining SLR with GRACE / GRACE-FO, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19563, https://doi.org/10.5194/egusphere-egu2020-19563, 2020.

EGU2020-8622 | Displays | G4.1

The research unit NEROGRAV: first results on stochastic modeling for gravity field determination with real GRACE and GRACE-FO data

Michael Murböck, Panafidina Natalia, Dahle Christoph, Neumayer Karl-Hans, Flechtner Frank, and Rolf König

The central hypothesis of the Research Unit (RU) NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions), funded for three years by the German Research Foundation DFG, reads: only by concurrently improving and better understanding of sensor data, background models, and processing strategies of satellite gravimetry, the resolution, accuracy, and long-term consistency of mass transport series from satellite gravimetry can be significantly increased; and only in that case the potential of future technological sensor developments can be fully exploited. Two of the individual projects (IPs) within the RU work on stochastic modeling for GRACE and GRACE-FO gravity field determination. TU München and TU Berlin are responsible for IP4 (OSTPAG: optimized space-time parameterization for GRACE and GRACE-FO data analysis), where besides optimal parameterization the focus is on the stochastic modeling of the key observations, i.e. GRACE and GRACE-FO inter-satellite ranging and accelerometer observations, in a simulation (TU München) and real data (TU Berlin) environment. IP5 (ISTORE: improved stochastic modeling in GRACE/GRACE-FO real data processing), which GFZ is responsible for, works on the optimal utilization of the stochastic properties of the main GRACE and GRACE-FO observation types and the main background models.

This presentation gives first insights into the TU Berlin and GFZ results of these two IPs which are both related on stochastic modeling for real data processing based on GFZ GRACE and GRACE-FO RL06 processing. We present the analyses of K-band inter-satellite range observations and corresponding residuals of three test years of GRACE and GRACE-FO real data in the time and frequency domain. Based on the residual analysis we show results of the effects of different filter matrices, which take into account the stochastic properties of the range observations in order to decorrelate them. The stochastic modeling of the background models starts with Monte-Carlo simulations on background model errors of atmospheric and oceanic mass variations. Different representations of variance-covariance matrices of this model information are tested as input for real GRACE data processing and their effect on gravity field determination are analyzed.

How to cite: Murböck, M., Natalia, P., Christoph, D., Karl-Hans, N., Frank, F., and König, R.: The research unit NEROGRAV: first results on stochastic modeling for gravity field determination with real GRACE and GRACE-FO data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8622, https://doi.org/10.5194/egusphere-egu2020-8622, 2020.

EGU2020-11953 | Displays | G4.1

Implementation of GRACE and GRACE-FO observation covariance estimates at JPL

Matthias Ellmer, David Wiese, Christopher McCullough, Dah-Ning Yuan, and Eugene Fahnestock

Developing meaningful uncertainty quantifications for GRACE or GRACE-FO derived products, e.g. water storage anomalies, requires a robust understanding of the information and noise content in the observables employed in their estimation.

The stochastic models for GRACE and GRACE-FO K-Band, LRI, and GPS carrier phase and pseudorange observables employed in upcoming JPL solutions, along with notes on their implementation and development, will be presented. Within these models, the time-domain correlations for each of the observations are estimated, and then applied in the least squares estimate of monthly gravity field solutions. Reproducing results from other groups, the resulting formal errors of monthly solutions are improved.

It is envisioned that possible new Level 3 products can make these improved uncertainty quantifications accessible to the GRACE user community at large. Possible specifications for such products will be presented, and feedback from the community and discussion will be appreciated.

How to cite: Ellmer, M., Wiese, D., McCullough, C., Yuan, D.-N., and Fahnestock, E.: Implementation of GRACE and GRACE-FO observation covariance estimates at JPL, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11953, https://doi.org/10.5194/egusphere-egu2020-11953, 2020.

One of the valuable products of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission is a centimeter-accuracy orbit of the GOCE satellite called the precise science orbit (PSO). This orbit, delivered by the European Space Agency (ESA), was the reference for the GOCE orbit modeling using the piecewise constant acceleration approach. Besides initial conditions, the piecewise constant accelerations (i.e. empirical accelerations) were estimated in the radial, along-track and cross-track direction, employing the dedicated package called Torun Orbit Processor (TOP). The TOP software is based on the classical least squares adjustment including the Cowell 8-th order numerical integration for an orbit prediction and the orbit improvement module, taking into account the gravity field model and the background models (BM) describing gravitational and non-gravitational perturbing forces. The positions of GOCE satellite on the reduced-dynamic PSO orbit were treated as observations in the orbit improvement process. A measure of the fit of estimated arcs and their accuracy was the RMS of the residuals between the estimated orbits and the corresponding reference ones. Different variants of the orbit estimation were obtained for the shorter  arcs (22.5, 45, 90 and 180 minutes)  and for the longer 1-day arcs. The solution variants were determined for different numbers of the estimated piecewise constant accelerations. Moreover, these numbers were different for the radial, along-track and cross-track direction. The obtained solutions depend on a kind of computational mode – with and without the BM models in the GOCE orbit modeling using the estimated piecewise constant accelerations. Additionally, for selected solutions, the distributions of the residuals in the aforementioned directions along the estimated arcs are presented. 

How to cite: Bobojć, A.: Efficiency of the piecewise constant acceleration modeling - GOCE case study , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1378, https://doi.org/10.5194/egusphere-egu2020-1378, 2020.

EGU2020-5721 | Displays | G4.1

ONERA accelerometers for future gravity mission

Marine Dalin, Vincent Lebat, Damien Boulanger, Francoise Liorzou, Bruno Christophe, Manuel Rodrigues, and Phuong-Anh Huynh

ONERA (the French Aerospace Lab) is developing, manufacturing and testing ultra-sensitive electrostatic accelerometer for space application. ONERA has procured the accelerometer for all the previous gravity missions (GRACE, GOCE, GRACE-FO) and works to improve the scientific return of the instruments.

One way is to propose an accelerometer with 3 sensitive linear acceleration measurements as well as 3 angular acceleration measurements for the attitude control or reconstruction. Two different configurations are proposed: CubSTAR, a miniaturized version with low accuracy but adapted for constellation or nanosat; and MicroSTAR, a high accuracy accelerometer.

CubSTAR accelerometer is a small volume instrument with the same performance on the 3 axes, the baseline being 20x20x20mm proof-mass in a 15x15x20cm volume envelope. A prototype was manufactured and tested during a drop-tower test. Moreover this prototype will be tested in vibration environment to check its good mechanical behavior.

MicroSTAR accelerometer is designed with a disruptive mechanical concept allowing using a 30x30x30mm proof-mass, with the same high-performance on the 3 axes. Modal and dynamic analyses have been performed and a prototype is under manufacturing.  

How to cite: Dalin, M., Lebat, V., Boulanger, D., Liorzou, F., Christophe, B., Rodrigues, M., and Huynh, P.-A.: ONERA accelerometers for future gravity mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5721, https://doi.org/10.5194/egusphere-egu2020-5721, 2020.

EGU2020-10626 | Displays | G4.1

V04 Level-1 data processing status for GRACE and GRACE Follow-On

Tamara Bandikova, Hui Ying Wen, Meegyeong Paik, William Bertiger, Mark Miller, Nate Harvey, Christopher McCullough, Christopher Finch, Sung Byun, Da Kuang, Felix Landerer, and Carmen Boening

On May 22, 2020, the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), will celebrate two years of successful in-orbit operation. The primary goal of this satellite mission is to provide information about time variations of the Earth’s gravity field. This is possible due to precise orbit determination and inter-satellite ranging by determining the relative clock alignment of the USOs, precise attitude determination and accelerometry. High quality satellite observations are one of the fundamental requirements for successful gravity field recovery. NASA/Caltech Jet Propulsion Laboratory is the official Level-1 data processing and analysis center. The GRACE-FO Level-1 data are currently being processed with software version V04. This software will be used also for final reprocessing of the GRACE (2002-2017) Level-1 data. Here we present the analysis of two years of GRACE-FO sensor data as well as a preview of the reprocessed GRACE data, and discuss the measurement performance.

How to cite: Bandikova, T., Wen, H. Y., Paik, M., Bertiger, W., Miller, M., Harvey, N., McCullough, C., Finch, C., Byun, S., Kuang, D., Landerer, F., and Boening, C.: V04 Level-1 data processing status for GRACE and GRACE Follow-On, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10626, https://doi.org/10.5194/egusphere-egu2020-10626, 2020.

EGU2020-3976 | Displays | G4.1

Precise LEO satellite orbit determination and Earth gravity field modeling with carrier-range method

Geng Gao, Xiancai Zou, Shoujian Zhang, and Bingshi Liu

Precise LEO satellite orbit determination(OD) and Earth gravity field modeling are researched in this study.

Firstly, on the basis of Precise Point Positioning Ambiguity Resolution(PPPAR), a kinematic LEO satellite OD algorithm based on the epoch-difference and post-facto iteration is introduced, which plays a vital rule in the detection of the phase cycle slip to achieve the best orbit accuracy. The experiments of GRACE satellite OD with zero-difference IF combination observations spanning one year of 2010 show that, compared to the JPL reference orbits, the daily average 3D RMS is generally below 5.0cm for the float solution, while that is below 4.0cm for the fixed solution.

Secondly, to solve the problem that specific a-priori information like earth gravity field model must be involved in LEO’ reduced dynamic OD, the simultaneous solution method, which is specially on the relation with the kinematic OD and reduced dynamic OD, is used and the carrier-range, which can be recovered from phase observations once the kinematic OD process using Integer Ambiguity Resolution (IAR) technology is carried out, is naturally applied to this method. With the experiments based on the data over a period of the year of 2010, comes some evacuations, including the external checks on the accuracy of the orbits and the analysis on the earth gravity model. The numerical results show that, compared to the JPL reference orbits, the 3D RMS is below 3.0cm and the RMS is below 2.0cm for each component. As for the accuracy of gravity field model, compared to some contemporary significant earth gravity model, the model of the single month solution behaves very well below the 60 degree of the gravity field’s coefficients, while over the 60 degree, only the UTCSR model quite corresponds to the model computed by this method. Therefore, due to the promotion of the orbital accuracy and gravity field model, we suggest that the recovered carrier-range should be implemented in the simultaneous method for the better product solution of the LEO’s missions.

How to cite: Gao, G., Zou, X., Zhang, S., and Liu, B.: Precise LEO satellite orbit determination and Earth gravity field modeling with carrier-range method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3976, https://doi.org/10.5194/egusphere-egu2020-3976, 2020.

EGU2020-12622 | Displays | G4.1

A Hybrid-Precision Numerical Orbit Integration Technique for Next Generation Gravity Missions

Yufeng Nie, Yunzhong Shen, and Qiujie Chen

In Next Generation Gravity Missions (NGGM) the Laser Ranging Interferometer (LRI) is applied to measure inter-satellite range rate with nanometer-level precision. Thereby the precision of numerical orbit integration must be higher or at least same as that of LRI and the currently widely-used double-precision orbit integration technique cannot meet the numerical requirements of LRI measurements. Considering quadruple-precision orbit integration arithmetic is time consuming, we propose a hybrid-precision numerical orbit integration technique, in which the double- and quadruple-precision arithmetic is employed in the increment calculation part and orbit propagation part, respectively. Since the round-off errors are not sensitive to the time-demanding increment calculation but to the least time-consuming orbit propagation, the proposed hybrid-precision numerical orbit integration technique is as efficient as the double-precision orbit integration technique, and as precise as the quadruple-precision orbit integration. By using hybrid-precision orbit integration technique, the range rate precision is easily achieved at 10-12m/s in either nominal or Encke form, and furthermore the sub-nanometer-level range precision is obtainable in the Encke form with reference orbit selected as the best-fit one. Therefore, the hybrid-precision orbit integration technique is suggested to be used in the gravity field solutions for NGGM.

How to cite: Nie, Y., Shen, Y., and Chen, Q.: A Hybrid-Precision Numerical Orbit Integration Technique for Next Generation Gravity Missions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12622, https://doi.org/10.5194/egusphere-egu2020-12622, 2020.

EGU2020-18877 | Displays | G4.1

Benchmark data for verifying background model implementations in orbit and gravity field determination software

Martin Lasser, Torsten Mayer-Gürr, Andreas Kvas, Igor Koch, Jean-Michel Lemoine, Karl Hans Neumayer, Christoph Dahle, Frank Flechtner, Jakob Flury, Ulrich Meyer, and Adrian Jäggi
In the framework of the COmbination Service of Time-variable Gravity fields (COST-G) gravity field solutions from different analysis centres are combined to provide a consolidated solution of improved quality to the user. As in many other satellite-related sciences, the correct application of background models plays a crucial role in gravity field determination. Therefore, we publish a set of data of various commonly used forces in orbit and gravity field modelling (gravity field, tides etc.) evaluated along a one day orbit arc of GRACE, together with some additional data to enable easy comparisons. The benchmark data is compiled with the GROOPS software by the Institute of Geodesy (IfG) at Graz University of Technology. It is intended to be used as a reference and provides the opportunity to test the implementation of these models at various analysis centres. In view of the COST-G GRACE (-FO) gravity field combinations, we show the outcome of such a background force field software validation for the GRACE-SIGMA software of the Leibniz University of Hannover (LUH), the GRGS GINS software, EPOS of the German Research Centre for Geosciences (GFZ) and the Bernese GNSS software from AIUB (Astronomical Institute, University of Bern). We consider differences in the force modelling for GRACE (-FO) of one order of magnitude less than the accelerometer noise to be negligible, and make an attempt to quantify and explain differences exceeding this threshold.

How to cite: Lasser, M., Mayer-Gürr, T., Kvas, A., Koch, I., Lemoine, J.-M., Neumayer, K. H., Dahle, C., Flechtner, F., Flury, J., Meyer, U., and Jäggi, A.: Benchmark data for verifying background model implementations in orbit and gravity field determination software, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18877, https://doi.org/10.5194/egusphere-egu2020-18877, 2020.

EGU2020-11686 | Displays | G4.1

Gravity Field Estimation from GRACE Follow-On Data: Results from CSR Analyses

Srinivas Bettadpur, Himanshu Save, Peter Nagel, Nadège Pie, Steven Poole, Zhigui Kang, and Furun Wang

At the time of presentation, nearly two years of flight data from the joint NASA/GFZ GRACE Folllow-On mission will have been collected. In this time, gravity field models have been produced using two independent inter-satellite tracking systems - the MWI and the LRI using radio and optical interferometry, respectively. The data have been analyzed over more than two complete cycles of the sun relative to the orbit plane, allowing a characterization of the environmental impacts on the flight data. Extended duration of analyses have also permitted an assessment of the GRACE-FO data relative to the corresponding GRACE data.

This poster presents the status and lessons learned from two years of estimation of Earth gravity field models from the GRACE-FO data at the science data system component at the University of Texas Center for Space Research.

How to cite: Bettadpur, S., Save, H., Nagel, P., Pie, N., Poole, S., Kang, Z., and Wang, F.: Gravity Field Estimation from GRACE Follow-On Data: Results from CSR Analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11686, https://doi.org/10.5194/egusphere-egu2020-11686, 2020.

EGU2020-20851 | Displays | G4.1

Processing of GRACE-FO satellite-to-satellite tracking data using the GRACE-SIGMA software

Igor Koch, Mathias Duwe, Jakob Flury, and Akbar Shabanloui

The dual-satellite mission GRACE Follow-On (GRACE-FO) was launched in May 2018 as the successor of the Gravity Recovery And Climate Experiment (GRACE). In May 2019 first level 1 data products were made available to the community and are now published regularly. These products, among others, include orbits, accelerometer measurements, star camera data and micron and sub-micron precise inter-satellite range measurements. The data products are used by different groups to compute estimates of monthly gravity fields of the Earth. The in-house developed GRACE-SIGMA software is used at the Institut of Geodesy/Leibniz University Hannover for the estimation of monthly gravity fields. Several parts of the software’s processing chain, such as background modeling, were updated recently and different parametrization scenarios were tested. First solutions were estimated based on laser ranging interferometer measurements. Moreover, different orbit types, such as reduced-dynamic and kinematic, were tested. In this contribution, we present the influence of these updates and tests on the quality of the gravity fields. The obtained solutions are assessed in terms of error degree standard deviations and post-fit residuals of the inter-satellite measurements.

How to cite: Koch, I., Duwe, M., Flury, J., and Shabanloui, A.: Processing of GRACE-FO satellite-to-satellite tracking data using the GRACE-SIGMA software, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20851, https://doi.org/10.5194/egusphere-egu2020-20851, 2020.

EGU2020-11504 | Displays | G4.1

Investigation of systematic errors in GRACE temporal gravity field solutions using the Improved Energy Balance Approach

Metehan Uz, Orhan Akyılmaz, Jürgen Kusche, Ck Shum, Aydın Üstün, and Yu Zhang

In this study, we investigate systematic errors in our temporal gravity solutions computed using the improved energy balance approach (EBA) (Shang et al. 2015) by reprocessing the GRACE JPL RL03 L1B data product. Our processing consists of two steps: the first part is the estimation of in-situ geopotential differences (GPD) at the satellite altitude using the energy balance formalism, the second part is the estimation of spherical harmonic coefficients (SHCs) of the global temporal gravity field model using the estimated GPDs. The first step includes daily dynamic orbit reconstruction by readjusting the reduced-dynamic (GNV1B) orbit considering the reference model, and estimating the accelerometer calibration parameters. This is coupled with the alignment of the intersatellite velocity pitch from KBR range rate observations. Due to the strategy of using KBR range-rate in our processing algorithm, the estimation of in-situ geopotential differences (GPD) includes both the systematic errors and the high-frequency noise that result from the range-rate observations. Since estimated GPDs are linearly connected with the spherical harmonic coefficients (SHCs) of the global gravity field model, our temporal models are affected by these errors, especially in high-degree coefficients of the temporal gravity field solutions (from n=25 to n=60).

In order to increase our solution accuracy, we fit additional empirical parameters for different arc lengths to mitigate the systematic errors in our GPD estimates, thus improving our temporal gravity field solutions. Our EBA approach GRACE monthly gravity field models are validated by comparisons to the official L2 data products, including the official solutions from CSR (Bettadpur et al., 2018), JPL (Yuan et al., 2018) and GFZ (Dahle et al., 2018).

How to cite: Uz, M., Akyılmaz, O., Kusche, J., Shum, C., Üstün, A., and Zhang, Y.: Investigation of systematic errors in GRACE temporal gravity field solutions using the Improved Energy Balance Approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11504, https://doi.org/10.5194/egusphere-egu2020-11504, 2020.

EGU2020-12732 | Displays | G4.1

A User Needs Assessment for the next Mass Change Satellite Mission

Margaret Srinivasan, Matthew Rodell, John Reager, Bradley Doorn, and Laura Rogers

Planning is underway for development of the next NASA Mass Change satellite mission, as identified in the National Science Foundation’s 2017-2027 Decadal Survey for Earth Science and Applications from Space  (Decadal Survey). NASA has identified a Mass Change Designated Observable (MCDO) Study Team to evaluate satellite mission architectures that could optimally support a range of science and applications needs of user communities (both research and operational) of future mass change missions (i.e., successors to the GRACE and GRACE Follow On missions). The primary science objective of the MCDO, as identified in the Decadal Survey, is the continued measurement of changes in the Earth’s dynamic gravity field over time. The Decadal Survey also emphasizes applications of the mission data products as a major focus, in addition to science outcomes. 

Operational use and societal benefit derived from the GRACE and GRACE FO data and information products demonstrate the value of these missions. Applications include drought monitoring, quantification of groundwater depletion, flood prediction, and thermal expansion of the ocean, which contributes to sea level rise, to name a few. In order to effectively identify the observational product requirements of future gravity mission applications data users and to develop actionable objectives for mission design, a Mass Change Mission Applications survey was developed. Information on user needs, current uses, and capabilities derived from the survey have provided insights as to desired or required spatial scales, data latency, data formats, and technical capabilities of the users, as well as how to prioritize tradeoffs. The survey focused on evaluating the needs of a broad range of existing and potential user communities in order to incorporate these needs into mission design and architecture studies that are underway.

The survey comprises general questions about requirements for a given application, and data use and demographic information to help characterize aspects of the user community. Analyses of the survey results are now being used to inform potential mission architecture designs, evaluate tradeoffs, and ensure that the data products are optimized for a broad user community.

How to cite: Srinivasan, M., Rodell, M., Reager, J., Doorn, B., and Rogers, L.: A User Needs Assessment for the next Mass Change Satellite Mission , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12732, https://doi.org/10.5194/egusphere-egu2020-12732, 2020.

EGU2020-13359 | Displays | G4.1

The MARVEL gravity and reference frame mission proposal

Jean-Michel Lemoine and Mioara Mandea and the MARVEL Team

The "MARVEL gravity and reference frame mission" proposal has been selected by CNES for the start of a pre-phase A study. 
MARVEL aims at reaching in one single mission two major and complementary goals:
- The monitoring of mass transfers within the Earth system with increased precision,
- The realization, at the millimeter level, of the terrestrial reference frame.

In the nominal configuration, a LEO satellite (400 - 450 km) in polar orbit, acting as a gravity sensor, performs optical ranging measurements on two MEO satellites (7000 km) orbiting on the same plane. The MEO satellites are equiped with the four geodetic techniques (GNSS, SLR, DORIS, VLBI), in order to meet the GGOS Earth reference frame accuracy objectives.

We also propose two alternative (and less costly) configurations, where only the first goal is fully reached:
- one by replacing the MEO satellites by two or more cubesats on the same orbit,
- the second one by using specially equipped GNSS satellites as targets for the LEO optical ranging measurements.

In any case, the goal of monitoring mass change with enhanced precision is attained through the use of high-low SST laser tracking.

We will present in detail the different configurations proposed and present the simulation plan for this pre-phase A study.

How to cite: Lemoine, J.-M. and Mandea, M. and the MARVEL Team: The MARVEL gravity and reference frame mission proposal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13359, https://doi.org/10.5194/egusphere-egu2020-13359, 2020.

EGU2020-12821 | Displays | G4.1

On the earthquake detectability by the Next Generation Gravity Mission (NGGM)

Gabriele Cambiotti, Karim Douch, Stefano Cesare, Alberto Anselmi, Nico Sneeuw, Anna Maria Marotta, and Roberto Sabadini

We perform Next Gerataion Gravity Mission (NGGM) simulations over a 12-year operational period by including in the background gravity field the time-dependent gravity anomalies caused by different earthquake scenarios and considering different sources of error on 28-day mean gravity field solutions: the instrumental errors of the interferometer and accelerometers, the time depenendent background model and the atmosphere-ocean dealiasing. In order to assess whether the observational errors mask or not the earthquake-induced gravity signals, we assume known the background gravity field and the spatial and temporal pattern of the earthquake-induced gravity anomalies. Then, for each earthquake, we estimate the amplitude of its gravity anomaly by inverting the NGGM synthetic data time series and we check its consistency with the expected amplitude, as well as with the null hypothesis. In order to investigate case studies representative of the main earthquake characteristics and their compliance with the NGGM specifications, we have considered normal, inverse and strike-slip focal mechanisms striking with different angles with respect to the polar orbit, reaching the Earth surface and in depth, occurring inland, off-shore and close to the coastlines and at the beginning (2-4 years), at the middle (5-7 years) and at the end (8-10 years) of the 12-year operational period. The fault dimensions and slip distribution vary with the seismic moment magnitude and are prescribed according to the circular fault model by Eshelby (1957). Furthermore, we also consider two different rheological stratifications with asthenospheric viscosity of 10¹⁸ and 10¹⁹ Pa s. In order to discuss whether the earthquake signal can be discriminated from other geophysical processes (like atmosphere, ocean, hydrology and glacial isostatic adjustment), we also perform the same inversion but, this time, its amplitude is estimated jointly with the time dependent background gravity field, which we simply model using static values, trends and periodical functions.

How to cite: Cambiotti, G., Douch, K., Cesare, S., Anselmi, A., Sneeuw, N., Marotta, A. M., and Sabadini, R.: On the earthquake detectability by the Next Generation Gravity Mission (NGGM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12821, https://doi.org/10.5194/egusphere-egu2020-12821, 2020.

EGU2020-16447 | Displays | G4.1

High-resolution combined global gravity field modelling – The d/o 5,400 XGM2020 model

Philipp Zingerle, Roland Pail, and Thomas Gruber

Within this contribution we present the new experimental combined global gravity field model XGM2020. Key feature of this model is the rigorous combination of the latest GOCO06s satellite-only model with global terrestrial gravity anomalies on normal equation level, up to d/o 2159, using individual observation weights. To provide a maximum resolution, the model is further extended to d/o 5400 by applying block diagonal techniques.

To attain the high resolution, the incorporated terrestrial dataset is composed of three different data sources: Over land 15´ gravity anomalies (by courtesy of NGA) are augmented with topographic information, and over the oceans gravity anomalies derived from altimetry are used.  Corresponding normal equations are computed from these data sets either as full or as block diagonal systems.

Special emphasis is given to the novel processing techniques needed for very high-resolution gravity field modelling. As such the spheroidal harmonics play a central role, as well as the stable calculation of associated Legendre polynomials up to very high d/o. Also, a new technique for the optimal low-pass filtering of terrestrial gravity datasets is presented.

On the computational side, solving dense normal equation systems up to d/o 2159 means dealing with matrices of the size of about 158TB. Handling with matrices of such a size is very demanding, even for today’s largest supercomputers. Thus, sophisticated parallelized algorithms with focus on load balancing are crucial for a successful and efficient calculation.

How to cite: Zingerle, P., Pail, R., and Gruber, T.: High-resolution combined global gravity field modelling – The d/o 5,400 XGM2020 model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16447, https://doi.org/10.5194/egusphere-egu2020-16447, 2020.

EGU2020-3378 | Displays | G4.1

Can Swarm and SLR contribute to closing the global sea level budget?

Christina Lück, Bernd Uebbing, Anno Löcher, Roelof Rietbroek, Jürgen Kusche, Alexey Androsov, Jens Schröter, Sergey Danilov, and Alisa Yakhontova

Sea level change is an important indicator of global warming. In order to predict future sea level changes, it becomes more and more important to understand the complex contribution of different components (steric changes, melting of ice sheets and glaciers, hydrology,…) to the total sea level change on global and regional scales.

To distinguish between steric and mass-related sea level changes, we consider (1) satellite altimetry, which measures total sea level change, and (2) Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) data to derive mass changes within the Earth system. The information of both methods can be combined in a joint inversion approach to derive the individual components of sea level change. However, there is a gap of 11 months between GRACE and GRACE-FO and there are numerous (bi-)monthly gaps since 2011, which means that there is no dedicated gravity field mission to derive ocean mass changes during these times.

In this contribution, we use time-variable gravity field data from the Swarm satellite mission and Satellite Laser Ranging (SLR) as an additional source of information on mass changes within the inversion approach. Thus, we are able to derive inversion results even in times without GRACE(-FO), albeit at the expense of an inevitably lower spatial resolution. We compare results with GRACE(-FO) data to those without GRACE(-FO) data. Furthermore, we quantify the leverage of Swarm and SLR on the low-resolution mass signal at basin scale in the combined inversion approach during the GRACE(-FO) lifetime.

How to cite: Lück, C., Uebbing, B., Löcher, A., Rietbroek, R., Kusche, J., Androsov, A., Schröter, J., Danilov, S., and Yakhontova, A.: Can Swarm and SLR contribute to closing the global sea level budget?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3378, https://doi.org/10.5194/egusphere-egu2020-3378, 2020.

EGU2020-4710 | Displays | G4.1

Satellite monitoring of mass changes and ground subsidence in Sudan’s oil fields using GRACE and Sentinel-1 data

Nureldin Gido, Hadi Amin, Mohammad Bagherbandi, and Faramarz Nilfouroushan

Monitoring environmental hazards, due to natural and anthropogenic causes, is one of the important issues, which requires proper data, models, and cross-validation of the results. The geodetic satellite missions, e.g. the Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1, are very useful in this aspect. GRACE missions are dedicated to model the temporal variations of the Earth’s gravity field and mass transportation in the Earth’s surface, whereas Sentinel-1 collects Synthetic Aperture Radar (SAR) data which enables us to measure the ground movements accurately. Extraction of large volumes of water and oil decreases the reservoir pressure, form compaction and consequently land subsidence occurs which can be analyzed by both GRACE and Sentinel-1 data. In this paper, large-scale groundwater storage (GWS) changes are studied using the GRACE monthly gravity field models together with different hydrological models over the major oil reservoirs in Sudan, i.e. Heglig, Bamboo, Neem, Diffra and Unity-area oil fields. Then we correlate the results with the available oil wells production data for the period of 2003-2012. In addition, using the only freely available Sentinel-1 data, collected between November 2015 and April 2019, the ground surface deformation associated with this oil and water depletion is studied. Due to the lack of terrestrial geodetic monitoring data in Sudan, the use of GRACE and Sentinel-1 satellite data is very valuable to monitor water and oil storage changes and their associated land subsidence over our region of interest. Our results show that there is a significant correlation between the GRACE-based GWS change and extracted oil and water volumes. The trend of GWS changes due to water and oil depletion ranged from -18.5 to -6.2 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 SAR data analysis using Persistent Scatterer Interferometry (PSI) method shows high rate of subsidence i.e. -24.5, -23.8, -14.2 and -6 mm/year over Heglig, Neem, Diffra and Unity-area oil fields respectively. The results of this study can help us to control the integrity and safety of operations and infrastructure in that region, as well as to study the groundwater/oil storage behavior.

How to cite: Gido, N., Amin, H., Bagherbandi, M., and Nilfouroushan, F.: Satellite monitoring of mass changes and ground subsidence in Sudan’s oil fields using GRACE and Sentinel-1 data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4710, https://doi.org/10.5194/egusphere-egu2020-4710, 2020.

EGU2020-21563 | Displays | G4.1

MASCON versus spherical harmonic solutions to global monthly time varying gravity field

Juraj Janák, Adam Novák, and Barbora Korekáčová

Satellite missions Gravity Field and Climate Experiment (GRACE) and its successor (GRACE-FO) plays very important role in nowadays research in geodesy, geophysics, hydrology, oceanography, glaciology and climatology. Various research centres adopted different procedures for processing the GRACE/GRACE-FO measurements in order to get the main final product – the global monthly gravity field model. Until now there have been developed and published two fundamentally different approaches to this problem. The first is well-known approach of spherical harmonic analysis and the second is more recent and more direct approach called in literature MASCON (Mass Concentration). The purpose of this contribution is to compare existing MASCON global monthly gravity field models with the selected models based on spherical harmonic approach. Comparison is performed in selected river basins and also in selected polar region. Chosen river basins differ both in size and seasonal changes of continental water storage to cover more situations. Comparison of different filtered versions of spherical harmonic solutions (DDK1 – DDK7) with MASCON solution is also performed in one of the analysed river basins. Differences are analysed and advantages and drawbacks of two approaches and of particular models are discussed.

How to cite: Janák, J., Novák, A., and Korekáčová, B.: MASCON versus spherical harmonic solutions to global monthly time varying gravity field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21563, https://doi.org/10.5194/egusphere-egu2020-21563, 2020.

EGU2020-380 | Displays | G4.1

Determination of homogenous GRACE FOLLOW-ON monthly displacements based on available solutions

Artur Lenczuk, Anna Klos, and Janusz Bogusz

Presently, Gravity Recovery and Climate Experiment (GRACE) mission data is widely used in various fields of science. The longest satellite gravimetric mission regularly explored changes of the gravity field from April 2002 to October 2017. Nowadays, its follow-on mission (GRACE-FO) observes gravity changes from May 2018, providing new greater research opportunities. In the following research, we present a completely new vertical deformations changes model of the first 14 months GRACE-FO observations. The study’s aim is to reduce the signal noise left after Gauss spatial smoothing. In this study, we use monthly gravity field in spherical harmonics form up to degree and order 96, provided by three different centers, i.e. the NASA’s Jet Propulsion Laboratory (JPL), the German Research Center for Geosciences (GFZ) and the Center for Space Research (CSR). In following study, we use all sets of data (JPL, GFZ and CSR) to test three various algorithms: (1) coefficient-wise and (2) field-wise non-iterative weighting methods and further, (3) estimation by iterative variance component method.  Finally, we obtain joined spherical harmonics changes by a weighted average scheme, which are converted to Earth crust vertical deformations. The used weighting methods reduce root mean square scatter of monthly deformation fields by nearly 5% for continental areas (excluding Amazon basin and Hudson Bay region) and by 10-15% changes for the ocean areas. However, with respect to each new-created model, differences in monthly deformation changes are in the range from ±3 mm to ±6 mm depending on the data center (JPL, GFZ or CSR). Furthermore, the analysis of signal information contained in each degree allows us to assess the quality of the created models. The highest signal variations in our models occur up to the degree and order 25. Additionally, the high differences in the signal are obtained for sectoral harmonics up to the maximum degree. Analysis showed that the applied field-wise weights much more effectively remove remaining noise after spatial averaging than per-order/degree weighting. Whereas, the obtained results indicate that observations provided by GFZ center have the smallest weights for each algorithm.

How to cite: Lenczuk, A., Klos, A., and Bogusz, J.: Determination of homogenous GRACE FOLLOW-ON monthly displacements based on available solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-380, https://doi.org/10.5194/egusphere-egu2020-380, 2020.

Groundwater plays a major role in the hydrological processes driven by climate change and human activities, particularly in upper mountainous basins. The Jinsha River Basin (JRB) is the uppermost region of the Yangtze River and the largest hydropower production region in China. With the construction of artificial cascade reservoirs increasing in this region, the annual and seasonal flows are changing and affecting the water cycles. Here, we first infer the groundwater storage changes (GWSC), accounting for sediment transport in JRB, by combining the Gravity Recovery and Climate Experiment (GRACE) mission, hydrologic models and in situ data. The results indicate: (1) the average estimation of the GWSC trend, accounting for sediment transport in JRB, is 0.76±0.10 cm/year during the period 2003–2015, and the contribution of sediment transport accounts for 15%; (2) precipitation (P), evapotranspiration (ET), soil moisture change (SMC), GWSC and land water storage changes (LWSC) show clear seasonal cycles; the interannual trends of LWSC and GWSC increase, but P, runoff (R), surface water storage change (SWSC) and SMC decrease, and ET remains basically unchanged; (3) the main contributor to the increase in LWSC in JRB is GWSC, and the increased GWSC may be dominated by human activities, such as cascade damming, and climate variations (such as snow and glacier melt due to increased temperatures). This study can provide valuable information regarding JRB in China for understanding GWSC patterns and exploring their implications for regional water management.

How to cite: Chao, N.: Groundwater storage change in the Jinsha River basin from GRACE, hydrologic models, and in situ data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1281, https://doi.org/10.5194/egusphere-egu2020-1281, 2020.

In this study, we use temporal solutions of the Gravity Recovery and Climate Experiment (GRACE) satellite mission to study the surface mass variations of hydrological origin in North America. The most recent release (RL06) of GRACE Level 2 data from three processing centers (CSR, JPL, GFZ) and mascon products are used in a combination scheme to produce estimates of terrestrial water storage (TWS) changes for the period 2002–2016. The land hydrology signal is isolated from GRACE data by removing the contribution of two major non-hydrologic processes, i.e., the glacial isostatic adjustment (GIA) and the ice mass melting from the glaciated areas of Alaska, Greenland and the Canadian Arctic.

The examination of long-term TWS trends revealed strong signatures of the 2011–2015 droughts in California and Texas, as well as accumulation of TWS in the central part of North America. Negative long-term TWS trends associated with ice melting were found around the Hudson Bay region. The TWS changes are dominated by a strong annual and semi-annual signal with higher magnitude in Alaska and along the west coast of North America.

An additional study on the estimation of groundwater storage (GWS) changes is performed using the Global Land Data Assimilation System (GLDAS) model. The GLDAS data are pre-filtered using the same strategy as GRACE data to ensure spectral consistency between them. The general behavior of GWS agrees well with the TWS, especially in terms of positive long-term GWS trends in central North America and strong annual signal in Alaska. Positive GWS trends are also identified in the east US coast.

How to cite: Sideris, M. and Piretzidis, D.: An analysis of terrestrial water and groundwater storage changes in North America using recent GRACE products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2478, https://doi.org/10.5194/egusphere-egu2020-2478, 2020.

The mesoscale ocean gyres within polar oceans, including Ross Gyre (RG), Weddell Gyre (WG) and Beaufort Gyre (BG), are important features of the polar climate and ocean systems. However, they are not well observed by satellite altimetry because of their high latitudes and wintertime sea-ice coverage. We employ the GRACE satellite’s time-variable gravity (TVG) dataset from the Centre National d'Etudes Spatiales/Groupe de Recherches de Géodésie Spatiale (CNES/GRGS) Release 03 solutions at nominal 10-day sampling between July 2002 to June 2016, to investigate the non-seasonal and high-frequency variations of the three gyres, a feat demonstrated in a previous work by Yu and Chao (2018) for studying the Argentine Gyre. We solve the empirical orthogonal functions (EOF) and confirm their barotropic structure and find the sea level variations in the RG and WG are strongly correlated with the Antarctic Oscillation (AAO) and the El Nino-Southern Oscillation (ENSO), and that in the BG is correlated with salinity changes and ENSO. Different from the Argentine Gyre, there are no short-period oscillations of dipole pattern within the three subpolar gyres based on the complex EOF (CEOF) analysis from GRACE data. The fact that GRACE does observe these signals, while the de-aliasing background ocean model (whose predictions were removed before-hand in the employed GRACE data) fails to, ascertains that GRACE TVG data can shed light on the ocean gyre variabilities unavailable by satellite altimetry and at spatial and temporal resolutions higher than practiced hitherto.

How to cite: Gao, C. and Chao, B. F.: Variations of Subpolar Ocean Gyres Observed by the GRACE Time-Variable Gravity: Antarctic Ross/Weddell and Arctic Beaufort Gyres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4022, https://doi.org/10.5194/egusphere-egu2020-4022, 2020.

EGU2020-8170 | Displays | G4.1

Ice mass change in the Amur Drainage Basin estimated from multi-source observations

Zhiming Xu and Zhengtao Wang

The Amur River, with a total length of 4440 kilometers, is one of the major Asian rivers as well as the tenth largest river in the world flowing through China, Mongolia and Russia. As one of the high latitude rivers, the characteristics of terrestrial water storage(TWS) in Amur Drainage Basin are different from those in the middle and low latitude rivers. Its runoff is influenced by precipitation as well as the ice melt water, in this case, the research on this region has a unique scientific significance. In this study, Gravity Recovery and Climate Experiment(GRACE) time-varying gravity data is used to inverse the change of TWS in order to study the seasonal and interannual change of water storage in Amur Drainage Basin. By introducing Global Land Data Assimilation System(GLDAS) hydrological model and Global Precipitation Measurement(GPM) precipitation data, we can get the mass change of ice and snow of this area with water balance method. The result shows that the mass change of ice and snow detected by GRACE fits well with the trend of temperature. Which means GRACE combined with multi-source data has the ability to detect the change of ice and snow in high latitude rivers during the ice age.

How to cite: Xu, Z. and Wang, Z.: Ice mass change in the Amur Drainage Basin estimated from multi-source observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8170, https://doi.org/10.5194/egusphere-egu2020-8170, 2020.

         The Tibetan Plateau (TP) experiences complex mass transfer and redistribution due to the effects from internal earth dynamics and external climate change, such as, land water change, crustal uplift, surface denudation, and Moho interface change. These phenomenas are accompanied by the gravity field change and could be observed by the Gravity Recovery and Climate Experiment (GRACE). This study applies GRACE data to estimate the corresponding mass changes expressed by water equivalent height (EWH) anomaly of the TP. In addition, we use ICESat data and hydrological models to estimate the effects of hydrological factors (lake, glaciers, snow, soil moisture, and groundwater), to separate them from the comprehensive mass field to obtain the tectonic information. The total hydrological contribution to the average EWH change is -0.30±0.21 cm/yr. We further estimate the rates of tectonic uplift and denudation based on GNSS and denudation, with results of 0.71±0.46 mm/yr and 0.38±0.10 mm/yr, respectively. Removing the effects of hydrological change, surface displacements and GIA from the GRACE data, we obtain the EWH change contributed from interior mass change of 0.21±0.27 cm/yr, which is equivalent to a mean Moho interface uplift rate of 3.63±4.32 mm/yr. Final results show that the crustal thickness of the northern TP is thinning because of the upwelling of Moho interface and the southern TP is thickening along with Moho deepening, coinciding with the tomographic results.

Key words: the Tibetan plateau, mass transfer, land water change, Moho interface change, GRACE

How to cite: Rao, W. and Sun, W.: Estimating the changes in the Moho interface beneath the Tibetan Plateau based on GRACE data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4537, https://doi.org/10.5194/egusphere-egu2020-4537, 2020.

EGU2020-5697 | Displays | G4.1

How much of GPS noise refers to hydrology loading? An insight from GRACE-assimilating hydrological modeling

Anna Klos, Makan A. Karegar, Jürgen Kusche, and Anne Springer

Global Positioning System (GPS) observations are able to resolve Earth’s surface vertical deformation which originates among others from continental hydrological mass changes. Although long-term signals and seasonal changes of hydrology loading are well-captured by GPS observations, it is still unanswered whether GPS detects also the short-term hydrology-related deformations or not. In this presentation, we use predictions of vertical deformations from a GRACE (Gravity Recovery and Climate Experiment)-assimilating land surface model to separate deterministic and stochastic parts of GPS height changes observed by a set of 221 European EPN (EUREF Permanent GNSS Network) stations. This approach is compared to conventional harmonic functions approach, in which deterministic and stochastic parts are separated by pre-defined annual and semi-annual periods. For the stochastic parts associated with two methods, the noise parameters (spectral indices and amplitudes of power-law noise) are estimated using the Maximum Likelihood Estimation (MLE). Comparing original GPS displacements to displacements reduced for hydrological loading, we notice that annual and semi-annual frequencies are significantly explained by the hydrological model, resulting 60% reduction on average in amplitudes. This means that large part of seasonal crustal deformation arises from hydrological loading or unloading of the lithosphere. We find that the annual and semi-annual peaks are greatly reduced (72% on average) once conventional harmonic functions approach is used instead of GRACE-assimilating hydrological model, but no physical interpretation can be made here since it is difficult to identify the magnitude of each individual processes contributing to seasonal changes. The GRACE-assimilated model can remove the effect of high-frequency hydrological deformations, producing residuals with spectrum closer to the white noise process. Many oscillations present in GPS displacements at periods between 15 and 90 days are well-explained by GRACE-assimilating deformation model. We find the greatest improvement in noise parameters for stations located in the eastern and central regions of Europe, encompassing the Rhine, Elbe, Danube and Oder drainage basins where hydrological mass changes are relatively larger comparing to western Europe. Using GRACE-assimilated model as a deterministic part of GPS displacement time series, we provide a totally new estimates of noise parameters for European sites, which has never been presented before. Our results show that GRACE-assimilating water storage re-analyses can provide essential information for obtaining improved unbiased estimates of GPS vertical velocity, including their uncertainty, which are essential for a range of applications such as upcoming reference frame realizations.

How to cite: Klos, A., A. Karegar, M., Kusche, J., and Springer, A.: How much of GPS noise refers to hydrology loading? An insight from GRACE-assimilating hydrological modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5697, https://doi.org/10.5194/egusphere-egu2020-5697, 2020.

EGU2020-6236 | Displays | G4.1

Drought Patterns over the Amazon River Basin (1993-2019) as Interpreted by the Climate-driven Total Water Storage Change Fields

Fupeng Li, Zhengtao Wang, Nengfang Chao, Wei Liang, Kunjun Tian, and Yu Gao

The Gravity Recovery and Climate Experiment (GRACE) mission, since 2002, has measured total water storage change (TWSC) and interpreted drought patterns in an unparalleled way. Nevertheless, there are still few sources could be used to understand drought patterns prior to the GRACE era. Here we derived multi-decadal climate-driven TWSC grids and used them to interpret drought patterns (1993-2019) over the Amazon basin. The correlations of climate-driven TWSC as compared to GRACE, GRACE Follow-on, and Swarm TWSC are 0.95, 0.92, and 0.77 in Amazon at grid scale (0.5° resolution). The drought patterns assessed by the climate-driven TWSC are consistent to those interpreted by the Palmer Drought Severity Index and GRACE TWSC. We also found that the 1998 and 2016 drought events in Amazon, both induced by the strong El Niño events, show similar drought patterns. This study provides a new perspective for interpreting long-term drought patterns prior to the GRACE period.

How to cite: Li, F., Wang, Z., Chao, N., Liang, W., Tian, K., and Gao, Y.: Drought Patterns over the Amazon River Basin (1993-2019) as Interpreted by the Climate-driven Total Water Storage Change Fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6236, https://doi.org/10.5194/egusphere-egu2020-6236, 2020.

EGU2020-6756 | Displays | G4.1

Spatial Distribution of Viscoelastic Relaxation Following a Subduction Earthquake

Yuting Ji, Wenke Sun, and He Tang

Viscoelastic relaxation is generally considered as the dominant process of the long-term post-seismic deformation, while viscoelastic characteristic relaxation time represents the time scale of deformation caused by viscoelastic relaxation effect after the earthquake. The subduction earthquakes which occurred at the boundary of the ocean and continental plates often release greater stress, and the stress relaxation of mantle materials is more significant due to the response to viscoelasticity. Satellite gravity mission GRACE (gravity recovery and climate experience) is able to observe the corresponding co-seismic and post-seismic gravity changes. Therefore, in this study, we use the monthly gravity field model data of GRACE RL06 to study the post-seismic gravity changes of 2011 Tohoku earthquake and 2004 Sumatra earthquake. After removing the influence of sea level changes, GIA changes and GLDAS on the seasonal precipitation changes in the land area, as well as the sea water correction, we get the post-seismic deformation only related to the deformation of the solid earth. Then we use the attenuation function to fit each grid value and obtain the spatial distribution of viscoelastic characteristic relaxation time after rejecting the afterslip from the total post-seismic deformation. Thus,we can capture  the viscous structure in the subduction area.

How to cite: Ji, Y., Sun, W., and Tang, H.: Spatial Distribution of Viscoelastic Relaxation Following a Subduction Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6756, https://doi.org/10.5194/egusphere-egu2020-6756, 2020.

EGU2020-8819 | Displays | G4.1

The Performances of GRACE Mascon Solutions in Studying Seismic Deformations

Lan Zhang, He Tang, Le Chang, and Wenke Sun

The GRACE mascon solutions, called the advanced products of GRACE data, are widely used in cryosphere science or hydrology research. It has been demonstrated that the mascon solutions have the same or better performances compared with the spherical harmonic (SH) solutions at the basin scale. However, although the mascon solutions are expected to have the ability to recover the transient gravity signals due to large earthquakes, few studies have investigated the performances of the mascon solutions in studying seismic deformations systematically. In this study, we attempt to examine the performances of the mascon solutions for transient gravity signals induced by three M9 class earthquakes: the 2011 Tohoku-Oki, 2004 Sumatra and 2010 Chile earthquakes, and compare them with the SH solutions and theoretical gravity changes modelled by dislocation theory. We analyse the co-seismic gravity changes and conclude that the mascon solutions contain almost identical information as the SH solutions and can retrieve the co-seismic gravity change signals in the resolutions equivalent to the Gaussian filter radii of 210~270 km. However, the mascon solutions have other strengthening gravity change signals, with magnitudes that are the same order as that of the SH solutions and contain pre-seismic gravity change signals in the Tohoku earthquake. These strengthening and pre-seismic signals are both considered artificially introduced noise due to the mathematical treatment before releasing rather than real geophysical signals.

How to cite: Zhang, L., Tang, H., Chang, L., and Sun, W.: The Performances of GRACE Mascon Solutions in Studying Seismic Deformations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8819, https://doi.org/10.5194/egusphere-egu2020-8819, 2020.

EGU2020-12931 | Displays | G4.1

GRACE-FO and Swarm integrated data analysis reveals ionospheric disturbances on the accelerometer measurements

Myrto Tzamali, Athina Peidou, and Spiros Pagiatakis

Low Earth Orbit (LEO) satellites are subject to numerous disturbances related to the Earth’s upper ionosphere. Perturbations induced by the activity of the electromagnetic field (EM) at the upper ionospheric layers have not been fully understood yet. This study focuses on the disturbances shown on GRACE-FO accelerometer measurements when the EM field was disturbed by an intense geomagnetic storm occurred on August 2018. A thorough analysis of the accelerometer measurements of GRACE-C as well as the magnetic and electric field measurements from Swarm constellation is conducted, to enlighten their impulse-response relationship. We derive the temporal variations of the magnetic field by removing the main static field and we calculate the Poynting vector employing the Swarm magnetic field measurements and electric field data, by implementing rigorous data analyses to analyze the spatiotemporal characteristics of the energy flow of the electromagnetic field. Results show that GRACE-C accelerometer measurements are highly disturbed in the higher latitudes especially near the auroral regions. The signature of the spatial temporal variations of the magnetic field and the Poynting vector demonstrates very similar behaviour with GRACE-C disturbances. Cross wavelet analysis between Poynting vector and GRACE-C accelerometer disturbances shows a very strong coherence. With the two LEO missions, i.e. GRACE-FO and Swarm, orbiting the Earth in very similar orbits, further analysis towards integrating their measurements will enhance our understanding of the interaction of LEO satellites with the space environment and how this interaction is depicted in their measurements.

How to cite: Tzamali, M., Peidou, A., and Pagiatakis, S.: GRACE-FO and Swarm integrated data analysis reveals ionospheric disturbances on the accelerometer measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12931, https://doi.org/10.5194/egusphere-egu2020-12931, 2020.

EGU2020-2563 | Displays | G4.1

Temporal gravity variations in GOCE release 6 gravitational gradients

Betty Heller, Frank Siegismund, Roland Pail, and Thomas Gruber

As opposed to the level 1B release 5 GOCE gravitational gradient data, the newly reprocessed release 6 gradients provide reduced noise amplitudes in the low frequency-range, leading to reduced noise amplitudes of the derived gravity field models at large spatial scales, where temporal variations of the Earth’s gravity field have their highest amplitudes. This is the motivation to test the release 6 gradients for their ability to resolve temporal gravity variations.

For the gravity field processing, we apply a conventional spherical harmonics approach using the time-wise (TIM) processing method as well as a mass concentration (mascon) approach using point masses as base elements, which are grouped to land or ocean mascons by taking into account the coastlines.

By means of a closed-loop simulation study, we find that the colored instrument noise of the GOCE gravitational gradiometer introduces noise amplitudes into the derived gravity field models that lie above the amplitude of the gravity trend signal accumulated over 5 years. This indicates that detecting gravity variations taking place during the four-year GOCE data period from GOCE gradients only is challenging.

Using real GOCE data, we test bimonthly gradiometry-only gravity field models computed by both the spherical harmonic and the mascon approach for gravity signals that are resolved by GRACE data, being the temporal signals due to the ice mass trends in Greenland and Antarctica and the 2011 earthquake in Japan. Besides, corresponding GRACE/GOCE combination models are used to test whether the incorporation of GOCE data increases the resolution of temporal gravity signals.

We found that high-amplitude long-wavelength noise prevented the detection of temporal gravity variations among the bimonthly GOCE-only models. Using the SH approach, it was possible to detect the mean trend signal contained in the data by averaging multiple bimonthly models and considering their difference to a reference model. Using the mascon approach, trend signals contained in GOCE data could be recovered by including a GRACE model truncated to d/o 45 in a GRACE/GOCE combination model and thus let the GOCE data determine the short-scale signal structures instead of GRACE.

Finally, compared to the temporal gravity signal as resolved by GRACE data, no significant benefit of using or incorporating GOCE gravitational gradient data was found. The reason are the still rather high noise amplitudes in the derived models at large spatial scales, where the considered signal is strongest.

In order to detect temporal gravity variations in satellite gravitational gradiometry data, the measurement noise amplitudes in the low-frequency range would need to be reduced.

How to cite: Heller, B., Siegismund, F., Pail, R., and Gruber, T.: Temporal gravity variations in GOCE release 6 gravitational gradients, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2563, https://doi.org/10.5194/egusphere-egu2020-2563, 2020.

G4.2 – Modern Concepts for Gravimetric Earth Observation

EGU2020-21892 | Displays | G4.2 | Highlight

Chronometric measurements in geodesy and geophysics

Pacôme Delva and Guillaume Lion

At the beginning of the 20th century the theories of special and general relativity were developed by Einstein and his contemporaries. These physical theories revolutionize our conceptions of time and of the measurement of time. The atomic clocks, which appeared in the 1950s, are so accurate and stable that it is now essential to take into account many relativistic effects. The development and worldwide comparisons of such atomic clocks allowed for some of the most stringent of fundamental physics, as well as new ideas for the search of dark matter. On a more applied level, when taking general relativity for granted, distant comparisons of atomic clocks can be used for navigation and positioning, as well as the determination of the geopotential. I will show how the chronometric observables can fit and be used within the context of classical geodesy and geophysics, presenting various applications: determination of the geopotential with high spatial resolution, vertical reference system, and discussing the possible applications associated to the geodynamic processes related to mass transfers.

How to cite: Delva, P. and Lion, G.: Chronometric measurements in geodesy and geophysics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21892, https://doi.org/10.5194/egusphere-egu2020-21892, 2020.

EGU2020-3831 | Displays | G4.2

Unification of global vertical height system using precise frequency signal links

Ziyu Shen, Wen-Bin Shen, and Shuangxi Zhang

The realization of International Height Reference System (IHRS) is one of the major tasks of the International Association of Geodesy (IAG). Here we formulate a framework for connecting two local VHSs using ultra-precise frequency signal transmission links between satellites and ground stations, which is referred to as satellite frequency signal transmission (SFST) approach. The SFST approach can directly determine the geopotential difference between two ground datum stations without location restrictions, and consequently determine the height difference of the two VHSs. Simulation results show that the China’s VHS and the US’s VHS can be unified at the accuracy of several centimeters, provided that the stability of atomic clocks used on board the satellite and on ground datum stations reach the highest level of current technology, about 4.8×10-18 in 100 s. The SFST approach is promising to unify the global vertical height datum in centimeter level in future, providing a new way for the IHRS realization. This study is supported by NSFCs (grant Nos. 41721003, 41631072, 41874023, 41804012, 41429401, 41574007) and Natural Science Foundation of Hubei Province of China (grant No. 2019CFB611).

How to cite: Shen, Z., Shen, W.-B., and Zhang, S.: Unification of global vertical height system using precise frequency signal links, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3831, https://doi.org/10.5194/egusphere-egu2020-3831, 2020.

EGU2020-1998 | Displays | G4.2

Validating future gravity missions via optical clock networks

Stefan Schröder, Anne Springer, Jürgen Kusche, and Simon Stellmer

Stationary optical clocks show fractional instabilities below 10-18 when averaged over an hour, and continue to be improved in terms of precision and accuracy, uptime and transportability. The frequency of a clock is affected by the gravitational redshift, and thus depends on the local geopotential; a relative frequency change of 10-18 corresponds to a geoid height change of about 1 cm. This effect could be exploited for sensing large-scale temporal geopotential changes via a network of clocks distributed at the Earth's surface. The CLOck NETwork Services (CLONETS) project aims to create an ensemble of optical clocks connected across Europe via optical fibre links.
A station network spread over Europe, which is already installed in parts, would enable us to determine temporal variations of the Earth's gravity field at time scales of days  and thus provide a new means for validating satellite missions such as GRACE-FO or potential Next Generation Gravity Missions. However, mass changes at the surface of an elastic Earth are accompanied by load-induced height changes, and clocks are sensitive to non-loading e.g. tectonic height changes as well. As a result, local and global mass redistribution as well as local height change will be entangled in clock readings, and very precise  GNSS measurements will be required to separate them.
Here, we show through simulations how ice (glacier mass imbalance), hydrology (water storage) and atmosphere (dry and wet air mass) signals over Europe could be observed with the currently proposed/established clock network geometry and how potential extensions can benefit this observability. The importance of collocated GNSS receivers is demonstrated for the sake of signal separation.

How to cite: Schröder, S., Springer, A., Kusche, J., and Stellmer, S.: Validating future gravity missions via optical clock networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1998, https://doi.org/10.5194/egusphere-egu2020-1998, 2020.

EGU2020-10476 | Displays | G4.2

Optical clocks for gravity field observation and further geodetic applications

Hu Wu, Jürgen Müller, and Annike Knabe

In the past three decades, optical clocks and frequency transfer techniques have experienced a rapid development. They are approaching a fractional frequency uncertainty of 1.0x10-18, corresponding to about 1.0 cm in height. This makes them promising to realize “relativistic geodesy”, and it opens a new door to directly obtain gravity potential values by the comparison of clock frequencies. Clocks are thus considered as a novel candidate for determining the Earth’s gravity field. We propose to use a spaceborne clock to obtain gravity potential values along a satellite orbit through its comparison with reference clocks on ground or with a co-orbital clock. The sensitivity of clock measurements is mapped to gravity field coefficients through closed-loop simulations.

In addition, clocks are investigated for other geodetic applications. Since they are powerful in providing the height difference between distant sites, clocks can be applied for the unification of local/regional height systems, by estimating the offsets between different height datums and the systematic errors within levelling networks. In some regions like Greenland, clocks might be a complementary tool to GRACE(-FO) for detecting temporal gravity signals. They can be operated at locations of interest and continuously track changes w.r.t. reference clock stations. The resulting time-series of gravity potential values reveal the temporal gravity signals at these points. Moreover, as the equipotential surface at a high satellite altitude is more regular than that on the Earth’s surface, a couple of clocks in geostationary orbits can realize a space-based reference for the determination of physical heights at any point on the Earth through clock comparisons.

We gratefully acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC-2123/1 (Project-ID: 390837967).

How to cite: Wu, H., Müller, J., and Knabe, A.: Optical clocks for gravity field observation and further geodetic applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10476, https://doi.org/10.5194/egusphere-egu2020-10476, 2020.

EGU2020-10566 | Displays | G4.2

Laser Ranging Interferometer on GRACE Follow-On: Current Status

Vitali Müller and the GRACE Follow-On LRI Team

The GRACE Follow-On satellites were launched on 22nd May 2018 to continue the measurement of Earth’s gravity field from the GRACE satellites (2002-2017). A few weeks later, an inter-satellite laser link was established with the novel Laser Ranging Interferometer (LRI), which offers an additional measurement of the inter-satellite range next to the one provided by the conventional microwave ranging instrument. The LRI is the first optical interferometer in space between orbiters, which has demonstrated to measure distance variations with a noise below 1 nm/rtHz at Fourier frequencies around 1 Hz, well below the requirement of 80 nm/rtHz.

In this talk, we provide an overview on the LRI and present the current status and results regarding the characterization of the instrument. We will address the scale factor, which is needed to convert the phase measurements to a displacement, and the removal of phase jumps that are correlated to attitude thruster activations. Moreover, the results comprise the coupling of attitude variations into the measured range, which is determined by means of the center-of-mass calibration maneuvers. This coupling is expected to be one of the major error sources at low frequencies, however, it is not directly apparent due to the large gravity signal.

We conclude with some learned lessons and potential modifications of the interferometry for future geodetic missions.

How to cite: Müller, V. and the GRACE Follow-On LRI Team: Laser Ranging Interferometer on GRACE Follow-On: Current Status, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10566, https://doi.org/10.5194/egusphere-egu2020-10566, 2020.

EGU2020-8924 | Displays | G4.2

Cold Atom Interferometer activities for measuring the Earth’s gravity field

Luca Massotti, Olivier Carraz, Paolo Bensi, Roger Haagmans, Philippe Martimort, and Pierluigi Silvestrin

In the past decade, it has been shown that atomic quantum sensors are a newly emerging technology that can be used for measuring the Earth’s gravity field. Whereas classical accelerometers, based e.g. on capacitive sensing and electrostatic actuation, are limited by relatively high noise at low frequencies, Cold Atom Interferometers (CAI) can be highly accurate over the entire frequency range, which also has the benefit that they do not need any calibration phase. Several studies related to these new sensor concepts were initiated at ESA, mainly focusing on technology development for different instrument configurations (gravity gradiometers and  satellite-to-satellite ranging systems) and including validation activities, e.g. two successful airborne surveys with a CAI gravimeter. We will present the first conclusions of these different mission and instrument studies:

  • The first airborne gravity survey during the ESA Cryovex/KAREN 2017 campaign using this technology was conducted by DTU and ONERA. The measurements did not show any drift and the accuracy was found to be less than 4 mGal at 11 km resolution. A second campaign has been conducted by ONERA and CNES in 2019 in the South of France and improved the accuracy by a factor 4, reaching classical airborne survey state-of the art performance.
  • A first space quantum gravity mission concept is based on a gravity gradiometer that delivers a very high common mode rejection, greatly relaxing the drag-compensation requirements.
  • The second concept is based on quantum accelerometers for correcting low frequency errors of electrostatic accelerometers that are used in a low-low satellite-to-satellite ranging concept in order to measure non-gravitational accelerations.

For both concepts we will present the expected improvement in measurement accuracy and in the derived Earth gravity field models, taking into account the different types of measurement (e.g. single axis vs. three axis, integration time, etc.) and different mission parameters (e.g. attitude control, altitude of the satellite, lifetime of the mission, etc.). A technology roadmap will be outlined for potential implementation of a quantum inertial sensor geodesy mission within 10-15 years.

How to cite: Massotti, L., Carraz, O., Bensi, P., Haagmans, R., Martimort, P., and Silvestrin, P.: Cold Atom Interferometer activities for measuring the Earth’s gravity field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8924, https://doi.org/10.5194/egusphere-egu2020-8924, 2020.

EGU2020-9185 | Displays | G4.2

Operating an industry-grade quantum differential gravimeter

Camille Janvier, Vincent Ménoret, Jean Lautier, Bruno Desruelle, Sebastien Merlet, Franck Pereira dos Santos, and Arnaud Landragin

After three years of development in collaboration with LNE-SYRTE, we report on the development, the integration and the preliminary operation of an industry-grade absolute differential gravimeter. This new generation of instrument goes beyond the possibilities offered by existing gravity gradiometers, as one differential gravimeter measures simultaneously g and the vertical gradient of g [1]. Relying on atom interferometry with cold 87 Rb atoms, a single vertical laser beam simultaneously measures the vertical acceleration experienced by two sets of laser-cooled atoms free-falling from different heights. For each drop, the half-sum of the two vertical accelerations gives access to g and the half-difference to dg / dz. As far as technology is concerned, our differential gravimeter relies on a physical principle and a set of technologies that have already been validated for absolute quantum gravimeters [2].


Our demonstrator is operational since November 2019 and has shown the ability to run continuously for more 18 days without any human attendance.  We will present in detail the experimental results for the measurement of g and dg / dz. Regarding the measurement of the vertical gradient of g, we obtain a short-term sensitivity of 76 E/√t (1E = 10 -9 s -2 = 0.1 µGal/m) and a resolution of a 4 E when data is averaged over 1000 s. Regarding the measurement of g itself, we obtain a short-term sensitivity of 36 µGal/√t and a resolution of a few µGal when data is averaged over 500 s. These are preliminary results and options and future plan to improve the sensitivity and the stability of the measurements will be discussed.


Such quantum differential gravimeter is to our knowledge the only technology that allows for an absolute continuous drift-free monitoring of simultaneously gravity and gravity gradient over timescales from a few minutes to several months.

 

This work has been supported by the DGA, the French Department of Defense.

 

[1] R. Caldani et al., "Simultaneous accurate determination of both gravity and its vertical gradient", Phys. Rev. A 99, 033601 (2019)

[2] V. Ménoret et al., "Gravity measurements below 10−9 g with a transportable absolute quantum gravimeter", Nature Scientific Reports, vol. 8, 12300 (2018)

How to cite: Janvier, C., Ménoret, V., Lautier, J., Desruelle, B., Merlet, S., Pereira dos Santos, F., and Landragin, A.: Operating an industry-grade quantum differential gravimeter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9185, https://doi.org/10.5194/egusphere-egu2020-9185, 2020.

EGU2020-1059 | Displays | G4.2

Assessment of Tscherning-Rapp covariance in Earth gravity modeling using gravity gradient and GPS/leveling observations

Hadi Heydarizadeh Shali, Sabah Ramouz, Abdolreza Safari, and Riccardo Barzaghi

Determination of Earth’s gravity field in a high accuracy needs different complementary data and also methods to combine these data in an optimized procedure. Newly invented resources such as GPS, GRACE, and GOCE provide various data with different distribution which makes it possible to reach this aim. Least Squares Collocation (LSC) is one of the methods that help to mix different data types via covariance function which correlates the different involved parameters within the procedure. One way to construct such covariance functions is involving two steps within the remove-compute-restore (RCR) procedure: first, calculation of an empirical covariance function from observations which the gravitational effects of global gravity field (Long-wavelength) and topography/bathymetry have been subtracted from it and then fitting the Tscherning–Rapp analytical covariance model to the empirical one. According to the corresponding studies, the accuracy of LSC is directly related to the ability to localize the covariance function which itself depends on the data distribution. In this study, we have analyzed the data distribution and geometrically fitting factors, on GPS/Leveling and GOCE gradient data by considering the various case studies with different data distributions. To make the assessment of the covariance determination possible, the residual observations were divided into two datasets namely, observations and control points. The observations point served as input data within the LSC procedure using the Tscherning – Rapp covariance model and the control points used to evaluate the accuracy of the LSC in gravity gradient, gravity anomaly, and geoid predicting and then the covariance estimation. The results of this study show that the Tscherning-Rapp (1974) covariance has different outcomes over different quantities. For example, it models accurate enough the empirical covariance of gradient gravity but requires more analysis for gravity anomalies and GPS/Leveling quantities to reach the optimized results in terms of STD of difference between the computed and control points.

How to cite: Heydarizadeh Shali, H., Ramouz, S., Safari, A., and Barzaghi, R.: Assessment of Tscherning-Rapp covariance in Earth gravity modeling using gravity gradient and GPS/leveling observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1059, https://doi.org/10.5194/egusphere-egu2020-1059, 2020.

EGU2020-16528 | Displays | G4.2

Fundamental Notions in Relativistic Geodesy - physics of a timelike Killing vector field

Dennis Philipp, Claus Laemmerzahl, Eva Hackmann, Volker Perlick, Dirk Puetzfeld, and Juergen Mueller

The Earth’s geoid is one of the most important fundamental concepts to provide a gravity field- related height reference in geodesy and associated sciences. To keep up with the ever-increasing experimental capabilities and to consistently interpret high-precision measurements without any doubt, a relativistic treatment of geodetic notions within Einstein’s theory of General Relativity is inevitable. 

Building on the theoretical construction of isochronometric surfaces we define a relativistic gravity potential as a generalization of known (post-)Newtonian notions. It exists for any stationary configuration and rigidly co-rotating observers; it is the same as realized by local plumb lines and determined by the norm of a timelike Killing vector. In a second step, we define the relativistic geoid in terms of this gravity potential in direct analogy to the Newtonian understanding. In the respective limits, it allows to recover well-known results. Comparing the Earth’s Newtonian geoid to its relativistic generalization is a very subtle problem. However, an isometric embedding into Euclidean three-dimensional space can solve it and allows an intrinsic comparison. We show that the leading-order differences are at the mm-level. In the next step, the framework is extended to generalize the normal gravity field as well. We argue that an exact spacetime can be constructed, which allows to recover the Newtonian result in the weak-field limit. Moreover, we comment on the relativistic definition of chronometric height and related concepts.

In a stationary spacetime related to the rotating Earth, the aforementioned gravity potential is of course not enough to cover all information on the gravitational field. To obtain more insight, a second scalar function can be constructed, which is genuinely related to gravitomagnetic contributions and vanishes in the static case. Using the kinematic decomposition of an isometric observer congruence, we suggest a potential related to the twist of the worldlines therein. Whilst the first potential is related to clock comparison and the acceleration of freely falling corner cubes, the twist potential is related to the outcome of Sagnac interferometric measurements. The combination of both potentials allows to determine the Earth’s geoid and equip this surface with coordinates in an operational way. Therefore, relativistic geodesy is intimately related to the physics of timelike Killing vector fields.

How to cite: Philipp, D., Laemmerzahl, C., Hackmann, E., Perlick, V., Puetzfeld, D., and Mueller, J.: Fundamental Notions in Relativistic Geodesy - physics of a timelike Killing vector field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16528, https://doi.org/10.5194/egusphere-egu2020-16528, 2020.

EGU2020-22614 | Displays | G4.2

Opto-Mechanical Inertial Sensors (OMIS) for High Temporal Resolution Gravimetry

Lee Kumanchik, Felipe Guzman, and Claus Braxmaier

Gravity field measurement by free-falling atoms has the potential for very high stability
over time as the measurement exposes a direct, fundamental relationship between mass
and acceleration. However, the measurement rate of the current state-of-the-art limits
the performance at short timescales (greater than 1 Hz). Classical inertial sensors operate
at much faster response times and are thus natural companions for free-falling atom
sensors. Such a hybrid device would gain the ultra-high stability of the free-falling atom
sensor while greatly extending the bandwidth to higher frequency using the classical
sensor. This requires the stable bandwidth of both devices to overlap sufficiently. We
have developed opto-mechanical inertial sensors (OMIS) with good long term stability for
just this purpose. The sensors are made of highly stable fused silica material, feature a
monolithic optical cavity for displacement readout, and utilize a laser diode stabilized to
a molecular reference. With no temperature control and only the thermal shielding
provided by the vacuum chamber, this device is stable down to 0.1 Hz which overlaps
with the bandwidth of free-falling atom sensors. The OMIS are self-calibrating by
converting the fundamental resonances of a molecular gas into length using the
free-spectral range of the optical cavity,  FSR = c/2nL,  and then sampling the OMIS
mechanical damping rate and resonance frequency using a nearby piezo. This
acceleration calibration is potentially transferable to a companion free-falling atom
sensor. Readout is performed by modulating the cavity length of the OMIS with one
cavity mirror being the OMIS itself and the other being a high frequency resonator. The
high frequency resonator is driven by a nearby piezo well above the response rate of the
OMIS and acts like an ultrastable quartz clock. The resulting highly stable tone is
demodulated by the readout electronics. For the low finesse optical cavity used here, this
yields a displacement resolution of 2x10-13 m/√Hz and a high frequency acceleration
resolution of 400 ng /√Hz. At 0.1 Hz the acceleration resolution is 1.5 μg /√Hz limited by
the stability of our vibration isolation stage. The OMIS dimensions are about 30 mm x 30
mm x 5 mm and can be fiber coupled to enable co-location with other sensors or as
standalone devices for future gravimetry both on Earth and in space

How to cite: Kumanchik, L., Guzman, F., and Braxmaier, C.: Opto-Mechanical Inertial Sensors (OMIS) for High Temporal Resolution Gravimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22614, https://doi.org/10.5194/egusphere-egu2020-22614, 2020.

EGU2020-4640 | Displays | G4.2

Future Electrostatic Accelerometer without Polarization Wire

Damien Boulanger, Bruno Christophe, Manuel Rodrigues, Françoise Liorzou, Vincent Lebat, Marine Dalin, and Phuong-Anh Huynh

ONERA (the French Aerospace Lab) is developing, manufacturing and testing ultra-sensitive electrostatic accelerometer for space application. Accelerometers have been successfully developed for the Earth-orbiting gravity missions CHAMP, GRACE, GOCE and GRACE-FO and for Earth-orbiting Fundamental Physics mission MICROSCOPE.

In ONERA accelerometer design, the proof mass was levitated and was maintained at the center of an electrode cage by electrostatic forces. Moreover this proof mass was connected by a thin conductive wire (typically 5, 7 or 10 µm diameter wire). This wire allows us to polarize the proof mass and to evacuate the random charges induced by space radiation.

By removing this polarization wire, there will be positive impacts on the accelerometer defaults such as the removal of the parasitic dumping noise at low frequencies created by wire or its bias contribution; but it is important to verify that there are not also negative impacts such as noisy charging process.

After studying the evolution of the space radiation energy distribution on interesting orbits for earth missions, an evaluation of implemented current on the proof mass has been performed. A UV LED had been tested; the set-up and first measurements will be presented. Moreover a prototype is developed by ONERA to characterized charge management capabilities of such a system on a representative environment.

How to cite: Boulanger, D., Christophe, B., Rodrigues, M., Liorzou, F., Lebat, V., Dalin, M., and Huynh, P.-A.: Future Electrostatic Accelerometer without Polarization Wire , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4640, https://doi.org/10.5194/egusphere-egu2020-4640, 2020.

EGU2020-21986 | Displays | G4.2

A transportable absolute Quantum Gravimeter employing collimated Bose-Einstein condensates

Waldemar Herr, Nina Heine, Jonas Matthias, Sven Abend, Ludger Timmen, Jürgen Müller, and Ernst M. Rasel

The transportable Quantum Gravimeter QG-1 will perform absolute measurements of local gravitational acceleration with an unrivalled uncertainty below 3 nm/s² by utilising collimated Bose-Einstein-Condensates for atom interferometry in a compact setup. To permit this performance, leading order error sources of today’s cold atom gravimeters, predominantly stemming from the horizontal velocity of the interrogated atoms, will be minimised by this novel approach.
This contribution elaborates on the design and implementation of the interferometry setup into the atom chip based experimental system. We discuss their impact on the targeted uncertainty of 3 nm/s² and present recent developments for further miniaturisation and further reduction of next-generation instrument's complexities.

We acknowledge financial support from "Niedersächsisches Vorab" through "Förderung von Wissenschaft und Technik in Forschung und Lehre" for the initial funding of research in the new DLR-SI Institute and by the Deutsche Forschungsgemeinschaft (DFG) in the project A01 of the SFB 1128 geo-Q and under Germany's Excellence Strategy - EXC 2123 QuantumFrontiers, Project-ID 390837967.

How to cite: Herr, W., Heine, N., Matthias, J., Abend, S., Timmen, L., Müller, J., and Rasel, E. M.: A transportable absolute Quantum Gravimeter employing collimated Bose-Einstein condensates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21986, https://doi.org/10.5194/egusphere-egu2020-21986, 2020.

EGU2020-9893 | Displays | G4.2

Hybridization of atomic and electrostatic accelerometers for satellite control and gravity field recovery

Annike Knabe, Hu Wu, Manuel Schilling, and Jürgen Müller

Satellite gravimetry missions like GRACE and now GRACE-FO measure the global gravity field and its variations in time. Gravity field solutions are typically estimated monthly, but a higher accuracy and a better temporal resolution is required for various applications in the geosciences. With the addition of the laser ranging interferometer (LRI) to GRACE-FO, a significant improvement over GRACE concerning inter-satellite ranging was achieved. The determination of the non-gravitational forces acting on the satellites, however, remained conceptually unchanged. In ground-based applications, e. g., gravimetry and inertial navigation, the progress in the development of cold atom interferometry (CAI) leads to drift-free, accurate, smaller, more robust and reliable quantum sensors. Experiments on sounding rockets and aeroplanes demonstrate the potential of this technique and open up possibilities for applications on satellite missions.

We investigate potential next-generation gravity missions (NGGM) following the GRACE design, employing an LRI with GRACE-FO characteristics and the utilisation of CAI in combination with classical accelerometers. A CAI accelerometer also offers the possibility to better determine degree 2 gravity field coefficients, due to its long-term stability. A closed-loop simulator has been developed to test different scenarios of orbit configurations and system/instrument parameters. Regarding the orbit configurations, parameters like inter-satellite distance, orbit altitude and repeat cycle are varied. The results will be evaluated based on recovered gravity fields.

As further benefit, the concept of a CAI based drag-free control system is investigated and its impact on possible satellite orbits for NGGMs and the resulting gravity fields is discussed. As the control system is of critical importance for the success of the mission, key parameters are analysed. Furthermore, the requirement for the drag compensation depends on the knowledge of the accelerometer’s scale factor. Related to this aspect, requirements on the drag compensation are derived for different scenarios. We will present first results of the simulation studies.

H.W. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC 2123 “QuantumFrontiers, Project-ID 390837967“. M.S. acknowledges initial funding for the DLR Institute by the Ministry of Science and Culture of the German State of Lower Saxony from “Niedersächsisches Vorab”.

How to cite: Knabe, A., Wu, H., Schilling, M., and Müller, J.: Hybridization of atomic and electrostatic accelerometers for satellite control and gravity field recovery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9893, https://doi.org/10.5194/egusphere-egu2020-9893, 2020.

EGU2020-21546 | Displays | G4.2

The space-wise approach for cold-atom interferometry geodetic data analysis: the MOCASS study

Federica Migliaccio, Mirko Reguzzoni, and Khulan Batsukh

In recent years, an innovative mission concept has been proposed for gravity measurements with the aim of continuously monitoring the Earth gravity and its changes. The concept is based on a satellite-borne interferometer exploiting ultra-cold atom technology. Among other studies, a team of researchers from Italian universities and research institutions proposed and carried out the MOCASS project, to investigate the performance of a cold atom interferometer flying on a low Earth orbiter and its impact on the modeling of different geophysical phenomena.

In this study, the basic idea was that of a GOCE follow-on mission, with a unique spacecraft carrying an instrument capable of measuring functionals of the Earth gravitational potential. The geodetic data analysis of the gravity gradient data attainable by such a mission was carried out following the space-wise approach developed at Politecnico di Milano. The mathematical model for the processing of the MOCASS data was formulated, including the filtering strategy applied to take into account the cold atom interferometer transfer function. Numerical simulations were performed, with different configurations of the satellite orbit and pointing mode of the interferometer; data were simulated for two cases: (i) a single-arm gradiometer observing Txx or Tyy or Tzz gradients; (ii) a double-arm gradiometer observing Txx and Tzz gradients or Tyy and Tzz gradients. The results of the simulations will be illustrated, showing the applicability of the proposed concept and the neat improvement in modeling the static gravity field with respect to GOCE.

Moreover, a new study called MOCAST+ has been lately started proposing an enhanced cold atom interferometer which can deliver not only gravity gradients but also time measurements. The study will investigate whether this could give the possibility of improving the estimation of gravity models even at low harmonic degrees, with inherent advantages in the modeling of mass transport and its global variations: this will represent fundamental information, e.g. in the study of variations in the hydrological cycle and relative mass exchange between atmosphere, oceans, cryosphere and solid Earth.

How to cite: Migliaccio, F., Reguzzoni, M., and Batsukh, K.: The space-wise approach for cold-atom interferometry geodetic data analysis: the MOCASS study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21546, https://doi.org/10.5194/egusphere-egu2020-21546, 2020.

EGU2020-14996 | Displays | G4.2

Advancing intersatellite laser interferometry for geodesy applications

Alexander Koch, Gerhard Heinzel, Alexander Wanner, and Wolfgang Ertmer

In the summer of 2019 the Deutsches Zentrum für Luft- und Raumfahrt (German Aerospace Center) Institute for Satellite Geodesy and Inertial Sensing (DLR-SI) was founded. This new institute is located in Hannover with one group in Bremen. It benefits from strong ties to different institutes from the Leibniz University in Hannover (Institute for Quantum Optics, Institute of Geodesy, Institute for Gravitational Physics), the Center of Applied Space Technology and Microgravity (ZARM) in Bremen and the National Metrology Institute (PTB) in Brunswick.

In this talk I will give an overview of the focus of the working group for Laser Interferometric Sensing. The overarching goal of our group is the technology development for laser interferometric satellite geodesy missions, like a possible Next Generation Gravity Mission (NGGM). Due to the technological overlap, collaboration with the LISA community is also possible. Specifically, the currently planned work packages include, but are not limited to the development of novel optical bench topologies for laser interferometric ranging instruments for geodesy missions and the design of low noise photoreceivers and laser link acquisition sensors. Furthermore, interferometric readout of monolithic accelerometers will be studied and flight data from the GRACE Follow-On Laser Ranging Interferometer (LRI) will be evaluated within our group. In my talk I will give an overview of these planned work packages and will point out the expected benefit of these novel technologies to the geodesy community.

How to cite: Koch, A., Heinzel, G., Wanner, A., and Ertmer, W.: Advancing intersatellite laser interferometry for geodesy applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14996, https://doi.org/10.5194/egusphere-egu2020-14996, 2020.

EGU2020-15569 | Displays | G4.2

Alternative Level 1A to 1B Processing of GRACE Follow-On LRI data

Malte Misfeldt, Vitali Müller, Gerhard Heinzel, and Karsten Danzmann

The Laser Ranging Interferometer (LRI) on-board GRACE Follow-On, which was launched in May 2018, provides ranging data between two satellites with previously unknown precision. The low noise level of approximately 200 pm/rtHz at Fourier frequencies around 10 Hz allows us to investigate features, that have not been seen before in the ranging data.  

Due to this high sensitivity of the LRI, we are able to assess spurious linear non-gravitational accelerations in direction of the line-of-sight caused by attitude thruster activation, which should ideally produce only angular motion. This analysis may help to refine the models used in the Calibrated Accelerometer Data (ACT) product. The ACT product is derived from raw accelerometer data and corrects artefacts present in the raw accelerometer (ACC) product. However, linear non-gravitational accelerations can only be measured in narrow frequency ranges by the LRI, where the gravity ranging signal decayed below other contributors.

The conversion of LRI Level-1A to 1B is a complex task that comprises non-trivial removal of phase jumps, scaling, filtering and interpolation of data. In order to access the high-quality ranging data and have low post-fit residuals, the LRI instrument team at the Albert-Einstein Institute (AEI) in Hanover, Germany derived an alternative LRI Level-1B data product for January 2019 with some improvements compared to the official SDS RL04 data. The data can be downloaded at https://wolke7.aei.mpg.de/s/AYza4wrFjYBxHHQ.

In this poster we compare the AEI release with RL04 and explain the differences in the preprocessing of the data, which mainly originate from a more sophisticated estimation of the scale factor (i.e. the absolute laser frequency or wavelength), a continuous data stream without biases at day bounds and a light time correction with less noise from numerical inaccuracies.

How to cite: Misfeldt, M., Müller, V., Heinzel, G., and Danzmann, K.: Alternative Level 1A to 1B Processing of GRACE Follow-On LRI data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15569, https://doi.org/10.5194/egusphere-egu2020-15569, 2020.

According to the general theory of relativity, two clocks placed at two different positions with different geopotential run at different rates. Thus one can determine the geopotential difference between these two points by comparing the running rates of the two clocks. In this paper, we propose, design and describe in detail an approach for determining the geopotential difference between The Atomic Clocks Ensemble in Space (ACES/PHARAO mission) and a ground station based upon a simulation experiment. The correction due to Ionosphere, troposphere and Sagnac effect will be taken into account. Our team is working on a wide range of problems that need to be solved in order to achieve high accuracy in (almost) real-time. In this paper, we will present some key aspects of the measurement, as well as the current status of the software's development. the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.

How to cite: Ashry, M., Shen, W., and Sun, X.: An Approach for Determining the Geopotential Difference between The Atomic Clocks Ensemble in Space (ACES) and a ground station, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13154, https://doi.org/10.5194/egusphere-egu2020-13154, 2020.

EGU2020-2349 | Displays | G4.2

Test of gravitational redshift based on tri-frequency combination of frequency links between Atomic Clock Ensemble in Space and a ground station

Xiao Sun, Wen-Bin Shen, Ziyu Shen, Chenghui Cai, Wei Xu, Pengfei Zhang, and Mostafa Ashry

Atomic Clock Ensemble in Space (ACES) is an ESA mission designed mainly to test gravitational redshift with high-performance atomic clocks in space and on the ground. Here we develop tri-frequency combination (TFC) method based on the measurements of frequency shifts of three independent microwave links between ACES and a ground station. The potential scientific object requires an accuracy of at least 3×10-16, thus we need to consider various effects including Doppler effect, second-order Doppler effect, atmospheric frequency shift, tidal effects, refraction caused by atmosphere, Shapiro effect, with accuracy level of tens of centimeters. The ACES payload will be launched in middle of 2021, and the formulation proposed in this study will enable us to test gravitational redshift at an accuracy level at least 2×10-6 level, one order more higher than the present accuracy level. This study is supported by NSFCs (grant Nos. 41721003, 41631072, 41874023, 41804012, 41429401, 41574007) and Natural Science Foundation of Hubei Province of China (grant No. 2019CFB611).

How to cite: Sun, X., Shen, W.-B., Shen, Z., Cai, C., Xu, W., Zhang, P., and Ashry, M.: Test of gravitational redshift based on tri-frequency combination of frequency links between Atomic Clock Ensemble in Space and a ground station, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2349, https://doi.org/10.5194/egusphere-egu2020-2349, 2020.

EGU2020-20120 | Displays | G4.2

Simulated experiment of recovering gravity field from the observations of satellite’s frequency signal

Xinyu Xu, Ziyu Shen, Wenbin Shen, and Yongqi Zhao

Recovering the gravity field with the satellite’s frequency signal might be an alternative measuring mode in the future when the accuracy of the onboard clock was good enough. On the one hand, we analyze the performance of recovering gravity field model from the gravitational potentials with different accuracies on different satellite altitudes (from 200 km to 350 km) based on semi-analytical (SA) method. On the other hand, we analyze the performance based on the numerical analysis. First, the gravitational potentials along the satellite orbit are computed from the clock observations based on the method of satellite’s frequency signal with the accuracies of 10-16 and 10-18s. Then, based on the derived gravitational potentials, we recovered the gravity field models up to degree and order 200 (corresponding to 100 km spatial resolution). At last, the errors of recovered models are validated by comparing with the reference model.

How to cite: Xu, X., Shen, Z., Shen, W., and Zhao, Y.: Simulated experiment of recovering gravity field from the observations of satellite’s frequency signal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20120, https://doi.org/10.5194/egusphere-egu2020-20120, 2020.

Recent advancements in atomic clocks have enabled us to measure gravitational potential differences with a precision which is applicable to geodetic uses, based on the gravitational red shift. In Europe, international fiber networks linking optical clocks have been developed for promoting the unification of height reference systems across countries, and 10 cm-level agreements in terms of the equivalent height difference to the gravitational potential have been achieved in the comparisons between chronometric and classical geodetic methods. In Japan, similar comparisons using two optical lattice clocks were carried out for i) a 15-km fiber connecting RIKEN in Wako city and the Hongo campus of the University of Tokyo and ii) a 450-m fiber link which vertically connected the observatory and the ground at the Tokyo Skytree. For the former comparison, agreement between chronometric and geodetic results was better than 10 cm, and for the latter, data are under analysis. A new clock site has been developed at the NTT Basic Research Laboratories in Atsugi City. Clocks in Wako, Hongo and Atsugi constitute an approximately 100-km-scale network. In this presentation, we report a preliminary result on the geodetic leveling survey to determine the gravitational potential difference between these three sites. To estimate uncertainties in the potential difference, we will compare the result partially with those determined from the geoid model and the GNSS ellipsoidal height. We will also consider the effects of crustal vertical motion, in addition to measurement errors.

How to cite: Tanaka, Y., Aoki, Y., and Nishiyama, R.: Geodetic determination of the gravitational potential difference for an optical lattice clock comparison in the Kanto region in Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6220, https://doi.org/10.5194/egusphere-egu2020-6220, 2020.

EGU2020-3388 | Displays | G4.2

Experiments of determining the geopotential difference using two hydrogen atomic clocks and two-way satellite time and frequency transfer technique

An Ning, Kuangchao Wu, Wen-Bin Shen, Ziyu Shen, Chenghui Cai, and Xiao Sun

Abstract In this study, we carried out experiments of the geopotential difference determination at CASIC, Beijing with the help of two hydrogen atomic clocks, using the two-way satellite time and frequency transfe technique. Here the ensemble empirical mode decomposition method is adopted to extract geopotential-related time-elapse signals from the original observations. The clock-comparison-determined geopotential difference in the experiments is determined, which is compared to the previously known results determined by conventional approach. Results show that the geopotential difference determined by time comparison deviates from that determined by conventional approach by about 1589 m2s-2, which is equivalent to 162 m in height, in consistence with the stability of the hydrogen atomic clocks applied in the experiments (at the level of 10-15/day). Since the stability of the optical clocks achieve 10-18 level, the geopotential determination by accurate clocks is prospective, and it is prospective to realize the unification of the world vertical height system. This study is supported by NSFCs (grant Nos. 41721003, 41631072, 41874023, 41804012, 41429401, 41574007) and Natural Science Foundation of Hubei Province of China (grant No. 2019CFB611).

How to cite: Ning, A., Wu, K., Shen, W.-B., Shen, Z., Cai, C., and Sun, X.: Experiments of determining the geopotential difference using two hydrogen atomic clocks and two-way satellite time and frequency transfer technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3388, https://doi.org/10.5194/egusphere-egu2020-3388, 2020.

EGU2020-1716 | Displays | G4.2

An experiment of determining the geopotential difference using two hydrogen atomic clocks

Kuangchao Wu, Wen-Bin Shen, Ziyu Shen, Chenghui Cai, Xiao Sun, An Ning, and Yifan Wu

According to general relativity theory, one may determine the geopotential difference between two arbitrary stations by comparing there-located clocks’ running rates. In this study, we provide experimental results of the geopotential determination based on the time elapse comparison between two hydrogen atomic clocks, one fixed clock  and one portable clock , using the common view satellite time transfer (CVSTT) technique. We compared the portable clock  located at Jiugongshan Time Frequency Station (JTFS) with the fixed clock  located at Luojiashan Time Frequency Station (LTFS) for 30 days. The two stations are separated by a geographic distance of around 240 km with height difference around 1230 m. Then the clock  was transported (without stopping its running status) to LTFS and compared with clock  for zero-baseline calibration for 15 days. The clock-comparison-determined geopotential difference between JTFS and LTFS is determined. Results show that the clock-comparison-determined result deviates from the EGM20080-determined result by about 2322±1609 m2s-2, equivalent to 237±164  m in height, in consistence with the stability of the hydrogen atomic clocks applied in the experiments (at the level of 10-15/day).

This study is supported by NSFCs (grant Nos. 41721003, 41631072, 41874023, 41804012, 41429401, 41574007) and Natural Science Foundation of Hubei Province of China (grant No. 2019CFB611).

How to cite: Wu, K., Shen, W.-B., Shen, Z., Cai, C., Sun, X., Ning, A., and Wu, Y.: An experiment of determining the geopotential difference using two hydrogen atomic clocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1716, https://doi.org/10.5194/egusphere-egu2020-1716, 2020.

G4.3 – Acquisition and processing of gravity and magnetic field data and their integrative interpretation

EGU2020-6625 | Displays | G4.3 | Highlight

Decoupling the crustal and mantle gravity signature at subduction zones with satellite gravity gradients: case study Sumatra

Bart Root, Wouter van der Wal, and Javier Fullea

The GOCE satellite mission of the European Space Agency has delivered an unprecedented view of the gravity field of the Earth. In this data set, the strongest gravity gradient signals are observed at subduction zones in the form of a dipole. Despite numerous studies on subduction zones, it is still unclear what is causing this strong signal. Is the source of the observed dipole situated in the crust, mantle, or a combination of these?

We have constructed a 3D geometry of the Sumatra slab using the global SLAB1.0 model. This geometry is substituted in a global upper mantle model WINTERC5.4, a product of the ESA Support to Science Element: 3DEarth. The density in the subducting crust, mantle, or a combination of both is fitted to the gravity gradients at satellite height. Lateral varying Green’s functions are used to compute the gravity gradients from the densities. In the case of a combined crust/mantle model, spectral information of the sensitivity of satellite gradients is used to construct a weighted inversion.

Preliminary results show that crustal mass transport (mostly from the overriding plate) in the direction of the subducting plate is mostly responsible for the negative anomaly observed in between the trench and the volcanic arc. This signal is, however, not visible along the complete subduction zone. Most crustal transport is seen where normal subduction takes place. Oblique subduction shows less crustal transport and more intra-crustal faulting. The satellite gravity gradients show high sensitivity to this particular crustal signature and therefore can be used to analyze subduction zones globally.

How to cite: Root, B., van der Wal, W., and Fullea, J.: Decoupling the crustal and mantle gravity signature at subduction zones with satellite gravity gradients: case study Sumatra , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6625, https://doi.org/10.5194/egusphere-egu2020-6625, 2020.

EGU2020-7399 | Displays | G4.3

New insights on the dynamics of the Sumatra and Mariana complexes inferred from the comparative analysis of gravity data and model predictions

Arcangela Bollino, Anna Maria Marotta, Federica Restelli, Alessandro Regorda, and Roberto Sabadini

Subduction is responsible for surface displacements and deep mass redistribution. This rearrangement generates density anomalies in a wide spectrum of wavelengths which, in turn, causes important anomalies in the Earth's gravity field that are visible as lineaments parallel to the arc-trench systems. In these areas, when the traditional analysis of the deformation and stress fields is combined with the analysis of the perturbation of the gravity field and its slow time variation, new information on the background environment controlling the tectonic loading phase can be disclosed.

Here we present the results of a comparative analysis between the geodetically retrieved gravitational anomalies, based on the EIGEN-6C4 model, and those predicted by a 2D thermo-chemical mechanical modeling of the Sumatra and Mariana complexes.

The 2D model accounts for a wide range of parameters, such as the convergence velocity, the shallow dip angle, the different degrees of coupling between the facing plates. The marker in cell technique is used to compositionally differentiate the system. Phase changes in the crust and in the mantle and mantle hydration are also allowed. To be compliant with the geodetic EIGEN-6C4 gravity data, we define a model normal Earth considering the vertical density distribution at the margins of the model domain, where the masses are not perturbed by the subduction process.

Model predictions are in good agreement with data, both in terms of wavelengths and magnitude of the gravity anomalies measured in the surroundings of the Sumatra and Marina subductions. Furthermore, our modeling supports that the differences in the style of the gravity anomaly observed in the two areas are attributable to the different environments – ocean-ocean or ocean-continental subduction – that drives a significantly different dynamic in the wedge area.

How to cite: Bollino, A., Marotta, A. M., Restelli, F., Regorda, A., and Sabadini, R.: New insights on the dynamics of the Sumatra and Mariana complexes inferred from the comparative analysis of gravity data and model predictions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7399, https://doi.org/10.5194/egusphere-egu2020-7399, 2020.

EGU2020-1035 | Displays | G4.3

3D gravity inversion across the area struck by the 2016-2017 seismic events in Central and Northern Apennines, Italy

Paolo Mancinelli, Cristina Pauselli, Dominique Fournier, Maurizio Fedi, Giorgio Minelli, and Massimiliano Barchi

In this work, the crustal volume struck by the 2016-2017 seismic sequence in Central and Northern Apennines is investigated using constrained 3D inversion of the Bouguer anomaly. After a preliminary regional field removal the residual dataset is then inverted into a 3D density contrast model. With an increasing complexity in the reference geometries, we test different geological scenarios and software settings. Geometries used in the reference models were retrieved from the available geological and geophysical information in the area. Starting with a reference model encompassing turbidites, carbonates and evaporites, and basement we finally test the effects of a low-density layer at the top of the basement. The retrieved density distribution with depth is compatible with previous models. Moreover, results support the hypothesis based on borehole evidence, of a low-density upper basement across the entire area, possibly phyllitic in composition. Comparison of the resulting models with the spatial distribution at depth of M>3 seismic events between August and November 2016, allows to locate volumes with the higher concentration of seismic events. Both at shallow and deep locations, the majority of the events enucleated in volumes relatively denser while deeper events occur in a region of major density change corresponding to the top of the basement.

How to cite: Mancinelli, P., Pauselli, C., Fournier, D., Fedi, M., Minelli, G., and Barchi, M.: 3D gravity inversion across the area struck by the 2016-2017 seismic events in Central and Northern Apennines, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1035, https://doi.org/10.5194/egusphere-egu2020-1035, 2020.

The North China Craton (NCC) is one of the oldest cratons in the world. Currently, the destruction mechanism and geodynamics of the NCC still remain controversial. All of the proposed views regarding the issues involve studying the internal density structure of the NCC lithosphere. Gravity field data are one of the most important data in regard to investigating the lithospheric density structure, the gravity gradient data and the gravity data possess their own advantages. Given the inconsistency of the on orbit GOCE satellite gravity gradient and surface gravity observation plane height, also effects of the initial density model upon of the inversion results, the joint inversion of gravity gradient and gravity are divided into two integrated processes. By using the preconditioned conjugate gradient (PCG) inversion algorithm, the density data are calculated using the preprocessed remaining gravity anomaly data. The newly obtained high resolution density data are then used as the initial density model, which can be served as the constraints for the subsequent gravity gradient inversion. Downward continuation, terrain correction, interface undulation correction and long wavelength correction are performed for the four gravity gradient tensor data(TxxTxzTyyTzz)of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite,  after which the remaining gravity gradient anomaly data(T'xxT'xzT'yyT'zz) are used as the new observation quantity. Finally, the ultimate lithospheric density distribution within the depth range of 0–180 km in the NCC is obtained using the same PCG algorithm.

How to cite: Tian, Y. and Wang, Y.: Joint inversion of the lithospheric density struture in the North China Craton based on GOCE satellite gravity gradient data and surface gravity data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3977, https://doi.org/10.5194/egusphere-egu2020-3977, 2020.

Multidisciplinary research shows the Red river fault zone’s (RRFZ) present movement and deformation state has complex segmentation feature. In order to further reveal its deep deformation mode, firstly, we extract tectonic movement gravity change information from mobile gravity measurement data by remove water storage varation and Vertical movement gravity effect; Secondly, together crust density interfaces model with gravity change information, then we can get the NMRFZ’s deformation mode of deep crust, which causes gravity variation.

The average effect with a 50km radius is calculated for the recent gravity change rate in the Sichuan-Yunnan region, then the background rate field and the residual gravity change rate field are obtained. The trend of -0.66μGal/yr gravity-low-speed change in Sichuan-Yunnan region indicates that there is an inheritance between the gravity field and the uplifting background of the southeastern Tibetan Plateau. The crustal uplift is an important reason for the negative surface gravity changes, but it is mainly related to the deep tectonic environment. There are local positive change zones in the block boundary area, with obvious lateral extrusion and deep mass accumulation. It reflects that under the dynamic environment of the eastward flow of the Tibetan Plateau, the crust of north and middle-south section of the RRFZ are extruded and the underground mass become densification which make the surface gravity raising. The positive gravity changes in up-middle crust are more obvious than lower crust and Moho in Sichuan-Yunnan area. The RRFZ also exhibits a strong demarcation feature as a plate boundary, and the northern segment is the dividing line of gravity positive and negative changes area, while the middle-southern segment and its two sides also showed a wide range of positive change trends, with deep mass continue accumulation.

The results of crustal deep deformation show that both the upper and the lower crust are obviously demarcated along the 101.5°E boundary, with the west side of the southwest Yunnan descending (moho: -0.05m/yr, upper-middle crust: -0.03m/yr) and east side of Sichuan-Yunnan block rising (moho : 0.05m/yr,upper-middle crust: 0.02m/yr), which shows that the control effects in depth of the Kangdian crustal axis. The deformation rate of the deep crust in the RRFZ is the largest, the middle-south is next and the south the smallest. Gradual zone between the middle-south segment of the RRFZ and the Chuxiong-Jianshui fault zone shows strong activity and difference in the upper middle crust.

How to cite: Wang, J.: Study on present deep crust deformation in northern and middle of the Red river fault zone by gravity method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7917, https://doi.org/10.5194/egusphere-egu2020-7917, 2020.

EGU2020-7340 | Displays | G4.3

Moho beneath Tibet based on a joint analysis of gravity and seismic data

Guangdong Zhao, Jianxin Liu, Bo Chen, and Mikhail K. Kaban

The Tibetan Plateau, known as the roof of the Earth, is considered as the “Golden Key” for understanding plate tectonics, continental collisions and continental orogenic formation. A reliable Moho structure is also vital for understanding the deformation mechanism of the Tibetan Plateau.

In this study, we use improved Parker−Oldenburg’s formulas that include a reference depth into the exponential term and employ a Gauss-FFT method to determine Moho depths beneath the Tibetan Plateau. The synthetic models demonstrate that the improved Parker’s formula has higher accuracy with the maximum absolute error less than 0.25 mGal.

Two inversion parameters, namely the reference depth and the density contrast are essential for the Moho estimation based on the gravity field, and they need to be determined in advance to obtain correct results. Therefore, the Moho estimates derived from existing seismic studies (Stolk et al., 2013) are used to reduce the non-uniqueness of the gravity inversion and to determine these parameters by searching for the maximum correlation between the gravity-inverted and seismic-derived Moho depths.

Another critical issue is to remove beforehand the gravity effects of other factors, which affect the observed gravity field. In addition to the topography, the gravity effects of the sedimentary layer and crystalline crust are removed based on existing crustal models, while the upper mantle impact is determined based on the seismic tomography model.

The inversion results show that the Moho structure under the Tibetan plateau is very complex with the depths varying from about 30 ~ 40 km in the surrounding basins (e.g., the Ganges basin, the Sichuan basin, and the Tarim basin) to 60 ~ 80 km within the plateau. This considerable difference up to 40 km on the Moho depth reveals the substantial uplift and thickening of the crust in the Tibetan Plateau.

Furthermore, two visible “Moho depression belts” are observed within the plateau with the maximum Moho deepening along the Indus-Tsangpo Suture and along the northern margin of Tibet bounding the Tarim basin with the relatively shallow Moho in central Tibet between them. The southern “belt” is likely formed in compressional environment, where the Indian plate underthrusts northwards beneath the Tibetan Plateau, while the northern one could be formed by the southward underthrust of the Asian lithosphere beneath Tibet.

Stolk, W., Kaban, M., Beekman, F., Tesauro, M., Mooney, W. D., & Cloetingh, S. (2013). High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas. Tectonophysics, 602, 55-68. https://doi.org/10.1016/j.tecto.2013.01.022

How to cite: Zhao, G., Liu, J., Chen, B., and K. Kaban, M.: Moho beneath Tibet based on a joint analysis of gravity and seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7340, https://doi.org/10.5194/egusphere-egu2020-7340, 2020.

EGU2020-22408 | Displays | G4.3

A Consistent Thermo-Compositional Model of the South American Cratonic Lithosphere from Integrated Inversion of Gravity and Seismic Data

Nils-Peter Finger, Mikhail Kaban, Magdala Tesauro, Carina Haeger, Walter Mooney, and Maik Thomas

We present an integrated model of the cratonic lithosphere of South America. Gravity and seismic data were jointly analyzed using mineral physics constraints to assess state and evolution of the cratonic roots in South America in terms of temperature, density and composition. At the cratons, our model enables separation of two counteracting effects: the increased density due to cooling with age and decreased density due to depletion of iron. The depletion of iron can be described by the Mg# which gives the partition of Mg2+ among the double positive ions. A new crustal model (including depth to the Moho) based on existing seismic data was used to correct the gravity field for crustal effects and to uncover the gravity signal of the mantle. In addition, residual topography was calculated as a measure of the part of topography not balanced by the crustal density variations and depth to the Moho. Temperatures within the lithospheric mantle were estimated based on seismic velocities and mineral physics equations, initially assuming a juvenile mantle composition (Mg# of 89). The residual fields were corrected for the respective effects. In the following inversion of residual gravity and topography, we have determined additional density variations which can be interpreted as compositional ones. Furthermore, these results were employed to recompute the upper mantle temperatures taking into account possible compositional changes in the cratonic roots. In this iterative procedure, a consistent thermo-compositional model of the upper mantle has been obtained. Negative compositional density variations imply depletion of iron, leading to higher Mg#s. The highest depletion occurs in the Amazonas and São Francisco Cratons reaching values in the cratons’ centers of up to 90 (Mg#). At the same time, their centers show very low temperatures, down to 600° C in the depth of 100 km. They stay below 1300° C even at a depth of 200 km, indicating deep lithospheric roots. Higher temperatures are found in the Andean forelands and along the Trans-Brasiliano-Lineament (TBL), dividing the Amazonas and São Francisco Cratons. Compositional density variations yield smaller to no amounts of depletion in the Amazonas Craton below a depth of 100 km. The São Francisco Craton still shows depletion in 200 km depth (Mg# up to 89.5). Slightly negative compositional density variations southwest of the São Francisco Craton also exist at depths up to 200 km, indicating the Paranapanema cratonic fragment.

How to cite: Finger, N.-P., Kaban, M., Tesauro, M., Haeger, C., Mooney, W., and Thomas, M.: A Consistent Thermo-Compositional Model of the South American Cratonic Lithosphere from Integrated Inversion of Gravity and Seismic Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22408, https://doi.org/10.5194/egusphere-egu2020-22408, 2020.

Inverting satellite and airborne magnetic data with a common model is challenging due to the spectral gap between the data sets, but needed to provide meaningful models of lithospheric magnetisation.

Here, we present a step-wise approach, where first spherical prisms (tesseroids) are used for global magnetic inversion of satellite-acquired lithospheric field models and second airborne data re inverted in their suitable spectral range for added details. For the synthetic test, the susceptibility model of Hemant (2003) was used as a starting point to calculate the spherical harmonic model of each tesseroid in the model. The resulting spherical harmonic coefficients were inverted for magnetic susceptibility in the global model, where the geometry is based on seismic or gravity observations. The projected gradient method is used to avoid negative susceptibilities in the result. After the global inversion, high-resolution local tile-wise inversion together with synthetic airborne data within a different wavelength range is performed for even higher resolution results.

The approach is applied to the Swarm-derived LCS-1 field model and for selected areas with high-resolution aeromagnetic coverage.

How to cite: Baykiev, E. and Ebbing, J.: Global and local high-resolution magnetic field inversion using spherical harmonic models of individual sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-170, https://doi.org/10.5194/egusphere-egu2020-170, 2020.

EGU2020-17868 | Displays | G4.3

On the accuracy of gravity fields obtained with Newton integrals on a hollow sphere

Ludovic Jeanniot, Cedric Thieulot, Bart Root, John Naliboff, and Wim Spakman

The mass-density distribution of the Earth drives mantle convection and plate tectonics but is poorly known. We aim to predict gravity fields as a constraint for geodynamical modelling. In order to compute synthetic Earth gravity one must define a spherical geometry filled with a density model. Density models for the whole mantle down to the CMB come from tomographic models which therefore require converting speed waves velocities to density using a scaling factor.

We use a discretised integration method to compute globally gravity acceleration, gravity anomalies, potential and gradients, in the state of the art finite element code ASPECT.

Three density models are tested separately: a density field obtained from SL2013 and S40RTS tomographic models for the deep mantle, and the density model CRUST1.0 for the thin upper lithosphere layer. We combine these 3 datasets into one to create a composite model which is compared to the global seismic model LLNL-G3D-JPS of Simmons et al. (2015). We test the sensitivity of gravity prediction on the use of various conversion scaling factors of shear wave velocity to density. We find that the scaling factor profile also has a major impact on gravity prediction.

Finally, we present early results of the gravity field prediction for two local areas, the Indian-Tibet plate boundary and the Mediterranean Sea. Gravity predictions are compared to satellite gravity.

How to cite: Jeanniot, L., Thieulot, C., Root, B., Naliboff, J., and Spakman, W.: On the accuracy of gravity fields obtained with Newton integrals on a hollow sphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17868, https://doi.org/10.5194/egusphere-egu2020-17868, 2020.

EGU2020-15729 | Displays | G4.3

Evaluating the accuracy of equivalent-source predictions using cross-validation

Leonardo Uieda and Santiago Soler

We investigate the use of cross-validation (CV) techniques to estimate the accuracy of equivalent-source (also known as equivalent-layer) models for interpolation and processing of potential-field data. Our preliminary results indicate that some common CV algorithms (e.g., random permutations and k-folds) tend to overestimate the accuracy. We have found that blocked CV methods, where the data are split along spatial blocks instead of randomly, provide more conservative and realistic accuracy estimates. Beyond evaluating an equivalent-source model's performance, cross-validation can be used to automatically determine configuration parameters, like source depth and amount of regularization, that maximize prediction accuracy and avoid over-fitting.

Widely used in gravity and magnetic data processing, the equivalent-source technique consists of a linear model (usually point sources) used to predict the observed field at arbitrary locations. Upward-continuation, interpolation, gradient calculations, leveling, and reduction-to-the-pole can be performed simultaneously by using the model to make predictions (i.e., forward modelling). Likewise, the use of linear models to make predictions is the backbone of many machine learning (ML) applications. The predictive performance of ML models is usually evaluated through cross-validation, in which the data are split (usually randomly) into a training set and a validation set. Models are fit on the training set and their predictions are evaluated using the validation set using a goodness-of-fit metric, like the mean square error or the R² coefficient of determination. Many cross-validation methods exist in the literature, varying in how the data are split and how this process is repeated. Prior research from the statistical modelling of ecological data suggests that prediction accuracy is usually overestimated by traditional CV methods when the data are spatially auto-correlated. This issue can be mitigated by splitting the data along spatial blocks rather than randomly. We conducted experiments on synthetic gravity data to investigate the use of traditional and blocked CV methods in equivalent-source interpolation. We found that the overestimation problem also occurs and that more conservative accuracy estimates are obtained when applying blocked versions of random permutations and k-fold. Further studies need to be conducted to generalize these findings to upward-continuation, reduction-to-the-pole, and derivative calculation.

Open-source software implementations of the equivalent-source and blocked cross-validation (in progress) methods are available in the Python libraries Harmonica and Verde, which are part of the Fatiando a Terra project (www.fatiando.org).

How to cite: Uieda, L. and Soler, S.: Evaluating the accuracy of equivalent-source predictions using cross-validation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15729, https://doi.org/10.5194/egusphere-egu2020-15729, 2020.

EGU2020-549 | Displays | G4.3

A better strategy for interpolating gravity and magnetic data

Santiago Rubén Soler and Leonardo Uieda

We present a new strategy for gravity and magnetic data interpolation and processing. Our method is based on the equivalent layer technique (EQL) and produces more accurate interpolations when compared with similar EQL methods. It also reduces the computation time and memory requirements, both of which have been severe limiting factors.

The equivalent layer technique (also known as equivalent source, radial basis functions, or Green’s functions interpolation) is used to predict the value of gravity and magnetic fields (or transformations thereof) at any point based on the data gathered on some observation points. It consists in estimating a source distribution that produces the same field as the one measured and using this estimate to predict new values. It generally outperforms other general-purpose 2D interpolators, like the minimum curvature or bi-harmonic splines, because it takes into account the height of measurements and the fact that these fields are harmonic functions. Nevertheless, defining a layout for the source distribution used by the EQL is not trivial and plays an important role in the quality of the predictions.

The most widely used source distributions are: (a) a regular grid of point sources and (b) one point source beneath each observation point. We propose a new source distribution: (c) divide the area into blocks, calculate the average location of observation points inside each block, and place one point source beneath each average location. This produces a smaller number of point sources in comparison with the other source distributions, effectively reducing the computational load. Traditionally, the source points are located: (i) all at the same depth or (ii) each source point at a constant relative depth beneath its corresponding observation point. Besides these two, we also considered (iii) a variable relative depth for each source point proportional to the median distance to its nearest neighbours. The combination of source distributions and depth configurations leads to seven different source layouts (the regular grid is only compatible with the constant depth configuration).

We have scored the performance of each configuration by interpolating synthetic ground and airborne gravity data, and comparing the interpolation against the true values of the model. The block-averaged source layout (c) with variable relative depth (iii) produces more accurate interpolation results (R² of 0.97 versus R² of 0.63 for the traditional grid layout) in less time than the alternatives (from 2 to 10 times faster on our test cases). These results are consistent between ground and airborne survey layouts. Our conclusions can be extrapolated to other applications of equivalent layers, such as upward continuation, reduction-to-the-pole, and derivative calculation. What is more, we expect that these optimizations can benefit similar spatial prediction problems beyond gravity and magnetic data.

The source code developed for this study is based on the EQL implementation available in Harmonica (fatiando.org/harmonica), an open-source Python library for modelling and processing gravity and magnetic data.

How to cite: Soler, S. R. and Uieda, L.: A better strategy for interpolating gravity and magnetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-549, https://doi.org/10.5194/egusphere-egu2020-549, 2020.

EGU2020-872 | Displays | G4.3

Gravity and magnetic data analysis based on Poisson wavelet-transforms

Kirill Kuznetsov, Bulychev Andrey, and Ivan Lygin

Studies of the Earth’s interior structure are one of the most complex topics in modern science. Integration of different geophysical methods plays a key role in effectively tackling the problem. In the last decade capabilities of potential field geophysical methods have been increasing due to development of advanced digital technologies. Improved resolution and accuracy of gravity and magnetic fields measurements made by modern equipment makes it possible to build more detailed geological models. Different tectonic and structural elements being interpreted in such models produce potential field signals with different spectral characteristics. Like any geophysical signals, potential fields can be described as a spatially non-stationary signal. This means its frequency content may change depending on a given signal sample, in particular with different spatial location of a sample. In this case, approaches of gravity and magnetic fields analysis based on Fourier transform or signal decomposition into a number of harmonic functions can lead to incorrect results. One of the ways to solve this challenge involves using wavelet transform based algorithms, since these transforms do not assume stationary signals and each function of a wavelet-based basis is localized in space domain.

In gravity and magnetic data analysis it is beneficial to use wavelets based on partial derivatives of the Poisson kernel, which correspond to derivatives of a point source gravity potential. Application of Poisson wavelets in potential field data analysis has begun in the 1990's and is predominantly aimed at studying gravity and magnetic fields singularity points during data interpretation.

Similar to Fourier-based potential field techniques, it is possible to construct a number of data filtering algorithms based on Poisson wavelets. Current work demonstrates that it is possible to construct algorithms based on Poisson wavelets for transforming profile and spatially gridded gravity and magnetic data, e.g. for calculation of equivalent density and magnetization distributions, upward and downward continuations, reduction to pole and many other filters that take into account spatial distribution of the signal.

Wavelet-transforms allow to account for spatially non-stationary nature of geophysical signals. Use of wavelet based techniques allows to effectively carry out potential field data interpretation in a variety of different geologic and tectonic settings in a consistent fashion.

How to cite: Kuznetsov, K., Andrey, B., and Lygin, I.: Gravity and magnetic data analysis based on Poisson wavelet-transforms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-872, https://doi.org/10.5194/egusphere-egu2020-872, 2020.

EGU2020-1713 | Displays | G4.3

A new source location and attribute recognition method based on correlation analysis of gravity and magnetic anomaly

Baoliang Lu, Tao Ma, Shengqing Xiong, and Wanyin Wang

The traditional gravity and magnetic correspondence analysis tends to have high correlation outside the field source area. In order to overcome the disadvantage, we propose a new method for identify the source position and attribute, which is based on similarity and vertical derivative of potential field. In this method, we put forward a new gravity and magnetic correlation parameter (GMCP), which can effectively reduce the range of potential field source and indicate the field intensity information. The distribution of the non-zero areas of GMCP reflects the size of the source. GMCP discriminant parameter values of positive and negative reflect the source attribute. When GMCP is greater than zero, it is a positive correlation indicating that there are high-density and high-magnetization or low-density and low-magnetization homologous bodies in this region; When GMCP is less than zero, it is negative correlation indicating that there are high-density and low-magnetic or low-density and high-magnetic density homologous bodies in this region. GMCP goes to zero, which means no gravity-magnetic homologous geological body. Complex models test results with different noise level and actual data processing of South China Sea Basin show the correctness and validity of identification of the proposed methods.

How to cite: Lu, B., Ma, T., Xiong, S., and Wang, W.: A new source location and attribute recognition method based on correlation analysis of gravity and magnetic anomaly, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1713, https://doi.org/10.5194/egusphere-egu2020-1713, 2020.

It is vital to quickly and effectively determine the extent and depth of geological body by using potential field data in gravity and magnetic survey. In this study, three key techniques studying the extent and depth of geological sources based on curvature attribute are studied: the optimal solutions to the objective function, the edge of geological bodies and picking out solutions. Firstly, the optimal solution to the objective function is studied, that is, the key extraction algorithm about the curvature attribute. The Huber norm is introduced into the extraction algorithm of curvature attribute, which more accurately detect the depth of edge of the geological bodies. Secondly, the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique is introduced into curvature attribute, which shows more continuous results about the edge position of the geological bodies and more sensitive to the small-scale tectonic structure. Finally, we study the way to pick out the inversion solution, that is, to solve the multi-solution equations in the inversion. The upward continuation of a certain height with strict physical significance was introduced into the inversion method, which was used to suppress the noise, and the final and actual inversion depth was equal to the inversion depth minus the height of upward continuation. And the average value of threshold limitation technology of the potential fields data was also introduced into this method. Using the two technologies, solutions of non-field source edge positions were eliminated, and make the inversion solutions closer to the actual situation. Through the above three key techniques, the accuracy, continuity and recognition to the small-scale structure of the inversion result are optimized. The theoretical models are used to verify the effectiveness of the above key technologies, the results show that the three key technologies have achieved good results, and the combined models are used to verify the effectiveness of the optimized inversion method. The measured aeromagnetic data were used to inversing the edge depth of the intrusive rock in a mining area, and the inversion results are in good agreement with the rock depth revealed by borehole.

How to cite: Liu, J., Wang, W., and Xiong, S.: The Method of Curvature Attribute applied in the Depth Inversion of the Geological Bodies Edge by Potential Field Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7034, https://doi.org/10.5194/egusphere-egu2020-7034, 2020.

Geophysical data such as gravity data can be inverted to get a subsurface image, which depicts the subsurface distribution of physical property. Consequently, inversion of geophysical data has an effective role for interpreting measured geophysical anomalies in hydrocarbons and mineral applications. Interest about ore deposits exploration and sedimentary basins interpretation is associated with their economic importance. The presence of sedimentary basins gives lower amplitude of gravity anomalies with negative signals, due to the negative density contrast as these sedimentary basins have lower density than that of the neighboring basement rocks. In prospecting ore deposits, studying the spatial distributions of densities in the subsurface is essential of significance.Two dimensional forward modelling strategy can be done via locating the rectangular cells with fixed size directly underneath the location of the observed data points using regular grid discretization. Density vector of the subsurface rectangular cells are obtained via solving the 2D gravity inverse problem by optimizing an objective function (i.e., the differences between observed and inverted residual gravity data sets). In this work, a hybrid algorithm merging a bat (BAT) algorithm with the preconditioned conjugate gradient (PCG) method is suggested as a mean for inverting surface gravity anomalies to obtain the density distribution in the subsurface. Like the hybrid, minimization algorithm has the capability to make use of the advantages of both two techniques. In this hybrid algorithm, the BAT algorithm was utilized to construct an initial solution for the PCG technique. The BAT optimizer acts as a rapid build-up of the model, whereas the second modifies the finer model approximated solution. This modern algorithm was firstly applied on a free-noise synthetic data and to a noisy data with three different levels of random noise, and good results obtained through the inversion. The validity and applicability of our algorithm are applied to real residual gravity anomalies across the San Jacinto graben in southern California, USA, and Sierra Mayor - Sierra Pinta graben, USA and prospecting of the Poshi Cu-Ni deposits, Xinjiang, northwest China. The obtained results are in excellent accordance with those produced by researchers in the published literature.

 

Keywords: Gravity data, 2D Inversion, BAT algorithm, Preconditioned Conjugate Gradient, Sedimentary Basins.

How to cite: Abdrabou, M., Abdelazeem, M., and Gobashy, M.: A Hybrid PCG- Bat Algorithm for 2D Gravity Inversion: Applications for Ore Deposits Exploration and Interpretation of Sedimentary Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1116, https://doi.org/10.5194/egusphere-egu2020-1116, 2020.

G4.4 – New tools for terrain gravimetry

EGU2020-8392 | Displays | G4.4

Quantum Absolute Sensors for Gravity Measurements

Sébastien Merlet, Raphael Piccon, Sumit Sarkar, and Franck Pereira Dos Santos

Gravity measurements are performed with two different classes of instruments: gravimeters, most widely used, measure the gravity acceleration gand its variations, whereas gradiometers measure its gradient.

Quantum gravity sensors, based on cold atom interferometry techniques, can offer higher sensitivities and accuracies than current state of the art commercial available technologies. Their limits in performances, both in terms of accuracy and long term stability, are linked to the temperature of the atomic cloud, in the low µK range, and more specifically, to the residual ballistic expansion of the atomic sources in the laser beams. To overcome these limits, we use ultracold atoms in the nano-kelvin range in our sensors.

I will first present our Cold Atom Gravimeter (CAG) used for the determination of the Planck constant with the LNE Kibble Balance [1]. It performs continuously 3 gravity measurements per second with a demonstrated long term stability of 0.06 nano-gin 40 000 s of measurement. Using ultracold atoms produced by evaporative cooling in a crossed dipole trap as a source, its accuracy, which is still to be improved, is currently at the level of 2 nano-g. This makes our CAG, the more accurate gravimeter [2]. It detects water table level variations. Then I will describe a « dual sensor » which performs simultaneous measurements of g and its gradient. This offers in principle the possibility to resolve, by combining these two signals, the ambiguities in the determination of the positions and masses of the sources, offering new perspectives for applications. It uses cold atom sources for proof of principle demonstrations [3, 4] and will soon combine ultra-cold atomic samples produced by magnetic traps on a chip and large momentum beamsplitters. With these two key elements, the gradiometer will perform measurements in the sub-E sensitivity range in 1 s measurement time on the ground. Such a level of performances opens new prospects for on field and on board gravity mapping, for drift correction of inertial measurement units in navigation, for geophysics and for fundamental physics.

 References

[1] M. Thomas et al. Metrologia 54, 468-480 (2017)

[2] R. Karcher, et al. New J. Phys. 20, 113041 (2018)

[3] M. Langlois et al. Phys. Rev. A 96, 053624 (2017)

[4] R. Caldani et al. Phys. Rev. A 99, 033601 (2019)

How to cite: Merlet, S., Piccon, R., Sarkar, S., and Pereira Dos Santos, F.: Quantum Absolute Sensors for Gravity Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8392, https://doi.org/10.5194/egusphere-egu2020-8392, 2020.

EGU2020-9076 | Displays | G4.4

Comparison and characterization of the field Atomic Quantum Gravimeter (AQG#B01)

Cédric Champollion, Anne-Karin Cooke, and Nicolas Le Moigne

The recent advancements in gravity quantum sensors promise maintenance-free, easy to use, continuous and accurate monitoring devices. This technological breakthrough in gravity instrumentation offers new possibilities for both laboratory and field experiments in different geosciences applications. These new gravity quantum sensors allow e.g. for the monitoring of transient processes in volcanology, plate tectonics (slow slip events) or hydro-geology (pumping tests).

The first commercial field quantum gravimeters are nowadays available (AQGB, Muquans TM). The AQG#B01 is actually under validation. It is tested and compared with a superconducting gravimeter (GWR iGrav#002 and an absolute ballistic gravimeter (MG-L FG5#228) in the French Larzac Observatory () during more than 1 month. A first small (50 nm/s²) transient gravity variation caused by hydro-geological charge has been recorded by both the quantum and superconducting gravimeter.

Additionally its sensitivity to environmental noise is characterized by its Allan variance. Absolute ballistic comparison during one month allows to estimate a maximum potential drift. Sensitivity tests on instrument tilts and orientation have been done. In order to evaluate the AQG-B as a field sensor, sensitivity to external temperature changes have been tested in the range 10°C-30°C. All the tests allow a clear characterization of the AQG-B for future field experimentation.

AQG#B01 development has been funded is the frame of the grant “investissement d’avenir” EquipEx RESIF-CORE.

How to cite: Champollion, C., Cooke, A.-K., and Le Moigne, N.: Comparison and characterization of the field Atomic Quantum Gravimeter (AQG#B01), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9076, https://doi.org/10.5194/egusphere-egu2020-9076, 2020.

EGU2020-12317 | Displays | G4.4

MEMS surface microgravimetry for geotechnical surveying

Zhijun Du, Arif Mustafazade, Yaoguo Li, Adrian Topham, Jeremy Lofts, and Ashwin Seshia

Microgravity measurements have enabled a variety of geophysical surveying and monitoring applications including advance warning of natural hazards, slope stability monitoring, discovery of buried tunnels, pipework, and other utilities, identification of sinkholes and other natural voids, buried aquifers and in monitoring groundwater hydrology. In the civil engineering context, microgravity measurements can provide valuable information for construction projects or intervention activities by locating buried utilities, hazards or other features of relevance.

Disruptive MEMS gravity sensor technologies are poised to provide entirely new approaches for microgravity measurements in the form of portable sensors that could ultimately be mounted on remotely operated vehicles or drones, integrated into land-based distributed sensor networks, or deployed in shallow borehole configurations. Instruments based on these sensors could enable vector gravity measurements as well as full tensor gravity gradiometry.

Trials are ongoing of a single-axis MEMS surface module with a noise floor of 50 µGal/rt-Hz and a resolution of < 10 µGal while allowing for measurement over the entire +/- 1g dynamic range. This paper discusses the background and context for gravity imaging in geotechnical applications, forward modelling of case studies of relevance, and ongoing developments in the construction of a unique portable surface gravimeter.

How to cite: Du, Z., Mustafazade, A., Li, Y., Topham, A., Lofts, J., and Seshia, A.: MEMS surface microgravimetry for geotechnical surveying, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12317, https://doi.org/10.5194/egusphere-egu2020-12317, 2020.

EGU2020-18528 | Displays | G4.4

A High-Sensitivity, Low-Drift MEMS Relative Gravimeter for Multi-Pixel Imaging Applications

Abhinav Prasad, Karl Toland, Andreas Noack, Kristian Anastasiou, Richard Middlemiss, Douglas Paul, and Giles Hammond

Novelty / Progress Claim(s)

This paper reports a capacitive readout-based MEMS relative gravimeter which can detect sub-Hz microseismic and slowly varying gravitational Earth tide signals. The gravimeter has a noise floor of 6-7 uGal/rt(Hz) at 1Hz and a linear drift of <250 uGal/day, metrics which are on a par with the commercially available gravimeters, and are leading in the field of MEMS accelerometers. The gravimeter is packaged in a standard ceramic-carrier and interfaced to a low-power, advanced FPGA-based readout. This setup is housed within a bespoke thermal enclosure, making the platform ideal for multi-pixel array-based implementation in the field.

Background/State-of-the-Art

Gravimeters are used to measure the local acceleration due to gravity (g). One of the emerging applications of gravimetry is in volcanology where gravimeters can be used to understand magma plumbing, providing information on volcanic activity/unrest events. However, this requires multi-pixel ‘gravity-imaging’ around volcanoes, a feat which is not possible using the expensive, complex, and large form-factor commercially available gravimeters.

Recently, researchers have developed MEMS-scale accelerometers which have excellent sensitivities but not yet demonstrated good long-term stability, making them non-viable for long-term monitoring of slow gravity changes (such as produced by magma flow). In a previous work, the authors have demonstrated an optical shadow-sensor readout based MEMS gravimeter with a sensitivity of 40 uGal/rt(Hz). Building on the work, a portable version of the gravimeter was also reported previously. The devices in both the setups were limited by the displacement noise of the optical shadow-sensor and the packageability of the setup.

In this paper, we are reporting a novel gravimeter which uses a capacitive-readout for sensing the proof-mass displacement, is embedded in a MEMS IC package, and uses advanced FPGA-based electronics for signal conditioning. The improved displacement sensitivity of the capacitive readout allows designing stiffer suspension-springs making the device more robust for operations in extreme environments. The acceleration sensitivity achieved using the new gravimeter is around 6-7 uGal/rt(Hz) at 1Hz, which is a significant improvement over the previous versions of the gravimeter. The device is currently being readied for field trials in the sectors of volcano gravimetry and oil & gas, showing the maturity of the technology.

Methodology

The reported gravimeter has a microfabricated silicon proof-mass which is suspended from thin flexures. Metal-combs are patterned on top of the proof-mass and a fixed glass layer with complementary combs is assembled to be at a close separation from the proof-mass. The overlapping combs act as a capacitor, the magnitude of which is dependent on the proof-mass displacement. The multi-layered gravimeter is embedded within a standard 32-pin ceramic DIP chip-carrier and wire bonded. The MEMS package is interfaced with analog signal conditioning electronics and a digital lock-in implementation is employed for converting the capacitance change into useful units (uGals).The electronics noise of the setup is measured to be <1 uGal. To reduce temperature-related effects, a mK active temperature control is implemented around the device. The packaged device is housed within a prototype thermal enclosure making the platform field-portable.

How to cite: Prasad, A., Toland, K., Noack, A., Anastasiou, K., Middlemiss, R., Paul, D., and Hammond, G.: A High-Sensitivity, Low-Drift MEMS Relative Gravimeter for Multi-Pixel Imaging Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18528, https://doi.org/10.5194/egusphere-egu2020-18528, 2020.

EGU2020-4647 | Displays | G4.4

Analytical and numerical optimization of gravimetric networks: a case study from Mount Etna, Italy

Mehdi Nikkhoo, Eleonora Rivalta, Daniele Carbone, and Flavio Cannavò

The transport of magma and magmatic fluids is a key process behind the occurrence, duration and intensity of volcanic crises. Volcano gravimetry allows for unequivocal inference of the location and mass of accumulated or removed magmatic fluids at volcanoes. This task is best accomplished through collecting gravity time series at multiple stations simultaneously. The performance of individual gravimeters and the configuration of the gravimetric array, however, determine the threshold of detectable mass change and the ability of the array to minimize the uncertainty on the inferred quantities.

We utilize numerical optimization techniques to design a network including one absolute quantum gravimeter (AQG), two superconducting relative gravimeters (iGRAVs) and several microelectromechanical system (MEMS) relative gravimeters at Mount Etna. We also develop analytical solutions for simple design problems. We show that the analytical solutions are essential for validating the numerical optimization procedure. We provide practical details and caveats that should be considered in similar gravimetric network optimizations. These include 1) specifying the target zone of the network by using the history of mass transport, 2) accounting for the relative importance of  different parts of the target zone, 3) accounting for logistic and instrumental constraints in the optimizations  4) calibrating the objective functions associated with various optimizations, 5) analyzing the network sensitivities to different parts of the target zone and identifying blind zones and  6) calculating the optimal number of gravimeters as a function of the sensor sensitivity and accuracies. We show that our optimal solution for Mount Etna provides an improved detection power across the target zone as compared to an equally spaced network of gravimeters with the same existing constraints, surface topography and sensor sensitivities. Furthermore, this optimal solution ensures that a certain range of mass change anywhere in the target zone can be sensed by a given minimum number of gravimeters and at the same time minimizes the impact of random observation errors on the inferred quantities.

How to cite: Nikkhoo, M., Rivalta, E., Carbone, D., and Cannavò, F.: Analytical and numerical optimization of gravimetric networks: a case study from Mount Etna, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4647, https://doi.org/10.5194/egusphere-egu2020-4647, 2020.

EGU2020-2184 | Displays | G4.4

Long-term monitoring with spring-based gravimeters: tilt-control benefits and application to the Rochefort Cave Laboratory (Belgium)

Benjamin Fores, Arnaud Watlet, Michel Van Camp, and Olivier Francis

Spring-based gravimeters are light and easy to install, with a precision around 5 μGal/√Hz. However, they are still not used for long-term gravity monitoring. The main reason for that is the non-linear drift of those instruments, which is very difficult to correct without removing geophysical signals. We will show that when the tilt is actively controlled, a gPhone spring-based gravimeter shows a quasi-linear drift and can reach a long-term stability at the µGal level.

This allows experiments such as the one in the Rochefort Cave Laboratory (Belgium). Thanks to the size of the gPhone and its low facility requirements, a monitoring from inside a cave was possible. Coupled with another gravity monitoring at the surface, it reveals new information on the local hydrology of this karstic site.

How to cite: Fores, B., Watlet, A., Van Camp, M., and Francis, O.: Long-term monitoring with spring-based gravimeters: tilt-control benefits and application to the Rochefort Cave Laboratory (Belgium), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2184, https://doi.org/10.5194/egusphere-egu2020-2184, 2020.

EGU2020-11801 | Displays | G4.4

Integrated microgravimetric and seismic monitoring approach in the Þeistareykir volcanic geothermal field (North Iceland).

Florian Schäfer, Philippe Jousset, Tania Toledo, Andreas Güntner, Tilo Schöne, David Naranjo, Kemal Erbas, Egill Juliusson, and Richard Warburton

In volcanic and hydrothermal systems, monitoring of mass and stress changes by continuous gravity field and ground motion records provides information for both volcanic hazard assessment and estimation of geothermal resources. We aim at a better understanding of volcanic and geothermal system processes by addressing mass changes in relation with external influences such as anthropogenic (reservoir exploitation) and natural forcing (local and regional earthquake activity, earth tides). Þeistareykir is a geothermal field located within the Northern Volcanic Zone (NVZ) of Iceland on the Mid-Atlantic Ridge. Geothermal power production started in autumn 2017. For the first time on a geothermal production field, we deployed a network of 4 continuously recording gravity meters (3 superconducting meter, iGrav and one spring gravity meter gPhone) in order to cover the spatial and the temporal changes of gravity and to detect small variations related to the geothermal power plant operation (e.g. extraction and injection). All gravity monitoring stations are equipped with additional instrumentation to measure parameters that may affect the gravity records (e.g. GNSS and hydrometeorological sensors). Additionally, we deployed a temporal seismic network consisting of 14 broadband stations to enhance the seismic activity monitoring of the permanent Icelandic network in this very active region of the NVZ. Results of this unique experiment contribute to determine reservoir properties and main structures and may also reveal details of active tectonic processes. Here, we present the instrumental setup at the site and first results of more than 24 months of continuous gravity and seismicity records.

How to cite: Schäfer, F., Jousset, P., Toledo, T., Güntner, A., Schöne, T., Naranjo, D., Erbas, K., Juliusson, E., and Warburton, R.: Integrated microgravimetric and seismic monitoring approach in the Þeistareykir volcanic geothermal field (North Iceland). , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11801, https://doi.org/10.5194/egusphere-egu2020-11801, 2020.

EGU2020-20906 | Displays | G4.4

Development of a MEMs gravimeter for drone-based field surveys.

Elizabeth Passey, Giles Hammond, Steven Bramsiepe, Abhinav Prasad, Richard Middlemiss, Douglas Paul, Richard Walker, Andreas Noack, and Kristian Anastasiou

Gravimetry allows us to study sub-surface structures remotely by measuring changes in Earth's surface gravitational field and using this data to infer the density of geological structures. Of its wide range of applications, it is mostly used in the oil and gas exploration industry, volcanology, civil engineering and even archaeological studies. Airborne gravimetry is a vital method of conducting a spatial gravimetric survey in areas which are difficult to access by foot, such as mountains. Generally, sensors are modified for air crafts platforms by installing them on large gimbal systems, or a strap-down gravimeter can be used as a lower-cost alternative. Now, a new MEMs gravimeter called “Wee-g” is enabling the development of a system to deploy the gravimeter on an unmanned aerial vehicle (UAV or drone). Wee-g was first developed with the objective of developing a low-cost MEMS accelerometer for gravimetric use which could be manufactured on a large scale. In 2016, Wee-g was used to measure Earth tides - the elastic deformation of the Earth caused by gravitational fields of the Moon and Sun. Since then, the device electronics have been miniaturised to make the system portable and has been tested at the Campsie Hills just north of Glasgow. Work is underway to build an isolation platform with active stabilisation on which the Wee-g can be mounted to be deployed on a drone which will reduce airborne surveys costs further and allow for more airborne gravimetric surveys to be carried out in remote locations.

How to cite: Passey, E., Hammond, G., Bramsiepe, S., Prasad, A., Middlemiss, R., Paul, D., Walker, R., Noack, A., and Anastasiou, K.: Development of a MEMs gravimeter for drone-based field surveys., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20906, https://doi.org/10.5194/egusphere-egu2020-20906, 2020.

EGU2020-1244 | Displays | G4.4

Pendulum MEMS gravimeters for semi-absolute gravimetry

Richard Middlemiss, Giles Hammond, Richard Walker, and Abhinav Prasad

By measuring tiny variations in the Earth’s gravitational acceleration, g, one can infer density variations beneath the ground.  Since magmatic systems contain rock of differing density, changes in gravity over time can tell us when/where magma is moving. Traditional gravity sensors (gravimeters) were costly and heavy, but with the advent of the technology used to make mobile phone accelerometers (MEMS – Microelectromechanical-systems), this is changing.

At Glasgow University we have already developed the first MEMS gravity sensor and we are now working with several other European institutions to make a network of gravity sensors around Mt Etna – NEWTON-g. It will be the first multi-pixel gravity imager – enabling unprecedented resolution of Etna’s plumbing system.

While this work is ongoing, a second generation of MEMS gravity sensor is now under development. The first-generation sensor comprises a mass on a spring, which moves in response to changing values of g. This, however, can only ever be used to measure changes in gravity, which means it can be difficult to tell the difference between a geophysical signal and instrumental drift. If we could measure absolute values of gravity, then instrumental drift would become less of a concern, and we could remove the need to calibrate the sensors against commercial absolute gravimeters.

One way of making absolute measurements of gravity is to use a pendulum. This method was used for hundreds of years until the scientists and engineers essentially ran out of fabrication tolerance about 100 years ago. But now nanofabrication is at our disposal, so pendulums are a valid approach to gravimetry again. Such a gravimeter is now being designed and fabricated at the University of Glasgow. It consists of a pair of coupled pendulums, who’s oscillation period is monitored to measure gravity. Here we present the intricacies of the gravimeter design, discuss the expected performance of this new tool, and propose some implications that this sensor could have on the field of volcano gravimetry.

How to cite: Middlemiss, R., Hammond, G., Walker, R., and Prasad, A.: Pendulum MEMS gravimeters for semi-absolute gravimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1244, https://doi.org/10.5194/egusphere-egu2020-1244, 2020.

EGU2020-8969 | Displays | G4.4

Operating the Absolute Quantum Gravimeter outside of the laboratory

Pierre Vermeulen, Laura Antoni-Micollier, Tommaso Mazzoni, Gabriel Condon, Vincent Ménoret, Camille Janvier, Bruno Desruelle, Arnaud Landragin, Jean Lautier-Gaud, and Philippe Bouyer

The Absolute Quantum Gravimeter (AQG) is the world’s first industrial gravimeter measuring g with laser-cooled atoms [1]. Today, several units have already been delivered to end-users.

After reviewing the key principles of the AQG, we will discuss the demonstrated measurement performances of the AQG in terms of sensitivity, stability and repeatability. In particular, we report on a reproducible sensitivity to gravity at a level of 1 μGal in various types of environment (1 µGal = 1e-8 m/s2 ~ 1e-9 g). We will also present our on-going efforts towards the thorough understanding of the uncertainty budget (accuracy) of the sensor. Finally, we will share the experience that we have acquired over the past years regarding the operability of the AQG, with a specific focus on the field version of the sensor.

This new type of gravimeter is presently the only technology that allows for continuous drift-free monitoring of gravity over timescales from a few minutes to several months, which opens new perspectives for the investigation of both spatial and temporal gravity variations [2]. The AQG has been developed by Muquans in collaboration with academic laboratories LP2N and LNE-SYRTE, and RESIF (the French Seismologic and Geodetic Network, [3]).

[1] V. Ménoret et al., "Gravity measurements below 10−9 g with a transportable absolute quantum gravimeter", Nature Scientific Reports, vol. 8, 12300 (2018)

[2] M. Van Camp, O. de Viron, A. Watlet, B. Meurers, O. Francis, C. Caudron, "Geophysics from terrestrial time-variable gravity measurements", Rev. Geophys. (2017).

[3] http://www.resif.fr/

How to cite: Vermeulen, P., Antoni-Micollier, L., Mazzoni, T., Condon, G., Ménoret, V., Janvier, C., Desruelle, B., Landragin, A., Lautier-Gaud, J., and Bouyer, P.: Operating the Absolute Quantum Gravimeter outside of the laboratory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8969, https://doi.org/10.5194/egusphere-egu2020-8969, 2020.

EGU2020-16329 | Displays | G4.4

The NEWTON-g "gravity imager": a new window into processes involving subsurface fluids

Daniele Carbone, Flavio Cannavò, Filippo Greco, Alfio Messina, Danilo Contrafatto, Giuseppe Siligato, Jean Lautier-Gaud, Laura Antoni-Micollier, Giles Hammond, Richard Middlemiss, Karl Toland, Elske de Zeeuw - van Dalfsen, Mathijs Koymans, Eleonora Rivalta, Mehdi Nikkhoo, Costanza Bonadonna, and Corine Frischknecht

Gravimetry is the only method able to directly track redistributions of bulk masses. Hence, it can supply unique information on geophysical processes that involve subsurface fluids like water, hydrocarbons, and magma. 
Nevertheless, the high cost of currently available gravimeters and the difficulty to use them in field conditions, has limited the applicability of the gravity method, that is indeed not as widely adopted as other geophysical methods.
A new system for gravity measurements is being developed  in the framework of the H2020 NEWTON-g project. This system, called “gravity imager”, includes an array of MEMS gravimeters, anchored to an absolute quantum device. It will enable, for the first time, gravity measurements at high spatio-temporal resolution. 
After the phases of design and production of the new devices, NEWTON-g involves a 2-year phase of field tests at Mt. Etna volcano (Italy), starting in the summer of 2020.

How to cite: Carbone, D., Cannavò, F., Greco, F., Messina, A., Contrafatto, D., Siligato, G., Lautier-Gaud, J., Antoni-Micollier, L., Hammond, G., Middlemiss, R., Toland, K., de Zeeuw - van Dalfsen, E., Koymans, M., Rivalta, E., Nikkhoo, M., Bonadonna, C., and Frischknecht, C.: The NEWTON-g "gravity imager": a new window into processes involving subsurface fluids, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16329, https://doi.org/10.5194/egusphere-egu2020-16329, 2020.

While studies on hydrological extremes, and floods in particular, usually take a retrospective approach, the German Helmholtz initiative MOSES (Modular Observation Solutions for Earth Systems) aims at understanding extreme events by observing the flood generation processes directly where they occur: in-situ and during the event. As part of this framework, we present a new concept of monitoring regional water storage changes by combining event-based ad-hoc field campaigns with continuous monitoring, using terrestrial gravimetry for total water storage variations and cosmic ray neutron sensing for near-surface soil moisture variations. In this concept, a key role is taken by a continuously monitoring gravimeter station: the gPhone solar cube. This station is energy self-sufficient and easily deployable at any remote location, hosting a gPhoneX, a full weather station, a GNSS antenna and receiver and a cosmic ray neutron probe. The purpose of this station is i) to provide data describing the longer term hydrological dynamics of the study area including the pre-event conditions and ii) to serve as the reference station for the gravity field campaigns during the event. These field campaigns, triggered by forecasts of extreme weather events, are carried out at least prior and after the event on a network of points across the study site. The locations are chosen with respect to the size of the area of interest, topography and travel times between the points. Measurements at each point include relative gravity with two CG-6 instruments, absolute gravity with a Muquans atom quantum gravimeter (AQG) and near-surface soil moisture using three cosmic ray neutron probes in a mobile rover setup. The same routine is strictly repeated at each point to assure uttermost comparability of the measurements. The AQG is also used to calibrate the permanently installed gPhoneX and, thus, to use the gravity reference station for correcting the high instrumental drift of the CG6 gravimeters. The monitoring concept is expected to be transferable to all areas where a similar interest in water storage dynamics at event time scales is strived for.

How to cite: Reich, M. and Güntner, A.: A concept of hybrid terrestrial gravimetry and cosmic ray neutron sensing for investigating hydrological extreme events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13624, https://doi.org/10.5194/egusphere-egu2020-13624, 2020.

EGU2020-9664 | Displays | G4.4

Experiences with relative microgravity surveying

Ola Eiken

Measurement techniques

High-precision aerial gravity surveys can be carried out by relative spring meters, with ties to stable reference stations or absolute measurements for time-lapse studies. Instrument drift is controlled by frequent repeat measurement and repeatability of 1-3 µGal has been common.  Free-fall gravimeters are heavier and costlier but provide absolute values and are immune to drift. Superconducting gravimeters are stationary and provide sub-µGal resolution over days and weeks, while drift uncertainty can build up to several μGal over years. Cold atom gravimeters are under development and may provide yet another survey alternative in the future.

Multiple sensors and multiple repeats are effective ways of improving survey precision, as much of the noise reduce at random noise (sqrt(N)). This holds also for the sensor drift residuals. An efficient, transparent and reproducible processing software is an integral part of such techniques.

Surface stations

Stability of measurement platforms over years is required for µGal time-lapse precision and can be achieved by installing geodetic monuments. For optimal monitoring of targets like a producing oil, gas or geothermal field, a water reservoir or a volcano, a grid of stations with spacing equal to or smaller than the overburden thickness is required. Surface subsidence or uplift requires sub-cm precision which can be obtained by optical leveling, InSAR or GPS.

Accuracy

Station repeatability is a robust accuracy measure for relative surveys with multiple occupations of each station. Together with multiple sensors they provide abundant statistics. The redundancy also allows for in-situ calibration of parameters for scale factor, tilt and temperature by minimizing residuals. Time-lapse precision can be judged at stations with minimal or known subsurface changes, and will be affected by gravity survey precision, accuracy of measured depth changes and other time-lapse effects such as benchmark stability and time-lapse signals outside interest. Groundwater variations could be one such noise term, unless the purpose is hydrology monitoring.

Efficiency and cost

Most microgravity projects have been carried out in a research or development setting, with one sensor, few stations repeat and implicit capital and personnel cost. In a more industrial setting, efficiency is likely to improve, together with reduced survey cost. More instruments and measurements will likely reduce the personnel and mobilization portion of the cost. Precision/cost tradeoffs and value of data will determine the economics of a project, whether in a scientific or commercial setting.

Conclusion

Currently proven survey repeatabilities of 1-2 µGal may be regarded state-of-the-art and become commonplace for microgravity surveys using relative gravimeters. This can widen the range of applications and reduce monitoring intervals. Further instrument developments may improve this limitation.

How to cite: Eiken, O.: Experiences with relative microgravity surveying, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9664, https://doi.org/10.5194/egusphere-egu2020-9664, 2020.

EGU2020-21470 | Displays | G4.4

In situ verification of refined predicted vertical gravity gradients on Etna

Peter Vajda, Pavol Zahorec, Juraj Papčo, Massimo Cantarero, Filippo Greco, and Daniele Carbone

In situ values of vertical gradients of gravity (VGGs) are often needed when compiling residual spatiotemporal gravity changes that are interpreted in volcanic areas with the objective of drawing inferences about sources of volcanic unrest or pending eruptions. VGG values are seldom acquired by in situ observations. Their availability in 4D volcano-microgravimetric surveys and studies can be mediated by predicting the VGGs based on high resolution high accuracy DEMs and modelling the topographic component (constituent) of the VGG. Based on a modelling effort and in situ verification of VGG predicted on Etna in the summit craters area, on the north-east rift and on benchmarks of the monitoring network covering the volcano in a wider context, we learned that the VGG prediction can be improved by using drone-borne photogrammetry with GNSS ground control to produce a finer DEM in the closest vicinity of the VGG point (benchmark or field point) with resolution higher than the available high-resolution LiDAR-derived DEM, and using detailed modeling of gravity effect (on VGG) of anthropogenic objects such as walls and buildings adjacent to the VGG points. In this poster we present the methods used in the refined VGG prediction and the results of the verification of VGGs predicted on Etna.

How to cite: Vajda, P., Zahorec, P., Papčo, J., Cantarero, M., Greco, F., and Carbone, D.: In situ verification of refined predicted vertical gravity gradients on Etna, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21470, https://doi.org/10.5194/egusphere-egu2020-21470, 2020.

We study the transient effect of groundwater mass changes on the observed gravity signal from a superconducting gravimeter deployed on Mt. Etna, Italy. Gravimeters are capable of detecting minor changes in the vertical component of gravity over time scales from minutes to years. Insight on geophysical phenomena that cause mass displacements in the subsurface can be obtained through the use of gravimetry. Gravity recordings integrate multiple components that contribute to the signal with different magnitudes. The effects of earth tides, atmospheric pressure changes, hydrological processes are among the above components. They need to be precisely evaluated, in order to isolate the signal caused by the volcanic processes. Here, we study the effect of groundwater mass changes on gravity, as a result of rainfall and snow melting, the latter estimated through GNSS interferometric reflectometry. A forward charge-discharge model is used to compare gravity recordings between 2018 - 2019 with observed precipitation events. We show that the observed gravity signal cannot be explained only through changes in groundwater mass, implying that other (volcanic) processes must have been at play.

How to cite: Koymans, M., Cannavò, F., and Carbone, D.: A strategy to study the effect of rainfall and snow melting on gravity recordings from a superconducting gravimeter installed on Mt. Etna volcano, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6955, https://doi.org/10.5194/egusphere-egu2020-6955, 2020.

EGU2020-3765 | Displays | G4.4

TGF: A New MATLAB-based Software for Terrain-related Gravity Field Calculations

Meng Yang, Christian Hirt, and Roland Pail

With knowledge of geometry and density-distribution of topography, the residual terrain modelling (RTM) technique has been broadly applied in geodesy and geophysics for the determination of the high-frequency gravity field signals. Depending on the size of investigation areas, challenges in computational efficiency are encountered when using an ultra-high-resolution digital elevation models (DEM) in the evaluation of Newtonian integration. This paper presents a new MATLAB-based program, terrain gravity field (TGF), for the accurate and efficient determination of the terrain-related gravity field based on an adaptive algorithm. Depending on the attenuation character of gravity field with distance, the adaptive algorithm divides the integration masses into four zones, and adaptively combines four types of geometries and DEMs with different spatial resolutions. The most accurate but least efficient polyhedron together with the finest DEM are only considered for the innermost zone, while prism approximation for the second zone, the third zone with the more efficient tesseroid and a coarse DEM, and the most efficient but least accurate point-mass with the coarsest DEM for distant masses. Compared to some publicly available algorithms depending on one type of geometric approximation, the TGF achieves accurate modelling of gravity field and greatly reduces the computation time. Besides, the TGF software allows to calculate ten independent elements of gravity field, supports two types of density inputs (constant density value and digital density map), and considers the sphericity of the Earth by involving spherical approximation and ellipsoidal approximation. Further to this, the TGF software is also capable of delivering the gravity field of full-scale topographic gravity field implied by masses between the Earth’s surface and mean sea level. Results from internal and external numerical validation experiments of TGF confirmed its accuracy of sub-mGal level. Based on TGF, the trade-off between accuracy and efficiency, values for the spatial resolution and extension of topography models are recommended. The TGF software has been extensively tested and recently been applied in the SRTM2gravity project to convert the global 3” SRTM topography to implied gravity effects at 28 billion computation points. This confirms TGF the capability of dealing with large datasets.

How to cite: Yang, M., Hirt, C., and Pail, R.: TGF: A New MATLAB-based Software for Terrain-related Gravity Field Calculations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3765, https://doi.org/10.5194/egusphere-egu2020-3765, 2020.

EGU2020-18917 | Displays | G4.4

The benefits of performing continuous gravity measurements at active volcanoes using superconducting gravimeters

Filippo Greco, Daniele Carbone, Flavio Cannavò, Alfio Messina, Danilo Contrafatto, Giuseppe Siligato, Richard Reineman, and Richard Warburton

Continuous gravity measurements at active volcanoes are mostly accomplished using spring gravimeters, that can be operated under harsh field conditions. Unfortunately, these instruments do not provide reliable continuous measurements over long time-scales, due to the instrumental drift and artifacts driven by ambient parameters.

An alternative to spring devices for continuous measurements is given by superconducting gravimeters (SGs), that are free from instrumental effects and thus allow to track even small gravity changes over time-scales from minutes to years. Nevertheless, SGs cannot be deployed in close proximity to the active structures of tall volcanoes, since they need host facilities with main electricity and a large installation surface.

The mini-array of three SGs that were installed on Etna between 2014 and 2016 makes the first network of SGs ever installed on an active volcano. Here we present results from these instruments and show that, even though they are installed at relatively unfavorable positions (in terms of distances from the summit active craters), SGs can detect volcano-related gravity changes that would otherwise remain hidden, thus providing unique insight into the bulk processes driving volcanic activity.

How to cite: Greco, F., Carbone, D., Cannavò, F., Messina, A., Contrafatto, D., Siligato, G., Reineman, R., and Warburton, R.: The benefits of performing continuous gravity measurements at active volcanoes using superconducting gravimeters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18917, https://doi.org/10.5194/egusphere-egu2020-18917, 2020.

EGU2020-554 | Displays | G4.4

Specific aspects of above-ice gravimetric observations

Alexey Shklyaruk, Kirill Kuznetsov, David Arutyunyan, and Ivan Lygin

Today, gravimetry is actively used in solving various detailed engineering problems, in researches of the underground fluid dynamics, etc. It is worth noting that the areas of large rivers and lakes are an interference in creating a regular network of observations, which is necessary to the above problems solution. For now the results of satellite, marine or aero surveys do not allow obtaining materials with the necessary resolution and accuracy parameters. The solution to this problem may be surveying in the winter period on frozen water reservoirs.

Gravimetric surveys were carried out on the surface of the ice covering the Ugra River as part of the field course of the Geological Faculty of Lomonosov Moscow State University in Kaluga region. Two high-precision relative gravimeters CG-5 Autograv by Scintrex Ltd were used.

During above-ice gravimetric observations, many factors influence the gravimeter. They can be divided into two groups: natural and human cause. The first group includes gusts of wind, melting ice, the flow of the river. The second group includes operator’s movements, interference of people passing by, etc.

The completed studies made it possible to evaluate the parameters of the standard deviation (SD) of the gravimeter records and the influence of the above factors on its tilt. An analysis of the observation results showed that high-precision relative gravimeters allow above-ice surveying with an accuracy of no worse than 5 μGal, which corresponds to the current level of ground gravity survey’s accuracy.

To minimize the influence of interfering factors, a special observation technique is required:

  • For an independent assessment of the accuracy of observations at each point, several gravimeters should be applied;
  • At each point, at least 10 measurements with one gravimeter should be performed;
  • The time of one measurement should be at least 60 seconds;
  • To minimize the influence of external factors on the measurements of gravimeters, it should be ensured that near the operator there are no outsiders, equipment, etc., creating oscillations of the surface which the device is installed on. At the same time, the operator of the gravimeter must constantly check the records of the gravimeter, the SD parameter and its levels.

How to cite: Shklyaruk, A., Kuznetsov, K., Arutyunyan, D., and Lygin, I.: Specific aspects of above-ice gravimetric observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-554, https://doi.org/10.5194/egusphere-egu2020-554, 2020.

EGU2020-4825 | Displays | G4.4

Terrestrial strapdown inertial gravimetry in the Bavarian Alps

Peter Schack, Roland Pail, and Thomas Gruber

Around 100km south of Munich, the Institute of Astronomical and Physical Geodesy of the Technical University of Munich established a gravimetric-astrogeodetic testing ground over the last 20 years. Precise gravity values as well as vertical deflections exist for hundreds of points. End of 2019, a car-based strapdown inertial gravimetry survey was realized in this area along a ~25km track. For this track, a few gravity values and several vertical deflections (spacing around 200m) are available (Hirt and Flury 2008). Navigation-grade IMU (inertial measurement unit), GNSS (global navigation satellite systems) and additional relative gravimeter observations were recorded during the survey. With this setup, it is possible to evaluate the capabilities of terrestrial scalar and vector strapdown inertial gravimetry.

This contribution gives an overview about the testing ground, the recently conducted survey and the data processing. The main part treats the analyses regarding the accuracy of 1D- and 3D-strapdown inertial gravimetry. Furthermore, attention is payed to the kinematic IMU performance (noise behavior), the benefit of special IMU calibrations (Becker 2016) and a comparison of the results with pure model based gravity disturbances.

Literature

  • Becker, D. (2016). Advanced Calibration Methods for Strapdown Airborne Gravimetry. PhD thesis, Technische Universität Darmstadt, Fachbereich Bau- und Umweltingenieurwissenschaften, Schriftenreihe der Fachrichtung Geodäsie Heft 51. ISBN 978-3-935631-40-2.
  • Hirt, C. and Flury J. (2008). Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and digital terrain model data. J Geod (2008) 82:231–248, Springer-Verlag. DOI 10.1007/s00190-007-0173-x.

How to cite: Schack, P., Pail, R., and Gruber, T.: Terrestrial strapdown inertial gravimetry in the Bavarian Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4825, https://doi.org/10.5194/egusphere-egu2020-4825, 2020.

EGU2020-18949 | Displays | G4.4

An integrated approach for understanding long-term volcano dynamics based on absolute gravity and GNSS measurements

Alessandro Bonforte, Filippo Greco, and Daniele Carbone

Here we present the results of repeated Absolute Gravity and GNSS measurements, collected at Mt. Etna (Italy) between 2009 and 2018. We aim at investigating the capabilities of this integrated approach for understanding the dynamics of magmatic sources over time-scales of months to years. The absolute gravity and GNSS campaign measurements were repeated roughly once a year; in order to improve the time resolution of gravity data, in some stations we performed, besides absolute gravity measurements, also relative measurements at intervals shorter than 1 year.

After being corrected for the effect of elevation changes, gravity data reveal an increase/decrease cycle, well spatio-temporal correlated with a general pattern of uplift/subsidence, during a period of intense lava fountains from the summit craters.

Our results provide insight into the processes that controlled the transfer of the magma from deeper to shallower levels of the plumbing system of Mt. Etna volcano, in periods preceding/accompanying the eruptive activity during 2009–2018.

Specifically, we propose that coupled changes in height-corrected gravity and elevation might be induced either by the magma storage/withdrawal below the volcanic pile, or by fluids pressurization/depressurization, or by a combination of both processes.

The application of the proposed approach could led to an improved capability to identify processes heralding eruptions.

How to cite: Bonforte, A., Greco, F., and Carbone, D.: An integrated approach for understanding long-term volcano dynamics based on absolute gravity and GNSS measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18949, https://doi.org/10.5194/egusphere-egu2020-18949, 2020.

G5.1 – Ionosphere, thermosphere and space weather: monitoring and modelling

EGU2020-284 | Displays | G5.1

Improving Total Electron Content (TEC) Models for Geodetic Applications

Mona Kosary, Saeed Farzaneh, Maike Schumacher, and Ehsan Forootan

Increasing the quality of ionosphere modeling is crucial and remains a challenge for many geodetic applications such as GNSS Precise Point Positioning (PPP) and navigation. Ionosphere models are the main tool to provide an estimation of Total Electron Content (TEC) to be corrected from GNSS career phase and pseudorange measurements. Skills of these models are however limited due to the simplifications in model equations and the imperfect knowledge of model parameters. In this study, an ionosphere reconstruction approach is presented, where global estimations of geodetic-based TEC measurements are combined with an ionospheric background model. This is achieved here through a novel simultaneous Calibration and Data Assimilation (C/DA) technique that works based on the sequential Ensemble Kalman Filter (EnKF). The C/DA method ingests the actual ionospheric measurements (derived from global GNSS measurements) into the IRI (International Reference Ionosphere) model. It also calibrates those parameters that control the F2 layer’s characteristics such as selected important CCIR (Comité Consultatif International des Radiocommunicationsand) URSI (International Union of Radio Science) coefficients.  The calibrated parameters derived from the C/DA are then replaced in the IRI to simulate TEC values in locations, where less GNSS ground-station infrastructure exists, as well as to enhance the prediction of TEC when the observations are not available or their usage is cautious due to low quality. Our numerical assessments indicate the advantage of the C/DA to improve the IRI’s performance. Values of the TEC-Root Mean Square of Error (RMSE) are found to be decreased by up to 30% globally, compared to the original IRI simulations. The importance of the new TEC estimations is demonstrated for PPP applications, whose results show improvements in navigation applications.

Keywords: Ionosphere, Calibration and Data Assimilation (C/DA), IRI, Total Electron Content (TEC), Precise Point Positioning (PPP), GNSS

How to cite: Kosary, M., Farzaneh, S., Schumacher, M., and Forootan, E.: Improving Total Electron Content (TEC) Models for Geodetic Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-284, https://doi.org/10.5194/egusphere-egu2020-284, 2020.

EGU2020-19447 | Displays | G5.1

The Spire TEC Environment Assimilation Model (STEAM)

Matthew Angling, Francois-Xavier Bocquet, German Olivares-Pulido, Sanita Vetra-Carvalho, Karl Nordstrom, Stacey Melville, and Giorgio Savastano

The ionosphere can affect a wide range of radio frequency (RF) systems operating below 2 GHz. One option for mitigating these effects is to produce assimilative models of the ionospheric density from which products can be derived for specific systems. Such models aim to optimally combine a background model of the ionospheric state with measurements of the ionosphere. This approach is analogous to the use of numerical weather prediction in the meteorological community, and has been evolving for ionospheric use for the last 10 to 15 years.

Published research has demonstrated the utility of this approach. However, obstacles to providing effective data products remain due to the sparseness of ionospheric data over large parts of the world and the timeliness with which data are available. Spire is working to overcome these issues through the use of its large constellation of satellites that can measure Total Electron Content (TEC) data in both zenith looking and radio occultation (RO) geometries and its large ground station network that will allow low data latency.

Spire data will be combined with an innovative data assimilation model (the Spire TEC Environment Assimilation Model, STEAM) to provide accurate and actionable ionospheric products. Data assimilation is required to overcome the limitations and assumptions of the traditional Abel Transform analysis of RO data (i.e., spherical symmetry; transmitter and receiver in free space and the same plane) and to effectively combine RO data, topside data, ground-based GNSS data, and other sources of ionospheric information (i.e., ionosondes).

STEAM uses a 4D Local ensemble transform Kalman Filter (LETKF). As with other ensemble methods, the LETKF uses an ensemble of models to approximate the background error covariance matrix. However, the LETKF provides a more efficient way to solve the ensemble equations. Furthermore, 4D operation permits the use of data with varying latency. Localisation means that grid points are only modified by data within a local volume; this restricts spurious long-range spatial correlations and means that the ensemble only has to span the space locally. The LETKF transforms the problem into ensemble space which makes each grid point independent, resulting in an algorithm that is easily parallelised.

This paper will describe the data collection and processing chain, the data assimilation model, and plans for the ongoing development of the combined system. 

How to cite: Angling, M., Bocquet, F.-X., Olivares-Pulido, G., Vetra-Carvalho, S., Nordstrom, K., Melville, S., and Savastano, G.: The Spire TEC Environment Assimilation Model (STEAM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19447, https://doi.org/10.5194/egusphere-egu2020-19447, 2020.

EGU2020-3450 | Displays | G5.1

Variations of TEC over Iberian Peninsula in 2015: effects of geomagnetic storms, solar flares, and solar eclipse

Teresa Barata, Anna Morozova, and Tatiana Barlyaeva

The total ionospheric content (TEC) over the midlatitudinal area of Iberian Peninsula was studied using data from two locations on the west and east coasts of the peninsula. The data are obtained both by the GNSS receivers and an ionosonde. The principal component analysis applied to the TEC data allowed us to extract two main modes.

The variations of these modes as well as the original TEC data were studied in relation to geomagnetic disturbances observed in March, June, October, and December of 2015. Seven of eight analyzed geomagnetic events were associated with positive-negative ionospheric storms (seen both in TEC daily cycle amplitude and in Mode 1).

Four out of eight analyzed geomagnetic events were associated with variations of Mode 2 that can be described as the appearance of the second daily peak on the 1st day of the storm and a deep in TEC variations on the 2nd day.

Besides, we analyzed the effects of solar flares and overall variations of the solar UV and XR fluxes on the TEC variations during those months. Since a partial solar eclipse was observed in March 2015, the TEC variations during this event were also studied. Only the amplitude of the daily TEC cycle (Mode 1) was found to respond to these types of events.

How to cite: Barata, T., Morozova, A., and Barlyaeva, T.: Variations of TEC over Iberian Peninsula in 2015: effects of geomagnetic storms, solar flares, and solar eclipse, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3450, https://doi.org/10.5194/egusphere-egu2020-3450, 2020.

EGU2020-325 | Displays | G5.1

Assessment of electron density profiles over the Brazilian region using radio occultation data aided by global ionospheric maps

Gabriel Jerez, Fabricio Prol, Daniele Alves, João Monico, and Manuel Hernández-Pajares

The development of GNSS (Global Navigation Satellite System) and LEO (Low Earth Orbiting) satellites missions enhanced new possibilities of the terrestrial atmosphere probing. The Radio Occultation (RO) technique can be used to retrieve profiles from the neutral and the ionized atmosphere. An important advantage of using RO data is the spatial distribution, which enables global coverage. The signal transmitted by GNSS satellites and tracked by receivers embedded at the LEO satellites is influenced by the atmosphere which causes signal refraction. Due to the signal and atmospheric interaction, instead of a straight line, the signal propagates as a curved line in the path between the transmitter and receiver. The satellites geometry allows the retrieval of atmospheric refractive index, which carries several characteristics from its composition, such as pressure and temperature of the neutral atmosphere, and electron density of the ionosphere. In 1995 GPS/MET (Global Positioning System/Meteorology) experiment was launched to prove the RO concept and, since then, several LEO missions with GNSS receiver embedded were developed, such as CHAMP (Challenging Mini-satellite Payload) (2001-2008), SAC-C (Satélite de Aplicaciones Cientificas-C) (2001-2013) and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) (2006-present). COSMIC is one of the RO missions with the greatest amount of atmospheric data available, mainly taking into account ionospheric information. In the RO technique, in general, the Abel retrieval is used to retrieve the refractive index. The Abel retrieval assumes a spherical symmetry of the atmosphere. When considering the electron density profiles, the main issue is related to regions with large horizontal gradients, where the spherical assumption presents the biggest degradation. In order to improve the ionospheric horizontal gradient used to retrieve electron density profiles, many researches have performed experiments using data from different sources. In this paper, we aimed to assess the electron density profiles over the Brazilian area (equatorial region), characterized by intense ionospheric variability, considering RO data and Global Ionospheric Maps (GIM). The data used is from COSMIC mission, in a period close to the last solar cycle peak (2013-2014). Ionosonde data were used as reference values to assess the RO with GIM aided data. Total Electron Content (TEC) data from GIM were used to estimate the variability of ionosphere between the ionosonde position and the profile locations. This research builds on a preliminary investigation related to the assessment of RO ionospheric profiles over a region under intense ionospheric variability, such as the Brazilian territory. Future works may take into consideration the use of other ionospheric information such as regional ionospheric maps, with higher resolution, and ionospheric tomography.

How to cite: Jerez, G., Prol, F., Alves, D., Monico, J., and Hernández-Pajares, M.: Assessment of electron density profiles over the Brazilian region using radio occultation data aided by global ionospheric maps , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-325, https://doi.org/10.5194/egusphere-egu2020-325, 2020.

EGU2020-1569 | Displays | G5.1

Extraction of electron density profiles with geostationary satellite-based GPS side lobe occultation signals

Wenwen Li, Min Li, Qile Zhao, Chuang Shi, and Rongxin Fang

Electron density profiles (EDP) obtained by GNSS radio occultation (RO) technique can improve the primary ionospheric parameters. However, current studies mainly focused on GNSS RO measurements observed by low Earth orbit satellites, which can only estimate EDP at low altitudes typically below 1000 km. We investigated the GPS RO measurements recorded on the geostationary earth orbit (GEO) satellite TJS-2 (telecommunication technology test satellite II). To improve EDP derivation precision, the total electron content derived from TJS-2 single-frequency excess phase is refined by a moving average filter, which can smooth high-frequency errors and indicate higher precision over the single-difference technique. By comparison with the ground-based digisonde, the IRI 2016 model and the Constellation Observing System for Meteorology, Ionosphere, and Climate satellite (COSMIC) EDPs, the TJS-2 ionospheric EDPs show good agreement with correlation coefficients exceeding 0.8. The TJS-2 average NmF2 differences compared to digisondes and COSMIC results are 12.9% and 1.4%, respectively, while the hmF2 differences are 1.65 km and 1.76 km, respectively. With a GEO satellite such as TJS-2, the side lobe GPS RO signals can also be received, and they are employed to estimate electron densities up to several thousand kilometers in height for the first time in this contribution. Our results also reveal that GEO-based RO signals can estimate EDPs at specific locations with daily repeatability, which makes it a very suitable technique for routinely monitoring EDP variations

How to cite: Li, W., Li, M., Zhao, Q., Shi, C., and Fang, R.: Extraction of electron density profiles with geostationary satellite-based GPS side lobe occultation signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1569, https://doi.org/10.5194/egusphere-egu2020-1569, 2020.

EGU2020-2837 | Displays | G5.1

Ionospheric irregularities detected by GEONET

Guanyi Ma, Qi Li, Takashi Maruyama, Jinghua Li, Qingtao Wan, Jiangtao Fan, Xiaolan Wang, and Jie Zhang

Ionospheric irregularities disrupt the propagation of radio waves in the frequency range below a few GHz, a band used by navigation and communication systems such as Global Navigation Satellite System (GNSS). Detailed understanding of the irregularity characteristics is helpful to estimate potential degradation of the performance of radio systems. We develop an algorithm to obtain high spatial resolution vertical total electron content (VTEC) and propose a spatial fluctuation of total electron content (TEC), SFT parameter, to analyze ionospheric irregularities by using the world’s densest GNSS Earth Observation Network (GEONET) of Japan. The data used in this study are carrier phase of the dual frequency GNSS signals from more than 1300 GNSS receivers of GEONET. VTEC is derived by assuming that it is identical in a 0.1°×0.1° grid, and removing a quantity representing inter-frequency hardware bias mixed with integer ambiguity. SFT is defined as the spatial dispersion of TEC within a specific area at a given time. The size of the specific area for SFT calculation is chosen as 0.8°× 0.8° in longitude and latitude, which corresponds to approximately 77 km×95 km at 400 km height at 35°N of Japan. An SFT map is generated by sliding window to show the spatial variation of ionospheric irregularities in two dimensions. The map can be used to obtain the size, shape, orientation and intensity distribution of the irregularity structures. Case studies are carried out for three strong irregularity events on 12 February 2000, 20 March 2001 and 10 November 2004. The irregularities are found to be anisotropic branching structures, which elongate in north-south direction when first seen at lower latitudes. The structures can move and deviate from their previous orientations, and eventually drift perpendicular to their orientations. Such analyses of SFT maps with GEONET observation successfully provide a new perspective of irregularity morphology and evolution.

How to cite: Ma, G., Li, Q., Maruyama, T., Li, J., Wan, Q., Fan, J., Wang, X., and Zhang, J.: Ionospheric irregularities detected by GEONET, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2837, https://doi.org/10.5194/egusphere-egu2020-2837, 2020.

EGU2020-10112 | Displays | G5.1

Characterization of Equatorial Low Latitude Ionospheric Scintillation of GPS Signals: An E-POP Experiment

Ali Mohandesi, David Knudsen, and Susan Skone

Ionospheric irregularities are a major error source in GNSS positioning and navigation as they affect trans-ionospheric signal propagation. They cause random, rapid fluctuations in the intensity and phase of the received signal, referred to as ionospheric scintillations. From a global point of view, GNSS signal scintillations are more severe and frequent in the equatorial region and during post-sunset hours. Characterizing irregularities that interfere most with navigation signals requires high-temporal resolution of measurements. In this work we utilize high-rate upward-looking measurements accomplished by the GAP RO receiver on CASSIOPE (Swarm Echo) satellite to study GPS signal scintillations and irregularities associated with them. This was done by reorienting CASSIOPE by approximately 90 degrees for short periods during November and December, 2019 while it passed through low-latitude region during post-sunset hours local time. High-rate GAP RO measurements provide a unique opportunity to investigate small-scale irregularities that are responsible for signal scintillations.

How to cite: Mohandesi, A., Knudsen, D., and Skone, S.: Characterization of Equatorial Low Latitude Ionospheric Scintillation of GPS Signals: An E-POP Experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10112, https://doi.org/10.5194/egusphere-egu2020-10112, 2020.

EGU2020-7800 | Displays | G5.1

Impact of electron density values from space-geodetic observation techniques on thermospheric density models

Armin Corbin, Kristin Vielberg, Michael Schmidt, and Jürgen Kusche

The neutral density in the thermosphere is directly related to the atmospheric drag acceleration acting on satellites. In fact, the atmospheric drag acceleration, is the largest non-gravitational perturbation for satellites below 1000 km that has to be considered for precise orbit determination. There are several global empirical and physical models providing the neutral density in the thermosphere. However, there are significant differences between the modeled neutral densities and densities observed via accelerometers. More precise thermospheric density models are required for improving drag modeling as well as orbit determination. We study the coupling between ionosphere and thermosphere based on observations and model outputs of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). At first, we analyse the model’s representation of the coupling using electron and neutral densities. In comparison, we study the coupling based on observations, i.e., accelerometer-derived neutral densities and electron densities from a 4D electron density model based on GNSS and satellite altimetry data as well as radio occultation measurements. We expect that increased electron densities can be related to increased neutral densities. This is indicated for example by a correlation of approximately 55% between the neutral densities and the electron densities computed by the TIE-GCM. Finally, we investigate whether neutral density simulations fit better to in-situ densities from accelerometry when electron densities are assimilated.

How to cite: Corbin, A., Vielberg, K., Schmidt, M., and Kusche, J.: Impact of electron density values from space-geodetic observation techniques on thermospheric density models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7800, https://doi.org/10.5194/egusphere-egu2020-7800, 2020.

EGU2020-15238 | Displays | G5.1

Calculation of temporally high-resolution scaling factors for the thermospheric density from SLR observations

Lea Zeitler, Michael Schmidt, Mathis Bloßfeld, and Sergei Rudenko

The motion of a satellite depends on gravitational and non-gravitational accelerations. A major problem in precise orbit determination (POD) of low-Earth orbiting (LEO) satellites is modelling the thermospheric drag. It is the largest non-gravitational acceleration acting on satellites with altitudes lower than 1000 km and decelerates them. In case of the Swarm satellites with an altitude of around 460 km not considering the drag within a POD would cause an error of around 3 meters per revolution in the along-track direction.

In this study, we present results of DGFI-TUM in the context of the project TIPOD (Development of High-Precision Thermosphere Models for Improving Precise Orbit Determination of Low-Earth-Orbiting Satellites) funded by DFG in the frame of the SPP 1788 ‘Dynamic Earth’. One aim of this project is the computation of scaling factors for the thermospheric density from different satellite observation techniques, such as SLR, DORIS, GNSS or accelerometry. For a joint estimation of thermospheric model parameters the spatial, temporal and spectral content of the different scaling factors have to be analysed and interpreted. For example, accelerometer measurements along the satellite orbit provide scaling factors as point values. In this study we derive scaling factors from SLR measurements which could be interpreted as quasi-point values.

For the POD of LEO satellites, DGFI-TUM’s software package DOGS (DGFI-TUM Orbit and Geodetic parameter estimation Software) is used. It is characterized by the ability to process observations of different space geodetic techniques and to combine their linear parameter estimation systems within a joint Gauss-Markov model.

Here, we estimate scaling factors for the thermospheric density with a time resolution much higher than in our previous studies. Therefore, we use information of short passages from selected spherical satellites above SLR ground stations. Different temporal resolutions for the scaling factors varying from 6 hours down to 5 minutes will be tested and discussed in terms of reliability.

How to cite: Zeitler, L., Schmidt, M., Bloßfeld, M., and Rudenko, S.: Calculation of temporally high-resolution scaling factors for the thermospheric density from SLR observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15238, https://doi.org/10.5194/egusphere-egu2020-15238, 2020.

We present a systematical study crossing both data analysis and model simulation to improve the specification of the energy and momentum inputs into the ionosphere-thermosphere (IT) system, especially at meso-scale, and the system response. Our results are organized in two parts, meso-scale forcing from above and from below. First, the meso-scale forcing from magnetosphere including flow burst, electric field variability, meso-scale particle precipitation and field-aligned current (FAC) has been analyzed using both satellite and ground-based measurements. The forcing distributions are then implemented in the Global Ionosphere-Thermosphere Model (GITM) to assess the relative contributions of meso-scale forcing to the ionosphere-thermosphere (I-T) system. Secondly, the acoustic gravity waves (AGWs) trigged by the geographic events, such as hurricane and volcano, propagate from lower atmosphere to I-T and cause disturbances observable for the Global Navigation Satellite Systems (GNSS). GITM with local-grid refinement (GITM-R) has been utilized to simulate ionospheric total electron content (TEC) variations induced by those events and compared with GNSS observations. These high-resolution simulations will strongly enhance our understanding and capability to specify the meso-scale forcing for the I-T system.

How to cite: Deng, Y.: What is the influence of meso-scale forcing on the ionosphere-thermosphere system?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12553, https://doi.org/10.5194/egusphere-egu2020-12553, 2020.

Slant Total Electron Content (sTEC) measurements can be obtained by dual-frequency GPS
onboard Low Earth Orbiting (LEO) satellites. Within the last few years, a fleet of LEO Satellites at
altitudes ranging from 450 km (Swarm A/C) to 815 km (Sentinel 3) became operational. With
Swarm B, the recently launched GRACE-FO, and the Sentinel 1 and 2 satellites orbiting at
intermediate altitudes, we gain insight into the altitude dependent profile of the topside ionosphere
and plasmasphere.
We make use of this constellation to estimate a global three dimensional model of the electron
density distribution and will also carefully asses the impact of different profile functions, geometry-
free phase center variation maps and the P1-P2 receiver biases. Since the absolute value of the P1-
P2 biases are generally unknown, we focus on a consistent estimation for the whole LEO
constellation.
We will present first results for selected months in 2019 and investigate the day to day variability of
the topside ionosphere and plasmasphere. We also intend to make use of COSMIC-2 data to
improve local time coverage in equatorial regions.

How to cite: Schreiter, L., Stolle, C., Arnold, D., and Jäggi, A.: Altitude dependent empirical modeling of the topside ionosphere and plasmasphere using GPS- TEC from Swarm, GRACE-FO and the Sentinel satellites., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4809, https://doi.org/10.5194/egusphere-egu2020-4809, 2020.

EGU2020-7526 | Displays | G5.1

Plasmaspheric electron density estimation based on COMISC/FORMOSAT-3 data

Fabricio Prol and Mainul Hoque

The plasmasphere is a region of continuous study due to some open questions related to the plasmaspheric internal dynamics, boundaries, and coupling processes with the magnetosphere and ionosphere, in particular during space weather events. Given such interests, the results of a new tomographic method to estimate the plasmaspheric electron density will be presented. The tomographic reconstruction is applied using measurements of Total Electron Content (TEC) from the Global Positioning System (GPS) receivers aboard the Constellation Observing System for Meteorology, Ionosphere, and Climate / Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3). Despite relevant challenges imposed by the orbital geometry to obtain stable electron density reconstructions of a large area such as the plasmasphere, the developed approach was capable of representing the natural variability of the plasma ambient in terms of geographic/geomagnetic latitude, altitude, solar activity, season, and local time. The quality assessment was carried out using two years of in-situ electron density measurements from spacecraft deployed by the Defense Meteorological Satellite Program (DMSP). Our investigation revealed that improvements over 20% can be achieved for electron density specification by TEC data assimilation into background ionization.

How to cite: Prol, F. and Hoque, M.: Plasmaspheric electron density estimation based on COMISC/FORMOSAT-3 data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7526, https://doi.org/10.5194/egusphere-egu2020-7526, 2020.

EGU2020-13485 | Displays | G5.1

The Daytime and Nighttime Mapped Whistler Plasmapause Observed by DEMETER

Chao-Yen Chen and Jann-Yenq Liu

This paper investigates the plasmapause positions in the ionosphere by measurement of the whistler count probed by DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite in the daytime at 1030 LT (local time) and the nighttime at 2230 LT during 2005-2010.  The whistler finds the plasmapause position which can be clearly allocated in both daytime and nighttime.  We examine the nighttime/daytime plasmapause in various longitudes, solar activities, seasons, and geomagnetic actives.  Results show that the daytime plasmapause appears in the equatorward side of the nighttime one.  Both the daytime and nighttime plasmapause are sensitive to solar activity, which move equatorward form the low to high solar activity in the study period.  The seasonal variation of the plasmapause are rather random and insignificant.  During magnetic disturbed condition, the plasmapause tend to move equatorward.

How to cite: Chen, C.-Y. and Liu, J.-Y.: The Daytime and Nighttime Mapped Whistler Plasmapause Observed by DEMETER, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13485, https://doi.org/10.5194/egusphere-egu2020-13485, 2020.

EGU2020-9382 | Displays | G5.1

Evaluation of E-Layer Dominated Ionosphere Events Using CHAMP, COSMIC/FORMOSAT-3 and FY3C Data

Sumon Kamal, Norbert Jakowski, Mohammed M. Hoque, and Jens Wickert

Under certain space weather conditions the ionization level of the ionospheric E layer can dominate over that of the F2 layer. This phenomenon is known as “E layer dominated ionosphere” (ELDI) and occurs primarily at high latitudes in the polar regions. The corresponding electron density profiles show their peak ionization at the E layer height between 80 km and 150 km above the Earth’s surface. In this work we have evaluated the influence of space weather and geophysical conditions on the occurrence of ELDI events at high latitudes in the northern and southern hemispheres. For this, we used electron density profiles derived from ionospheric radio occultation measurements aboard CHAMP, COSMIC and FY3C satellites. The used CHAMP data covers the years from 2001 to 2008, the COSMIC data the years from 2006 to 2018 and the FY3C data the years from 2014 to 2018. This provides us continuous data coverage for a long period from 2001 to 2018, containing about 4 million electron density profiles. In addition to the geospatial distribution, we have also investigated the temporal occurrence of ELDI events in the form of the diurnal, the seasonal and the solar activity dependent variation. We have further investigated the influence of geomagnetic storms on the spatial and temporal occurrence of ELDI events.

How to cite: Kamal, S., Jakowski, N., Hoque, M. M., and Wickert, J.: Evaluation of E-Layer Dominated Ionosphere Events Using CHAMP, COSMIC/FORMOSAT-3 and FY3C Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9382, https://doi.org/10.5194/egusphere-egu2020-9382, 2020.

EGU2020-12026 | Displays | G5.1

Simulated GPS radio occultation signals from sporadic-E layers

Daniel Emmons

A multiple phase screen model is used to simulate GPS radio occultation signals through varying sporadic-E layers.  The length, vertical extent, and plasma frequency of the sporadic-E layers are varied to analyze the effect on the signal received by a low earth orbiting satellite.  A nonlinear relationship between the maximum variance in the signal amplitude and the plasma frequency is observed.  For certain frequency ranges, the predictions match previous studies that have used the S4 scintillation index to predict fbEs values. Additionally, the spectra of the signals are analyzed as a function of the different parameters providing an alternative approach for extracting sporadic-E parameters from GPS radio occultation measurements. 

How to cite: Emmons, D.: Simulated GPS radio occultation signals from sporadic-E layers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12026, https://doi.org/10.5194/egusphere-egu2020-12026, 2020.

EGU2020-8281 | Displays | G5.1

IGS RTS for real-time global ionospheric total electron content modeling: Method and Applications

Ningbo Wang, Zishen Li, and Liang Wang

To enable GNSS applications with low or no time latency, real-time services (RTS) of the International GNSS Services (IGS) has been launched since 2013. The IGS RTS provides real-time data streams with latencies of less than few seconds, containing multi-frequency and multi-constellation GNSS measurements from a global network of high-quality GNSS receivers, which provides the opportunity to reconstruct global ionospheric models in real-time mode. For the computation of real-time global ionospheric maps (RT-GIM), a 2-day predicted global ionospheric model is introduced along with real-time slant ionospheric delays extracted from real-time IGS global stations. GPS and GLONASS L1+L2, BeiDou B1+B2 and Galileo E1+E5a signals with a sampling rate of 1 Hz are used to extract slant TEC (STEC) estimates. Spherical harmonic expansion up to degree and order 15 is employed for global vertical TEC (VTEC) modeling by combining the observed and predicted ionospheric data in real-time mode. Real-time ionospheric State Space Representation (SSR) corrections are then distributed in RTCM 1264 message (123.56.176.228:2101/CAS05) aside from the generation of RT-GIM in IONEX v1.0 format (available at ftp://ftp.gipp.org.cn/product/ionex/). The quality of CAS RT-GIMs is assessed during an 18-month period starting from August 2017, by comparison with GPS differential slant TECs at the selected IGS stations over continental areas, Jason-3 VTECs over the oceans and IGS combined final GIMs on a global scale, respectively. Results show that CAS’s RT-GIM products exhibit a relative error of 13.9%, which is only approximately 1-2% worse than the final ones during the test period. Additionally, the application of RT-GIM on the single-frequency precise point positioning (PPP) of smartphones is also presented.

How to cite: Wang, N., Li, Z., and Wang, L.: IGS RTS for real-time global ionospheric total electron content modeling: Method and Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8281, https://doi.org/10.5194/egusphere-egu2020-8281, 2020.

EGU2020-8770 | Displays | G5.1

ARTEMIS: Advanced methodology development for Real-TimE Multi-constellation (BDS, Galileo and GPS) Ionosphere Services

Zishen Li, Ningbo Wang, Andrzej Krankowski, Xingliang Huo, libo Liu, and Liang Li

In recent years the development of satellite navigation systems sped up and is no longer limited to well-known GPS and GLONASS systems. A good example of which are Europe’s Galileo and China’s BeiDou systems, which can be integrated for various scientific applications. ARTEMIS is a Chinese-Polish joint project concentrating on an important area of space research – space weather monitoring – through the development of new technologies and methods of Earth’s ionosphere monitoring. The main objective of the project is a development of the methodology for ionospheric real-time services using observations from BeiDou, Galileo and GPS systems, which are of extreme importance from professional (precise positioning, satellite navigation) and scientific points of view in the areas requiring current and accurate information on the state of the ionosphere.

 

The concept of ARTEMIS for real-time ionospheric space weather service is presented at first in this contribution, followed by the scientific progress from both Chinese and Polish sides during the year 2019. Benefiting from the real-time multi-constellation and multi-frequency GNSS data streams from regional and global permanent network stations, a prototype service system for real-time ionospheric monitoring was developed, which supports at current stage, the generation of global real-time Total Electron Content (TEC) maps, global Rate of TEC Index (ROTI) maps, as well as regional TEC/ROTI maps over Chinese and European regions. Using the home-made ionospheric scintillation (IS) monitoring receiver, i.e. BDSMART, an experimental campaign was carried out at low-latitude stations of China for the quality examination of BDSMART IS receivers. The ionospheric scintillation monitoring results from both GNSS L band and Low Frequency Array (LOFAR) low-frequency radio astronomical observations are highlighted by the Polish partner. The Chinese low-latitude Ionospheric Experimental Network (CHINE) for low-latitude ionospheric scintillation monitoring is now under construction. The generation of regional and global three-dimensional ionospheric electron densities in real-time is still in progress.

How to cite: Li, Z., Wang, N., Krankowski, A., Huo, X., Liu, L., and Li, L.: ARTEMIS: Advanced methodology development for Real-TimE Multi-constellation (BDS, Galileo and GPS) Ionosphere Services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8770, https://doi.org/10.5194/egusphere-egu2020-8770, 2020.

A series of studies have suggested that a geomagnetic storm can accelerate the formation of plasma depletions and the generation of ionospheric irregularities. Using observation data from the Continuously Operating Reference Stations (CORS) network in the USA, the responses of the ionospheric total electron content (TEC) to the geomagnetic storm on September 8, 2017 are studied in detail. A mid-latitude trough was discovered from 01:00 UT to 06:00 UT in the USA with a length exceeding 5000 km. The probable causes are the combination of a classic negative storm response with increments in the neutral composition and the expansion of the auroral oval, pushing the mid-latitude trough equatorward.  Super-scale plasma depletion was observed by SWARM data accompanied by the expansion of mid-latitude trough. Both PPEF from high latitudes and pole-ward neutral wind are responsible for the large-scale ionospheric irregularities. Medium-scale travelling ionospheric disturbances (MSTID) with wavelengths of 600–700 km were generated accompanied by a drop and perturbation in the electron density. The intensity of the MSTID fluctuations reached over 2.5 TECU, which were discovered by filtering the differential TEC. The evolution of plasma depletions were associated with the MSTID propagating from high latitudes to low latitudes. SWARM spaceborne observations also showed a drop in the electron density from 105 to 103 compared to the background values at 28° N, 96° W, and 25° N, 95° W. This research investigates super-scale plasma depletions generated by geomagnetic storms using both CORS GNSS and spaceborne observations. The proposed work is valuable for better understanding the evolution of ionospheric depletions during geomagnetic storms.

How to cite: Liu, Y., Li, Z., and Wang, J.: Studying the Ionospheric Responses Induced by a Geomagnetic Storm in September 2017 with Multiple Observations in America, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1906, https://doi.org/10.5194/egusphere-egu2020-1906, 2020.

EGU2020-3499 | Displays | G5.1

Analysis of a severe geomagnetic storm on August 26, 2018 and the related effects on the GRACE-FO mission

Sandro Krauss, Manuela Temmer, Saniya Behzadpour, and Christoph Lhotka

On August 20, 2018 a complex interplanetary coronal mass ejections (ICME) occurred on the Sun, which subsequently triggered an unexpected large geomagnetic storm on August 25. We present a detailed analysis of the ICME eruption and explore the occurred perturbation of the neutral mass density in the upper Earth's atmosphere. The analysis is based on accelerometer observations from the satellite mission GRACE Follow-On as well as interplanetary magnetic field measurements by the DSCOVR and ACE spacecraft. Through the evaluation of solar observations by the SECCHI instrument on-board of the STEREO-A satellite in form of white-light, the early evolution of the ICME can be aptly illustrated. Furthermore, due to the heating and the subsequent expansion of the thermosphere also the drag force acting on the spacecraft is enhanced. This leads to an additional storm induced orbit decay, which we calculate by means of variations in the semi-major axis. The findings are compared with predictions from our preliminary thermospheric forecasting tool, which is based on the study by Krauss et al. 2018.

How to cite: Krauss, S., Temmer, M., Behzadpour, S., and Lhotka, C.: Analysis of a severe geomagnetic storm on August 26, 2018 and the related effects on the GRACE-FO mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3499, https://doi.org/10.5194/egusphere-egu2020-3499, 2020.

EGU2020-3694 | Displays | G5.1

Geomagnetically induced currents in central Europe

Tatiana Výbošťoková, Michal Švanda, and Zdeněk Němeček

Eruptive events on the Sun interacts with the magnetosphere and can affect even the Earth-bound structures such as power transmission networks via geomagnetically induced electric currents (GICs). We quantify the geomagnetic activity by the K-index computed from local measurements of the geomagnetic field and investigate its effects on the Czech electric power grid represented as disturbances recorded in the maintenance logs of the power network operators in course of last 12 years. In data sets recording the disturbances on high and very high voltage power lines, we found a statistically significant increase of anomaly rates within tens of days around maxima of a geomagnetic activity compared to the adjacent activity minima. Moreover, we modeled GICs for two (east-west and north-south oriented) high-voltage transmission lines in the Czech Republic and found surprisingly high values of currents, in the order of tens of amperes. Based on in-situ observations, we study propagation and properties of the largest CMEs and their relation to the disturbances in the transmission networks of the Central European countries. Our results provide an evidence that GICs may affect the occurrence rate of anomalies registered on power-grid equipment even in the mid-latitude countries.

How to cite: Výbošťoková, T., Švanda, M., and Němeček, Z.: Geomagnetically induced currents in central Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3694, https://doi.org/10.5194/egusphere-egu2020-3694, 2020.

EGU2020-10986 | Displays | G5.1

How the magnetosphere-ionosphere/thermosphere-ground system is coupled by waves

Paul Song and Jian-Nan Tu

We study the polar magnetospheric coupling to the ionosphere/thermosphere and ground system along the field by examining a spectrum of perturbations propagating from the magnetosphere downward. What distinguishes this study from conventional treatments of the magnetosphere-ionosphere/thermosphere system is that our treatment self-consistently includes the responses of the neutrals to the magnetic and plasma velocity perturbations. The thermosphere is coupled to the magnetosphere-ionosphere (M-I) system in a degree that depends on the time scale of the perturbations. There are three major processes that affect the perturbation propagation: damping that reduces the energy flux while producing heating, the neutral-inertia loading that reduces the propagation speed, and reflection which, associated with structures of the ionosphere and thermosphere, reduces the downward energy flux. The damping is stronger in higher frequencies, 10-2~0 Hz for M-I coupling. As a result of reflection, significant energy fluxes of the magnetospheric perturbations cannot reach the lower ionosphere and hence the ground although some heating and energization may occur in the lower ionosphere resulting from the strong damping of high frequency fluctuations. However, the amplitude of the magnetic fluctuations of the transmitted flux into the lower ionosphere can be enhanced in lower frequencies because of the decrease in the propagation speed due to strong neutral-inertia loading. Combining the attenuation and amplitude enhancement effects, the net enhanced amplitudes occur in frequencies less than few Hertz, which may explain the ready observations of PC waves that are enhanced magnetic oscillations in periods from 0.5 sec to 30 min on the ground while little enhancement is observed below this period range. On the other hand, the smallness of the propagation velocity results in very small electric perturbations, forming a magneto-static condition for coupling from the lower ionosphere to the ground in low-frequencies, casting doubts on any ionosphere-ground coupling mechanisms based on static electric field in the lower frequencies.

How to cite: Song, P. and Tu, J.-N.: How the magnetosphere-ionosphere/thermosphere-ground system is coupled by waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10986, https://doi.org/10.5194/egusphere-egu2020-10986, 2020.

EGU2020-12646 | Displays | G5.1

The three-dimensional ionospheric tomography in Japan by using the adaptive Kalman Filter algorithm

Rui Song, Katsumi Hattori, and Chie Yoshino

  The three-dimensional (3-D) tomographic inversion is a crucial technique for imaging the ionospheric electron distributions (IEDs) on both the horizontal and vertical directions based on the total electron content (TEC) data. In this study, a regional 3-D tomography was realized in Japan using the Kalman Filter (KF) algorithm. In addition, to deduce the divergences, the adaptive Sage-Husa KF (SHKF) was proposed to determine the unknown priori information of the noise covariance encountered in the conventional KF (CKF). From this base, slant TEC (STEC) data observed by 55 GPS (Global Positioning System) receivers in the years of 2013 and 2018 was selected for IED reconstructions with the resolution 1º×1º×30 km in latitude, longitude and altitude, respectively. As for the ionospheric diurnal and annual variations, by comparing the F2 layer peak electron density (NmF2) simulated by SHKF, CKF, and the International Reference Ionosphere (IRI) model with the observed values detected by 4 Japanese ionosondes (Okinawa, Yamagawa, Kokubunji, and Wakkanai) during April 3-9, 2018 and 2013, the Root-Mean-Square-Error (RMSE) and co-releation index (ρ) were adopted to evaluate the simulated effciency. Results showed that the least RMSE (0.3084 in 2018, 0.5397 in 2013) and the best ρ values (0.9517 in 2018, 0.9896 in 2013) were both given by the SHKF-CIT method. Then, seasonal characteristics were implemented on January 02, March 20, June 14 and September 24, 2018, where the variations of northern EIA, winter and semiannual anomalies were accurately captured by the SHFK method. Meanwhile, the recalculated TEC values as well as the inverted vertical profiles manifested that SHKF-based tomography was outperformed the other methods. In the end, taking a strong geomagnetic storm happened on 26 August, 2018 as an example, both the meridional and latitudinal (along 135°E and 35°N, respectively) IEDs displayed more significant promotions than IRI model, and the results indicates that the IED around Japan developed by SHKF-based tomography is promising for the ionospheric studies and practical applications.

How to cite: Song, R., Hattori, K., and Yoshino, C.: The three-dimensional ionospheric tomography in Japan by using the adaptive Kalman Filter algorithm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12646, https://doi.org/10.5194/egusphere-egu2020-12646, 2020.

EGU2020-13348 | Displays | G5.1

Analysis of ionospheric disturbances caused by the severe weather event in Poland on 11th August 2017

Grzegorz Nykiel, Yevgen Zanimonskiy, Mariusz Figurski, Zofia Baldysz, Aleksander Koloskov, and Andrey Sopin

The coupling of the ionosphere with the tropospheric processes is a complex problem and the necessity of its resolve is highlighted in numerous publications. They mainly focus on lightning, hurricanes, tornadoes, as well as tsunamis, which induce disturbances in the ionosphere. Current works suggest that they are generated by the two major mechanisms: electrical effects during lightning, and atmospheric gravity waves propagated vertically and horizontally. However, these mechanisms are still not precisely examined.

The aim of this study is investigation of the coupling of severe weather event with ionosphere. This phenomenon, which can be classified as derecho occurred on 11th August 2017 in Poland. It was a 300 km length bow echo heavy storm, characterized by wind gusts of about 150 km/h, lightning, strong rain and hail drops. All these factors may have caused disturbances not only in the troposphere but also affect the ionosphere. In order to investigate a coupling mechanism and determination of morphological characteristics of the ionospheric disturbances, we used a dense network of GNSS receivers. Using GPS and GLONASS observations, we estimated total electron content (TEC) variations with 30-second interval. This has allowed to obtain high spatial and temporal resolution maps of ionospheric disturbances which have been compared with other data derived from in situ meteorological measurements, weather radars, and the Weather Research and Forecasting (WRF) numerical weather model. We investigated that during the main phase of the storm the wavy-like ionospheric disturbances occurred for some of the observed satellite with magnitude of about 0.2 TECU. In this work, we present detailed analysis of this event and discussion about troposphere-ionosphere coupling.

How to cite: Nykiel, G., Zanimonskiy, Y., Figurski, M., Baldysz, Z., Koloskov, A., and Sopin, A.: Analysis of ionospheric disturbances caused by the severe weather event in Poland on 11th August 2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13348, https://doi.org/10.5194/egusphere-egu2020-13348, 2020.

Ionosphere is one of the main errors in the signal propagation of global navigation system satellite (GNSS), and it is also the key issue of space weather. The International Reference Ionosphere (IRI) is the most important empirical model described the ionospheric characteristics, and it provides the monthly averages of electron densities and vertical total electron content (VTEC) in the altitude range of 50km-2000km. The IRI-2016 model is the latest version. But some studies showed that the accuracy of the IRI model is not high enough in China due to the use of fewer data sources. This paper will assess the performance of IRI-2016 model in China, and a modified IRI 2016 model by adjusting the driving parameters IG and RZ index of IRI2016 model with GNSS TEC data are also investigated. In this contribution, GNSS data from the Crustal Movement Observation Network of China (CMONC) are used to estimate TEC values, and the ionosonde data from three stations are used as references for the ionospheric electron densities. Three ionosonde stations are located at Beijing (BP440, 40.3°N/116.2°E), Wuhan (WU430, 30.5°N/114.4°E) and Sanya (SA418, 18.3°N/ 109.6°E). The above data respectively cover a period of 6 days in the high year (2015) and low year (2019) of solar activity.

The study shows that the biggest reason for the difference (DTEC) between GPS-TEC and IRI2016-TEC in China is that the poor estimation of NmF2 and hmF2 by IRI model, and the driving parameters IG and RZ index of IRI2016 can be updated by constraining DTEC. Finally, the performance of the modified IRI-2016 model is improved by the updated IG and RZ indexes as the short-term driving values of ionospheric parameters. The analysis show that the modified IRI-2016 model is more accurate at estimating both the TEC and the electron density profile than the original model.

How to cite: zhang, W., Huo, X., and Liu, H.: Assessment of the IRI-2016 and modified IRI 2016 models in China: Comparison with GNSS-TEC and ionosonde data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16646, https://doi.org/10.5194/egusphere-egu2020-16646, 2020.

EGU2020-1524 | Displays | G5.1

Analysis of a new regional ionospheric assimilated H2PT model for Europe

Paulina Woźniak, Anna Świątek, Mariusz Pożoga, and Łukasz Tomasik

The signal emitted by the GNSS (Global Navigation Satellite System) satellite, on the way to the receiver located on the Earth’s surface, encounters a heterogeneous layer of ionized gas and free electrons, in which the radio wave is dispersed. As the ionosphere is the source of the highest-value errors among the different factors that affect GNSS positioning accuracy, it is necessary to minimize its negative impact. Various methods are used to compensate for the ionospheric delay, one of which is the usage of models.
The intensity of the processes occurring in the ionosphere is closely related to the Sun activity. As a consequence, with respect to a given location on the Earth's surface, the activity of the ionosphere changes throughout the year and day. Therefore, a model dedicated to a specific region is especially important in case of high-precision GNSS applications.
The assimilated H2PT model was based on the dual-frequency observations from GNSS stations belonging to EPN (EUREF Permanent Network), as well as on ionosondes participating in the DIAS (European Digital Upper Atmosphere Server) project. The H2PT model covers the Europe area, data with a 15-minutes interval were placed in similar to IONEX (IONosphere Map EXchenge) files in two versions of spatial resolution: 1- and 5-degree. Data provided by the H2PT model are the VTEC (Vertical Total Electron Content) values and the hmF2 (maximum height of the F2 layer) parameters.
The subject of this research is the comparison of the H2PT model with NeQuick-G model and IONEX data published by IGS (International GNSS Service) in the context of TEC values as well as determining differences between regional hmF2 data and its commonly used fixed value for the entire globe, amounting to 450 km. In order to perform the analysis, appropriate visualizations were made and statistical parameters determined. Additionally, data from selected periods of positive and negative disturbances were analysed in details based on the developed time series.
The relatively high temporal and spatial resolution is undoubtedly an advantage of the H2PT model, because unlike global models, the regional one allows conscientious analysis of the ionosphere characteristics for the area of Europe. Importantly, solutions regarding hmF2 show significant deviations from the fixed value approximated for the whole Earth. Taking into account the parameter appropriate for a given location and time during GNSS data processing may improve the obtained positioning quality. 

How to cite: Woźniak, P., Świątek, A., Pożoga, M., and Tomasik, Ł.: Analysis of a new regional ionospheric assimilated H2PT model for Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1524, https://doi.org/10.5194/egusphere-egu2020-1524, 2020.

The ionospheric delay is one of the main error-sources in applications that rely on the Global Navigation Satellite System (GNSS) observations. Dual-frequency receivers allow the elimination of the major part of the ionospheric range error by forming an ionosphere-free linear combination (L3). However, although global models broadcasted by the satellite systems are available, single-frequency mass-market receivers are not able to correct the signal’s delay with sufficient accuracy and precise regional ionosphere models are necessary. Today no regional ionosphere models, based on the national GNSS/GPS infrastructure, are available in the Western Balkans countries.

In this study, an ionosphere vertical total electron content (VTEC) model IONO_WB is derived from dual-frequency GPS observations of Continuously Operating Reference Stations (CORS) belonging to the following positioning networks: ALPBOS and IGEWE (Albania), BIHPOS (Bosnia and Herzegovina), CROPOS (Croatia), MAKPOS (North Macedonia), and SIGNAL (Slovenia). In addition, observations from 8 permanent stations of the EUREF Permanent Network (EPN) in this region are used. The chosen network comprises in total about 70 CORS and EPN stations in the range from about 40⁰ N to 47⁰ N and 13⁰ E to 23⁰ E. The estimation of the ionosphere VTEC model parameters is based on the geometry-free (L4) linear combination of phase (zero-difference) observations. The ionosphere is approximated by a single-layer model at a height of 450 km. TEC modelling is performed by two-dimensional Taylor series expansions in a Sun-fixed reference frame with a degree and order of 2 and a temporal resolution of 1 hour. Corrections for positioning with a single frequency (L1) are estimated and evaluated in positioning application. Data processing, model estimation and positioning evaluation are performed in the Bernese GNSS Software v.5.2

The developed ionosphere IONO_WB model is tested for periods of the solar maximum (March 2014) and the St. Patrick´s geomagnetic storm (March 2015). For validation purposes, the model is compared to Global Ionosphere Maps (GIM) issued by the IGS Associate Analysis Centers (CODE, ESA/ESOC, JPL, gAGE/UPC) and the regional high-resolution VTEC maps from DGFI-TUM realized as multi-scale B-spline representations. The model`s applicability is evaluated with single-frequency positioning, where selected EPN and CORS stations are processed applying the corrections estimated from the regional model IONO_WB. Resulting 3D position errors (RMS) were in most cases at least 20% to 50% lower compared to CODE ionosphere products during high solar activity and severe geomagnetic storm.

How to cite: Natras, R. and Goss, A.: Regional Ionosphere VTEC Modelling and Application for Single-Frequency Positioning in the Western Balkans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19166, https://doi.org/10.5194/egusphere-egu2020-19166, 2020.

EGU2020-13197 | Displays | G5.1

Global-scale data-model comparison of the July 2nd, 2019 total solar eclipse’s thermospheric effect

Saurav Aryal, J. Scott Evans, Stanley C. Solomon, Alan G. Burns, John Correira, Tong Dang, Jiuhou Lei, Geonhwa Jee, Huixin Liu, Wenbin Wang, and Richard W. Eastes

NASA’s Global-scale Observation of Limb and Disk’s (GOLD) instrument observed the July 2, 2019 total solar eclipse’s effect in the thermosphere from a geostationary orbit above South America. GOLD’s observations of compositional and neutral temperature changes induced by the eclipse are different from the modeled effects. Combined Thermospheric Ionospheric Electrodynamics General Circulation Model (TIE-GCM) and GLobal airglOW (GLOW) modeling of GOLD’s observation is relatively successful in reproducing morphologically changes. However, the model underestimates the compositional changes. GOLD observation show a ΣO/N2 column density ratio enhancement of ~ 80 % near the totality, but the model predicts ~ 10 % enhancement. This indicates that there are inadequacies in current modeling capabilities for thermospheric changes during an eclipse. GOLD’s thermospheric measurements provide an important, new test of the models. We will present detailed data-model comparisons of measurements versus modeling results for the July 2nd eclipse.

How to cite: Aryal, S., Evans, J. S., Solomon, S. C., Burns, A. G., Correira, J., Dang, T., Lei, J., Jee, G., Liu, H., Wang, W., and Eastes, R. W.: Global-scale data-model comparison of the July 2nd, 2019 total solar eclipse’s thermospheric effect , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13197, https://doi.org/10.5194/egusphere-egu2020-13197, 2020.

EGU2020-20867 | Displays | G5.1

Flexible Radio Array for Ionospheric and Atmospheric research (FRAIA)

Anders M. Jorgensen, An Ngoc, Kyler King, Willie Lopez, Alexander Mazarakis, Leviy Jungling, Wesley McHaley, Delos Edick, and Richard Sonnenfeld

We present the Flexible Radio Array for Ionospheric and Atmospheric
research (FRAIA). FRAIA consists of 18 relocatable RF receiver
stations with the capability to receive in the VLF band (0-50 kHz),
the HF/VHF band (3-85 MHz), as well as at discrete beacon satellite
frequencies 150, 400, and 1067 MHz. The antennas are monopole for the
VLF reception, all-sky broad-band crossed dipoles for the HF/VHF band,
and co-centric all-sky quadrifilar antennas for the beacon satellite
bands. Each station contains a 8-core CPU and a high-end
software-defined radio for real-time sampling and processing of the RF
signals. Each station include GPS timing to 50 ns, and three
synchronization devices allows for the 18 stations to be used together
in a single phased array or up to three phased arrays. FRAIA stations
can be used for observing VLF whistler waves, receiving standard
VHF/UHF beacon satellite signals for ionospheric tomography, for
riometry, for lightning observations and lightning interferometry, as
ionosonde receivers, HF radar receivers, over-the-horizon radar
receivers, and receivers for a future HF beacon satellite which we
propose, for ionospheric tomography.

How to cite: Jorgensen, A. M., Ngoc, A., King, K., Lopez, W., Mazarakis, A., Jungling, L., McHaley, W., Edick, D., and Sonnenfeld, R.: Flexible Radio Array for Ionospheric and Atmospheric research (FRAIA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20867, https://doi.org/10.5194/egusphere-egu2020-20867, 2020.

EGU2020-11622 | Displays | G5.1

Structure function analysis of plasma density fluctuations during total loss of lock of GPS signal events

Hossein Ghadjari, David Knudsen, and Susan Skone

Ionospheric irregularities are fluctuations or structures of plasma density that affect the propagation of radio signals. Whenever large-scale irregularities break up into meso and small-scale irregularities, these processes become similar to a turbulence cascade. In order to have a better comparison between this and plasma density irregularities, we study different orders of structure functions of plasma density of total loss of lock events measured with the faceplate measurements of plasma density and the GPS measurements from the Swarm mission. Total loss of lock of GPS signal is a physical proxy for severe degradation of GPS signals. In addition to different orders of structure-function, we study the existence of self-similarity or multifractality of plasma density of total loss of lock events to investigate any possible intermittent fluctuations. 

How to cite: Ghadjari, H., Knudsen, D., and Skone, S.: Structure function analysis of plasma density fluctuations during total loss of lock of GPS signal events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11622, https://doi.org/10.5194/egusphere-egu2020-11622, 2020.

When sensing the Earth’s ionosphere using pseudorange observations of global navigation satellite systems (GNSS), the satellite and receiver Differential Code Biases (DCBs) account for one of the main sources of error. For the sake of convenience, Receiver DCBs (DCBs) are commonly assumed as constants over a period of one day in the traditional carrier-to-code leveling (CCL) method. Thus, remarkable intraday variability in the receiver DCBs have been ignored in the commonly-used assumption and may seriously restrict the accuracy of ionospheric observable retrieval. The Modified CCL (MCCL) method can eliminate the adverse impact of the short-term variations of RDCBs on the retrieval of ionospheric TEC. With the rapid development of the GPS, GLONASS, Galileo and BeiDou systems, there is a strong demand of precise ionospheric TEC products for multiple constellations and frequencies. Considering the existed MCCL method can only be used for dual-frequency GNSS data, in this study, we extend the two-frequency MCCL method to the multi-frequency and multi-GNSS case and further carry out a series of investigations. In our proposed method, a newly full-rank multi-frequency (more than triple frequency) model with raw observations are established to synchronously estimate both the slant ionospheric delays and the RCB offset with respect to the reference epoch at each individual frequency. Based on the test results, compared to the traditional CCL-method, the accuracy of the ionospheric TEC retrieved using our proposed method can be improved from 5.12 TECu to 0.95 TECu in the case that significant short-term variations existed in receiver DCBs. In addition, the between-epoch fluctuations experienced by receiver code biases at all frequencies tracked by a single receiver can be detected by our the proposed method, and the dependence of multi-GNSS and multi-frequency RDCB offsets upon ambient temperature further are verified in this study. Compared to Galileo system, the RDCB in BDS show higher correlation with temperature. We also found that the RDCB at different frequencies of the same system show various characteristics.

How to cite: Li, M., Zhang, B., and Zhang, X.: Determation of the ionospheric observable and short-term variations of receiver DCBs using modified carrier‑to‑code leveling method with multi-frequency and multi-GNSS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20967, https://doi.org/10.5194/egusphere-egu2020-20967, 2020.

G5.2 – Atmospheric and Environmental Monitoring with Space-Geodetic Techniques

EGU2020-3272 | Displays | G5.2

Space geodetic study of the 2019 typhoon Hagibis: PWV and crustal subsidence

Kosuke Heki, Syachrul Arief, Mizuki Yoshida, and Zhan Wei

Strong typhoons hit the Japanese Islands repeatedly in 2019. Here we study one of these typhoons (2019 #19 Hagibis 915 hPa, 86 casualties) that landed central Japan on Oct.12 (local time) during the Rugby World Cup tournament, using two different space geodetic approaches, i.e. water vapor and crustal deformation. The first approach is the recovery of Precipitable Water Vapor (PWV) using the zenith wet delays (ZWD) estimated by the dense GNSS array in Japan GEONET. Because atmospheric water vapor concentrates in relatively low altitudes, high humidity is often difficult to recognize in ZWDs when the surface altitude is high. To overcome the difficulty, we reconstructed ZWDs, converted to sea-level values, by spatially integrating the tropospheric delay gradient (azimuthal asymmetry of water vapor) vectors. We also calculated convergence of such delay gradients, equivalent to water vapor convergence index (WVCI) proposed by Shoji (2013 Jour. Met. Soc. Japan). We found that very strong rainfall occurs in the region where both reconstructed ZWD and the delay gradient convergence index are high. Next, we studied vertical crustal movements associated with the water load brought by the typhoon, using the two solutions of the GEONET station coordinates, one from the official F3 solution and the other from the UNR data base. We confirmed subsidence down to ~2 cm in multiple regions where severe flood occurred. Such subsidence was observed to recover with a time constant of 1-2 days reflecting rapid drain of rain water to ocean due to large topographic slope and proximity to the sea. We could not identify, however, crustal uplift due to the low atmospheric pressure at the center of the typhoon.

How to cite: Heki, K., Arief, S., Yoshida, M., and Wei, Z.: Space geodetic study of the 2019 typhoon Hagibis: PWV and crustal subsidence , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3272, https://doi.org/10.5194/egusphere-egu2020-3272, 2020.

EGU2020-3443 | Displays | G5.2

Improving GNSS Zenith Wet Delay Interpolation by Utilizing Tropospheric Gradients: Results from the dense station network in Japan

Florian Zus, Kyriakos Balidakis, Christos Pikridas, Galina Dick, and Jens Wickert

In a recent study we have shown how GNSS Zenith Wet Delay (ZWD) interpolation and therefore Integrated Water Vapor (IWV) maps can be improved by utilizing tropospheric gradients (Zus et al., 2019). For a station configuration with an average distance of 50 km in Germany and a period of two months in the summer 2013 we demonstrated an average improvement of 10% in interpolated ZWDs. We extended this work by a new study. It differs from the previous one in two respects: (1) we consider more than 1,200 stations with an average distance of 20 km in Japan and (2) ZWDs and tropospheric gradients are taken from the Nevada Geodetic Laboratory (NGL) (Blewitt et al., 2018). We present results and propose future directions. For example, we may consider a mixed approach where ZWDs and tropospheric gradients from a numerical weather prediction model are utilized as well.

Zus, F.; Douša, J.; Kačmařík, M.; Václavovic, P.; Balidakis, K.; Dick, G.; Wickert, J. Improving GNSS Zenith Wet Delay Interpolation by Utilizing Tropospheric Gradients: Experiments with a Dense Station Network in Central Europe in the Warm Season. Remote Sens. 2019, 11, 674. 

Blewitt, G., W. C. Hammond, and C. Kreemer (2018), Harnessing the GPS data explosion for interdisciplinary science, EOS, 99, https://doi.org/10.1029/2018EO104623.

How to cite: Zus, F., Balidakis, K., Pikridas, C., Dick, G., and Wickert, J.: Improving GNSS Zenith Wet Delay Interpolation by Utilizing Tropospheric Gradients: Results from the dense station network in Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3443, https://doi.org/10.5194/egusphere-egu2020-3443, 2020.

EGU2020-4898 | Displays | G5.2

Improved estimates of non-tidal environmental loading contribution into Zenith Total Delay series over Europe

Janusz Bogusz, Anna Klos, Rosa Pacione, Vincent Humprey, and Henryk Dobslaw

The motivation of this study is to assess the spatio-temporal patterns in the Zenith Total Delay (ZTD) time series estimated within the second re-processing campaign (1996-2014) of the EUREF Permanent GNSS Network (EPN, http://www.epncb.oma.be) for a set of European stations. In particular we used AS0 solution provided by the EPN analysis center ASI (Agenzia Spaziale Italiana Centro di Geodesia Spaziale, Italy), and GO1 and GO4 solutions provided by the EPN analysis center GOP (Geodetic Observatory Pecny, Czech Republic) along with the combined EPN Repro-2 products. Solutions differ by processing options and number of stations processed. We find that all individual ZTD solutions are characterized by pure autoregressive noise, which is reduced during the combination, meaning that some part of information is lost in the combination procedure. Combination procedure does not however affect spatial patterns of ZTD residuals (trend and seasonal signals are removed beforehand). They are almost the same for both individual and EPN Repro-2 combined solutions. This means that regional ZTD estimates reflect tropospheric dynamics even at very high-frequency signals of small variance. Therefore, we compute ZTD differences from the two GOP solutions GO1 and GO4, which only differ by unmodelled non-tidal atmospheric loading. We find that there is a similarity between the ZTD differences and non-tidal atmospheric loading which is strongly demonstrated in terms of unusual loading events, as significant non-linear trends or large seasonal peaks. As these similarities are only observed for GO1 and GO4 differences, this indicates that unmodelled vertical loading effects contribute 50% of the ZTD noise, affecting errors of trends.

How to cite: Bogusz, J., Klos, A., Pacione, R., Humprey, V., and Dobslaw, H.: Improved estimates of non-tidal environmental loading contribution into Zenith Total Delay series over Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4898, https://doi.org/10.5194/egusphere-egu2020-4898, 2020.

EGU2020-10138 | Displays | G5.2

Diurnal cycle of GNSS-derived precipitable water vapour in tropical regions

Zofia Bałdysz, Grzegorz Nykiel, Dariusz Baranowski, Beata Latos, and Mariusz Figurski

Convective processes in the tropical atmosphere and their diurnal cycles have important repercussions for the circulations in the tropical regions and beyond. Monitoring of the water vapour content in the tropical atmosphere remains a challenge due to its high temporal and spatial variability. Global models tend to fail to correctly capture the diurnal convection, limiting forecasting accuracy. In this work, we investigated precipitable water vapour (PWV) diurnal cycle, precipitation and infrared  brightness temperature (TB) data over the tropical area. We used in-situ observations from 44 IGS (International GNSS Service) stations covering time span of 18 years, together with satellite-based precipitation and cloudiness data, taken from the Tropical Rainfall Measurement Mission gridded dataset (TRMM 3B42 v7) and the global, merged infrared (IR) dataset, respectively. The data provided an opportunity to examine the characteristics of a diurnal cycle of PWV, precipitation and TB over the study area in greater detail than before.

In particular, our results show that the diurnal cycle of PWV and TB were almost entirely dominated by mono-modal distributions. The diurnal cycle of precipitation onshore (continental areas or big islands; continental regime) had a single late afternoon peak, and that offshore (small islands; oceanic regime) had both a midday and a nocturnal peak. Daily amplitude phase shift of PWV and precipitation at onshore stations with a continental regime consistently occurred at the same time, while TB maximum peaked about five hours later. Furthermore, results show that the daily mean and the amplitude of the diurnal cycle of PWV, precipitation and TB appeared smaller on offshore stations, exhibited to an oceanic regime, than on onshore, continental stations. Additional analysis of seasonal variations of GNSS-derived PWV shows the usefulness of such measurements for tracking propagation of longer-scale phenomena, such as Inter Tropical Convergence Zone (ITCZ), Southeast Asian monsoon or East Asian summer monsoon.

How to cite: Bałdysz, Z., Nykiel, G., Baranowski, D., Latos, B., and Figurski, M.: Diurnal cycle of GNSS-derived precipitable water vapour in tropical regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10138, https://doi.org/10.5194/egusphere-egu2020-10138, 2020.

EGU2020-6956 | Displays | G5.2

IWV retrieval from ground and shipborne GPS receivers during NAWDEX

Pierre Bosser, Bock Olivier, and Laurain Nicolas

For the documentation of time and space variations of water vapor in atmosphere during the Nawdex campaign (North Atlantic, Autumn 2016), a ground network of more than 1200 coastal continuously operation reference GNSS stations has been analyzed. This network spreads from Caribbeans to Morocco through Greenland. Retrieved IWV have been used to evaluate ERAI and ERA5 reanalysis and highlight improvements made by ERA5 (-0.2 +/- 1.6 kg/m2 vs -0.3 +/- 2.1 kg/m2 overall). They are also used to describe high impact weather events that took place during the experiment.

The analysis of this ground GNSS network has been completed with the IWV retrieved from GPS data acquired by the French RV Atalante which cruises in the area during the experiment. IWV from shipborne receiver are consistent with both ERAI and ERA5 reanalysis (1.0 +/- 3.2 kg/m2 and 1.3 +/- 2.0 kg/m2 respectively) ; shipborne IWV also agree with IWV from nearby ground GNSS stations (-0.4 +/- 0.9 kg/m2). These results confirm the quality of shipborne IWV retrievals and opens up prospects for use in climatology and meteorology.

How to cite: Bosser, P., Olivier, B., and Nicolas, L.: IWV retrieval from ground and shipborne GPS receivers during NAWDEX, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6956, https://doi.org/10.5194/egusphere-egu2020-6956, 2020.

EGU2020-6517 | Displays | G5.2

Assessment on atmospheric parameters at co-location sites

Chaiyaporn Kitpracha, Kyriakos Balidakis, Robert Heinkelmann, and Harald Schuh

Atmospheric ties are affected by the differences of atmospheric parameters of space geodetic techniques at co-location sites. Similar to local ties, they could be applied along with local ties for a combination of space geodetic techniques to improve the realization of terrestrial reference frames (TRF). Theoretically, atmospheric ties are affected by the height differences between antennas at the same site and meteorological conditions. Therefore, atmospheric ties could be determined by analytical equation based on meteorological information from in situ measurements or weather model. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis, thus potentially degrading a combined atmospheric ties solution. In this study, we analyse the time series of zenith delays from co-located GNSS antennas at Wettzell (height differences below 3 meters), for 11 years (2008–2018). GNSS observations were analyzed with Bernese GNSS software version 5.2 with double-differencing technique and relative tropospheric delay and gradients were estimated with L1, L2, and the ionosphere-free (L3) linear combination thereof. Atmospheric ties were derived analytically employing meteorological data from Global Pressure and Temperature model 3 (GPT3) and ERA5 reanalysis, as well as corrections derived from ray tracing (Potsdam Mapping Functions, PMF). The comparison shows that zenith delay differences are dominated by equipment changes. The discrepancies between atmospheric ties and estimated zenith delay differences are frequency dependent, with the L1 solutions being the least biased. For these small vertical differences, seasonal signals are not significant for all frequencies.

How to cite: Kitpracha, C., Balidakis, K., Heinkelmann, R., and Schuh, H.: Assessment on atmospheric parameters at co-location sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6517, https://doi.org/10.5194/egusphere-egu2020-6517, 2020.

EGU2020-9418 | Displays | G5.2 | Highlight | G Division Outstanding ECS Lecture

Tropospheric products as a signal of interest – overview of troposphere sensing techniques

Karina Wilgan, Witold Rohm, Jaroslaw Bosy, Alain Geiger, M. Adnan Siddique, Jens Wickert, and Galina Dick

Microwave signals passing through the troposphere are delayed by refraction. Its high variations, both in time and space, are caused mainly by water vapor. The tropospheric delay used to be considered only as a source of error that needed to be removed. Nowadays, these delays are also a source of interest, for example, tropospheric delays or integrated water vapor information are being assimilated into nowcasting or numerical weather prediction (NWP) models. Moreover, long time series of tropospheric observations have become an important source of information for climate studies. On the other hand, the meteorological data is supporting the space-geodetic community by providing models that can be used to reduce the troposphere impact on the signal propagation.

There are several ways of observing the troposphere, especially considering water vapor.  First one are the classical meteorological: in-situ measurements, radiosondes or radiometers, from which we can sense directly the amount of water vapor. Another, indirect way of observing the water vapor distribution is by using the Global Navigation Satellite Systems (GNSS). This method is called GNSS meteorology. Other microwave techniques such as Very Long Baseline Interferometry (VLBI), Interferometric Synthetic Aperture Radar (InSAR) or space-based Radio Occultations (RO) can also be used in a similar way to GNSS.

This contribution presents an overview of the troposphere sensing techniques with examples of their applications. We present a multi-comparison of the tropospheric products, i.e. refractivity, tropospheric delays in zenith and slant directions and integrated water vapor. The integration of the different data sources often leads to an improved accuracy of the tropospheric products but requires a careful preparation of data. The combination of the data sources allows for using techniques of complementary properties, for example InSAR with very high spatial resolution with GNSS observations of high temporal resolution. With the emergence of new technologies, some traditional ways of tropospheric measurements can be augmented with the new methods. For example, we have tested meteo-drones as an alternative to radiosondes. The comparisons with GNSS data shows a good agreement of the drone and microwave data, even better than with radiosondes.

How to cite: Wilgan, K., Rohm, W., Bosy, J., Geiger, A., Siddique, M. A., Wickert, J., and Dick, G.: Tropospheric products as a signal of interest – overview of troposphere sensing techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9418, https://doi.org/10.5194/egusphere-egu2020-9418, 2020.

EGU2020-2709 | Displays | G5.2

Sea state observation using ground-based GNSS-SNR data

Jörg Reinking, Ole Roggenbuck, and Gilad Even-Tzur

The signal-to-noise ratio (SNR) data is widely used in GNSS reflectometry to derive water or snow surface heights and surface characteristics like roughness or soil moisture. In a marine environment the attenuation of the SNR oscillation is related to the roughness of the sea surface. It was shown that the significant wave height (SWH) of the water surface can be calculated from the analysis of the attenuation.

The attenuation depends strongly on the relation between the coherent and the incoherent part of the scattered power. The correlation length of the sea surface governs the incoherent part and varies with respect to the direction of the line of sight relative to the wave direction. The resulting anisotropic characteristic of the attenuation yields a directional pattern of the cutoff angle at which the coherence is lost. The cutoff angle can be deduced from the attenuation of the SNR data, from which the wave direction can be derived. The contribution will recapitulate the relation between the sea state and the cutoff angle based on sea surface simulations and present the analysis of experimental data from a GNSS station in the North Sea.

A sea state observation would be incomplete without an information about the wave period. The wave period does not influence the SWH but the correlation length of the sea surface. Hence, for a particular SWH, different peak wave periods should yield different correlation length for a line of sight in the wave direction. Analysis based on sea surface simulations show that it should be possible to derive the peak wave period as a function of the SWH and the maximum cutoff angle of the SNR attenuation. The results of this analysis will be presented here, too.

How to cite: Reinking, J., Roggenbuck, O., and Even-Tzur, G.: Sea state observation using ground-based GNSS-SNR data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2709, https://doi.org/10.5194/egusphere-egu2020-2709, 2020.

EGU2020-12986 | Displays | G5.2

First Field-Test results of iGNSS-R instrument of the PRETTY payload

Andreas Dielacher, Heinz Fragner, Michael Moritsch, Jens Wickert, Otto Koudelka, Per Hoeg, Estel Cardellach, Manuel Martin-Neira, Maximilian Semmling, Roger Walker, Andreas Hörmer, and Manuela Wenger

The PRETTY mission is a 3U CubeSat mission, hosting two different payloads, a radiation dosimeter and an interferometric GNSS reflectometer. The intended launch is planned in 2022.

The reflectometer payload has been built, using flight representative hardware and mounted inside a portable setup. Two campaigns have been carried out, a first one to verify the setup in real world condition and the second one to record reflectometry data over the Danube river. The reflections over the river are analyzed and compared to a reference data set obtained from basemap.at (which is released under Open Government Data Österreich Lizenz CC-BY 4.0).

The hardware is capable of generating complex and power waveforms at the same time, and the reflection events are visible in both. Since PRETTY is aiming for phase altimetry, only coherent measurements are conducted with an integration time of 20ms .

The re-tracking algorithm for the specular point and height estimation are based on [1]. Due to the low elevation angle and receiver height, the effects from the ionosphere is not considered , however effects from the atmosphere have to be included in the data re-tracking process. The reflection peaks, and the signal to noise ratio of the peaks, are large enough detect the peak and to calculate the height of the reflection point. The height retrieval is shown in the paper.

The results are promising w.r.t. the performance of the overall structure of the PRETTY GNSS-R payload  in order to deliver altimetry results on a low-cost CubeSat platform.

[1] W. Li, E. Cardellach, F. Fabra, S. Ribó and A. Rius, "Assessment of Spaceborne GNSS-R Ocean Altimetry Performance Using CYGNSS Mission Raw Data," in IEEE Transactions on Geoscience and Remote Sensing, vol. 58, no. 1, pp. 238-250, Jan. 2020. doi: 10.1109/TGRS.2019.2936108

How to cite: Dielacher, A., Fragner, H., Moritsch, M., Wickert, J., Koudelka, O., Hoeg, P., Cardellach, E., Martin-Neira, M., Semmling, M., Walker, R., Hörmer, A., and Wenger, M.: First Field-Test results of iGNSS-R instrument of the PRETTY payload, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12986, https://doi.org/10.5194/egusphere-egu2020-12986, 2020.

EGU2020-21823 | Displays | G5.2

On the Impact of Sea State on GNSS-R Polarimetric Observations

Mostafa Hoseini, Maximilian Semmling, Erik Rennspiess, Markus Ramatschi, Rüdiger Haas, Joakim Strandberg, Hossein Nahavandchi, and Jens Wickert

We investigate a long-term ground-based GNSS-R dataset to evaluate the effect of sea state on the polarization of the reflected signals. The dataset consists of one-year polarimetric observations recorded at Onsala space observatory in Sweden in 2016 using right- and left-handed circular polarization (RHCP and LHCP) antennas. One up-looking antenna to receive direct signal and two side-looking antennas to collect reflections are installed at about 3 meters above sea level. The data is collocated with the measurements from a nearby tide-gauge and meteorological station.

We focus on precise power estimation using a polarimetric processor based on Lomb–Scargle periodogram at precisely observed sea levels. The processor converts 0.1 Hz coherent in-phase and quadrature correlation sums provided by a reflectometry receiver to power estimates of the direct and reflected signals. The power estimates are reduced to three power ratios, i.e. cross-, co-, and cross to co-polarization. A model, describing the elevation dependent power loss due to sea surface roughness, is then utilized to invert the calculated power ratios to the standard deviation of sea surface height.

Analysis of about 14000 events found in the dataset (~40 continuous tracks per day) shows a fair agreement with the wind speeds as an indicator of the sea state. Although an increasing sensitivity to sea state is observed for all the power ratios at elevation angles above 10 degrees, the measurements from the co-polar link seem to be less affected by the surface roughness. The results reveal that the existing model cannot predict the effect of sea surface roughness in a comprehensive way. The different response of RHCP and LHCP observations to roughness is evident, however, the polarization dependence is not covered by the model. The deviations from the model are particularly clear at lowest elevations (<5 deg) where the roughness effect is expected to vanish. The results indicate that roughness also affect observations at lowest elevation angles. In this elevation range the expected dominance of the RHCP component above the LHCP component is not observed.  A different approach is required to model the influence of sea state in GNSS-R. The increasing amount of reflectometry data may allow to retrieve an empirical relation between coherent reflection power and sea state in future investigation.

How to cite: Hoseini, M., Semmling, M., Rennspiess, E., Ramatschi, M., Haas, R., Strandberg, J., Nahavandchi, H., and Wickert, J.: On the Impact of Sea State on GNSS-R Polarimetric Observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21823, https://doi.org/10.5194/egusphere-egu2020-21823, 2020.

EGU2020-20553 | Displays | G5.2

Influence of Assimilating CYGNSS Ocean Surface Wind Data on Tropical Cyclone Analyses and Predictions

Bachir Annane, Mark Leidner, Ross Hoffman, Feixiong Huang, and James Garrisson
For the analysis and forecasting of tropical cyclones, the main benefits of data from the CYGNSS constellation of satellites are the increased revisit frequency compared with polar-orbiting satellites and the ability to provide ocean surface wind observations through convective precipitation. Consequently, CYGNSS delivers an improved capability to observe the structure and evolution of ocean surface winds in and around tropical cyclones. This study quantifies the impact of assimilating CYGNSS delay-Doppler maps, CYGNSS retrieved wind speeds and derived CYGNSS wind vectors on 6-hourly analyses and 5-day forecasts of developing tropical cyclones, using the 2019 version of NOAA's operational Hurricane Weather Research and Forecasting (HWRF) model.

How to cite: Annane, B., Leidner, M., Hoffman, R., Huang, F., and Garrisson, J.: Influence of Assimilating CYGNSS Ocean Surface Wind Data on Tropical Cyclone Analyses and Predictions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20553, https://doi.org/10.5194/egusphere-egu2020-20553, 2020.

EGU2020-14965 | Displays | G5.2

Analysis of GOES-R as a Constraint in GNSS Tropospheric Tomography

Zohreh Adavi and Robert Weber

GNSS tomography is an all-weather condition remote sensing technique in the field of meteorology that is gaining considerable attention in recent years. The water vapor distribution and related parameters like wet refractivity in the troposphere can be reconstructed with reasonable Spatio-temporal resolution in this method. To achieve this goal, the troposphere is divided into a number of 3D elements (voxels). Then, the system of the observation equations is defined by a relation between the wet refractivity field and the distance traveled by GNSS rays through voxels. However, propagated signals do not pass through some of the model elements. Thereby, the reconstructed wet refractivity field suffers in terms of solution uniqueness. Consequently, additional data sources and horizontal and/or vertical constraints should be applied to avoid the singularity of the estimated field. In this presentation, the combination of wet refractivity maps computed from Geostationary Operational Environmental Satellite (GOES) sounder and refractivity fields obtained by GNSS tomography is demonstrated to achieve a unique solution. The GOES-R sounder products are provided hourly with a 10 km spatial resolution. Therefore, GOES-R wet refractivity maps are used to constrain the system of equations and consequently, the tomographic solution leads to an improved reconstructed wet refractivity field. To analyze the efficiency of the proposed data, a 3D tomographic model is defined over a regional area covered by the Continuously Operating Reference Station (CORS) Network in the United States. Moreover, radiosonde measurements in the area of interest are used to achieve the feasibility and correctness of the estimated 3D wet refractivity images.

How to cite: Adavi, Z. and Weber, R.: Analysis of GOES-R as a Constraint in GNSS Tropospheric Tomography , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14965, https://doi.org/10.5194/egusphere-egu2020-14965, 2020.

EGU2020-12556 | Displays | G5.2

COSMIC-2 Status and GNSS Radio Occultation Results

Jan-Peter Weiss and Wei Xia-Serafino

We present status and atmospheric retrieval results for the FORMOSAT-7/COSMIC-2 (COSMIC-2) mission. COSMIC-2 mission jointly managed by NOAA and Taiwan's National Space Organization (NSPO) and consists of six satellites launched on June 25, 2019 into a 24-degree inclination orbit. The primary payload is the JPL developed Tri-GNSS Radio-occultation System (TGRS). Tracking data from two upward looking precise orbit determination antennas are used for orbit and clock determination as well as ionospheric total electron content retrieval. Two limb-viewing radio occultation antennas provide more than 4000 daily profiles of the neutral atmosphere (e.g. bending angle, refractivity and temperature) from typically 60 km to 1 km above the Earth's surface. The secondary payloads are the Ion Velocity Meter (IVM) and tri-band Radio Frequency Beacon (RFB). The UCAR data processing center receives level-0 data from a set of downlink stations and processes them into higher level weather and space weather products in near real-time and post-processing modes. Products are transferred in near real-time to NOAA, NSPO, and operational weather centers worldwide. In this presentation we summarize mission/instrument status and summarize science results from the cal/val and initial operating phases of the mission. Results presented will include geographic coverage, neutral atmosphere profile quality and impacts on numerical weather prediction, as well as space weather product evaluation. We conclude with future activities and timelines.

How to cite: Weiss, J.-P. and Xia-Serafino, W.: COSMIC-2 Status and GNSS Radio Occultation Results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12556, https://doi.org/10.5194/egusphere-egu2020-12556, 2020.

EGU2020-17920 | Displays | G5.2

From InSAR derived relative tropospheric Slant Total Delay maps to absolute Zenith Total Delay maps: comparisons between tropospheric delay products to define a strategy for meteorological applications.

Stefano Barindelli, Andrea Gatti, Martina Lagasio, Marco Manzoni, Alessandra Mascitelli, Andrea Monti Guarnieri, Marco Montrasio, Eugenio Realini, Giulio Tagliaferro, and Giovanna Venuti

InSAR derived Atmospheric Phase Screens (APSs) contain the difference between the atmospheric delay along the SAR sensor line-of-sight of two acquisition epochs: the slave and the master epochs. Using estimates of the atmospheric state at the master epoch, coming from independent sources, the APSs can be transformed into maps of tropospheric Zenith Total Delay (ZTD), that is related to the columnar atmospheric water vapor content. Assimilation experiments of such products into numerical weather prediction (NWP) models have shown a positive impact in the prediction of convective storms.

In this work, a systematical comparison between various APS and ZTD products aims at determining the optimal procedure to go from APSs to InSAR-derived absolute ZTD maps, i.e. to estimate the master delay map. Two different approaches are compared.

The first is based on a stack of ZTD maps produced with the assimilation of GNSS ZTD observations into an NWP model. This acts as a physically based interpolator of the GNSS values, which have a spatial resolution much coarser than the InSAR APS one.

The second is based on a stack of ZTD maps derived by an Iterative Tropospheric Decomposition (ITD) model, as implemented in the GACOS service. In this case, the high-resolution ZTD maps are obtained by an iterative interpolation of a global atmospheric circulation model values and GNSS values where available.

The results of the comparisons and sensitivity tests on the number of ZTD maps needed to derive the unknown master delay map are shown.

 

 

 

 

 

How to cite: Barindelli, S., Gatti, A., Lagasio, M., Manzoni, M., Mascitelli, A., Monti Guarnieri, A., Montrasio, M., Realini, E., Tagliaferro, G., and Venuti, G.: From InSAR derived relative tropospheric Slant Total Delay maps to absolute Zenith Total Delay maps: comparisons between tropospheric delay products to define a strategy for meteorological applications., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17920, https://doi.org/10.5194/egusphere-egu2020-17920, 2020.

EGU2020-3646 | Displays | G5.2

Water vapour trends in Switzerland from radiometry, FTIR and GNSS ground stations

Leonie Bernet, Elmar Brockmann, Thomas von Clarmann, Niklaus Kämpfer, Emmanuel Mahieu, Christian Mätzler, Gunter Stober, and Klemens Hocke
Water vapour in the atmosphere is not only a strong greenhouse gas, but also affects many atmospheric processes such as the formation of clouds and precipitation. With increasing temperature, Integrated Water Vapour (IWV) is expected to increase. Analysing how atmospheric water vapour changes in time is therefore important to monitor ongoing climate change. To determine whether IWV increases in Switzerland as expected, we asses IWV trends from a tropospheric water radiometer (TROWARA) in Bern, from a Fourier transform infrared (FTIR) spectrometer at Jungfraujoch and from the Swiss network of ground-based Global Navigation Satellite System (GNSS) stations. In addition, trends are assessed from reanalysis data, using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) and the Modern-Era Retrospecitve Analysis for Research and Applications (MERRA-2).
Ground-based GNSS data are well suited for IWV trends due to their high temporal resolution and the spatially dense networks. However, they are highly sensitvie to instrumental changes and care has to be taken when determining GNSS based trends. We therefore use a straightforward trend method to account for jumps in the GNSS data when instrumental changes were performed.
Our data show mostly positive IWV trends between 2 and 5% per decade in Switzerland. GNSS trends are significant for some stations and the significance has the tendency to increase with altitude. Further, we found that IWV scales on average to lower tropospheric temperatures as expected, except in winter. However, the correlation between IWV and temperature based on reanalysis data is spatially incoherent. Besides our positive IWV trends, we found a good agreement of radiometer, GNSS and reanalysis data in Bern. Further, we found a dry bias of the FTIR compared to GNSS data at Jungfraujoch, due to the restriction of FTIR to clear-sky conditions. Our results are generally consistent with the positive water vapour feedback in a warming climate. We show that ground-based GNSS networks provide a valuable source for regional climate monitoring with high spatial and temporal resolution, but homogeneously reprocessed data and advanced trend techniques are needed to account for data jumps.

How to cite: Bernet, L., Brockmann, E., von Clarmann, T., Kämpfer, N., Mahieu, E., Mätzler, C., Stober, G., and Hocke, K.: Water vapour trends in Switzerland from radiometry, FTIR and GNSS ground stations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3646, https://doi.org/10.5194/egusphere-egu2020-3646, 2020.

EGU2020-11728 | Displays | G5.2

Statistical significance of trend estimations for integrated water vapor time series obtained from GPS technique: a case study in Europe

Peng Yuan, Addisu Hunegnaw, Felix Norman Teferle, and Hansjörg Kutterer

Water vapor is an important medium for the transmission moisture and latent heat in the atmosphere. It is one of the most abundant and dominant greenhouse gases in the atmosphere, which is crucial for global warming. With higher temperatures, the specific humidity will also increase as predicted by the nonlinear Clausius-Clapeyron relationship, indicating a positive feedback loop. Hence, estimation of the trend of Integrated Water Vapor (IWV) in the atmosphere is of great importance for global warming research. However, previous studies have shown that the trends of IWV are usually rather small. Therefore, it is important to estimate the IWV trend and its associated uncertainty with a reasonable mathematical model for the homogenized time series from homogenously reprocessed GPS data sets. Since the 1990s, the Global Positioning System (GPS) has successfully been employed to retrieve IWV with a high temporal resolution, all-weather condition and with global coverage. In this work, we used the hourly GPS Zenith Total Delay (ZTD) time series for 1995.0-2017.0 at 21 European GPS stations derived from a homogeneous data reprocessing. For the conversion of ZTD to IWV, we employed the meteorological variables from ERA5, a state-of-the-art atmosphere reanalysis product newly released by the European Centre for Medium-Range Weather Forecasts (ECMWF). Then, we investigated the influence of noise model assumptions within the mathematical model on the uncertainties of IWV trend estimates. As expected, the results confirmed that the assumption of a white noise only model tends to underestimate the trend uncertainty. A first-order autoregressive process is the preferred mathematical model for a more realistic estimation of the IWV trend uncertainty.

How to cite: Yuan, P., Hunegnaw, A., Teferle, F. N., and Kutterer, H.: Statistical significance of trend estimations for integrated water vapor time series obtained from GPS technique: a case study in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11728, https://doi.org/10.5194/egusphere-egu2020-11728, 2020.

EGU2020-20989 | Displays | G5.2

Long-term ZTD and ZWD series and climate normals using NCEP1

Marcelo C. Santos, Marlon Moura, Thalia Nikolaidou, and Kyriakos Balidakis

The World Meteorological Organization (WMO) recommends the use of climate normals for dealing with the analysis of variations and trends of the meteorological parameters or be used as input to predictive climate models. The suggested period is 30 years, but shorter periods can also be employed. We computed zenith total delay (ZTD) and zenith wet delay (ZWD) series for each node of NCEP1 numerical weather model, starting in 1948. We computed climate normals of those two parameters using periods of 1, 5, 10, 15, 20 and 30 years, with and without the annual signature. To assess window size impact, we looked at variations and correlation of trends derived from the various solutions. Results shows the obvious better smoothing using larger windows and the decrease of the impact of annual signature. Regions with positive trends appear to be concentrated in continental masses and the equator line, and the most significant negative trends are in the oceans. ZTD increase is caused primarily by an increase in ZWD and is an indication of variations in ZWD variables. In the case of water vapor, such an increase in ZWD shows us a probable increase in the amount of water vapor in the atmosphere. Comparisons with trends computed from GNSS-derived ZTD and ZWD series are included with the caveat that time period for such comparisons must be shorter.

How to cite: C. Santos, M., Moura, M., Nikolaidou, T., and Balidakis, K.: Long-term ZTD and ZWD series and climate normals using NCEP1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20989, https://doi.org/10.5194/egusphere-egu2020-20989, 2020.

EGU2020-7518 | Displays | G5.2

IWV retrieval from shipborne GPS receiver on hydrographic ship Borda

Olivier Bock, Pierre Bosser, Olivier Caumont, Raphael Legouge, and Nicolas Laurain

This work aims to provide a quick review of different experiments conducted in the past for the estimation of integrated water vapor content from shipborne GNSS receiver. This state of the art will be confronted with results obtained using GPS data acquired by the French Hydrographic Ship Borda on a cruise over Atlantic Ocean and Mediterranean Sea, from Brest to Toulon in August 2015; the estimated IWV are compared with satellite observations (MODIS) and outputs from numerical weather prediction models (ERAI, ERA5, Arpege, Arome); while differences between GPS and MODIS retrievals reach almost 4 kg/m2 in terms of RMS, agreement is generally much better with numerical models (2 up to 3 kg/m2 in terms of RMS). Use of real-time orbit and clocks product is also investigated in order to assess the performance of near real-time GPS-IWV estimation for NWP purposes. We will draw out the prospects in terms of possibilities and opportunities for the use of shipborne GNSS IWV for meteorology and climatology.

How to cite: Bock, O., Bosser, P., Caumont, O., Legouge, R., and Laurain, N.: IWV retrieval from shipborne GPS receiver on hydrographic ship Borda, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7518, https://doi.org/10.5194/egusphere-egu2020-7518, 2020.

EGU2020-19217 | Displays | G5.2

A ship-based network for GNSS-meteorology over the northwestern Mediterranean Sea

Andrea Antonini, Alberto Ortolani, Aldo Sonnini, Massimo Viti, Luca Fibbi, Simone Cristofori, and Simone Montagnani

Atmospheric events are driven by surface sea physical parameters, including the exchanges of water vapor with the overlying atmosphere. Oceans cover around 70 percent of the Earth's surface and influence the atmospheric circulation, causing some of the main weather events. The lack of surface observations over the vast ocean areas is a critical problem to be addressed for improving the performance of weather forecasting.

Even if weather observations over sea from ships have been collected for over 200 years and used for meteorological research and climate applications, only recently the availability of different telecommunication solutions make real time access to measurements possible, even from remote areas. This is consequently opening new opportunities to use data from marine areas in operational weather applications.

Ground based GNSS receivers has been used for many years to determine a quantity that is of major interest for meteorologists and climatologists, the water vapor content, derived from the Zenith Path Delay. GNSS meteorology has been also tested over ships during some measurement campaigns in the past.

This work presents the implementation of the first GNSS meteo infrastructure on ships operating on the northwestern Mediterranean Sea, involving 9 commercial vessels, real-time collecting a list of GNSS meteo parameters: the signals from Galileo, GPS, GLONASS and Beidou constellations, measurements of pressure, temperature, humidity, wind and precipitation. These 9 moving platforms are complemented by a number of fixed ground platforms, used as a reference.

The difficulties in ship based GNSS meteorology, with respect to the classical approaches from fixed stations, lie both in the exposure of the hardware instruments to challenging environmental conditions as in the open sea and in the computation algorithms, which must be applied to kinematic conditions and continuously solve the receiver position with very high accuracy.

Two different processing schemes have been applied to the dataset (i.e. few months): the first one is based on differential GNSS using the TRACK suite of GAMIT software, and the second one is based on precise point positioning using the GLAB software. As it is well known, if network solutions are adopted (as in the first case), the satellites and receivers clock errors can be eliminated with very high accuracy, while PPP-based methods (as in the second case) require ultrafast precise satellite ephemeris products, but they give the possibility to implement standalone instruments, so not to send large amounts of full RINEX files to a ground processing centre.

The ZPD quantities retrieved from the first period of observations aboard ships are shown, using both the techniques. The comparison shows some discrepancies both in the absolute quantity and in the short-term trends. Even if preliminary, the comprehension of the quality of such an unprecedent source of information is of great interest, because the perspectives of this infrastructure are both scientific and operational, thinking for example to the data assimilation into numerical weather prediction models.

How to cite: Antonini, A., Ortolani, A., Sonnini, A., Viti, M., Fibbi, L., Cristofori, S., and Montagnani, S.: A ship-based network for GNSS-meteorology over the northwestern Mediterranean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19217, https://doi.org/10.5194/egusphere-egu2020-19217, 2020.

China has built  national BDS reference stations (≥210 ) covering the entire territory and has been operating continuously for more than 3 years. In 2020, BDS  satellite navigation and positioning system will be fully built and provide global services, providing a good source of data for the use of ground-based BDS observations for water vapor detection and analysis. The author used national BDS reference stations observation data which covered China area  in 2019, combined with sounding observation data, to detect and analyze the temporal and spatial changes of water vapor , and given preliminary analysis results of the  water vapor detection performance and accuracy based on BDS observation . The results show that the detection results of atmospheric precipitation between BDS and sounding system are more consistent, which can reflect the change of atmospheric precipitation.  The system errors and standard deviations of the calculation results which based on  the BDS  observations and the sounding observations are relatively large, which may be related to orbit model and  the system stability of BDS needs to be improved.

How to cite: Zhang, Q.: Detection of Spatiotemporal Changes of Water Vapor based on Large-scale BDS Reference Stations in China Area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6837, https://doi.org/10.5194/egusphere-egu2020-6837, 2020.

EGU2020-17964 | Displays | G5.2

Retrieving tropospheric parameters using predicted multi-GNSS orbit and clock

Zhiguo Deng, Florian Zus, Kyriakos Balidakis, Wickert Jens, and Harald Schuh

During the last decade the stability of GNSS clocks has increased dramatically. New generation GNSS satellites are equipped with highly precise and stable clocks and the clock parameters can be predicted with even picoseconds accuracy for several hours. In this work we determined and predicted 90 days precise orbits and clocks of up to 115 satellites from GPS, GLO, GAL, BDS2/3 and QZSS. Based on the calculated and predicted orbit and clock products (SP3) we processed data from about 140 globally distributed stations using PPP in 24 hours static mode. The first 22 hours part uses the calculated satellite products and the last two hours part uses the predicted satellite products. The estimated parameters are daily station coordinates and 30 min tropospheric parameters (ZTD). To validate the last 2-hours of ZTD we generate a reference solution based on 24-hour calculated SP3 products. We also performed a statistical comparison with ECMWF weather model data which yields a root mean square deviation of about 12 mm. This initial comparison indicates that the ZTD estimated from predicted satellite orbit and clocks are sufficiently accurate for time critical meteorological applications.

How to cite: Deng, Z., Zus, F., Balidakis, K., Jens, W., and Schuh, H.: Retrieving tropospheric parameters using predicted multi-GNSS orbit and clock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17964, https://doi.org/10.5194/egusphere-egu2020-17964, 2020.

Precipitable water vapor (PWV) is one of the key variables in the water and energy cycles, whereas current PWV products are subject to spatiotemporal discontinuity, low accuracy, and/or coarse resolution. Based on two widely used global PWV products, i.e., satellite-based MODIS and reanalysis-based ERA5 products, here we propose a data fusion approach to generate PWV maps of spatiotemporal continuity and high resolution (0.01°, daily) for the Upper Brahmaputra River (UBR, referred to as the Yarlung Zangbo River in China) basin in the Tibetan Plateau (TP) during the monsoon period (May‒September) from 2007‒2013. Results show that the fused PWV estimates have good agreement with ground-based PWV measurements from eight GPS stations (correlation coefficient = 0.87‒0.97, overall bias = -0.35‒1.78 mm, and root mean square error = 1.17‒2.04 mm), which greatly improve the accuracy of the MODIS PWV product. The high-resolution fused PWV maps provide detailed spatial variations which are generally consistent with those from the MODIS estimates under confident clear conditions and ERA5. During the monsoon period from 2007‒2013, monthly average PWV estimates across the UBR basin vary from ~6 to ~12 mm, and for each month high PWV values are found mainly along the UBR valley and at the basin outlet. The developed data fusion approach maximizes the potential of satellite and reanalysis-based PWV products for monitoring PWV and can be extended to other data available sources and study regions. The generated PWV estimates are highly valuable in understanding the water and energy cycles and retrieving atmospheric and surface variables for the south TP and its downstream areas.

How to cite: Li, X. and Long, D.: An improvement in accuracy and spatiotemporal continuity of the MODIS precipitable water vapor product based on a data fusion approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6282, https://doi.org/10.5194/egusphere-egu2020-6282, 2020.

EGU2020-17756 | Displays | G5.2

A new method of PWV retrieval over land with remote sensing data: a case of AMSR2

Nan Jiang, Yan Xu, and Tianhe Xu

Precipitable water vapor (PWV) is an important parameter reflecting the amount of solid water in the atmosphere, which is widely utilized in the studies of numerical weather prediction (NWP) and climate change. The microwave radiance measurements made by the space-based remote sensing satellites give us the opportunity to make the climate studies on a global scale. So far, PWV retrieval over the ocean has a long data record and the technology is very mature, but in the case of PWV retrieval over land, it is more challenging to isolate the atmospheric signals from the varied surface signals. In this study, we will apply a new retrieval method over land based on the dual-polarized difference (vertical and horizontal) at 19 GHz and 23 GHz using the brightness temperatures from the Global Change Observation Mission-Water (GCOM-W)/Advanced Microwave Scanning Radiometer 2 (AMSR2). We found polarization difference in brightness temperatures has an exponential relation on the amount of PWV. The validation results of the PWV retrieval from the ground-based GNSS stations show that the proposed method has a mean accuracy of 3.9 mm. Thus, the proposed method can give a possibility to improve the accuracy of data assimilation in the NWP applications and is useful for the studies of global climate change with the long-term data records.

How to cite: Jiang, N., Xu, Y., and Xu, T.: A new method of PWV retrieval over land with remote sensing data: a case of AMSR2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17756, https://doi.org/10.5194/egusphere-egu2020-17756, 2020.

EGU2020-9663 | Displays | G5.2

Improving the antenna performance for Zenith Tropospheric Delay estimations with consumer-grade antennas and a low-cost dual-frequency receiver

Andreas Krietemeyer, Hans van der Marel, Marie-claire ten Veldhuis, and Nick van de Giesen

The recent release of mass-marked dual-frequency receivers opens up the opportunity to facilitate the cost-efficient estimation of Zenith Tropospheric Delays (ZTDs) from Global Navigation Satellite System (GNSS) observations. We present results of ZTD estimations from a low-cost dual-frequency GNSS receiver (U-blox ZED-F9) equipped with a range of different quality and priced antennas. It is demonstrated that the receiver itself is able to produce high quality ZTD estimations with higher grade antennas. However, the noise introduced by applying the ionosphere-free linear combination in Precise Point Positioning (PPP), makes the low-cost antenna performance initially a major challenge. With Root Mean Square Errors (RMSE) between 15 mm and 24 mm for low-cost antennas the results were at first not adequate for meteorological purposes. We demonstrate an easy-to-apply relative antenna calibration that increased the ZTD accuracy significantly for the tested low-cost antennas. After applying antenna corrections the error is reduced to a level that is adequate for meteorological applications (RMSE ~4 mm).

How to cite: Krietemeyer, A., van der Marel, H., ten Veldhuis, M., and van de Giesen, N.: Improving the antenna performance for Zenith Tropospheric Delay estimations with consumer-grade antennas and a low-cost dual-frequency receiver, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9663, https://doi.org/10.5194/egusphere-egu2020-9663, 2020.

Water vapor (WV) is the most variable greenhouse gas in the atmosphere, which acts as a key feature in climate change studies and plays a crucial role in global warming. Its spatiotemporal distribution is necessary for understanding the hydrological cycle, and consequently can be used as an input factor in climatological studies at global, regional, and local scales. Integrated water vapor (IWV), which is defined as the amount of vertically integrated water vapor, can also augment atmospheric modeling at local and regional scales because it is frequently used in energy budget and evapotranspiration assessments. Currently, there are numerous existing atmospheric models which are able to estimate IWV amount, nevertheless, they fail to obtain extremely accurate results compared with in-situ measurements such as radiosondes. Here, we present a new methodology for improving Weather Research and Forecast (WRF) model predictions accuracy, by using data assimilation technique, which combines estimated 2D IWV regional maps, derived from GPS tropospheric path delays, along with the WRF numerical model output to generate an optimal approximation of the evolving sate of the system. This is done as opposed to pervious works, which assimilated single point measurements, either from radiosondes or GPS zenith wet delay (ZTD) estimation, demonstrating some extant of improvement in the WRF prediction accuracy compare to the standalone WRF numerical runs. Using the suggested technique, our results shows a decrease of up to 30% in the root mean square difference relative to the radiosonde data for WRF predictions assimilated with 2D GPS-IWV regional maps compare to the standalone WRF numerical runs.

How to cite: Reuveni, Y. and Leontiev, A.: Using 2D integrated water vapor (IWV) maps derived from GPS tropospheric path delays for augmenting Weather Research and Forecast (WRF) model predictions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10831, https://doi.org/10.5194/egusphere-egu2020-10831, 2020.

EGU2020-9669 | Displays | G5.2

Advanced MUlti-GNSS Array for Monitoring Severe Weather Events (AMUSE): Project overview

Karina Wilgan, Jens Wickert, Galina Dick, Florian Zus, Torsten Schmidt, and Roland Potthast

Global Navigation Satellite Systems (GNSS) have revolutionized positioning, navigation, and timing, becoming a common part of our everyday life. Aside from these well-known civilian and commercial applications, GNSS is currently established as a powerful and versatile observation tool for geosciences. An outstanding application in this context is the operational monitoring of atmospheric water vapor with high spatiotemporal resolution. The water vapor is the most abundant greenhouse gas, which accounts for about 70% of atmospheric warming and plays a key role in the atmospheric energy exchange. The precise knowledge of its highly variable spatial and temporal distribution is a precondition for precise modeling of the atmospheric state as a base for numerical weather forecasts especially with focus to the strong precipitation and severe weather events.

The data from European GNSS networks are widely operationally used to improve regional weather forecasts in several countries. However, the impact of the currently provided data products to the forecast systems is still limited due to the exclusively focusing on GPS-only based data products; to the limited atmospheric information content, which is provided mostly in the zenith direction and to the time delay between measurement and providing the data products, which is currently about one hour.

AMUSE is a recent research project, funded by the DFG (German Research Council) and performed in close cooperation of TUB, GFZ and DWD during 2020-2022. The project foci are the major limitations of currently operationally used generation of GNSS-based water vapor data. AMUSE will pioneer the development of next generation data products. Main addressed innovations are:  1) Developments to provide multi-GNSS instead of GPS-only data, including GLONASS, Galileo and BeiDou; 2) Developments to provide high quality slant observations, containing water vapor information along the line-of-sight from the respective ground stations; 3) Developments to shorten the delay between measurements and the provision of the products to the meteorological services.

This GNSS-focused work of AMUSE will be complemented by the contribution of German Weather Service DWD to investigate in detail and to quantify the forecast improvement, which can be reached by the new generation GNSS-based meteorology data. Several dedicated forecast experiments will be conducted with focus on one of the most challenging issues, the precipitation forecast in case of severe weather events. These studies will support the future assimilation of the new generation data to the regional forecast system of DWD and potentially also to other European weather services.

How to cite: Wilgan, K., Wickert, J., Dick, G., Zus, F., Schmidt, T., and Potthast, R.: Advanced MUlti-GNSS Array for Monitoring Severe Weather Events (AMUSE): Project overview, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9669, https://doi.org/10.5194/egusphere-egu2020-9669, 2020.

EGU2020-16122 | Displays | G5.2

TWIGA project activities for the enhancement of heavy rainfall predictions in Africa: low-cost GNSS network deployment and NWP model parameterization.

Alessandra Mascitelli, Agostino Niyonkuru Meroni, Stefano Barindelli, Marco Manzoni, Giulio Tagliaferro, Andrea Gatti, Eugenio Realini, Giovanna Venuti, and Andrea Monti Guarnieri

One of the objectives of the H2020 project TWIGA - Transforming Weather Water data into value-added Information services for sustainable Growth in Africa - is the improvement of heavy rainfall prediction in Africa. In this area, the scarcity of data to support such predictions makes it fundamental to enhance the monitoring of atmospheric parameters.

In this project, GNSS observations and SAR images from Sentinel missions are used to produce water vapor products to be assimilated into Numerical Weather Prediction Models (NWPs).

GNSS observations, collected by ad-hoc networks of geodetic and low-cost stations, are processed to obtain near real-time (NRT) Zenith Total Delay (ZTD) time series, while Sentinel-1 SAR images are used to derive Atmospheric Phase Screens, APSs. The free and open source GNSS software goGPS, developed by the Politecnico di Milano spin-off Geomatics Research and Development (GReD), is used for the retrieval of ZTDs time series.

After proper calibration and validation procedures, the delay maps from SAR and the delay time series from GNSS will be finally assimilated into NWP models to improve the prediction of heavy rainfall.

The GNSS-related activities will be presented in terms of network deployment and processing settings evaluation. A network of 5 single-frequency low-cost GNSS stations was installed in Uganda, and a new network of dual-frequency low-cost stations is going to be installed in Kenya. To improve the outputs provided by these networks, preliminary tests on ionospheric delay corrections at various distances were performed. Different methods, focused on the reconstruction of a synthetic L2 observation for the single-frequency receivers, were employed and evaluated with the aim to define the optimal approach.

In order to demonstrate the capability to achieve GNSS NRT processing within TWIGA, an automated procedure was set up to estimate hourly ZTDs from two geodetic permanent stations located in South Africa (Cape Town and Southerland) and to upload them to the TWIGA project web portal.

Meanwhile, first sets of WRF NWP model parameterizations have been defined for both South Africa and Kenya. A cooperation has been established with the Kenya Meteorological Department on the exploitation of 3DVAR tool for water vapor data assimilation into WRF. Studies to define a strategy for ZTD maps retrieval from InSAR APS have been performed on Italian datasets and further investigations on TWIGA-collected African datasets will follow.

 

  

 

How to cite: Mascitelli, A., Meroni, A. N., Barindelli, S., Manzoni, M., Tagliaferro, G., Gatti, A., Realini, E., Venuti, G., and Monti Guarnieri, A.: TWIGA project activities for the enhancement of heavy rainfall predictions in Africa: low-cost GNSS network deployment and NWP model parameterization., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16122, https://doi.org/10.5194/egusphere-egu2020-16122, 2020.

EGU2020-22264 | Displays | G5.2

E-GVAP Status and future

Henrik Vedel (1), Jonathan Jones (2), Owen Lewis (2), and Siebren de Haan (3)

E-GVAP (the EIG EUMETNET GNSS Water Vapour Programme) is an operational service providing atmospheric delay estimates for use in operational meteorology in near real-time. This is done in a close collaboration between geodetic and meteorological institutions. The use of the GNSS delay estimates is found to increase the skill of weather forecasts. By the start of 2019 E-GVAP did, along with EUMETNET itself, entered a new phase. In E-GVAP 4 the main product will still be zenith total delays (ZTD), with a focus on improving timeliness, in support of the high resolution, local weather models with frequent updates being set up these years. But in addition there will be focus on GNSS derived slant total delay (STD) estimates. Several of the weather models used in Europe are being prepared for STD assimilation. The STDs provide additional information, on atmospheric asymmetries, on top of the information contained in a single ZTD estimate

How to cite: Vedel (1), H., Jones (2), J., Lewis (2), O., and de Haan (3), S.: E-GVAP Status and future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22264, https://doi.org/10.5194/egusphere-egu2020-22264, 2020.

EGU2020-22293 | Displays | G5.2

Correlation between tropical-like cyclones in the Mediterranean Sea and the space weather

Medžida Mulić, Džana Halilović, and Anesa Lavić

The ionosphere is the dominant source of the errors in the Global Navigation Satellite Systems  (GNSS), which causes delays and degradation of the GNSS signal. These errors have an impact on many terrestrial and space applications that rely on GNSS. The key parameter for the study of the ionosphere is the Total Electron Content (TEC). In an effort to eliminate the impact of delayed GNSS signal caused by the ionospheric refraction on the accuracy of GNSS positioning and navigation, the researchers made significant advances and began other ionospheric research. This paper studies the variability of GNSS derived TEC values in the International quiet and disturbed days, but also in periods when three tropical-like cyclones in the Mediterranean developed. However, the term tropical-like cyclone distinguishes tropical cyclones developing outside the tropics (like in the Mediterranean Basin) from those developing inside the tropics. Mediterranean tropical cyclones, known as a Medicane, show no difference to other tropical cyclones and can be developed into a hurricane.

Hence, the variability of GNSS derived TEC values time series were analyzed during periods when three Medicanes happened in the fall of 2014, 2016, 2017. Data from eight GNSS stations of the European Permanent Network (EPN) were used and TEC calculations were performed using the VShell program. The results demonstrated that the TEC variability is reflected in daily variations within one month, for three different years of consideration. When the state of the ionosphere was disturbed by external influences, such as the space weather storms, the results demonstrated extreme changes in the number of electrons in the ionosphere. Variations of the TEC and parameter VTEC*sigma were analyzed in the weeks before and after three subtropical cyclones in the Mediterranean Sea, recorded in November 2014, November 2016 and November 2017. Special attention was given to the time series analysis of the variable VTEC*sigma for the GNSS stations located nearby the area where the Medicane developed and stations in regions away from the storm.

The results demonstrated higher VTEC values derived from GNSS stations in the area of the storm on the storm days, as well as the days before and after. Also, the results for the storm in November 2014 showed higher VTEC values compared to the other two tropical-like cyclones. The recorded events of space weather are in correlation with the days when three analyzed Medicanes developed. Therefore, it is difficult to distinguish whether the TEC variability was caused by the space weather storm or the Medicane.

How to cite: Mulić, M., Halilović, D., and Lavić, A.: Correlation between tropical-like cyclones in the Mediterranean Sea and the space weather, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22293, https://doi.org/10.5194/egusphere-egu2020-22293, 2020.

EGU2020-5339 | Displays | G5.2

TOMOREF operator for assimilation of GNSS tomography wet refractivity fields in WRF DA system

Natalia Hanna, Estera Trzcina, Maciej Kryza, and Witold Rohm

The amount of water vapor in the atmosphere is highly variable and not easy to measure. One of the methods to provide reliable information about the amount and distribution of the humidity in the troposphere is GNSS (Global Navigation Satellite Systems) tomography. The GNSS tomography uses the observations of signal delays between satellites and ground-based receivers over the field covered by a GNSS network. This method enables deriving the 3D distribution of wet refractivity at a low cost in all weather conditions, with high temporal and spatial resolution.

The first applications of the GNSS tomography data in the Weather Research and Forecasting Data Assimilation (WRF DA) system were performed by the adaptation of the GPSREF observation operator. In this study, we present a new tool, namely the TOMOREF observation operator, which consists of three parts: forward, tangent linear, and adjoint operators. As the input data in the assimilation process, the wet refractivity fields from two tomographic models (TUW, WUELS) are used. The analysis is carried out for a 2-week long period (May 29 – June 14, 2013) in Central Europe when severe weather conditions occurred, including heavy precipitation events. The data assimilation results are verified against radiosonde observations, synoptic data, and ERA5 reanalysis. Moreover, the performance of the TOMOREF and GPSREF operators is examined. For the forecasts of relative humidity (RH) at a pressure level of 300 hPa, the implementation of the TOMOREF operator vanishes the negative impact caused by the GPSREF operator. Additionally, the improvement of the root mean square error of the forecasts of RH up to 0.5% is observed. Comparing to the assimilation of Zenith Total Delay observations, the application of the tomographic data has overall a greater influence on the WRF model. Consequently, the GNSS tomography data can be valuable in operational weather forecasting.

How to cite: Hanna, N., Trzcina, E., Kryza, M., and Rohm, W.: TOMOREF operator for assimilation of GNSS tomography wet refractivity fields in WRF DA system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5339, https://doi.org/10.5194/egusphere-egu2020-5339, 2020.

EGU2020-8469 | Displays | G5.2

Sensing small-scale structures in the troposphere with tomographic principles (IAG working group)

Gregor Moeller, Chi Ao, Zohreh Adavi, Hugues Brenot, André Sá, George Hajj, Natalia Hanna, Chaiyaporn Kitpracha, Eric Pottiaux, Witold Rohm, Endrit Shehaj, Estera Trzcina, Kuo-Nung Wang, Karina Wilgan, and Kefei Zhang

Within the International Association of Geodesy (IAG), a new working group was formed with the intention to bring together researchers and professionals working on tomography-based concepts for sensing the neutral atmosphere with space-geodetic techniques. Hereby the focus lies on Global Navigation Satellite Systems (GNSS) but also on complementary observation techniques, like Interferometric Synthetic Aperature Radar (InSAR) or microwave radiometers, sensitive to the water vapor distribution in the lower atmosphere.

In the next four years (2019-2023), we will address current challenges in tropospheric tomography with focus on ground-based and space-based measurements, the combination of measurement techniques and the design of new observation concepts using tomographic principles. While geodetic GNSS networks are nowadays the backbone for troposphere tomography studies, further local densifications, e.g. at airports, cities or fundamental stations are necessary to achieve very fine spatial and temporal resolution. Besides, the combination of ground-based GNSS with other microwave techniques like radio occultation or InSAR seems to be beneficial due their complementary nature. Therefore, several further developments in the field of tropospheric tomography are required. This includes more dynamical tomography models - adaptable to varying input data, advanced ray-tracing algorithms for the reconstruction of space-based observations and the coordination of a benchmark campaign.

In this presentation, we will give an overview about the current challenges in tropospheric tomography and the objectives of working group. The latter will also include standards for data exchange and therefore, make tomographic products available for the assimilation into numerical weather prediction models but also for various other disciplines, which rely on accurate wet refractivities or derived products like tropospheric signal delays.

How to cite: Moeller, G., Ao, C., Adavi, Z., Brenot, H., Sá, A., Hajj, G., Hanna, N., Kitpracha, C., Pottiaux, E., Rohm, W., Shehaj, E., Trzcina, E., Wang, K.-N., Wilgan, K., and Zhang, K.: Sensing small-scale structures in the troposphere with tomographic principles (IAG working group), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8469, https://doi.org/10.5194/egusphere-egu2020-8469, 2020.

EGU2020-12133 | Displays | G5.2

Single station GNSS tomography as a replacement of mapping function for high precision troposphere radio wave delay correction

Feng Peng, Li Fei, Jean-Pierre Barriot, Yan Jianguo, Zhang Fangzhao, and Ye Mao

With its relatively low cost, high availability and continuous observation ability, zenith delays from GPS combined with mapping function have been used in satellite tracking media calibration since early 2000. The mapping functions are used to model elevation dependency of radio wave delays in the troposphere. It assumes that the ratio of signal slant delay over zenith delay is less variable w.r.t time and location than the signal delay itself. Thus the parameters of signal delay elevation dependency can be modeled and unknowns of the tropospheric delay were reduced. However, the parameterization comes with a loss of accuracy. For example, the state-of-art VMF series mapping functions have a time resolution of 6 hours, which means variations that took place in less than 6 hours are smoothed. Nowadays GPS has evolved to multi-constellation GNSS with many more satellites in visibility. Here we propose a single station GNSS tomography algorithm for radio wave delay correction by directly using slant delays. This algorithm can extract the information of the troposphere variations in all the signal directions of GNSS observations with high time resolution. Thus it will be beneficial to the radio wave delay correction of precise satellite tracking. We assess the performance of this algorithm with a collocated water vapor radiometer.

How to cite: Peng, F., Fei, L., Barriot, J.-P., Jianguo, Y., Fangzhao, Z., and Mao, Y.: Single station GNSS tomography as a replacement of mapping function for high precision troposphere radio wave delay correction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12133, https://doi.org/10.5194/egusphere-egu2020-12133, 2020.

EGU2020-15460 | Displays | G5.2

Assessment of single-frequency observations in GNSS Tropospheric Tomography

Robert Weber, Zohreh Adavi, and Marcus Franz Glaner

Water vapor is one of the most variable components in the Earth’s atmosphere, which has a significant role in the formation of clouds, rain and snow, air pollution and acid rain. Therefore, increasing the accuracy of estimated water vapor can lead to more accurate predictions of severe weather, upcoming storms, and reducing natural hazards. In recent years, GNSS has turned out to be a valuable tool for remotely sensing the atmosphere. GNSS tomography is one of the most valuable tools to reconstruct the Spatio-temporal structure of the troposphere. However, locating dual-frequency receivers with a sufficient spatial resolution for GNSS tomography of a few tens of kilometers is not economically feasible. Therefore, in this research, the feasibility of using single-frequency receivers in GNSS tomography as a possible alternative approach has been investigated. The accuracy of the reconstructed model of water-vapor distribution using low-cost receivers is verified using radiosonde measurements in the area of the EPOSA (Echtzeit Positionierung Austria) GNSS network, which is mostly located in the east part of Austria for the period DoYs 233-246 in 2019.

How to cite: Weber, R., Adavi, Z., and Glaner, M. F.: Assessment of single-frequency observations in GNSS Tropospheric Tomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15460, https://doi.org/10.5194/egusphere-egu2020-15460, 2020.

EGU2020-12060 | Displays | G5.2

Determination of Coastal Sea Level Heights around Taiwan by improved GNSS Reflectometry

Chi Ming Lee, Shao Lun Hung, Chung Yen Kuo, Jian Sun, Tzu Pang Tseng, Kwo Hwa Chen, Ck Shum, Yuchan Yi, and Kuo En Ching

Rapid sea level rise, a severe consequence of global warming, could significantly damage the lives and properties of numerous human beings living in low-lying coastal areas. Therefore, realizing and monitoring coastal sea level variations are of great importance for human society. Conventionally, sea level heights are measured by using tide gauges; however, the records are contaminated by vertical land motions which are difficult to be separated. Recently, Global Navigation Satellite System Reflectometry (GNSS-R) technology has been proved to effectively monitor the coastal sea level changes from GNSS signal-to-noise ratio (SNR) data. However, the generation of detrended SNR ( SNR) depending on different satellite elevation angle intervals via a quadratic fitting, considerably influences the accuracy of sea level retrievals. Moreover, the quadratic fitting cannot perfectly describe the trend of SNR data. Therefore, we proposed a method combining ensemble empirical mode decomposition (EEMD) and ocean tide model to compute SLHs. EEMD can decompose the original SNR data into several intrinsic mode functions (IMFs) corresponding to specific frequencies. Then, Lomb-Scargle Periodogram (LSP) is applied to calculate the dominant frequency of the IMF with maximum spectral power. EEMD is not only suitable for dealing with nonlinear and nonstationary data but also eliminates the mode mixing problem of empirical mode decomposition (EMD) by adding white noises. In addition, we set an empirical SLH interval from ocean tide model as a quality control. In this study, the existing GNSS stations at the coasts of Taiwan are used to examine the proposed approach and then compare the results with those from the traditional quadratic fitting. Finally, the measurements from co-located or nearby traditional tide gauges are served as ground truth to evaluate the accuracy and stability of the mentioned methods.

How to cite: Lee, C. M., Hung, S. L., Kuo, C. Y., Sun, J., Tseng, T. P., Chen, K. H., Shum, C., Yi, Y., and Ching, K. E.: Determination of Coastal Sea Level Heights around Taiwan by improved GNSS Reflectometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12060, https://doi.org/10.5194/egusphere-egu2020-12060, 2020.

EGU2020-16032 | Displays | G5.2

Airborne Experiment for Soil Moisture Retrieval using GNSS Reflectometry

Hamza Issa, Georges Stienne, Serge Reboul, Maximilian Semmling, Mohamad Raad, Ghaleb Faour, and Jens Wickert

Measurement of soil moisture content on a global scale have gained increased interest over the years, due to its essential role in agriculture and most importantly in predicting the occurrence of natural disasters. This paper is dedicated to a study on GNSS Reflectometry (GNSS-R) using a low-altitude airborne carrier for soil moisture estimation with 1 ms rate of carrier-to-noise ratio observations. The principle of GNSS-R is the exploitation of L-band navigation signals as sources of opportunity to characterize the earth surface, because the reflected signals are often affected by the nature of the reflective surface. To scan large regional surface areas and quickly reach the areas to monitor, a dynamic GNSS-R system is considered.
The GNSS-R setup used in this study consists of RHCP and LHCP antennas mounted on the nose of a gyrocopter and of a Syntony front-end GNSS receiver. In addition, the gyrocopter is equipped with a signal digitizer and mass storage devices for digitizing and storing the base-band GNSS direct and reflected signals along the flight. A drone sensors board is also attached to the gyrocopter, which records the gyrocopter’s attitude and position at 1000 Hz rate along its trajectory. To cope with the rapid displacement of the satellites’ footprints along the receiver trajectory, high rate (1 ms) of carrier-to-noise ratio observations are processed with the data collection of the base-band RHCP and LHCP signals.
In the context of the study, it is very important to localize the reflective surfaces (satellites’ footprints) from which each processed signal has reflected, and thus detect which areas were scanned during the flight. The link between the reflected signals and the satellites' footprints is based on the GPS time, attitude and position provided by the drone board and the GPS time extracted from the digitized GNSS signals. We show that these parameters allow to determine, at ms rate, the satellites’ footprints locations (i.e. the surface areas) from which each signal has reflected at a specific GPS Time. A Geographic Information System is developed based on this principle to map the measurements obtained from the GNSS-R airborne setup along a real receiver trajectory. The ultimate aim of this study is to link the obtained GNSS-R measurements with the scanned surfaces to provide a soil moisture mapping of the studied area.

How to cite: Issa, H., Stienne, G., Reboul, S., Semmling, M., Raad, M., Faour, G., and Wickert, J.: Airborne Experiment for Soil Moisture Retrieval using GNSS Reflectometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16032, https://doi.org/10.5194/egusphere-egu2020-16032, 2020.

EGU2020-19944 | Displays | G5.2

Airborne GNSS reflectometry for coastal monitoring of sea state

Mario Moreno, Maximilian Semmling, Georges Stienne, Serge Reboul, and Jens Wickert

Global Satellite Navigation Systems (GNSS) applications like navigation and positioning generally focus on the use of the direct radio signal broadcasted by the navigation satellites. From these signals, very highly precise coordinates can be obtained. However, there is a proportion of signals, that do not reach the receivers directly, that is, the signals that are reflected off Earth’s surface before reaching the receivers. That phenomenon gave way to one of the techniques that is taking an important role in the scope of GNSS remote sensing called GNSS-Reflectometry (GNSS-R). Due to the high reflection coefficient of the water and its importance within the climate system, the ocean is one of the surfaces with greatest interest in GNSS-R research projects. The objective of this study is to retrieve information about ocean height measured through the delay of the signal, and sea state and wind retrieval (ocean surface roughness) from the analysis of the signal amplitude.

During this study, GNSS-R measurements were executed along the North Sea coast between the cities of Calais and Boulogne, France, onboard of a gyrocopter. The setup consisted of a front-end data recorder with a right-handed circular polarization (RHCP) antenna. The campaign was conducted in July 2019 within a total of 9h 40m flight time. Each flight was performed at an altitude of about 800 m above sea level going on two legs forth and back along the coast. The legs differed in the distance from the coastline, of 700 m and 2 km, respectively.

Reflectometry signal processing involves three data levels. Level (0): The raw data samples of Syntony front-end receiver. Level (1): The Delay-Doppler Map (DDM) of the correlated reflected signal and the carrier phase, from which geophysical information can be derived. And Level (2): height estimation (from signal correlation in delay and frequency domain) and roughness estimation (from signal amplitude).

By using the DDM and the carrier phase delay the sea state shall be assessed including the achievable precision and reliability of estimates. An additional aim is also to validate the configuration in terms of the used platform, antenna setup, and flight design.

How to cite: Moreno, M., Semmling, M., Stienne, G., Reboul, S., and Wickert, J.: Airborne GNSS reflectometry for coastal monitoring of sea state, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19944, https://doi.org/10.5194/egusphere-egu2020-19944, 2020.

EGU2020-21372 | Displays | G5.2

A straightforward approach for obtaining quantitative dielectric constant using reflected GNSS signals

Junchan Lee, Sunil Bisnath, and Regina Lee

Dielectric constant describes the electrical properties of a material and is related to soil moisture. The latter is known as a critical parameter in hydrological and climate science; however, computing such dielectric constants is a challenging problem as many factors effect the constant values, e.g., soil type, texture and temperature. Global Navigation Satellite System-Reflectometry (GNSS-R) is a relatively new remote sensing technique being used to infer geophysical information by measuring not only the signals coming directly from the GNSS satellites, but also the reflected GNSS signals from the Earth’s surface. This research presents a new, straightforward approach for computing relative dielectric constant by means of reflectivity, which is the ratio between the signal-to-noise ratio (SNR) of direct waves and SNR of reflected waves. With the well-known relationship between the reflectivity, Fresnel coefficient, and surface roughness, the dielectric constant can be expressed as the combination of horizontal and vertical Fresnel coefficients. Dual, circular-polarized antennas in the zenith and nadir directions were used to capture electromagnetic waves emitted from GNSS satellites and transform them into electrical signals. The zenith direction antenna senses the direct signals which have right-hand circular polarization, and the nadir direction antenna senses right and left-hand circular polarization of reflected GNSS signals created by electromagnetic reflections on the surfaces. An in-house Software Defined Radio (SDR) receiver, coupled with a commercial radio frequency frontend were used to collect, store and analyze both direct and reflected signals. Data collection experiments were carried in areas of smooth surface, and the observed SNR values were applied to the method of quantitative dielectric constant. The computation results demonstrate that derived dielectric constants have the values around 10 and are independent on the incident angle of waves coming to the specular point. Applying the additional data processing to the results, it is relevant to the dielectric constant measured by Time Domain Reflectometry techniques used commercial soil moisture probes at the same time. There have been few attempts to establish the dielectric constant model using forward scattered electromagnetic signals, especially GNSS signals. The proposed calculation method is able to solve the difficulties in analyzing with respect to the incident angle, as well as the polarization. Therefore, it is expected that the inversion approach of the retrieval algorithm makes the GNSS-R applicable to not only the scientific but also the industrial applications. In the future, the dielectric constant will be enhanced to include roughness information of the Earth’s surface and to attempt to calibrate surface soil moisture measurements for various soil types.

How to cite: Lee, J., Bisnath, S., and Lee, R.: A straightforward approach for obtaining quantitative dielectric constant using reflected GNSS signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21372, https://doi.org/10.5194/egusphere-egu2020-21372, 2020.

EGU2020-21966 | Displays | G5.2

Sea Surface Wind Speed Estimation based on USV borne System by BDS Reflectometry

Yanling Chen, Jianming Wu, Peng Guo, and Xiaoya Wang

Previously ship-borne GNSS-R (Global Navigation Satellite System Reflectometry) experiments have been carried out on the Kiloton scientific research vessel or above with relatively stable attitude. In this paper, we developed a GNSS-R platform based on the unmanned surface vessel(USV) for the first time, whose main functions include receiving, storing and processing BDS(BeiDou navigation satellite system) direct and reflected signal. In order to overcome the affect of rapidly changed attitude of the small ship, we designed and installed a three axis stabilizer to keep the antenna stable. Meanwhile, we made full use of the geostationary characteristics of BDS GEO satellite, and calculated the interference complex field (ICF) between the direct and reflected signal so as to estimate sea wind speed near the track of USV. The case study in Hengsha Island, Shanghai from June 9 to 11, 2019 showed that the RMS of wind speed is better than 0.50m/s by comparison with the hot-film anemometer measurement.

Key words: Wind speed; unmanned surface vessel; attitude;  BDS Reflectometry; hot-film anemometer

Acknowledgements:  This work is supported by Natural Science Foundation of Shanghai (No. 17ZR1435700), National Natural Science Foundation of China project (No. 41074019) and State Key Laboratory of Estuarine and Coastal Research, East China Normal University.

How to cite: Chen, Y., Wu, J., Guo, P., and Wang, X.: Sea Surface Wind Speed Estimation based on USV borne System by BDS Reflectometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21966, https://doi.org/10.5194/egusphere-egu2020-21966, 2020.

G6.1 – Open Session in Geodesy with Focus on Ionosphere and Gravity

EGU2020-18785 | Displays | G6.1

Global Multi-layer Electron Density Modeling Based on Constraint optimization

Ganesh Lalgudi Gopalakrishnan, Michael Schmidt, and Eren Erdogan

Electron density is the most important key parameter to describe the state of the ionospheric plasma varying with latitude, longitude, altitude and time. The upper atmosphere is decomposed into the four layers D, E, F1 and F2 of the ionosphere as well as the plasmasphere. Space weather events manifest themselves with specific "signatures" in distinct ionospheric layers. Therefore, the role of each layer in characterizing the ionosphere during nominal and extreme space weather events is highly important for scientific and operational purposes.

Accordingly, we model the total electron density as the sum of the electron densities of the individual layers. The key parameters of each layer, namely peak electron density, the corresponding peak height and scale height, are modeled by series expansions in terms of polynomial B-splines for latitude and trigonometric B-splines for longitude. The Chapman profile function is chosen to define the electron density along the altitude. This way, the electron density modeling is setup as a parameter estimation problem. In the case of modelling multiple layers simultaneously, the estimation of coefficients of the key parameters becomes challenging due to the correlations between the different key parameters.

One possibility to address the above issue is by imposing constraints on the ionospheric key parameters (and by extension on the B-spline coefficients). As an example, we constrain the F2 layer peak height to be always above the F1 layer peak height. We also constrain the key parameters to be non-negative and possibly to to certain well defined bounds. This way the physical properties of the ionosphere layers are included in the modelling. We estimate the coefficients with regard to the imposition of the bounds in form of inequality constraints using a convex optimization approach. We describe the underlying mathematical procedure and validate it using the IRI model as well as GNSS observations and electron density measurements from occultation missions. For the specific case of using IRI model data as the reference “truth”, we show the performance of the optimization algorithm using a “closed loop” validation. Such a validation allows an in-depth analysis of the impact of choosing a desired number of unknown coefficients to be estimated and the total number of constraints applied. We describe the parameterization of the different ionosphere key parameters considering the specific requirements from operational aspects (such as the need for modelling F2 layer), scientific aspects with regard to ionosphere-thermosphere studies (need for modelling the D, E or F1 layers) and also considering the aspects related to computation load.

We describe the advantages of using the optimization approach compared to the unconstrained least squares solution. While such constraints on key parameters can be fixed under nominal ionospheric conditions, but under adverse space weather effects these constraints need to be modified (constraints become stricter or more relaxed). For this purpose, we show the dynamic effect of modifying the constraints on global modelling performance and accuracy. We also provide the uncertainty of the estimated coefficients using a Monte-Carlo approach.

How to cite: Lalgudi Gopalakrishnan, G., Schmidt, M., and Erdogan, E.: Global Multi-layer Electron Density Modeling Based on Constraint optimization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18785, https://doi.org/10.5194/egusphere-egu2020-18785, 2020.

EGU2020-15908 | Displays | G6.1

Real-time regional VTEC modeling based on B-splines using real-time GPS, GLONASS and GALILEO observations

Eren Erdogan, Andreas Goss, Michael Schmidt, Denise Dettmering, Florian Seitz, Jennifer Müller, Barbara Görres, and Wilhelm F. Kersten

The project OPTIMAP is at the current stage a joint initiative of BGIC, GSSAC and DGFI-TUM. The development of an operational tool for ionospheric mapping and prediction is the main goal of the project.

The ionosphere is a dispersive medium. Therefore, GNSS signals are refracted while they pass through the ionosphere. The magnitude of the refraction rate depends on the frequencies of the transmitted GNSS signals. The ionospheric disturbance on the GNSS signals paves the way of extracting Vertical Total Electron Content (VTEC) information of the ionosphere.

In OPTIMAP, the representation of the global and regional VTEC signal is based on localizing B-spline basis functions. For global VTEC modeling, polynomial B-splines are employed to represent the latitudinal variations, whereas trigonometric B-splines are used for the longitudinal variations. The regional modeling in OPTIMAP relies on a polynomial B-spline representation for both latitude and longitude.

The VTEC modeling in this study relies on both a global and a regional sequential estimator (Kalman filter) running in a parallel mode. The global VTEC estimator produces VTEC maps based on data from GNSS receiver stations which are mainly part of the global real-time IGS network. The global estimator relies on additional VTEC information obtained from a forecast procedure using ultra-rapid VTEC products. The regional estimator makes use of the VTEC product of the real-time global estimator as background information and generates high-resolution VTEC maps using real-time data from the EUREF Permanent GNSS Network. EUREF provides a network of very dense GNSS receivers distributed alongside Europe.

Carrier phase observations acquired from GPS, GLONASS and GALILEO constellations, which are transmitted in accordance with RTCM standard, are used for real-time regional VTEC modeling. After the acquisition of GNSS data, cycle slips for each satellite-receiver pair are detected, and ionosphere observations are constructed via the linear combination of carrier-phase observations in the data pre-processing step. The unknown B-spline coefficients, as well as the biases for each phase-continuous arc belonging to each receiver-satellite pair, are simultaneously estimated in the Kalman filter.

Within this study, we compare the performance of regional and global VTEC products generated in real-time using the well-known dSTEC analysis.

How to cite: Erdogan, E., Goss, A., Schmidt, M., Dettmering, D., Seitz, F., Müller, J., Görres, B., and Kersten, W. F.: Real-time regional VTEC modeling based on B-splines using real-time GPS, GLONASS and GALILEO observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15908, https://doi.org/10.5194/egusphere-egu2020-15908, 2020.

An accurate estimation of the Thermospheric Neutral Density (TND) is important to compute drag forces acting on Low-Earth-Orbit (LEO) satellites and debris. Empirical thermospheric models are often used to compute TNDs (along-track of LEO satellites) for the Precise Orbit Determination (POD) experiments. However, recent studies indicate that the TNDs of available models do not perfectly reproduce TNDs derived from accelerometer observations. In this study, we use TND estimates from the Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) missions and merge them with the NRLMSISE00 from the Mass Spectrometer and Incoherent Scatter family. The integration is implemented by applying a simultaneous Calibration and Data Assimilation (C/DA) technique. The application of C/DA is advantageous since it uses model equation to interpolate and extrapolate TNDs that are not covered by CHAMP and GRACE. It also modifies the model's selected parameters to simulate TNDs that are closer to those of CHAMP and GRACE. The C/DA of this study is implemented daily using CHAMP- and/or GRACE-TNDs, while using the Ensemble Kalman Filter (EnKF) and Ensemble Square-Root Kalman Filter (EnSRF) as merger. Compared to the original model, on average, we found 27% (in the range of 2% to 56%) improvements in the estimation of TNDs. In addition, the results of the C/DA are compared with the TND outputs of the JB2008 model along the CHAMP and GRACE orbits, whose results indicate that the daily C/DA outputs are 60% closer to the observed TNDs (that are not used for the C/DA). Overall, our assessment indicates that EnSRF results in more realistic TND simulation and prediction compared to those derived from EnKF. We show that the improved TND estimates of this study will be beneficial for Precise Orbit Determination (POD) studies.  

Keywords: Thermosphere, Calibration and Data Assimilation (C/DA), NRLMSISE00, Ensemble Kalman Filter (EnKF), Ensemble Square-Root Kalman Filter (EnSRF)

How to cite: Forootan, E., Farzaneh, S., Kosary, M., and Schumacher, M.: How can Thermospheric Neutral Density (TND) estimates from CHAMP and GRACE accelerometer observations be used to improve empirical models?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-369, https://doi.org/10.5194/egusphere-egu2020-369, 2020.

EGU2020-20492 | Displays | G6.1

New GGOS JWG3 on Improved understanding of space weather events and their monitoring

Alberto Garcia-Rigo and Benedikt Soja

Multiple space geodetic techniques are capable of measuring effects caused by space weather events. In particular, space weather events can cause ionospheric disturbances correlated with variations in the vertical total electron content (VTEC) or the electron density (Ne) of the ionosphere.

In this regard and in the context of the new Focus Area on Geodetic Space Weather Research within IAG’s GGOS (International Association of Geodesy; Global Geodetic Observing System), the Joint Working Group 3 on Improved understanding of space weather events and their monitoring by satellite missions has been created as part of IAG Commission 4, Sub-Commission 4.3 to run for the next four years.

Within JWG3, we expect investigating different approaches to monitor space weather events using the data from different space geodetic techniques and, in particular, combinations thereof. Simulations will be beneficial to identify the contribution of different techniques and prepare for the analysis of real data. Different strategies for the combination of data will also be investigated, in particular, the weighting of estimates from different techniques in order to increase the performance and reliability of the combined estimates. Furthermore, existing algorithms for the detection and prediction of space weather events will be explored and improved to the extent possible. Furthermore, the geodetic measurement of the ionospheric electron density will be complemented by direct observations from the Sun gathered from existing spacecraft, such as SOHO, ACE, SDO, Parker Solar Probe, among others. The combination and joint evaluation of multiple datasets with the measurements of space geodetic observation techniques (e.g. geodetic VLBI) is still a great challenge. In addition, other indications for solar activity - such as the F10.7 index on solar radio flux, SOLERA as EUV proxy or rate of Global Electron Content (dGEC)-, provide additional opportunities for comparisons and validation.

Through these investigations, we will identify the key parameters useful to improve real-time/prediction of ionospheric/plasmaspheric VTEC, Ne estimates, as well as ionospheric perturbations, in case of extreme solar weather conditions. In general, we will gain a better understanding of space weather events and their effect on Earth’s atmosphere and near-Earth environment.

How to cite: Garcia-Rigo, A. and Soja, B.: New GGOS JWG3 on Improved understanding of space weather events and their monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20492, https://doi.org/10.5194/egusphere-egu2020-20492, 2020.

EGU2020-7525 | Displays | G6.1

Mobile GNSS reflectometry measurements

Joakim Strandberg and Rüdiger Haas

A major benefit of ground-based GNSS reflectometry (GNSS-R) over e.g. traditional tide gauge installations is the lower cost and basically maintenance-free operations. Still, a geodetic GNSS antenna is not exactly free of charge, so using cheaper equipment can make the technology available to even more people. With the ever increasing computing power and functionality in mobile phones and tablet computers, some new models are capable of recording raw GNSS data in e.g. RINEX-files. Therefore, they can act as a complete GNSS-R system, with both antenna, receiver, and processing done on a single unit. We make a proof of concept by using GNSS data received with a tablet computer to calculate sea level heights using spectral Lomb-Scargle retrievals. The latter strategy is used  for their low computational cost and simplicity. In comparing the resulting sea level retrievals to a traditional tide gauge and a geodetic quality GNSS-R installation, we show that the two GNSS-R installations perform on similar levels of precision. At the same time, the recorded GNSS data can also be used to derive the position of the tablet computer. Thus, mobile devices can be used as a cheap, and mobile, GNSS-R installation with possible applications in both oceanography and agriculture.

How to cite: Strandberg, J. and Haas, R.: Mobile GNSS reflectometry measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7525, https://doi.org/10.5194/egusphere-egu2020-7525, 2020.

EGU2020-2072 | Displays | G6.1

Development of a global geoid model 2020 (GGM2020)

WenBin Shen, Youchao Xie, Jiancheng Han, and Jiancheng Li

We present an updated 5′ ×5′ global geoid model 2020 (GGM2020), which is determined based on the shallow layer method (or simply Shen method). We choose an inner surface S below the EGM2008 global geoid by 15 m, and the layer bounded by the inner surface S and the Earths geographical surface E is referred to as the shallow layer. We formulate the 3D shallow mass layer model using the refined 5′ ×5′ crust density model, CRUST1.0-5min, which is an improved 5′ ×5′ density model of the CRUST1.0 with taking into account the corrections of the areas covered by ice sheets and the land-ocean crossing regions. Based on the shallow mass layer model and the gravity field EGM2008 that is defined in the region outside the Earth’s geographical surface E, we determine the gravity field model EGM2008S that is defined in the whole region outside the inner surface S. Based on the gravity field EGM2008S and the geoid equation W(P) =W0, where W0 is the geopotential constant on the geoid and P is the point on the geoid G, we established a 5′ ×5′ global geoid model GGM2020. Comparisons show that in average the GGM2020 fits the globally available GPS/leveling points better than the EGM2008 global geoid. This study is supported by NSFCs (grant Nos. 41721003, 41631072, 41874023, 41804012, 41429401, 41574007).

How to cite: Shen, W., Xie, Y., Han, J., and Li, J.: Development of a global geoid model 2020 (GGM2020) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2072, https://doi.org/10.5194/egusphere-egu2020-2072, 2020.

EGU2020-9884 | Displays | G6.1

Introducing EGM2020

Daniel Barnes, Daniel Barnes, James Beale, Howard Small, and Sarah Ingalls

The National Geospatial-Intelligence Agency [NGA], in conjunction with its U.S. and international partners, has completed its next Earth Gravitational Model (EGM2020), to replace EGM2008. The new ‘Earth Gravitational Model 2020’ [EGM2020] will retain the same harmonic basis and resolution as EGM2008. As such, EGM2020 will be a ellipsoidal harmonic model up to degree (n) and order (m) 2159, but will be released as a spherical harmonic model to degree 2190 and order 2159. EGM2020 has benefited from new data sources and procedures. Updated satellite gravity information from the GOCE and GRACE mission, will better support the lower harmonics, globally. Multiple new acquisitions (terrestrial, airborne and shipborne) of gravimetric data over specific geographical areas (Antarctica, Greenland …), will provide improved global coverage and resolution over the land, as well as for coastal and some ocean areas. Ongoing accumulation of satellite altimetry data as well as improvements in the treatment of this data, will better define the marine gravity field, most notably in polar and near-coastal regions. NGA and partners are evaluating different approaches for optimally combining the new GOCE/GRACE satellite gravity models with the terrestrial data. These include the latest methods employing a full covariance adjustment. NGA is also working to assess systematically the quality of its entire gravimetry database, towards correcting biases and other egregious errors where possible, and generating improved error models that will inform the final combination with the latest satellite gravity models. Outdated data gridding procedures have been replaced with improved approaches. For EGM2020, NGA intends to extract maximum value from the proprietary data that overlaps geographically with unrestricted data, whilst also making sure to respect and honor its proprietary agreements with its data-sharing partners.

How to cite: Barnes, D., Barnes, D., Beale, J., Small, H., and Ingalls, S.: Introducing EGM2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9884, https://doi.org/10.5194/egusphere-egu2020-9884, 2020.

EGU2020-59 | Displays | G6.1

Subtleties in spherical harmonic synthesis of the gravity field

Ropesh Goyal, Sten Claessens, Will Featherstone, and Onkar Dikshit

Spherical harmonic synthesis (SHS) can be used to compute various gravity functions (e.g., geoid undulations, height anomalies, deflections of vertical, gravity disturbances, gravity anomalies, etc.) using the 4pi fully normalised Stokes coefficients from the many freely available Global Geopotential Models (GGMs).  This requires a normal ellipsoid and its gravity field, which are defined by four parameters comprising (i) the second-degree even zonal Stokes coefficient (J2) (aka dynamic form factor), (ii) the product of the mass of the Earth and universal gravitational constant (GM) (aka geocentric gravitational constant), (iii) the Earth’s angular rate of rotation (ω), and (iv) the length of the semi-major axis (a). GGMs are also accompanied by numerical values for GM and a, which are not necessarily identical to those of the normal ellipsoid.  In addition, the value of W0, the potential of the geoid from a GGM, needs to be defined for the SHS of many gravity functions. W0 may not be identical to U0, the potential on the surface of the normal ellipsoid, which follows from the four defining parameters of the normal ellipsoid.  If W0 and U0 are equal and if the normal ellipsoid and GGM use the same value for GM, then some terms cancel when computing the disturbing gravity potential.  However, this is not always the case, which results in a zero-degree term (bias) when the masses and potentials are different.  There is also a latitude-dependent term when the geometries of the GGM and normal ellipsoids differ.  We demonstrate these effects for some GGMs, some values of W0, and the GRS80, WGS84 and TOPEX/Poseidon ellipsoids and comment on its omission from some public domain codes and services (isGraflab.m, harmonic_synth.f and ICGEM).  In terms of geoid heights, the effect of neglecting these parameters can reach nearly one metre, which is significant when one goal of modern physical geodesy is to compute the geoid with centimetric accuracy.  It is also important to clarify these effects for all (non-specialist) users of GGMs.

How to cite: Goyal, R., Claessens, S., Featherstone, W., and Dikshit, O.: Subtleties in spherical harmonic synthesis of the gravity field , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-59, https://doi.org/10.5194/egusphere-egu2020-59, 2020.

EGU2020-4304 | Displays | G6.1

Gravity changes before and after the 2015 Mw7.8 Nepal earthquake

Weimin Xu, Shi Chen, and Hongyan Lu

Based on the absolute gravity measurements of 4 gravimetric stations (Shigatse, Zhongba, Lhasa and Naqu) in southern Tibet surveyed from 2010 to 2013, we modeled the source region as a disk of 580 km in diameter by Hypocentroid model, shown that the gravity increase at these stations may be related to mass changes in the source region of the 2015 Mw7.8 Nepal earthquake. We analyzed the characteristics of gravity variations from the repeated regional gravity network, which including the 4 absolute gravimetric stations and 13 relative gravimetric stations from 2010 to 2019, to study the characteristics of gravity changes before and after the earthquake.

We firstly estimated the reliability of the absolute gravity measurements by the errors of each station, and considered the effect of vertical displacement, denudation of surface mass, GIA correction and the secular and background gravity changes. Secondly we employed the Bayesian adjustment method for the relative gravimetric network data analysis, which was more robust and adaptive for solving problems caused by irregular nonlinear drift of different gravimeters, and then carried out error analysis for the repeated relative gravity measurements. Furthermore, we took the Shigatse station as example, which covered absolute and relative measurements and was most close to the Hypocenter of the inversion Hypocentroid model, the hydrologic effects of the Shigatse station was modeled exactly, and the results shown that the secular and background gravity changes were much smaller than the observed gravity changes. Lastly we studied the characteristics of gravity changes before and after the earthquake through the Hypocentroid model, we found the coincident gravity increase both in absolute and repeated regional gravity results before the earthquake, and gravity decreased after the earthquake, which suggested that the pre-earthquake gravity increase may be caused by strain and mass (fluid) transfer in broad seismogenic source regions of the earthquake. Moreover, the study indicated that high-precision ground gravity measurements (absolute and relative) may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes.

 

Acknowledgment: This research is supported by National Key R&D Program of China (Grant No.2018YFC1503806 and No.2017YFC1500503) and National Natural Science Foundation of China (Grant No.U1939205 and No.41774090).

How to cite: Xu, W., Chen, S., and Lu, H.: Gravity changes before and after the 2015 Mw7.8 Nepal earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4304, https://doi.org/10.5194/egusphere-egu2020-4304, 2020.

EGU2020-12331 | Displays | G6.1

Comparison of 1D vs 3D viscosity models for glacial isostatic adjustment

Paoline Prevost and Jeffrey Freymueller

Accurate calculation of displacements due to glacial isostatic adjustment (GIA) are essential for studies of tectonics, sea level projection, and the estimation of recent ice melting or other mass transport. However, most GIA studies to date have used a 1D viscosity model, with earth parameters varying only in the radial direction, while surface geology and seismic tomography show that the thickness of the lithosphere and the structure of the mantle also varies laterally. Therefore, models with 3D earth structure are needed. Using a 3D earth model requires finite element models, which are computationally expensive and hence make it difficult to compute a wide range of potential parameter values. Consequently, the question is for which application is a 3D model necessary, and for which parameters (and where) do 1D models give sufficiently accurate predictions?

 

In this study, we investigate the sensitivity of the GIA modeling to the earth structure, using the Abaqus finite element analysis software, an ice model assumed to be known, and various viscosity models. We start with Patagonia as a test region, because the 3D structure of the mantle is complex due to the proximity of the subduction of the Antarctic plate below South American and the Chile triple junction. In this region, the GIA contributes significantly to the regional recent rapid uplift.

How to cite: Prevost, P. and Freymueller, J.: Comparison of 1D vs 3D viscosity models for glacial isostatic adjustment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12331, https://doi.org/10.5194/egusphere-egu2020-12331, 2020.

EGU2020-7083 | Displays | G6.1

Expected impact of the 2016 central Italy earthquakes on the local gravity field

Federica Riguzzi, Hongbo Tan, and Chong-yang Shen

We have modelled the surface volume and gravity changes caused by the three mainshocks (moment magnitudes Mw 6.0, 5.9, 6.5) occurred during the last seismic period started on 2016, August 24 in central Italy. Our calculations start from the source parameters estimated by the inversion of the largest dataset of InSAR and GNSS observations ever managed in Italy after earthquake occurrences, based on the half-space elastic dislocation theory. The vertical displacements modelled after the 2016 events allow to infer a substantial unbalance between the subsided and uplifted volumes. In particular, we detected ~106∙106 m3 of hangingwall subsidence against ~37∙106 m3 of footwall uplift, that accounts for ~74% of the total volume mobilization. From the ratio between the footwall and total deformed volumes, we have computed an average fault dip of ~47°, in line with the values retrieved by seismological methods. The total gravity variations which affected the study area are of the order of ~1 μGal (1 μGal = 10−8 ms−2) in the far field, and ~170 μGal in the near field.
The area affected within a gravity change of 1 μGal is ~140 km long and ~57 km wide, parallel to the Apennines chain. The larger contribution is given by positive variations which account for the tensional style of deformation and larger subsided area.

How to cite: Riguzzi, F., Tan, H., and Shen, C.: Expected impact of the 2016 central Italy earthquakes on the local gravity field , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7083, https://doi.org/10.5194/egusphere-egu2020-7083, 2020.

EGU2020-8834 | Displays | G6.1

Indoor height determination of the new absolute gravimetric station of L'Aquila

Augusto Mazzoni, Marco Fortunato, Alberico Sonnessa, Giovanna Berrino, Filippo Greco, and Federica Riguzzi

In 2018 INGV funded a project aimed to detect gravity variations and ground deformations over different time-scale possibly associated with the postseismic relaxation affecting the area where the recent seismic events of L'Aquila (2009 Mw 6.3) and Amatrice-Norcia (2016 Mw 6.1 and 6.5) took place. To this aim a network of five absolute gravity stations was realized (Terni, Popoli, Sant’Angelo Romano, L’Aquila University and L'Aquila Laboratori Nazionali del Gran Sasso). The site of L'Aquila University was chosen since location of the permanent GNSS station (AQUI) managed by the Italian Space Agency and contributing to the EUREF network. AQUI is continuously operating on the roof of the Science Faculty (Coppito, L'Aquila).

In the basement of the same building we realized the absolute gravimetric station (AQUIg), indoor the Geomagnetic laboratory of the Physics Department. This is one of the numerous applications where satellite systems must be integrated with traditional terrestrial surveying techniques. These include the case of underground or indoor gravimetric surveys, where the height of the gravimetric reference point should be determined precisely starting from an outdoor reference point with known coordinates. In this case, the use of classical observation techniques and instruments (e.g., total stations, levels) is crucial to measure the height difference between a reference GNSS station and a gravimetric benchmark. We will draw the steps followed to estimate the height difference between AQUIg and AQUI by a classical topographic survey and therefore the height of AQUIg from estimating first the height of AQUI.

How to cite: Mazzoni, A., Fortunato, M., Sonnessa, A., Berrino, G., Greco, F., and Riguzzi, F.: Indoor height determination of the new absolute gravimetric station of L'Aquila, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8834, https://doi.org/10.5194/egusphere-egu2020-8834, 2020.

EGU2020-544 | Displays | G6.1

Can we use regional runoff models for correcting time series of absolute gravimetry?

Brian Bramanto, Vegard Ophaug, Christian Gerlach, and Kristian Breili

Absolute gravity time series are available at various stations in Norway. The data have mainly been used for investigation of secular variations due to glacial isostatic adjustment. Previous work indicates that some of the estimated gravity trends suffer from unmodeled geophysical effects, like hydrological mass variations. Here we try to correct for hydrological effects by employing a combination of global and regional hydrological models. We use gravity data at two locations in the Norwegian network (NMBU and TRYC) which have frequently been observed with the absolute gravimeter FG5-226. 

For computing the gravity corrections, we test various Global Hydrological Models (GHMs) and combine them with a Regional Runoff Model (RRM) for Norway, run by the Norwegian Water Resources and Energy Directorate (NVE). We distinguish between an outer and an inner zone. In the outer zone, Newtonian attraction and loading effects are derived from the GHMs, while the RRM is used in the inner zone. Both types of models provide information on soil moisture and snow layers. The RRM provides groundwater variations in addition. Furthermore, we try to consider the ‘umbrella effect’ that accounts for local disturbances in subsurface water flow caused by the existence of the building in which the gravity site is located.  

Neglecting the GIA trend, both NMBU and TRYC gravity time series show different amplitude and pattern. NMBU shows a lower amplitude, and with no prominent periodic pattern in the data, while TRYC shows the opposite. Significant discrepancies occurring in the NMBU gravity dataset between 2014 and 2015 are likely due to an instrumental effect, such as maintenance. The total modelled hydrological signal ranges from -4 and 4 µGal. Application of the correction reduces the standard deviation in the gravity time series, at its best, by about 33% or 0.8 µGal for NMBU, and by about 43% or two µGal for TRYC. Secular gravity rates have been derived from both, the uncorrected and the corrected time series. We find that application of the hydrological correction improves the fit of the computed secular gravity rates as compared to rates derived from the state-of-the-art Fennoscandian land uplift model NKG2016LU_abs. The uncorrected trends are 75% and 50% of the expected trend (0.77 and 1.12 µGal/year), while the hydrological corrections improve the fit to 82% and 93% for NMBU and TRYC, respectively.

How to cite: Bramanto, B., Ophaug, V., Gerlach, C., and Breili, K.: Can we use regional runoff models for correcting time series of absolute gravimetry?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-544, https://doi.org/10.5194/egusphere-egu2020-544, 2020.

EGU2020-2493 | Displays | G6.1

Regional-residual separation of microgravity data based on data clustering

Hyoungrea Rim, Gyesoon Park, and Chang-Ryol Kim

we propose a method to apply the polynomial fitting for regional-residual separation of microgravity data based on the characteristics of gravity anomaly without a prior information. Since the microgravity survey is usually carried out in small regions, it is common to approximate regional anomaly by the first-order polynomial plane. However, if the regional anomaly patterns are unsuited to be approximated to a first-order plane, the complete gravity anomaly is divided into small zones enough to approximate first-order plane by means of Parasnis density estimation method. The regional-residual separation is then applied on the splitted zones individually. When the gravity anomalies can be splitted spatially, we showed that the residual anomalies can be more effectively extracted based on the regional geological structures by regional anomaly separation from each of the divided regions, rather than applying the entire data set at one time.

Acknowledgment: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2019R1F1A1055093).

How to cite: Rim, H., Park, G., and Kim, C.-R.: Regional-residual separation of microgravity data based on data clustering, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2493, https://doi.org/10.5194/egusphere-egu2020-2493, 2020.

EGU2020-17734 | Displays | G6.1

Quantifying the contribution of airborne gravity data for geoid modeling: two case studies

Tao Jiang, Yamin Dang, and Chuanyin Zhang

Airborne gravimetry has become increasingly important for geoid modeling because of its capability of collecting large scale gravity data over difficult areas. In order to quantify the contribution of airborne gravity data for geoid determination, two regions with distinct topographical condition, a hilly desert area in Mu Us of China and a mountainous region in Colorado of the USA were selected for gravimetric geoid modeling experiment. The gravimetric geoid model computed by combining satellite gravity model, terrestrial and airborne gravity data fits with GPS leveling data to 0.8 cm for Mu Us case and 5.3 cm for Colorado case. The contribution of airborne gravity data to the signal and accuracy improvement of the geoid was quantitatively evaluated for different spatial distribution and density of terrestrial gravity data. The results demonstrate that in the cases of the spacing of terrestrial gravity points exceeds 15 km, the additions of airborne gravity data improve the accuracies of gravimetric geoid models by 11.1%~48.3% for Mu Us case and 13%~20% for Colorado case.

How to cite: Jiang, T., Dang, Y., and Zhang, C.: Quantifying the contribution of airborne gravity data for geoid modeling: two case studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17734, https://doi.org/10.5194/egusphere-egu2020-17734, 2020.

In this paper, by combining the Global Geopotential Model (GGM, specifically, EGM2008 is used) and the Residual Terrain Model (RTM) data, we have modeled the Gravity Gradient Tensor (GGT) in eastern Tian shan mountains areas, China. The RTM data are obtained from the Shuttle Radar Topography Mission (SRTM) elevation model and the DTM2006.0 high degree spherical harmonic reference surface. The integration of RTM data reduces the truncation errors (or called omission errors) due to the finite expansion terms of the spherical harmonic coefficients of the GGM, and compensates for the high frequency information and spatial resolution of the GGT within the study area.

How to cite: Liu, J.: Combining GGM and RTM to model the gravity gradient tensor, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4407, https://doi.org/10.5194/egusphere-egu2020-4407, 2020.

EGU2020-3297 | Displays | G6.1

Evaluation of global ocean tide models based on tidal gravity observations in China

Hongbo Tan, Chongyong Shen, and Guiju Wu

Solid Earth is affected by tidal cycles triggered by the gravity attraction of the celestial bodies. However, about 70% the Earth is covered with seawater which is also affected by the tidal forces. In the coastal areas, the ocean tide loading (OTL) can reach up to 10% of the earth tide, 90% for tilt, and 25% for strain (Farrell, 1972). Since 2007, a high-precision continuous gravity observation network in China has been established with 78 stations. The long-term high-precision tidal data of the network can be used to validate, verifying and even improve the ocean tide model (OTM).

In this paper, tidal parameters of each station were extracted using the harmonic analysis method after a careful editing of the data. 8 OTMs were used for calculating the OTL. The results show that the Root-Mean-Square of the tidal residuals (M0) vary between 0.078-1.77 μgal, and the average errors as function of the distance from the sea for near(0-60km), middle(60-1000km) and far(>1000km) stations are 0.76, 0.30 and 0.21 μgal. The total final gravity residuals (Tx) of the 8 major constituents (M2, S2, N2, K2, K1, O1, P1, Q1) for the best OTM has amplitude ranging from 0.14 to 3.45 μgal. The average efficiency for O1 is 77.0%, while 73.1%, 59.6% and 62.6% for K1, M2 and Tx. FES2014b provides the best corrections for O1 at 12 stations, while SCHW provides the best for K1 ,M2and Tx at 12,8and 9 stations. For the 11 costal stations, there is not an obvious best OTM. The models of DTU10, EOT11a and TPXO8 look a litter better than FES2014b, HAMTIDE and SCHW. For the 17 middle distance stations, SCHW is the best OTM obviously. For the 7 far distance stations, FES2014b and SCHW model are the best models. But the correction efficiency is worse than the near and middle stations’.

The outcome is mixed: none of the recent OTMs performs the best for all tidal waves at all stations. Surprisingly, the Schwiderski’s model although is 40 years old with a coarse resolution of 1° x 1° is performing relative well with respect to the more recent OTM. Similar results are obtained in Southeast Asia (Francis and van Dam, 2014). It could be due to systematic errors in the surroundings seas affecting all the ocean tides models. It's difficult to detect, but invert the gravity attraction and loading effect to map the ocean tides in the vicinity of China would be one way.

How to cite: Tan, H., Shen, C., and Wu, G.: Evaluation of global ocean tide models based on tidal gravity observations in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3297, https://doi.org/10.5194/egusphere-egu2020-3297, 2020.

EGU2020-11518 | Displays | G6.1

Gravity networks for the Geodetic Reference Framework of Albania

Hamza Reci, Alexandros Stampolidis, Perparim Ndoj, Gregory Tsokas, Roman Pašteka, Branislav Hábel, Salvatore Bushati, and Kristaq Qirko

This paper presents a general overview of gravimetric measurements carried out for the first order gravimetric network of Albania.   Data compensation, correction methodologies, interpretation and related results have been presented as well. Relative gravimetric measurements were carried out in 42points,  with two CG-5 instruments. Real Vertical Gradients have been measured at all the points of first order network which together with other corrections,  are used in the final data compensation in order to bring the final values at reference point as absolute ones. Apart from the first order network, other 38 second order and 138 third order gravimetric points have been measured in a grid 2x2 km, in the  flat and most dense area (Tirana-Durresi) of Albania,  with the  scope the determination of  Geoid Gravimetric Height on that region. The gravimetric measurements were realized with two Scintrex CG-5 gravimeters for three orders. For the first order points were used two gravimeters simultaneously, whereas for the points of second and third order only one. In this paper we present the results for only the first order measurements. The measurements were carried out during the period from August to October 2018, in collaboration with Aristotle University of Thessaloniki, Department of Geophysics. The project was supported by the Agency of Geospatial Information of Albania.

How to cite: Reci, H., Stampolidis, A., Ndoj, P., Tsokas, G., Pašteka, R., Hábel, B., Bushati, S., and Qirko, K.: Gravity networks for the Geodetic Reference Framework of Albania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11518, https://doi.org/10.5194/egusphere-egu2020-11518, 2020.

EGU2020-20420 | Displays | G6.1

The digital zenith camera as an additional technique for quasi-geoid model determination of Latvia

Katerina Morozova, Gunars Silabriedis, Ansis Zarins, Janis Balodis, and Reiner Jaeger

The digital zenith camera VESTA (VErtical by STArs) was designed by the Institute of Geodesy and Geoinformatics (GGI) of the University of Latvia and completed in 2016. By 2020 more than 400 terrestrial vertical deflection measurements were observed in the territory of Latvia. These observations were post-processed by the GGI developed software and the accuracy was evaluated at 0.1 arc seconds. In 2019 two new cameras have been developed, which will be used in future projects, e.g., in determination of properties of local geological structure or Earth crust movement monitoring. Measurement control software corrections and complements, data processing improvements and automation and transition to GAIA data release 2 star catalog were done. The accuracy of the measurements of improved camera was evaluated at 0.05 arc seconds.

Terrestrial vertical deflection observations were compared with global geopotential models, e.g. GGM+ and EGM2008. The results show a better correspondence with GGM+ model by evaluating the standard deviation: 0.314 and 0.307 arc seconds for ξ and η components respectively in comparison to 0.346 and 0.358 arc seconds for ξ and η components for EGM2008 model. The comparisons of average and minimum/maximum differences are introduced in this study for better evaluation of the results. Moreover, vertical deflections have been used as additional terrestrial data in DFHRS (Digital Finite-element Height Reference Surface) software v. 4.3 in combination with GNSS/levelling data (B, L, hH) and global geopotential model EGM2008 for gravity field and quasi-geoid improvement (www.dfhbf.de). This approach is based on parametric modelling and computation of height reference surfaces (HRS) from geometric and physical observation components in a hybrid adjustment approach. The results of the computed quasi-geoid models using different types of data are introduced in this research, representing several solutions, as well as these solutions are compared with the national quasi-geoid model LV’14.

How to cite: Morozova, K., Silabriedis, G., Zarins, A., Balodis, J., and Jaeger, R.: The digital zenith camera as an additional technique for quasi-geoid model determination of Latvia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20420, https://doi.org/10.5194/egusphere-egu2020-20420, 2020.

EGU2020-6651 | Displays | G6.1

Preliminary Study on Fusion Scheme of Multi-dimensional and Multi-scale Potential Field Data

Xiaolin Ji, Wanyin Wang, Fuxiang Liu, Min Yang, Shengqing Xiong, and Jie Ma

Gravity and magnetic surveys are widely used in geology exploration because of its advantages, such as efficient and economy, green and environment-friendly, widely coverage and strong horizontal resolution. In order to well study in the geology exploration, it is required to comprehensively combine the different scales (different scales data) and different dimensions (satellite data, aeronautical data, ground data, ocean data, well data, etc.) of gravity and magnetic data that were observed in different periods, however, the comprehensive application of the multi-dimensional and multi-scale gravity and magnetic data still stays in the initial stage. In this paper, we do research on the key point of the fusion of potential field data (gravity and magnetic data): the way to fuse the different scales and different dimensions of potential field data into a benchmark and the same surface. Based on this research, we propose a scheme to fuse the multi-dimensional and multi-scale gravity and magnetic data. The synthetic models show that this fusion scheme is able to fuse the multi-dimensional and multi-scale gravity and magnetic data with great fusion results and small errors, in addition, the most important is that the fusion data conform to the characteristics of the potential field data and can meet the needs of data processing in the following steps. One of case studies in China has been accomplished to fuse aeronautical and ground gravity data that are different scales by using this fusion scheme. The fusion scheme we proposed in this study can be used in the fusion of the multi-dimensional (aeronautical, ground and ocean) and multi-scale gravity and magnetic data, which is good for interpretation and popularization.

How to cite: Ji, X., Wang, W., Liu, F., Yang, M., Xiong, S., and Ma, J.: Preliminary Study on Fusion Scheme of Multi-dimensional and Multi-scale Potential Field Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6651, https://doi.org/10.5194/egusphere-egu2020-6651, 2020.

EGU2020-18453 | Displays | G6.1

Optimal Vertex Interval Determination for Efficient Shoreline Length Calculation

Hee Sook Woo, Kwang Seok Kwon, and Byung Guk Kim

Coastline extraction and decisions have important implications for efficient land management and national policy formulation. Therefore, shorelines should be determined in a reasonable manner, and consistent results should be produced for the same area. This must be calculated efficiently. For example, simple shoreline areas should be constructed using relatively large vertex intervals (point-to-point distances) for efficiency, while complex shoreline areas should be constructed using small vertex intervals, thus improving accuracy. In this study, we suggest an optimum vertex interval that can represent more than 99.7% (3σ) of the original shoreline data using a grid generated by applying a box-counting method. All coastline areas were gridded using 11 grid sizes. Generalization was performed on the shorelines contained within each grid, and the sum of the generalized shoreline lengths was calculated. As the grid size used increases, the shoreline will become more simplified, and the difference from the original data will increase. As the grid size decreases, the more precisely the shoreline will be represented, and the sum will be similar to the original value. As a result of regression analysis, using the sum of the generalized shoreline length, we could predict the vertex interval that would represent more than 99.7% (3σ) of the original data. For the experiment, three regions with distinct coastline characteristics were selected. The grid was generated by the box-counting method, a representative fractal technique, and the vertex interval was estimated. From this, the fractal dimension was then calculated. As a result of the experiment, it was confirmed that the area A had a vertex interval of 0.7m, and the areas B and C had vertex intervals of 1m. These optimal vertex interval values mean that when the coastline was reconstructed, it was the closest, efficient representation of the actual coastline. Furthermore, these interval values suggest that the area A has a more complex coastline, and therefore the coastline should be constructed with a smaller vertex interval than the other areas. Using fractal dimensions, we also found that the area B has a more complex coastline than the area C. Overall, we confirmed that the optimal vertex interval for the accurate and efficient construction of the shoreline is able to be calculated by the approach presented in this paper. This research is expected to contribute to efficient land management and national policy establishment and progress. 

How to cite: Woo, H. S., Kwon, K. S., and Kim, B. G.: Optimal Vertex Interval Determination for Efficient Shoreline Length Calculation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18453, https://doi.org/10.5194/egusphere-egu2020-18453, 2020.

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