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 fi