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 Teunissen^1,2

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

G1 – Geodetic Theory and Algorithms

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

Instantaneous Ambiguity Resolved GLONASS FDMA Attitude Determination

PJG Teunissen^1,2, 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 17^th and 18^th 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.

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.

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.

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.

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.

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.

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.

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 (x_p, y_p), 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 (χ_x, χ_y, 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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

On the impact of gravitational deformation on VLBI-derived parameters

Sahar Shoushtari^1,2, Susanne Glaser¹, Kyriakos Balidakis¹, Robert Heinkelmann^1,2, James M. Anderson^1,2, Harald Schuh^1,2

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Key words: Russian continuously operating reference stations network

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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