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279 results on '"Mayer-Gürr, Torsten"'

5. International Combination Service for Time-Variable Gravity Fields (COST-G) : Start of Operational Phase and Future Perspectives

Author

Jäggi, Adrian, Meyer, Ulrich, Lasser, Martin, Jenny, Barbara, Lopez, Teodolina, Flechtner, Frank, Dahle, Christoph, Förste, Christoph, Mayer-Gürr, Torsten, Kvas, Andreas, Lemoine, Jean-Michel, Bourgogne, Stéphane, Weigelt, Matthias, Groh, Andreas, Freymueller, Jeffrey T., Series Editor, and Sánchez, Laura, Assistant Editor

Published
2022
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7. Kalman filter framework for a regional mass change model from GRACE satellite gravity.

Author

Wöhnke, Viviana, Eicker, Annette, Weigelt, Matthias, Reich, Marvin, Güntner, Andreas, Kvas, Andreas, and Mayer-Gürr, Torsten

Abstract

In this study a regional modelling framework for water mass changes is developed. The approach can introduce geodetic observation types of varying temporal and spatial resolution including their correlated error information. For this purpose a Kalman filter process was set up using a regional parameterisation by space-localising radial basis functions and a process model based on stochastic prediction. The feasibility of the approach is confirmed in a closed-loop simulation experiment using gridded water storage estimates derived from simulated monthly solutions of the GRACE satellite gravimetry mission and considering realistic error patterns. The resulting mass change time series exhibit strongly reduced noise and a very high agreement with the reference model. The modelling framework is designed to flexibly allow a future extension towards combining satellite gravimetry with other geodetic observations such as GNSS station displacements or terrestrial gravimetry. [ABSTRACT FROM AUTHOR]

Published
2025
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8. Analysis of GRACE range-rate residuals with focus on KBR instrument system noise

Author

Goswami, Sujata, Devaraju, Balaji, Weigelt, Matthias, and Mayer-Gürr, Torsten

Subjects
Physics - Space Physics, Astrophysics - Earth and Planetary Astrophysics
Abstract

We investigate the post-fit range-rate residuals after the gravity field parameter estimation from the inter-satellite ranging data of the gravity recovery and climate experiment (GRACE) satellite mission. Of particular interest is the high-frequency spectrum (f gt 20 MHz) which is dominated by the microwave ranging system noise. Such analysis is carried out to understand the yet unsolved discrepancy between the predicted baseline errors and the observed ones. The analysis consists of two parts. First, we present the effects in the signal-to-noise ratio (SNRs) of the k-band ranging system. The SNRs are also affected by the moon intrusions into the star cameras field of view and magnetic torque rod currents in addition to the effects presented by Harvey et al. [2016]. Second, we analyze the range-rate residuals to study the effects of the KBR system noise. The range-rate residuals are dominated by the non-stationary errors in the high-frequency observations. These high-frequency errors in the range-rate residuals are found to be dependent on the temperature and effects of sun intrusion into the star cameras field of view reflected in the SNRs of the K-band phase observations.

Published
2017
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9. Least travel time ray tracer, version Two (LTT v2) adapted to the grid geometry of the OpenIFS atmospheric model.

Author

Vasiuta, Maksym, Trastoy, Angel Navarro, Motlaghzadeh, Sanam, Tuppi, Lauri, Mayer-Gürr, Torsten, and Järvinen, Heikki

Subjects
GLOBAL Positioning System, OBJECT-oriented programming, NUMERICAL weather forecasting, TRAVEL time (Traffic engineering), ATMOSPHERIC models, COMPUTER software quality control
Abstract

Electromagnetic signals commonly used in geodetical applications, such as the Global Navigation Satellite System (GNSS), undergo bending and delay in the neutral gas atmosphere of the Earth. The least-travel-time (LTT) concept is one of the approaches to model signal slant delays via a ray tracing (RT) procedure. In this study, we developed an LTT-based RT algorithm (LTT v2), where the 3-dimensional refractivity field of the atmosphere is based on the atmospheric model data. This representation is complete in a sense that the domain of the RT conforms to the native grid geometry of the atmospheric model. In addition, some physical and numerical approximations are improved compared to the previous version (LTT v1). The atmospheric states are generated using a global numerical weather prediction model, the Open Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts. The slant delays of LTT v2 are compared with the products of the original least-travel-time GNSS delay model (LTT v1) and the products of the state-of-the-art VieVS Ray Tracer (RADIATE). The skill of slant delay estimation is assessed using metrics that are indicative of the quality of GNSS products derived using the GROOPS (Gravity Recovery Object Oriented Programming System) orbit solver software toolkit of the Graz University of Technology. Employment of slant delay products of the LTT RT algorithm shows radical improvement in GNSS processing. When using LTT v2 delay estimates, the GNSS orbit midnight discontinuities are reduced by more than 10 % compared to RADIATE, and more than 2 % compared to LTT v1. The residuals of ground station precise positioning are analysed with respect to the IGS14 reference positions. The RMS of residuals (accuracy) and standard deviation (precision) are substantialy reduced compared to RADIATE. [ABSTRACT FROM AUTHOR]

Published
2024
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21. International Combination Service for Time-Variable Gravity Fields (COST-G)

Author

Jäggi, Adrian, primary, Meyer, Ulrich, additional, Lasser, Martin, additional, Jenny, Barbara, additional, Lopez, Teodolina, additional, Flechtner, Frank, additional, Dahle, Christoph, additional, Förste, Christoph, additional, Mayer-Gürr, Torsten, additional, Kvas, Andreas, additional, Lemoine, Jean-Michel, additional, Bourgogne, Stéphane, additional, Weigelt, Matthias, additional, and Groh, Andreas, additional

Published
2020
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23. Gravity field recovery process of GRACE-like systems with conditional equations

Author

Ebadi, Sahar, Weigelt, Matthias, Mayer-Gürr, Torsten, and Öhlinger, Felix

Abstract

Intersatellite ranging systems as implemented in the GRACE and GRACE-FO mission are considered one-dimensional observation systems. The intersatellite range is observed in the direction of the line-of-sight between the two satellite. In the modelling process, range-rate and range-accelerations are typically connected to the relative position and velocity projected on the line-of-sight, respectively. We investigate the possibility of adding conditional equations in directions perpendicular to the line-of-sight and present gravity field solutions developed at the Leibniz University Hannover using GRACE and GRACE Follow-On range-rate and range-accelerations as observations. We will show the mathematical derivations and investigates the feasibility of using these additional directions in the gravity field recovery process., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

29. COST-G: release of GRACE-FO RL02 combination

Author

Jaeggi, Adrian, primary, Meyer, Ulrich, additional, Lasser, Martin, additional, Flechtner, Frank, additional, Dahle, Christoph, additional, Boergens, Eva, additional, Förste, Christoph, additional, Mayer-Gürr, Torsten, additional, Kvas, Andreas, additional, Behzadpour, Saniya, additional, Öhlinger, Felix, additional, Lemoine, Jean-Michel, additional, Bourgogne, Stéphane, additional, Koch, Igor, additional, and Flury, Jakob, additional

Published
2023
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32. The extended GRACE combination COST-G GRACE RL02

Author

Meyer, Ulrich, Lasser, Martin, Darbeheshti, Neda, Jäggi, Adrian, Dahle, Christoph, Borgens, Eva, Förste, Christoph, Flechtner, Frank, Kvas, Andreas, Behzadpour, Saniya, Oehlinger, Feliix, Mayer-Gürr, Torsten, Lemoine, Jean-Michel, Bourgogne, Stephane, Koch, Igor, Flury, Jakob, Döhne, Torben, Horwath, Martin, Sasgen, Ingo, Eicker, Annette, Blazquez, Alejandro, Meyssignac, Benoit, Zhou, Hao, Guo, Xiang, and Feng, Wei

Abstract

In 2019 the Combination Service for Time-variable Gravity fields (COST-G) started operation with the release of the complete time-series of combined GRACE monthly gravity fields COST-G GRACE RL01. Meanwhile additional time-series of monthly GRACE gravity fields have become available, mainly from Chinese analysis centers. The COST-G quality control confirms the high quality of these solutions that are derived with independent analysis tools.In the frame of the Horizon 2020 project Global Gravity-based Groundwater Product (G3P) the weighting scheme of the monthly GRACE-FO gravity fields was adapted to take into account the limitations on the solution space imposed by the specific observation geometry of the GRACE/GRACE-FO missions.We present the new COST-G GRACE RL02 combination, based on an extended set of time-series including COST-G's new Chinese partners, and combined applying the G3P weighting scheme., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

43. COST-G: towards a new GRACE and GRACE-FO combination

Author

Meyer, Ulrich, primary, Lasser, Martin, additional, Darbeheshti, Neda, additional, Jäggi, Adrian, additional, Flechtner, Frank, additional, Dahle, Christoph, additional, Förste, Christoph, additional, Güntner, Andreas, additional, Mayer-Gürr, Torsten, additional, Kvas, Andreas, additional, Behzadpour, Saniya, additional, Lemoine, Jean-Michel, additional, Koch, Igor, additional, Flury, Jakob, additional, Bourgogne, Stephane, additional, and Feng, Wei, additional

Published
2022
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50. COST-G: Status and recent developments

Author

Jaeggi, Adrian, primary, Meyer, Ulrich, additional, Peter, Heike, additional, Teixeira Encarnacao, Joao, additional, Lasser, Martin, additional, Flechtner, Frank, additional, Dahle, Christoph, additional, Boergens, Eva, additional, Förste, Christoph, additional, Mayer-Gürr, Torsten, additional, Kvas, Andreas, additional, Behzadpour, Saniya, additional, Lemoine, Jean-Michel, additional, Bourgogne, Stéphane, additional, Koch, Igor, additional, Flury, Jakob, additional, Groh, Andreas, additional, Eicker, Annette, additional, Blazquez, Alejandro, additional, and Meyssignac, Benoit, additional

Published
2022
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