G2.1 | Precise Orbit Determination for Geodesy and Earth Science
EDI
Precise Orbit Determination for Geodesy and Earth Science
Convener: Adrian Jaeggi | Co-conveners: Alexandre CouhertECSECS, Jose van den IJssel, Oliver Montenbruck, Urs Hugentobler
Orals
| Fri, 19 Apr, 14:00–15:40 (CEST), 16:15–17:55 (CEST)
 
Room -2.47/48
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
 
Hall X2
Orals |
Fri, 14:00
Posters on site
Thu, 16:15
Precise orbit determination is of central importance for many applications of geodesy and earth science. The challenge is to determine satellite orbits in an absolute sense at the centimeter or even sub-centimeter level, and at the millimeter or even sub-millimeter level in a relative sense. Four constellations of GNSS satellites are available and numerous position-critical missions (e.g. altimetry, gravity, SAR and SLR missions) are currently in orbit. Altogether, outstanding data are available offering new opportunities to push orbit determination to the limit and to explore new applications.

This session aims to make accessible the technical challenges of orbit determination and modelling to the wider community and to quantify the nature of the impact of dynamics errors on the various applications. Contributions are solicited from, but not limited to, the following areas: (1) precise orbit determination and validation; (2) satellite surface force modelling; (3) advances in modelling atmospheric density and in atmospheric gravity; (4) advances in modelling earth radiation fluxes and their interaction with space vehicles; (5) analysis of changes in geodetic parameters/earth models resulting from improved force modelling/orbit determination methods; (6) improvements in observable modelling for all tracking systems, e.g. SLR, DORIS, GNSS and their impact on orbit determination; (7) advances in combining the different tracking systems for orbit determination; (8) the impact of improved clock modelling methods/space clocks on precise orbit determination; (9) advances in modelling satellite attitude; (10) simulation studies for the planned co-location of geodetic techniques in space mission GENESIS.

Orals: Fri, 19 Apr | Room -2.47/48

Chairpersons: Adrian Jaeggi, Oliver Montenbruck, Urs Hugentobler
14:00–14:10
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EGU24-5385
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On-site presentation
Application of ITRS 2020 realizations for the SLR-based POD of selected geodetic and Earth-observing satellites 
Mathis Bloßfeld, Julian Zeitlhöfler, Sergei Rudenko, and Manuela Seitz

Since 2023, three different solutions for the latest (2020) realization of the International Terrestrial Reference System (ITRS) are publicly available, namely the ITRF2020, the JTRF2020 and the DTRF2020. All solutions are based on the same input data but were derived using different combination approaches and data correction strategies. Since the ITRS realizations are used as a priori reference frames for precise orbit determination (POD) of Earth orbiting satellites, it is important to investigate the impact of the different frames on the POD results.

In this study, we briefly introduce the different features of the ITRS realizations and elaborate how the data correction models (e.g., periodic variations vs. non-tidal loading corrections) of the different xTRF2020 solutions can be optimally applied for the POD of selected satellites tracked by Satellite Laser Ranging (SLR) stations. We conclude the study with results obtained for various orbital parameters, such as the scaling factor of the non-gravitational (non-conservative) accelerations as well as the estimated empirical accelerations. Finally, we summarize the optimal settings of each ITRS realization for the satellite PODs discussed in this paper (i.e., LAGEOS-1, LARES-2, Jason-1/2/3).

How to cite: Bloßfeld, M., Zeitlhöfler, J., Rudenko, S., and Seitz, M.: Application of ITRS 2020 realizations for the SLR-based POD of selected geodetic and Earth-observing satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5385, https://doi.org/10.5194/egusphere-egu24-5385, 2024.

14:10–14:20
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EGU24-5366
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ECS
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On-site presentation
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Contribution of SLR to satellite-only global gravity field model 
Barbara Suesser- Rechberger, Torsten Mayer-Guerr, Sandro Krauss, Patrick Dumitraschkewitz, Felix Oehlinger, and Cornelia Tieber-Hubmann

Combined satellite-only global gravity field models represent a combined solution of gravity field observations from multiple geodetic measurement principles and satellite missions. The advantage of such a combination is that it compensates for the weaknesses of individual observing techniques. However, when combining solutions estimated by different institutions, inconsistencies may arise due to the different algorithms and models used in the actually available software, leading to a deterioration in performance. To mitigate such performance degradation, it is advantageous to perform all evaluations with a uniform software package. Since our in-house Gravity Recovery Object Oriented Programming System (GROOPS) software tool has become a widely accepted tool in the scientific community, we have now also incorporated the Satellite Laser Ranging (SLR) functionality to ensure the continued development of the software. On this basis, the opportunity arises to uniformly determine all the contributions to the combined gravity field using a single software package. This contribution is intended as a preliminary study for the next Gravity Observation Combination (GOCO) model. In this regard, we present low-degree solutions based on SLR observations using GROOPS and compare them with findings from other research groups (e.g., Cheng et al. 2013, Krauss et al. 2019) as well as solutions based on the satellite mission GRACE and GRACE-FO.

How to cite: Suesser- Rechberger, B., Mayer-Guerr, T., Krauss, S., Dumitraschkewitz, P., Oehlinger, F., and Tieber-Hubmann, C.: Contribution of SLR to satellite-only global gravity field model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5366, https://doi.org/10.5194/egusphere-egu24-5366, 2024.

Discussion Post a comment
14:20–14:30
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EGU24-5649
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ECS
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On-site presentation
Stochastic Modeling of SLR Observations and its Impact on the Parameter Estimation 
Linda Geisser, Ulrich Meyer, Daniel Arnold, and Adrian Jäggi

Satellite Laser Ranging (SLR) observations are provided by a global station network of the International Laser Ranging Service (ILRS). Since almost all SLR stations are unique in terms of utilized equipment, e.g., laser system, photo-detector or timing devices, their measurement performances may slightly differ. Furthermore, the tracked satellites have various properties, e.g., material composition (number and type of retro-reflectors or mantel material), diameter, area-to-mass ratio, altitude or inclination, which have an impact on the measurement precision and the requirements on the background force modeling. A reliable estimation of geodetic parameters solely based on SLR can only be performed by combining SLR observations to several spherical satellites provided by the entire ILRS network. To take the quality of each individual SLR measurement into account, several stochastic models, e.g., static or time-variable station- and/or satellitespecific weights, are introduced and their impact on the parameter estimation is studied.

How to cite: Geisser, L., Meyer, U., Arnold, D., and Jäggi, A.: Stochastic Modeling of SLR Observations and its Impact on the Parameter Estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5649, https://doi.org/10.5194/egusphere-egu24-5649, 2024.

14:30–14:40
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EGU24-876
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ECS
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On-site presentation
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Optimizing Multi-GNSS Orbit Combination: A Comprehensive Study on Weighting Strategies and Outlier Detection ; 
Radosław Zajdel, Gustavo Mansur, Andreas Brack, Pierre Sakic, and Benjamin Männel

Combined precise satellite orbits and clocks stand as core contributions from the International GNSS Service (IGS), integrating the individual inputs of various Analysis Centers (AC). The availability and quality of multi-GNSS products developed by ACs within the IGS multi-GNSS Pilot Project propel IGS towards replacing combined GPS and GLONASS products with homogeneous combined products encompassing all GPS, GLONASS, Galileo, BeiDou, and QZSS systems. A primary challenge faced by the IGS lies in refining the combination algorithm for multi-GNSS orbits and clocks to provide users with the utmost quality products.

This study delves into concepts aimed at enhancing the orbit combination algorithm, with a specific focus on adjusting the weighting scheme and detecting outlier observations. The core of the combination methodology adheres to the concept proposed by GFZ, employing a least-squares framework wherein weights used for combining AC orbits are determined through least-squares variance component estimation (VCE).

Four distinct weighting strategies are introduced and compared in this study. These strategies involve utilizing either the constellation, satellite type, satellite type on the same orbital plane, or each satellite individually to form datasets used in determining weights for each AC. Furthermore, a novel approach is developed to correct the weights for individual ACs based on the results of Satellite Laser Ranging orbit validation. This serves as an additional factor in the combination, mitigating the impact of systematic AC-dependent orbit mismodeling issues. All proposed strategies underwent testing using multi-GNSS orbit solutions over a 10-month period in 2023.

Firstly, the combination results show an agreement between the different AC’s input orbits around 15, 20, 30, 50, and 100 mm for GPS, GLONASS, Galileo, BeiDou, and QZSS, respectively. Regarding the AC weighting strategy, the constellation-specific weighting approach provides the most robust solution and allows for handling differences between AC-specific issues in the orbit modeling of individual constellations. The satellite-specific weighting approach offers better resilience against the adverse effects caused by the inhomogeneous quality of satellite blocks/types/generations within a constellation, especially for BeiDou. However, the satellite-specific weighting encounters problems related to the appearance of invalid negative variances/weights for individual satellites as the output of VCE, mainly for BDS-3 and QZSS. The negative variance component can be an important indication of defects in our variance component model. Grouping satellites of similar characteristics in a satellite-type-specific weighting approach increases redundancy and reduces the issue but not entirely. Ultimately, we demonstrate potential solutions to address this issue. This involves simplifying the iterated VCE or resorting to the legacy inverse mean square differences between the mean orbit and the AC’s orbits as weights, particularly in cases where the classic VCE proves ineffective.

How to cite: Zajdel, R., Mansur, G., Brack, A., Sakic, P., and Männel, B.: Optimizing Multi-GNSS Orbit Combination: A Comprehensive Study on Weighting Strategies and Outlier Detection ;, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-876, https://doi.org/10.5194/egusphere-egu24-876, 2024.

Discussion Post a comment
14:40–14:50
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EGU24-16819
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On-site presentation
The Galileo for Science project: Non-Conservative Forces modeling for the Galileo FOC satellites 
Carlo Lefevre, Massimo Visco, David Lucchesi, Feliciana Sapio, Roberto Peron, Marco Cinelli, Alessandro Di Marco, Emiliano Fiorenza, Pasqualino Loffredo, Marco Lucente, Carmelo Magnafico, Francesco Santoli, and Francesco Vespe

The Galileo for Science Project (G4S_2.0) is funded by the Italian Space Agency and has several goals in the field of Fundamental Physics to be achieved by exploiting the satellites of the Galileo-FOC Constellation. In this regard, a key point is to obtain a suitable satellite orbit solution by performing an accurate Precise Orbit Determination (POD). To this purpose modeling in a reliable way the complex effects of the Non-Conservative Forces, i.e. of Non-Gravitational Perturbations (NGPs), is essential. The activities undertaken in the construction of a Box-Wing model and of a Finite Element Model of the satellite will be presented with the preliminary results obtained by including these models into the POD of the Galileo satellites. In particular, using the orbital element residuals obtained from a POD we can test our new models and the improvements in POD quality.

How to cite: Lefevre, C., Visco, M., Lucchesi, D., Sapio, F., Peron, R., Cinelli, M., Di Marco, A., Fiorenza, E., Loffredo, P., Lucente, M., Magnafico, C., Santoli, F., and Vespe, F.: The Galileo for Science project: Non-Conservative Forces modeling for the Galileo FOC satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16819, https://doi.org/10.5194/egusphere-egu24-16819, 2024.

14:50–15:00
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EGU24-10767
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ECS
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Virtual presentation
Solar radiation pressure modeling for BDS-3 MEO satellites precise orbit determination
(withdrawn)
Chao Yang, Jing Guo, and Xiaolong Xu
15:00–15:10
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EGU24-16959
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On-site presentation
Review the IGS Strategy for Precise Point Positioning Applications 
Rolf Dach, Daniel Arnold, Elmar Brockmann, Maciej Kalarus, Lars Prange, Stefan Schaer, Pascal Stebler, and Adrian Jäggi

Within the IGS, it was agreed that Precise Point Positioning (PPP) based on satellite orbit and clock corrections of the IGS analysis centers allow a direct access to the IGS realization of the International Terrestrial Reference Frame (ITRF). This convention is considered convenient for all PPP users and should not be changed in future.

On the other hand, the groups determining the GNSS satellite orbits do prefer an origin of the frame that is related to the Earth instantaneous center of mass since this is the reference of the gravitational orbit force model. With this background, some discussions take place to change the convention related to the origin of the terrestrial frame because it is convenient for the orbit determination. This convention is, however, in contradiction to the expected needs of the PPP users that do prefer a stable coordinate origin in time.

We will introduce a strategy to serve both needs by applying the center of mass corrections for the orbit determination only.

How to cite: Dach, R., Arnold, D., Brockmann, E., Kalarus, M., Prange, L., Schaer, S., Stebler, P., and Jäggi, A.: Review the IGS Strategy for Precise Point Positioning Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16959, https://doi.org/10.5194/egusphere-egu24-16959, 2024.

15:10–15:20
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EGU24-19764
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ECS
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On-site presentation
Combined Orbit Determination Based on Carrier-Range observation
(withdrawn)
Hengyi Wang, Xingyu Zhou, Zilu Cui, and Hua Chen
15:20–15:30
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EGU24-7776
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ECS
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On-site presentation
Enhanced orbit determination for BDS-3 satellites with LEO onboard GNSS and inter-satellite link data 
Hanlin Chen, Tao Geng, Xin Xie, Qiang Li, Xing Su, and Qile Zhao

All BeiDou global navigation satellite system (BDS-3) satellites are equipped with Ka-band inter-satellite link (ISL) payloads to achieve the inter-satellite ranging and communication. With the rapid development of low earth orbit (LEO) satellites, the LEO onboard BDS-3 observations also become available. The LEO onboard and ISL data can be an effective supplement for precise orbit determination (POD) of the BDS-3 satellite. In this research, we processed the integrated POD of BDS-3 and LEO satellites with the real ground station, LEO onboard GNSS, and ISL observations. To analyze the contribution of different data to BDS-3 POD accuracy, four POD schemes are present: ground stations only, ground stations + 1 LEO, ground stations + ISL, and ground stations + 1 LEO + ISL. The ground tracking data are from about 40 globally distributed ground stations and 10 stations in Asia-Pacific region, respectively. The LEO onboard GNSS observations are from a dual-constellation GNSS receiver of the LUTAN-01A satellite, which is a Chinese LEO synthetic-aperture-radar (SAR) satellite for geological observation. The Ka-band observations from more than 400 ISL established between BDS-3 satellites are also used in the integrated POD. The obtained orbits are evaluated by orbit overlaps comparison, the comparison with IGS analysis center precise orbits, and SLR (satellite laser ranging) validation. Compared to the POD using the observation of only 10 ground stations, the addition of 1 LEO onboard GNSS or ISL observations can improve the orbit accuracy of BDS-3 by more than 60%. Furthermore, adding both LEO onboard GNSS and ISL observations simultaneously can lead to further improvements in BDS-3 orbit accuracy.

How to cite: Chen, H., Geng, T., Xie, X., Li, Q., Su, X., and Zhao, Q.: Enhanced orbit determination for BDS-3 satellites with LEO onboard GNSS and inter-satellite link data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7776, https://doi.org/10.5194/egusphere-egu24-7776, 2024.

15:30–15:40
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EGU24-13048
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On-site presentation
Precise Relative Navigation in Medium Earth Orbits with Global Navigation Satellite Systems and Intersatellite Links for Black Hole Imaging 
María Salas, Jaime Fernández, and Jose van den IJssel
The Event Horizon Telescope (EHT) is a ground-based array of Very Long Baseline Interferometry (VLBI) telescopes designed to image the event horizon of black holes. To overcome its limitations, this work explores a mission concept involving a two-satellite constellation of VLBI telescopes deployed in circular and polar Medium Earth Orbit (MEO) at more than 8000 km altitude.  The attainment of high-resolution black hole images requires extremely precise baseline determination at the few millimetre level. To address this challenge, each satellite within the constellation is equipped with two Global Navigation Satellite System (GNSS) receivers and an optical Intersatellite Link (ISL) for relative navigation. This work assesses the feasibility of achieving highly accurate relative positioning within the constellation, particularly considering the large intersatellite distances involved.

The methodology employed in this simulation study encompasses several steps. Initially, the satellite orbits are estimated independently for each satellite using GNSS observations. Following this, the orbit of one of the satellites is held fixed as a reference, while the orbit of the other satellite is re-estimated by incorporating the ISL observations. To enhance the accuracy of the orbit estimation, integer GNSS ambiguity resolution is implemented in the precise orbit determination process. The simulated data incorporates an extensive set of realistic error sources, including thermal noise, instrumental delays, clock biases, errors in the GNSS ephemerides and clocks, uncertainties in the geopotential and solar radiation pressure models, and white noise in the ISL observations.

The results highlight the importance of integer ambiguity resolution in meeting the stringent relative navigation requirements of the mission. The analysis also reveals that the ISL observations primarily improve the baseline estimation along the direction of the link itself. However, in the direction of the black hole, the impact of ISL observations is minimal, indicating that the ISL does not significantly contribute to meeting the specific relative navigation requirements. Furthermore, the study identifies that large intersatellite distances lead to degraded relative orbit accuracy due to fewer shared errors between the two satellites. The work will show the accuracy obtained with the simulations, the assumptions considered, and the next steps needed.

How to cite: Salas, M., Fernández, J., and van den IJssel, J.: Precise Relative Navigation in Medium Earth Orbits with Global Navigation Satellite Systems and Intersatellite Links for Black Hole Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13048, https://doi.org/10.5194/egusphere-egu24-13048, 2024.

Coffee break
Chairpersons: Adrian Jaeggi, Alexandre Couhert, Jose van den IJssel
16:15–16:25
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EGU24-12683
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On-site presentation
GNSS-based orbit and geodetic parameter estimation by means of simulated GENESIS data 
Daniel Arnold, Alexandra Miller, Cyril Kobel, Oliver Montenbruck, Peter Steigenberger, and Adrian Jäggi

The ESA GENESIS mission, which obtained green light at ESA's Council Meeting at Ministerial Level in November 2022 and which is expected to be launched in 2027, aims to significantly enhance the accuracy and stability of the Terrestrial Reference Frame (TRF). This shall be achieved by equipping one satellite at approximately 6000 km altitude with well-calibrated instruments for all four space-geodetic techniques contributing to TRF realizations, i.e., Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and by exploiting the such realized very precise space collocations.

The GENESIS satellite is foreseen to carry a zenith- and nadir-pointing GNSS antenna to track (at least) GPS and Galileo signals. Because of its very high altitude, GENESIS will cover much larger nadir angles as seen from the GNSS transmitting antennas, compared to receivers at ground or in low Earth orbit. This will partly result in GNSS observations with lower signal-to-noise ratios. Furthermore, to date, only little reliable information is available on the GNSS transmit antenna gain and carrier phase patterns at very large nadir angles. These problems lead to questions with respect to the best possible exploitation of GNSS data by GENESIS, e.g., whether phase pattern calibrations will need to be performed by means of tracked GNSS data (which would weaken the GNSS contribution to GENESIS).

The aim of this study is to assess the impact of GNSS transmit antenna phase pattern errors on the GNSS-based POD of GENESIS, as well as global GNSS network solutions for GNSS orbits and clock corrections, Earth rotation and geocenter parameters and station coordinates based on GNSS observations from GENESIS and terrestrial stations. To accomplish this, we employ simulated GNSS pseudo-range and carrier phase data for GENESIS and ground stations, which have been generated based on detailed link-budget computations and a comprehensive set of transmit antenna gain patterns. The data are used for closed-loop simulation investigations, which allow to compare the reconstructed orbit and geodetic parameter solutions to the simulation truth and offer a quantification of the impact of transmit antenna phase pattern uncertainties on the estimated parameters.

How to cite: Arnold, D., Miller, A., Kobel, C., Montenbruck, O., Steigenberger, P., and Jäggi, A.: GNSS-based orbit and geodetic parameter estimation by means of simulated GENESIS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12683, https://doi.org/10.5194/egusphere-egu24-12683, 2024.

16:25–16:35
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EGU24-6359
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ECS
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On-site presentation
Sensitivity of different variants of GENESIS orbit to global geodetic parameters 
Tomasz Kur and Krzysztof Sośnica

The GENESIS mission plays a pivotal role in the FutureNAV program envisioned by the European Space Agency. This groundbreaking venture aims to co-locate four space geodetic techniques on a single platform in space. One of the primary mission objectives is accurately determining geodetic parameters, including geocenter motion, low-degree gravity field, Earth rotation parameters, and the positions of ground stations in tracking networks. Although preliminary satellite inclination and altitude were provided, there is untapped potential for studying ways to enhance the efficiency of incorporating GENESIS into geodetic products.

This research focuses on the preliminary optimization of GENESIS orbital parameters – semi-major axis, inclination, and eccentricity- to assess the benefits arising from diverse observation geometries on geodetic products. The analysis is based on simulations of different variants of GENESIS orbital parameters tracked by a network of 20 satellite laser ranging (SLR) stations. We provide GENESIS-only solutions as well as the combined solution with a selected subset of geodetic satellites that are used today or in the future for the realization of the terrestrial reference frames: LAGEOS-1, LAGEOS-2, LARES-1, and LARES-2. GENESIS will be equipped with two GNSS receivers contributing to high-accuracy orbit determination, serving as a priori parameters for SLR-based solutions. Therefore, we check the GENESIS sensitivity to global geodetic parameters, assuming that the precise orbits are not derived from SLR but can be well-defined from other techniques.

We study the impact of different GENESIS orbits on the gravity potential parameters, especially the zonal terms, Earth rotation parameters, and geocenter coordinates. Our findings underscore that, through meticulous processing, GENESIS has the potential to significantly contribute to achieving the goals of the Global Geodetic Observing System (GGOS), particularly in terms of refining the Z component of the geocenter coordinates.

How to cite: Kur, T. and Sośnica, K.: Sensitivity of different variants of GENESIS orbit to global geodetic parameters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6359, https://doi.org/10.5194/egusphere-egu24-6359, 2024.

16:35–16:45
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EGU24-2806
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ECS
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On-site presentation
Potential of VLBI observations to satellites to estimate orbital elements  
Helene Wolf, Johannes Böhm, and Urs Hugentobler

Orbital elements define the shape, size, and orientation of a satellite’s orbit, as well as the position of the orbiting satellite along the ellipse at a specific time. Currently, precise orbit determination relies solely on satellite observations. However, future plans involve equipping Genesis and Galileo satellites with Very Long Baseline Interferometry (VLBI) transmitters. This would enable to observe satellites with VLBI radio telescopes and allow to determine orbital elements from VLBI observations to satellites.

This study investigates the potential of VLBI observations to satellites to contribute to the determination of orbital elements. In a first step, schedules, including satellite and quasar observations, are created using VieSched++.  The Vienna VLBI and Satellite Software (VieVS) is used to simulate and analyze these schedules.  To introduce the orbital elements in the Least Squares Adjustment, the partial derivatives of the position vector with respect to the orbital elements are needed. There are different approaches available for computing these partials, including numerical, analytical, or using partials obtained from the ORBGEN module in the Bernese GNSS software.  Next, the partials of the position vector are utilized to determine the partial derivative of the time delay tau with respect to the orbital elements.

This enables the estimation of orbital elements from simulated VLBI observations to satellites. The estimated parameters' quality is evaluated based on the mean formal errors and repeatabilities. Furthermore, the correlations between all orbital elements are examined.

How to cite: Wolf, H., Böhm, J., and Hugentobler, U.: Potential of VLBI observations to satellites to estimate orbital elements , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2806, https://doi.org/10.5194/egusphere-egu24-2806, 2024.

16:45–16:55
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EGU24-16139
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ECS
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On-site presentation
On the potential of highly accurate clocks and inter-satellite clock synchronization for GNSS satellite precise orbit and geocenter determination 
Patrick Schreiner, Susanne Glaser, Rolf König, Karl Hans Neumayer, Shrishail Raut, and Harald Schuh

Improving the concepts of Global Navigation Satellite Systems (GNSS) has become a vital task for subsequent GNSS applications like the determination of the Terrestrial Reference Frame (TRF). A promising goal is the reduction of uncertainties in non-conservative force modeling such as Solar Radiation Pressure (SRP) modelling in Precise Orbit Determination (POD) and the effect on the estimated orbits and geocenter coordinates. In previous simulation studies, accelerometers on next-generation GNSS satellites have proven to be a promising opportunity. In this way, the periodic signals in the estimated geocenter coordinates induced by SRP mismodeling can be eliminated regardless of the angle of the Sun to the satellite and its orbital plane. At the same time, the satellite clock can be effectively decoupled from the satellite position estimates. In this study, we focus on the impact of highly accurate clocks and the synchronization of clocks between satellites, which would make it possible to estimate common clock parameters for the synchronized satellites. In doing so, we start with Galileo-type POD using prior simulated observations with the assumption of perfectly known clocks. Then, we simulate various scenarios assuming different clock models and compare the results with the perfect case scenario. This procedure will explore the potential of various ground reference and satellite clock accuracies. Additionally, we use inter-satellite links to synchronize the satellite clocks over one and over multiple orbital planes. Finally, we strive to assess the potential of improved clock modeling on the TRF, focusing on the estimation of geocenter coordinates.

How to cite: Schreiner, P., Glaser, S., König, R., Neumayer, K. H., Raut, S., and Schuh, H.: On the potential of highly accurate clocks and inter-satellite clock synchronization for GNSS satellite precise orbit and geocenter determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16139, https://doi.org/10.5194/egusphere-egu24-16139, 2024.

16:55–17:05
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EGU24-18289
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ECS
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On-site presentation
The Galileo for Science project: Constraints on Dark Matter with the Galileo-FOC Constellation 
Alessandro Di Marco, Feliciana Sapio, Massimo Visco, David Lucchesi, Marco Cinelli, Emiliano Fiorenza, Carlo Lefevre, Pasqualino Loffredo, Marco Lucente, Carmelo Magnafico, Roberto Peron, Francesco Santoli, and Francesco Vespe

The Galileo for Science Project (G4S_2.0) is funded by the Italian Space Agency and has
several goals in the field of Fundamental Physics to be achieved by exploiting the satellites
of the Galileo-FOC Constellation and the accuracy of their onboard atomic clocks. In
particular, the clock-bias, estimated in the data reduction of the tracking observations
allows to place constraints on the possible presence of Dark Matter in our galaxy in the
form of Domain Walls (DW) eventually produced in the very early Universe by ultralight
scalar field(s). The impact of the DW on an atomic clock would provide a delta-like
transient shift on the pseudo-derivative of the clock-bias. Such signal depends both on the
nature of the clock and the characteristics of the ultralight scalar comprising the DW.
Ongoing work on the clock-bias will be introduced as regards to data pre-processing and
simulations on false alarm and detection efficiency.

How to cite: Di Marco, A., Sapio, F., Visco, M., Lucchesi, D., Cinelli, M., Fiorenza, E., Lefevre, C., Loffredo, P., Lucente, M., Magnafico, C., Peron, R., Santoli, F., and Vespe, F.: The Galileo for Science project: Constraints on Dark Matter with the Galileo-FOC Constellation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18289, https://doi.org/10.5194/egusphere-egu24-18289, 2024.

17:05–17:15
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EGU24-8756
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On-site presentation
Copernicus POD Service – Impact of High Solar activity on POD 
Sonia Lara Espinosa, Carlos Fernández, Marc Fernández, Heike Peter, and Pierre Féménias

The Copernicus Precise Orbit Determination (CPOD) Service delivers, as part of the Ground Segment of the Copernicus Sentinel-1, -2, -3, and -6 missions, orbital products and auxiliary data files for their use in the corresponding Payload Data Ground Segment (PDGS) processing chains at ESA and EUMETSAT, and to external users through the newly available Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).

For the last few years, a progressive degradation of the accuracy of some of the CPOD orbital products has been observed, caused by the increasing solar activity. Solar activity follows an 11-year cycle, and since the minimum in 2020, overall solar activity has been higher and geomagnetic storms have been happening more often. This has two impacts on POD: a more “turbulent” atmosphere which brings higher frequency density changes, making the modelling of the satellite´s drag more challenging, and an increase of ionospheric scintillation, particularly over the polar regions, that causes an increase of the GNSS carrier phase noise.

This study aims at characterising better the impact of the solar activity on the different POD products, with a focus on the degradation of orbit determination and predictions required by the Sentinel-1 mission. Overall tendencies since the solar minimum in 2020 are analysed, including a detailed look on strong geomagnetic storms. Mitigation strategies to overcome this situation are evaluated, namely adapting the POD processing dynamic parametrisation, and updating the solar activity proxies (particularly the geomagnetic indexes) more frequently.

How to cite: Lara Espinosa, S., Fernández, C., Fernández, M., Peter, H., and Féménias, P.: Copernicus POD Service – Impact of High Solar activity on POD, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8756, https://doi.org/10.5194/egusphere-egu24-8756, 2024.

17:15–17:25
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EGU24-7841
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ECS
|
On-site presentation
Tuning thermal reradiation pressure accelerations for Sentinel-6 
Kristin Vielberg, Jürgen Kusche, and Heike Peter

For radar altimetry missions such as Sentinel-6, a precise orbit is mandatory for deriving reliable sea surface heights. In addition to accurate tracking measurements, precise orbit determination relies on high-fidelity non-gravitational force models. At 1300km the solar radiation pressure (SRP), which varies mainly with the satellite’s orientation towards the Sun, is the dominating non-gravitational force. Additionally, the acceleration due to the Earth radiation pressure (ERP) acts on the satellite and decreases with increasing satellite altitude. As the radiation of Sun and Earth is partly absorbed at the satellite’s surface, the satellite experiences an additional force due to the thermal reradiation of heat (thermal reradiation pressure, TRP). Aerodynamic forces are in constrast negligible at around 1300km altitude.

In previous investigations, we extended the conventional radiation pressure force models with a focus on a GRACE-like satellite. Our SRP and ERP model extensions can be easily applied to other satellites with available geometry and thermo-optical material properties. However, transferring the heat-conductive TRP model to other satellites is more challenging, as assumptions on the materials’ thermal diffusivity and thickness as well as inner heat sources need to be made to adequately model the satellite’s surface temperature.

In this study, we attempt to develop a TRP force model for Sentinel-6. We depart from GRACE settings and refine our model stepwise. Boundary conditions are updated and the material properties are replaced with available information or assumptions. Then, a stepwise tuning is necessary to match the modelled surface temperatures with thermistor measurements. We choose one beta cycle during the year 2023 for our experiments. Preliminary investigations reveal that the tuning of the satellite’s thermal properties varies strongly with the beta angle.

How to cite: Vielberg, K., Kusche, J., and Peter, H.: Tuning thermal reradiation pressure accelerations for Sentinel-6, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7841, https://doi.org/10.5194/egusphere-egu24-7841, 2024.

17:25–17:35
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EGU24-20733
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On-site presentation
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Tailored accelerometer calibration by POD for thermospheric density computation with GRACE and GRACE-FO 
Florian Wöske, Benny Rievers, and Moritz Huckfeldt

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites. Especially the accelerometers of geodetic satellites, measuring the non-gravitational accelerations acting on them are a very viable observation.

The density estimation is mainly based on three separate disciplines, which are: (1) Precise radiative non-gravitational force modelling, (3) Modelling of the interaction between the rarefied atmospheric gases and the satellite, i.e. modelling of drag coefficients, and (3) the calibration of the accelerometer data by dynamic Precise Orbit Determination (POD). This contribution focuses mainly on the last point. Nevertheless, we also validate the modelled radiative accelerations and use them as reference for the calibration results.

The accelerometers of all geodetic satellites are affected by a drifting bias and scale factors unequal to one. Therefore a calibration of the data is indispensable. Usually time dependent bias and scale factors are estimated. For standard POD or Gravity Field Recovery (GFR) these parameters are estimated together with empiric and other model parameters. In both cases, the estimated accelerometer calibration parameters are not of major interest, but improve the orbit fit or gravitational field coefficients. The used parametrizations and weighting strategies of the observation data, do not give realistic or physical accelerometer calibration results because parameters are not sensitive and effects are absorbed or smeared into other parameters and models. This is unsatisfying, especially for the anticipated use for the density determination.

In this contribution we use dynamic POD and investigate different parametrization strategies tailored for a physical accelerometer calibration. We investigated the effect of constraining the accelerometer calibration parameters in that way, that a continuous calibration over all arcs is achieved, where normally each arc is treated locally separated from all other arcs. The scale factor is concurrently estimated, but over a longer batch of arcs. We varied the length between one day and years. Furthermore, different calibration equations, different observation data and combinations (kinematic positions, science orbit data, inter-satellite ranging), weighting strategies, initial parameters and pre-processing of the accelerometer data is investigated. The validation of the results is not easy, because usual metrics like post-fit residuals do not reflect the quality of the accelerometer calibration. We introduce a validation approach using the modelled non-gravitational forces and also show the influence of the different calibration options on the resulting density or drag acceleration.

All results and data for the whole GRACE and GRACE-FO missions are available on our data server (link in presentation/ uploaded material). 

How to cite: Wöske, F., Rievers, B., and Huckfeldt, M.: Tailored accelerometer calibration by POD for thermospheric density computation with GRACE and GRACE-FO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20733, https://doi.org/10.5194/egusphere-egu24-20733, 2024.

Discussion Post a comment
17:35–17:45
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EGU24-827
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ECS
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On-site presentation
Improving Orbit Propagation of LEO Satellites Using Atmospheric Drag Analysis    
Soumyajit Dey, Phillip Anderson, and Aaron Bukowski

The variability of the atmospheric drag force on satellites is influenced by several factors, which include neutral density and gas composition, solar activity, and the orientation and shape of the satellite. During periods of geomagnetic activity, changes in these properties contribute to significant variations in the drag force, impacting the satellite trajectory. Therefore, the atmospheric drag force is considered as one of the largest sources of error in the orbit estimation for Low Earth Orbit (LEO) satellites. The methods presently used for satellite orbit determination define a constant term to represent the drag force, which can result in significant errors in long-term propagation and prediction of satellite positions. This work aims to improve SGP4 orbit propagation method by updating the drag term at regular intervals. The estimation of the drag term implements atmospheric drag analysis, which involves calculating the satellite drag coefficients using different Gas-Surface Interaction (GSI) models and neutral density data from Global Ionosphere Thermosphere Model (GITM) to estimate the mean motion derivative. The results demonstrate improved orbit propagation and estimation of orbital decay for the Gravity Recovery and Climate Experiment (GRACE) and Communication/Navigation Outage Forecasting System (C/NOFS) satellites during selected periods containing quiet and storm times.

How to cite: Dey, S., Anderson, P., and Bukowski, A.: Improving Orbit Propagation of LEO Satellites Using Atmospheric Drag Analysis   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-827, https://doi.org/10.5194/egusphere-egu24-827, 2024.

17:45–17:55
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EGU24-3521
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ECS
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On-site presentation
In-flight GNSS phase map calibration modelling with Zernike polynomials 
Adrian Baños Garcia

GNSS processing for POD suffers from systematic errors when the location of the instantaneous phase center is not known
with a few millimeter accuracy. The traditional approach to model the GNSS phase center origin and variations is to
determine antenna phase maps iteratively from the residuals. A more direct approach consists in modeling the antenna
phase map through an expansion in well-chosen Zernike polynomials, in order to reduce potential correlations with dynamic
modeling errors. This strategy has been applied to derive the GNSS antenna phase maps of several altimetry missions such
as Sentinel-3A, Jason-3, Sentinel-6 MF and SWOT. The derived phase corrections were tested on CNES POE-G GNSS-only
reduced-dynamic orbit solutions to assess their impact and validate their benefits owing to independent SLR observations. 

How to cite: Baños Garcia, A.: In-flight GNSS phase map calibration modelling with Zernike polynomials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3521, https://doi.org/10.5194/egusphere-egu24-3521, 2024.

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X2

Display time: Thu, 18 Apr 14:00–Thu, 18 Apr 18:00
Chairperson: Adrian Jaeggi
X2.1
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EGU24-8672
Copernicus POD Service – POD RESULTS BASED ON DORIS 
Marc Fernández, Carlos Fernández, Heike Peter, Pierre Féménias, and Carolina Nogueira Loddo

The Copernicus Precise Orbit Determination (CPOD) Service delivers, as part of the Ground Segment of the Copernicus Sentinel-1, -2, -3, and -6 missions, orbital products and auxiliary data files for their use in the corresponding Payload Data Ground Segment (PDGS) processing chains at ESA and EUMETSAT, and to external users through the newly available Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).

The CPOD Service is based on FocusPOD, a suite of tools for POD and geodesy powered by GMV MAORI, a new GMV in-house Flight Dynamics & Geodesy library, written from scratch in modern C++ and python. The CPOD Service makes use of GNSS measurements to generate the orbital products, and of Satellite Laser Ranging (SLR) measurements for validation purposes. Recently, DORIS-processing capabilities have been added to FocusPOD to generate orbit solutions based on this geodetic technique, which is available on-board Sentinel-3 and -6 missions.

The purpose of this work is to present the DORIS processing capabilities recently developed, including DORIS RINEX data parsing, observation preprocessing steps, and precise orbit determination results. The highlight will be the achievable accuracy based on DORIS and an analysis of the obtained residuals depending on the chosen parametrisation, including validation against GNSS-based solutions and SLR.

How to cite: Fernández, M., Fernández, C., Peter, H., Féménias, P., and Nogueira Loddo, C.: Copernicus POD Service – POD RESULTS BASED ON DORIS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8672, https://doi.org/10.5194/egusphere-egu24-8672, 2024.

X2.2
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EGU24-5427
Orbit parameterization aspects in global solutions of spherical Laser Ranging Satellites 
Ulrich Meyer, Linda Geisser, Daniel König, Rolf Dach, Daniela Thaller, and Adrian Jäggi

Laser ranging to spherical satellites is a major source for the determination of geophysical and geometric parameters like the scale of the reference system and the lowest degree (1-2) gravity field coefficients, i.e. geocenter motion, dynamic oblateness and the orientation of the rotation axis of the Earth. The International Laser Ranging Service (ILRS) is collecting Satellite Laser Ranging (SLR) observations of a global station network, providing the range data as normal points to its analysis centers, which perform precise orbit determination (POD) and network solutions based on 7 day orbital arcs. Currently, efforts are undertaken to extend the classical ILRS processing of the LAGEOS and ETALON satellites by LARES 2, as well as lower-flying satellites, i.e. LARES, Stella and Starlette, necessitating an adaption of the SLR-POD model and parametrization due to the increased sensitivity to orbit perturbations at low orbit altitudes.

We present the status of the SLR-POD at AIUB, where in support of the ILRS analysis center at BKG the incorporation of the low-flying SLR satellites into the 7 day POD and network solution of LAGEOS/ETALON/LARES-2 is beeing tested, making use of long-arc stacking techniques of daily arcs to continuous 7 day arcs. All orbit and geophysical parametes are estimated in one common estimation process to avoid implicit regularization by apriori information. Special attention is paid to the co-estimation of the low-degree gravity field coefficients and the correlations with the empirical dynamic parameters deployed in the classical LAGEOS/ETALON POD model.

How to cite: Meyer, U., Geisser, L., König, D., Dach, R., Thaller, D., and Jäggi, A.: Orbit parameterization aspects in global solutions of spherical Laser Ranging Satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5427, https://doi.org/10.5194/egusphere-egu24-5427, 2024.

X2.3
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EGU24-7245
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ECS
LEO constellation optimization for BDS precise orbit determination in LEO enhanced BDS
(withdrawn)
Tianhao Wu, Bofeng Li, and Haibo Ge
X2.4
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EGU24-8395
Assessment of GPS-based accelerometry performance with adaptive filter settings 
Jose van den IJssel, Christian Siemes, and Pieter Visser

High-quality GPS observations from low Earth orbiting (LEO) satellites can be used to derive thermosphere densities along the satellite orbit. Such GPS-derived densities are currently computed operationally for all three Swarm satellites, in the framework of the Swarm Data, Innovation, and Science Cluster. Considering the increasing number of LEO satellites equipped with GPS receivers, this so-called GPS-based accelerometry approach offers great potential for improving thermosphere models and for studying the influence of solar and geomagnetic activity on the thermosphere.

To better quantify the accuracy that can be obtained with this approach, we assess the performance using the GRACE mission as a test case. For this mission high quality accelerometer data are available, which we can use to validate our GPS-based results. In addition, the GRACE mission has experienced a large variation in density signals, which allows us to assess the performance under a large range of conditions.

We present our GPS-based accelerometry processing strategy, which is based on a Kalman filter approach. The radiation pressure accelerations are accurately modelled and empirical accelerations capture the remaining aerodynamic signal. The empirical accelerations are modeled as Gauss-Markov processes defined by a steady-state variance, process noise and correlation time, which require careful tuning. This applies in particular to the setting of the process noise in the along-track direction, due to the large variations in the encountered aerodynamic signal. Best performance is obtained when the process noise setting is adapted to these variations. Using these adaptive filter settings, results are shown for periods with low, moderate, and high density. In a next step, we will implement the improved filter settings into our regular Swarm GPS-derived density processing chain.

How to cite: van den IJssel, J., Siemes, C., and Visser, P.: Assessment of GPS-based accelerometry performance with adaptive filter settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8395, https://doi.org/10.5194/egusphere-egu24-8395, 2024.

X2.5
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EGU24-16732
Precise orbit determination for the maneuvering satellites 
Maciej Kalarus, Daniel Arnold, Sebastiano Padovan, Rolf Dach, and Adrian Jäggi

Routine and occasional/emergency orbital maneuvers are essential for many satellites to maintain their optimal trajectory and to achieve a wide range of operational objectives in a continuous way. However, incorrectly modelled highly dynamic changes of the orbit during maneuvers can significantly reduce the accuracy of precise orbit determination (POD) to an extent that is unacceptable for scientific requirements.

The aim of this study is to investigate strategies for maneuver handling of Low Earth Orbiting (LEO) satellites based on observations from on-board GNSS receivers complemented by a priori knowledge of thrust intensity and maneuver epochs that are provided by telemetry measurements. Assuming that the initial information is subject to instrumental biases, corrections for the maneuver accelerations are estimated together with nominal deterministic and pseudo-stochastic orbit parameters such as instantaneous velocity changes and piecewise constant accelerations.

Several estimation strategies are tested using recent developments in the Bernese GNSS software, which is continuously maintained and further developed at the Astronomical Institute of the University of Bern (AIUB). In particular, the test cases cover single long/short maneuvers as well as two consecutive maneuvers within one orbital arc. Depending on the length of the maneuver and the number of available observations, different polynomial functions (up to degree 2) are used to model the thrust acceleration. Finally, the quality of the solution is evaluated internally by comparing it to the days without maneuvers and by checking the consistency between the reduced dynamic and kinematic orbit. External validation is also performed with respect to the official independent products.

How to cite: Kalarus, M., Arnold, D., Padovan, S., Dach, R., and Jäggi, A.: Precise orbit determination for the maneuvering satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16732, https://doi.org/10.5194/egusphere-egu24-16732, 2024.

X2.6
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EGU24-16831
Assessment of Jason-3 and Sentinel-6 MF radiation pressure model 
Eléonore Saquet, Marie Cherrier, Alexandre Couhert, and Flavien Mercier

Since the launch of Seasat (1978), the first satellite to study ocean topography, our knowledge of the rise of 
mean sea level has evolved. Since then, 18 additional satellites were launched, with more and more satellite 
missions (up to 10 satellites are now simultaneously flying) dedicated to the measurement of the global and 
regional sea-surface height, carrying on board state of the art precision orbit determination tracking techniques 
and instruments. 


Jason-3 (2016) and Sentinel-6 MF (2020) are part and parcel of these ocean topography missions. The two 
reference satellites were operated in tandem (with Sentinel-6 MF flying 30 seconds behind its predecessor) 
between mid-December 2020 to April 2022 for calibration purposes. The main difference between these two 
satellites has to do with their respective platform design. Indeed, Sentinel-6 MF solar panels are fixed on the 
satellite and has an almost fixed attitude, unlike Jason-3 which has some yaw steering periods. 


In this study, we focus on the solar radiation pressure modeling errors of both Sentinel-6 MF and Jason-3 
during their tandem phase (4.5 beta cycles). The idea is to analyze the estimated empirical accelerations of 
these two satellites as a function of their beta angle. The Solar Radiation Pressure (SRP) depends only on two 
parameters: the orbital angle with respect to the sub-solar point and the beta angle. We will then propose 
updates of the SRP models. The effect of the terrestrial radiative perturbations will also be assessed.

How to cite: Saquet, E., Cherrier, M., Couhert, A., and Mercier, F.: Assessment of Jason-3 and Sentinel-6 MF radiation pressure model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16831, https://doi.org/10.5194/egusphere-egu24-16831, 2024.

X2.7
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EGU24-19842
Treatment of Modern Global Ocean and Atmospheric Tide Atlases in Precise Orbit Determination 
Volker Klemann, Roman Sulzbach, Alexander Kehm, Mathis Blossfeld, Michael Hart-Davis, Henryk Dobslaw, and Torsten Mayer-Guerr

Tidal variability originating from the orbital dynamics of the Sun and the Moon can be observed in virtually all subsystems of the Earth. The evoked tidal phenomena in the atmosphere, the solid Earth, and the world oceans cause a large-scale redistribution of masses, primarily on daily and sub-daily time scales. The implied tidal variability impacts geodetic measurements. For example, the induced mass transport induces temporal changes in the Earth's gravity field which impact the orbits of artificial satellites. However, observations of a single satellite are generally insufficient to precisely estimate tidal signatures, resulting in a decreased accuracy of the Precise Orbit Determination (POD) of near-Earth satellites. Therefore, a priori prediction of tidal signals, especially ocean tidal signatures, by tidal atlases is necessary to exploit the full potential of geodetic data sets.

The most accurate ocean tide atlases are produced by incorporating satellite altimetry observations into the modeling process. However, limitations arising from the ambient signal-to-noise level have hindered their ability to accurately estimate small signals associated with minor tidal constituents. For those minor constituents, data-unconstrained ocean tide models can yield valuable constraints. For processing satellite altimetry data, initial experiments have been undertaken to integrate empirical and numerical models, aiming to deliver comprehensive tidal corrections (Hart-Davis et al., 2021, doi: 10.3390/rs13163310). It has been proposed that experimentation is necessary across all geodetic applications to determine the preferred model for specific tidal constituents and the optimal approach for merging models. This also includes the possibility of including minor ocean tides only implicitly, by deriving their admittance function from suitable neighboring tidal constituents.

How to cite: Klemann, V., Sulzbach, R., Kehm, A., Blossfeld, M., Hart-Davis, M., Dobslaw, H., and Mayer-Guerr, T.: Treatment of Modern Global Ocean and Atmospheric Tide Atlases in Precise Orbit Determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19842, https://doi.org/10.5194/egusphere-egu24-19842, 2024.

X2.8
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EGU24-18467
On multi technique precise orbit determination for SWOT with respect to altimetry applications. 
Anton Reinhold, Patrick Schreiner, and Tilo Schöne

SWOT (Surface Water and Ocean Topography) is a recently launched international satellite mission developed in close collaboration between CNES and NASA space agencies aimed to reach a new level of accuracy in observing global water systems of the Earth. In order to meet the high accuracy requirements of the mission most precise determined orbits are crucial. Therefore we generate orbits using dynamic Precise Orbit Determination (POD) with multiple techniques, i.e. DORIS, GPS and SLR with the aim of generating a highly precise orbit with minimal residual error. For this purpose, single technique orbits are generated based on DORIS and GPS only, using SLR for validation only. For quality analysis we evaluate the estimated parameters of the dynamic POD and perform orbit comparisons to external orbit solutions. Subsequently, to reduce technique-specific effects of the dynamic modeling, we generate a combined orbit solution based on DORIS and GPS, and estimate the reference points of the observation techniques on the satellite to examine the calibration by the manufacturer. Based on the generated orbit solutions altimetry evaluation such as cross-over point analysis is made and discussed.

How to cite: Reinhold, A., Schreiner, P., and Schöne, T.: On multi technique precise orbit determination for SWOT with respect to altimetry applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18467, https://doi.org/10.5194/egusphere-egu24-18467, 2024.

X2.9
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EGU24-10249
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ECS
SPOCC - a GFZ Software Tool for a Multi-GNSS Orbit and Clock Combination 
Andreas Brack, Gustavo Mansur, Pierre Sakic, Radosław Zajdel, and Benjamin Männel

Among the core products of the International GNSS Service (IGS) are precise satellite orbits and clocks, which are generated by the Analysis Center Coordinator (ACC) as a combination of the solutions provided by different Analysis Centers (AC). A strategic goal of the IGS is to facilitate multi-GNSS solutions, implying that the currently operational system-wise GPS and GLONASS combinations should be replaced by a consistent set of multi-GNSS products, eventually containing at least GPS, GLONASS, Galileo, BeiDou, and QZSS.

Over the past years, the Satellite Precise Orbit and Clock Combination (SPOCC) software tool has been developed at GFZ. It provides a fully consistent multi-GNSS orbit and clock combination that covers all available and possible future constellations and is based on a well-defined unified least-squares framework. The resulting combined orbit and clock products are a weighted average of the individual AC solutions with weights determined through least-squares variance component estimation (VCE). A main objective is to support multi-GNSS precise point positioning (PPP) users.

We will introduce the combination workflow, which essentially consists of alignments harmonizing the AC products followed by the VCE and the weighted averaging, and is complemented by quality checks such as outlier detection. For the orbit combination, the alignment consists of Helmert transformations applied to the AC orbits, which is iterated with the VCE-based weighted averaging until convergence. The clock alignments consist of a radial correction from the orbit differences between the AC solutions, a removal of the impact of different reference clocks in the AC solutions, as well as an adjustment of all non-GPS satellite clocks for different inter-system bias (ISB) references at the ACs. The combination can be configured for different weighting schemes, including AC specific weights, AC+constellation specific weights, up to satellite type or even satellite specific weights, and the Helmert transformations can be based on different sets of satellite orbits.

The SPOCC software has been extensively tested with the operational IGS products, the IGS Multi-GNSS Experiment (MGEX) products, and the IGS repro3 products. Performance evaluations by means of a comparison of the combination with the input products and the official IGS combination, through a satellite laser ranging (SLR) validation, and with PPP results will be used to show that the software achieves reliable results that are suitable for the users’ high precision GNSS applications.

SPOCC is implemented in Python and will be provided as open source software.

How to cite: Brack, A., Mansur, G., Sakic, P., Zajdel, R., and Männel, B.: SPOCC - a GFZ Software Tool for a Multi-GNSS Orbit and Clock Combination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10249, https://doi.org/10.5194/egusphere-egu24-10249, 2024.

X2.10
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EGU24-10344
Towards a GEodesy and Time Reference In Space (GETRIS): A simulation study 
Stefan Marz, Anja Schlicht, and Urs Hugentobler

Progress in precise satellite orbit determination (POD) and navigation depends on the future ranging and time transfer capabilities. This leads to the need for high-precision links as well as high-precision clocks. However, not only a higher accuracy is required, but also the use of combination of complementary observation techniques to reduce systematic errors within an observation network. In a simulation study, we show our first concept of a GEodesy and Time Reference In Space (GETRIS). The initial GETRIS concept is based on the idea to have the reference in space build on geosynchronous orbit (GSO) satellites, but using Medium Earth Orbit (MEO) satellites is also possible. The goal is to achieve orbit accuracies of the GETRIS satellites at the same level as for ground stations – a few millimeters. Using high-precision optical links, the GETRIS shall establish connections to satellites in the near Earth environment and in deep space. When creating our GETRIS concept, we focus on three key pillars of a simulation study: Instrumentation, geometry and modelling. In terms of instrumentation, we performed scenarios using the synergy between L-band observations as well as high-precision dual one-way Optical Inter-Satellite Links (OISL) and ground-space based dual one-way links, called Optical Two-Way Links (OTWL), in different combinations. The geometry changes depending on the used observations network and the satellite constellation. Thereby, we analyze scenarios using a MEO-only and MEO+GSO constellations. To finally achieve mm-level orbit accuracies, an advanced modelling of non-gravitational forces is essential. A GETRIS can not only help with the connection of near Earth and deep space satellites, but also support the Global Geodetic Observing System (GGOS) and satellite missions such as GENESIS, which aim to realize a precise terrestrial reference frame with 1 mm accuracy and a stability of 0.1 mm/year.

How to cite: Marz, S., Schlicht, A., and Hugentobler, U.: Towards a GEodesy and Time Reference In Space (GETRIS): A simulation study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10344, https://doi.org/10.5194/egusphere-egu24-10344, 2024.