The computation of TRFs relies on space geodetic observations acquired by ground networks of stations and requires the estimation of a large number of parameters including station positions and Earth Orientation Parameters. Nowadays, measurement biases and imperfect background models are the main factors limiting the accuracy of TRFs. This session therefore welcomes contributions that develop strategies to overcome systematics in space geodetic observing systems such as long-term mean range biases in SLR observations, gravitational deformation of VLBI antennas, GNSS antenna phase patterns, etc.
The second objective of this session is to bring together contributions from individual technique services, space geodetic data analysts, ITRS combination centers and TRF users to discuss the TRF solutions produced by different groups, with a special focus on their comparison, evaluation and updates. The understanding of the discrepancies between the terrestrial scale observed by the different space geodetic techniques, the determination of new local tie vectors at co-location sites, the improvement of geocentre motion determination and the assessment of observed non-linear station motions by comparison with geophysical deformation models are of particular interest.
Papers on the exploitation of past ITRF solutions and the latest 2020 solution updates are of course welcome, as well as presentations regarding any type of development that could improve future TRF solutions. With the development of the GENESIS mission, any contributions on the handling and the impact of co-located instruments of individual techniques onboard satellite missions (space ties) for TRF realization are strongly encouraged. Contributions concerning TRF construction strategies based on combination at the observation level are also welcome.
Orals: Thu, 7 May, 08:30–10:15 | Room 0.96/97
The International Terrestrial Reference Frame (ITRF) is the foundation for Earth science and operational geodesy applications. It is built on international cooperation over more than three decades for the benefit of countries, regions and global geodesy. Substantial improvements have been constantly made in the data analysis strategy, at the level of both individual geodetic techniques, as well as the ITRF combination, with the aim to improve the ITRF accuracy and reliability. Motivated by a number of reasons that will be exposed in this paper, the ITRS Center decided to regularly (yearly) update the ITRF2020, with a first update (ITRF2020-u2023) released in December 2024, a second update (ITRF2020-u2024) released in September 2025 and a third update foreseen in 2026. Results of these updates will be presented and discussed, with a special focus on the uncertainty evaluation regarding the stability of the frame physical parameters (origin and scale), as well as Earth Rotation Parameters when adding extended data from the four techniques: VLBI, SLR, GNSS and DORIS. Future plans and perspectives regarding the ITRF2020 updates and consequences for the most demanding user needs conclude the presentation.
How to cite: Altamimi, Z., Rebischung, P., Collilieux, X., Metivier, L., Chanard, K., and de La Serve, M.: ITRF2020 Updates and Future Perspectives, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22667, https://doi.org/10.5194/egusphere-egu26-22667, 2026.
The International VLBI Service for Geodesy and Astrometry (IVS) provides a unique and fundamental contribution to the determination of the International Terrestrial Reference Frame (ITRF), most notably as a primary technique for defining the frame's scale. While the last comprehensive reprocessing of the VLBI data archive was conducted for the ITRF2020 submission, subsequent updates (u2023 and u2024) were limited to the addition of recent years.
For the ITRF2020-u2025 update, the IVS has undertaken a full reprocessing of the entire history of VLBI observing sessions. This decision was motivated by the identification of critical issues within the data archive: station naming inconsistencies and systematic errors in ionospheric corrections, which required the re-creation of some of the databases. Furthermore, the reprocessing incorporated several refined station-specific models, including newly determined gravitational deformation models and updated antenna axis offsets.
A major highlight of this reprocessing effort is the expansion of the included frequency bands to K-band (24 GHz). While previous ITRF submissions relied solely on legacy S/X-band and broadband VLBI Global Observing System (VGOS) sessions, this update integrates approximately 200 K-band VLBI sessions for the first time, comparable to the total number of VGOS sessions. Nevertheless, the legacy S/X-band network remains the dominant backbone of the contribution, encompassing about 7,600 sessions.
This contribution presents preliminary results of the IVS-combined solution, generated by the IVS Combination Center from individual Analysis Center contributions. We evaluate the quality of the resulting geodetic parameters, with a primary focus on the stability of station coordinates, terrestrial scale realisation, and the precision of EOP.
How to cite: Soja, B., Kehm, A., Bachmann, S., Raut, S., Behrend, D., and Haas, R.: The Full Reprocessing Effort for the ITRF2020-u2025 Update by the IVS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15008, https://doi.org/10.5194/egusphere-egu26-15008, 2026.
The International DORIS Service (IDS) has contributed to the third annual update of the 2020 realization of the International Terrestrial Reference Frame (ITRF2020). As part of this effort, IDS has estimated DORIS station positions and velocities, as well as Earth Rotation Parameters (ERPs), using DORIS data. These computations are based on the latest weekly multi-satellite series from the five IDS Analysis Centers and an IDS Associated Analysis Center, covering data from 2025 and backward 2021. Note that for the first time, the IDS combined series will include daily LOD (Length-Of-Day) estimates.
The primary objectives of this study are to evaluate the DORIS contribution to this update of the ITRF2020 in terms of: (1) geocenter motion and scale, (2) station positions and week-to-week position repeatability, (3) ERPs, and (4) a cumulative position and velocity solution. A particular focus is placed on the LOD estimates and on the impact of including SWOT (Surface Water Ocean Topography) DORIS data.
How to cite: Moreaux, G., Lemoine, F., Capdeville, H., Štěpánek, P., Otten, M., Nahmani, S., Pollet, A., and Schreiner, P.: IDS contribution to the third update of the ITRF2020, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13383, https://doi.org/10.5194/egusphere-egu26-13383, 2026.
Geocenter motion can be derived through various space geodetic techniques and hydrological models using different methods, such as direct and inverse. Each technique suffers from specific issues associated with a sparse observing network, orbit modeling errors, or limited sensitivity of the observing techniques to particular components of the geocenter motion, especially to the Z component. Modeling issues result in the spurious signals observed in the time series of the geocenter motion, such as the draconitic periods, orbit resonance terms, and tidal aliasing signals.
No official combined products currently exist for the geocenter motion and low-degree gravity field coefficients. Hence, different geocenter models are employed in various applications, such as altimetry, the analysis of GNSS station motions, or GRACE-based gravity field studies.
We propose a combination and comparison campaign for the geocenter motion and low-degree gravity field parameters. The first step of the campaign includes technique-specific combinations, such as GNSS-only, DORIS-only, SLR-only, LEO-only, and a confrontation with hydrological models. In the second step, the system-specific solutions will be compared and combined, considering different methods of deriving geocenter motion, including the network shift approach, deriving degree-1 gravity field coefficients, and inverse methods based on surface load displacements, as well as GRACE-derived products supported by geophysical models. The following step will consist of the combination of low-degree gravity field coefficients using the variance component estimation (VCE) technique and other combination techniques to separate system-specific signals from those signals that have geophysical justification. Finally, the combination will be applied to the low-degree gravity field harmonics to expose software-specific issues in SLR-based values, as well as differences between the values obtained from SLR, GRACE, LEO satellites, and inverse methods applied to a dense GNSS network.
How to cite: Sośnica, K., Nowak, A., Kur, T., Gałdyn, F., and Zajdel, R.: Analysis and Combination of Geocenter Motion and Low-Degree Gravity Field Parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12208, https://doi.org/10.5194/egusphere-egu26-12208, 2026.
Global Navigation Satellite Systems (GNSS) are based on measuring signal propagation time, so that clock information is required for both the transmitting satellite and the receiving ground station. For Precise Point Positioning (PPP), synchronization errors of the receiver clock are usually estimated as epoch-wise biases with white noise as stochastic behavior. A major issue for the receiver clock estimates is the high correlation with the station height and the tropospheric zenith delay that results from the observation geometry. Introducing models to reduce the number of unknown clock parameters is one way to mitigate these correlations. However, adequate modeling requires a high degree of stability for the corresponding clock.
In this contribution, we show the results of modeling highly stable GNSS receiver clocks in PPP using piece-wise linear representations. We discuss different options to control the deterministic and stochastic part of the piece-wise linear model (interval length, parameter weighting, etc.). For 56 highly stable hydrogen maser (H-maser) stations of the International GNSS service (IGS), the impact of piece-wise linear clock modeling on correlated parameters, especially the sub-daily height estimates, is presented. The differences in the modeling impact of the individual receiver clocks are explained by categorizing the stations based on statistical and observational quality measures. In addition, the effects of individual processing options (used GNSS constellations, elevation cutoff angle) are shown.
How to cite: Widczisk, J. S., Männel, B., and Wickert, J.: Piece-wise linear clock modeling for highly stable IGS H-maser stations in Precise Point Positioning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3083, https://doi.org/10.5194/egusphere-egu26-3083, 2026.
Genesis is an ESA mission conducted by the ESA Navigation Directorate as part of the FutureNAV program. Its primary objective is the contribution to the improvement of the International Terrestrial Reference Frame (ITRF) towards an accuracy of 1mm and a long-term stability of 0.1mm/year. Secondary objectives include the contribution to a high number of other scientific disciplines (geodesy, geodynamics, earth rotation, geophysics, atmosphere and ionosphere sciences, metrology, relativity…) [1].
The Genesis Space Segment consists of a single spacecraft in MEO (400kg, 6000km altitude, 95° inclination) co-locating for the first time in space the four geodetic instruments used for the realisation of the ITRF: a GNSS receiver, an SLR reflector, a VLBI transmitter and a DORIS receiver. The Ground Segment is composed of a Mission Control Centre (including a Ground Station) and will make use of the existing ground infrastructure, operated by the Services of the International Association of Geodesy: GNSS sensor stations network of the IGS, SLR stations of the ILRS, VLBI antennas of the IVS, and DORIS beacons of the IDS. The scientific mission data will be processed, archived, and distributed by ESA Data PROcessing, Archiving and Delivery facility (PROAD), under the responsibility of the Navigation Support Office and the GNSS Science Support Centre, in close collaboration with the scientific community.
Genesis’ fully calibrated satellite will establish precise and stable ties between the key geodetic techniques, implementing a unique dynamic space geodetic observatory. As the ITRF is recognised to be the foundation of countless space and ground-based applications, Genesis will have a major impact on almost any space mission and on Navigation and Earth Science.
On the industrial side, the company OHB Italia has been contracted by ESA as prime for the development, qualification, launch and 2 years operation of the mission (with option for extension), with a launch currently planned in 2028. Antwerp Space, as payload prime, is responsible for the geodetic instruments. Industrial activities were kicked-off in April 2024, the System Requirements Review was successfully closed-out in Q4 2024, the System Preliminary Design Review was successfully carried out in Q4 2025, and work is on-going to consolidate the design towards a Critical Design Review starting in Q4 2026.
On the scientific side, a Genesis Scientific Exploitation Team (GSET) was set-up and members appointed in Q2 2024. This structure encompasses representatives of ESA, a lead Scientific Coordinator and Co-Coordinator, as well as five Working Groups covering the four geodetic techniques and their combination. The GSET includes members of the international geodetic services and will interact with them for the coordination of the ground infrastructure. Two successful Genesis Scientific Workshops were held in February 2024 and April 2025, and a third will be held in March 2026. The GSET has been actively supporting the mission development, the requirements/design consolidation, and will play a key role in the future exploitation of the mission data.
This presentation will provide an up-to-date overview of the Genesis mission from a system, programmatic, and scientific point of view.
[1]: Delva et al. Earth, Planets and Space 75, 5 (2023)
How to cite: Fusco, G., Gidlund, S., Waller, P., Honoré-Livermore, E., Bieringer, A., Schoenemann, E., Berton, J.-C., and Gini, F.: Genesis: A Unique Geodetic Satellite Mission at the Foundation of Navigation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19242, https://doi.org/10.5194/egusphere-egu26-19242, 2026.
Genesis is an ESA mission in preparation within the Navigation Directorate under the FutureNAV Programme, dedicated to advancing space geodetic science and the International Terrestrial Reference Frame (ITRF). It co-locates GNSS, SLR, DORIS, and a pioneering VLBI transmitter on a single satellite in near-polar orbit (~6000 km), creating a dynamic space geodetic observatory that delivers well-calibrated space ties between all techniques.
These co-located measurements enable rigorous integration of space-geodetic techniques, revealing and mitigating inter-technique biases that currently limit ITRF scale, origin, and orientation. The Genesis objectives demand a stable and well-characterised platform as well as rigorous calibration of instruments and antennas, including phase/group delays and phase center offsets. The mission's novelty and methodology at mm-level demand also the careful preparation of observation strategies and adoption of data analysis and combination techniques for Genesis data exploitation.
Here, we present an overview of the ongoing activities relevant to the science community and ITRF realisation, including the scientific objectives and the status and plans of science instruments and calibrations. The scientific datasets and expected data products, along with their planned availability to the scientific community, will also be discussed.
How to cite: Karatekin, Ö., Vespe, F., Altamimi, Z., Seitz, F., Dach, R., Männel, B., Haas, R., Moreaux, G., courde, C., Bieringer, A., Schoenemann, E., Waller, P., Fusco, G., and Gidlund, S. and the Genesis Science Exploitation Team: Science objectives of ESA's Genesis mission: a flying geodetic observatory to improve ITRF accuracy and stability , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22731, https://doi.org/10.5194/egusphere-egu26-22731, 2026.
The Federal Agency for Cartography and Geodesy (BKG) is currently taking part in the research project GENESIS-D (a consortium of the main German geodetic institutes). The goal of this project and our studies therein is to be able to consistently process, combine and validate observation data of ESA’s upcoming Genesis mission in the future. Genesis will allow, for the first time, the co-location in space of all four main space geodetic techniques, namely VLBI, SLR, GNSS, and DORIS. The orbit combination will enable a quantification of inter-technique systematic discrepancies, and will increase the inter-technique consistency during the determination of the international terrestrial reference frame (ITRF). Already now, several Low-Earth-Orbiting (LEO) satellites represent a co-location in-space for the three satellite-based space-geodetic techniques, i.e., GNSS, SLR and DORIS. Using such LEOs allows to study potential hurdles in harvesting the full potential of Genesis and preparing the analysis and combination software to fully exploit satellite co-locations.
In this work, we have chosen the altimetry satellite Sentinel-6A Michael Freilich (S6A) as a proxy for Genesis in order to conduct research and software development regarding the combination of SLR and GNSS. For now, SLR data to S6A and to the SLR specific satellites LAGEOS-1 and LAGEOS-2 have been analyzed.
For the two cannonball-shaped LAGEOS satellites we estimate weekly arcs, whereas for S6A daily arcs are set up, due to the lower altitude and more complicated radiation-pressure modelling. By accumulating the daily arc S6A normal equations (NEQs) into weekly NEQs and stacking them with the LAGEOS-based NEQs, we obtain weekly solutions that include satellite orbits, station coordinates, Earth rotation parameters, geocenter coordinates, and SLR range biases. We compare all parameters estimated in the framework of the three solution types, that are (i) LAGEOS-only; (ii) S6A-only; and (iii) LAGEOS+S6A.
We find that the station coordinate repeatability for (i) LAGEOS is better than for (ii) S6A, which is expected given the use of a single-satellite LEO solution. Generally, the single-satellite solution of (ii) S6A yields worse results compared to the other two solutions as these are multi-satellite solutions. On the other hand, the advantage of S6A shows up, e.g., in the six-fold increase in low-elevation observations to S6A compared to LAGEOS, which facilitates the decorrelation between range bias and station height. The analysis of the impact of S6A data on the global LAGEOS solution offers insight into the potential impact that Genesis will have on current SLR products. It also ensures the early identification and resolution of software issues, allowing Genesis data to be evaluated from the outset of the mission. This study will be expanded in the future by a global GNSS solution as well as GNSS analysis of S6A data, as well as the subsequent combination with SLR.
How to cite: Weinem, L., Balidakis, K., Flohrer, C., Thaller, D., Kehm, A., König, D., Arnold, D., Meyer, U., and Geisser, L.: Integration of space-based co-locations for enhanced reference frames: Investigating the Potential of ESA’s Genesis Mission , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12473, https://doi.org/10.5194/egusphere-egu26-12473, 2026.
The objective of the future Global Geodetic Observing System (GGOS) to realize the terrestrial reference system (TRS) with 1 mm accuracy and 0.1 mm/yr long-term stability remains challenging when the four space geodetic techniques – GNSS, SLR, VLBI, and DORIS – are processed independently in the traditional, technique-specific manner. Key challenges arise from the sparse and highly inhomogeneous global distribution of co-location sites used to tie the individual solutions together, as well as from the treatment of technique-specific calibration parameters, such as GNSS antenna phase center offsets and SLR range biases. In this presentation, we present work carried out by the ESA/ESOC Navigation Support Office on the joint processing of GNSS and SLR at the observation level. Our approach – fittingly referred to as COOL (“COmbination at the Observation Level”) – incorporates the primary geodetic ILRS targets LAGEOS-1, LAGEOS-2, LARES-2, Etalon-1, and Etalon-2, and makes use of space ties provided by the Sentinel and Galileo satellites to directly link the two geodetic techniques. Particular attention is given to the Galileo transmit antenna z-offsets and the numerous SLR range biases, which require careful treatment, as they are known to directly influence the scale of the reference frame solution. The primary motivation for this work is to ensure full readiness for the future ESA GENESIS mission, which aims to establish a highly accurate, next-generation International Terrestrial Reference Frame (ITRF) through the use of all four space geodetic techniques, including DORIS and VLBI, on a single platform and the exploitation of the space ties between them.
How to cite: Dilssner, F., Springer, T., Sermanoukian, I., Otten, M., Gini, F., and Schönemann, E.: Keeping It COOL: GNSS–SLR Combination at the Observation Level, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18349, https://doi.org/10.5194/egusphere-egu26-18349, 2026.
Proper a priori knowledge of the phase center location and pattern of the GNSS antenna is an essential prerequisite for use of GNSS measurements in the determination of the terrestrial reference frame. This is well known for terrestrial GNSS stations, but likewise applies for space-borne GNSS tracking. In the context of the upcoming Genesis mission, the analysis of flight data from existing low Earth orbit (LEO) missions offering co-location of multiple space-geodetic instruments and their possible contribution to the TRF refinement has gained renewed interest. With this background, we investigate the quality of ground-based calibrations from the two most widely-used geodetic-grade LEO GNSS antenna types and compare these calibration with in-flight measurements for a range of scientific Earth observation missions. More specifically, we analyse the combination of an aviation patch antenna with JPL chokering using flight data from the GRACE, Jason-2/3, and TerraSAR-X satellites as well as the RUAG (now Beyond Gravity) patch antenna with integrated choke ring from GNSS observations of the GRACE-FO and Sentinel-3A/3B/6A satellites.
Overall, the analysis covers a period of at least 10 years and makes use of pre-computed precise GNSS orbit, clock, and bias products from the International GNSS Service for precise orbit determination of the LEO satellites. The analysis period includes different reference frames (IGSR3, IGS14, IGS20) to verify the consistency of changes in the estimated phase center offsets (PCOs) with TRF scale changes. Following a discussion of conceptual problems in the definition and measurements of "the" antenna phase center, we assess the expected uncertainty of LEO force models to characterize the expected stability of the dynamical reference frame of the various LEO satellites that serves as a reference for the PCO determination from in-flight observations. The results reveal notable discrepancies between ground calibrations and in-flight results, which obviously hamper the use of existing LEO GNSS data for independent TRF scale determination. These include notable phase pattern distortions attributed to the impact of the local antenna environment as well as systematic PCO differences, which can only partly be attributed to center-of-mass uncertainties. In the context of Genesis, adequate measures need to be taken to avoid launch-related structural deformations changing the center-of-mass location from the design values and to calibrate the GNSS antenna characteristics after satellite integration in a flight-representative configuration.
How to cite: Steigenberger, P. and Montenbruck, O.: Comparison of LEO GNSS antenna phase characteristics from ground and in-flight calibrations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8224, https://doi.org/10.5194/egusphere-egu26-8224, 2026.
Posters on site: Wed, 6 May, 08:30–10:15 | Hall X1
DTRF2020, the latest realization of the ITRS calculated by DGFI-TUM, has been updated with two new solutions, DTRF2020-u2023 and DTRF2020-u2024. They contain additional observation data of the four contributing techniques, VLBI SLR, GNSS and DORIS, from three and four years, respectively.
We present the results of these two DTRF updates and discuss the challenges associated with performing annual updates in comparison with calculating new DTRF solutions every five to six years.
In early 2026, the ITRS Center requested new contributions from the IAG Technique Services for the third update, covering data up to the end of 2025. Where new time series are already available, we present initial analysis results, focusing in particular on the datum parameters.
How to cite: Seitz, M., Bloßfeld, M., Zeitlhöfler, J., Angermann, D., Klug, J., Reber, M., and Seitz, F.: The DTRF2020 Updates: DTRF2020-u2023 and DTRF2020-u2024, and Preparation of the Third Update, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9773, https://doi.org/10.5194/egusphere-egu26-9773, 2026.
The NASA GSFC/UMBC Joint Center for Earth Systems Technology (JCET) ILRS Analysis Center supports the International Laser Ranging Service (ILRS) through routine SINEX submissions, network validation, and contributions toward future updates of the International Terrestrial Reference Frame (ITRF). As an ILRS Analysis Center (AC) and the designated ILRS backup combination center (ILRS-B), JCET/NASA GSFC generates daily and weekly SINEX solutions and combines contributions from eight ILRS ACs to produce the ILRS-B solution, complementing the official ILRS-A solution provided by ASI for the ITRF Combination Centers (DGFI, JPL & IGN).
Since LARES-2 was launched in August 2022, ILRS Analysis Centers began generating v90-format solutions in April 2025, retroactively covering data from September 2022. These solutions incorporate LARES-2 tracking using the new Data Handling Format (DHF), improving geodetic coverage and supporting future reference frame updates. The v90 series will be reprocessed to apply updated mass corrections, include newly available stations, and reinstate sites previously quarantined during earlier processing cycles. This v90 SINEX will represent the core of our contribution to the development of ITRF2020-u2025, which will be based on a full reprocessing of SLR data from 2021.0 to 2026.0
In this paper, we provide information on the v80 & v90 series that contribute to this ITRF contribution. We summarize the impact of adding LARES-2 compared to the legacy geodetic satellite contributions from LAGEOS-1,2 and Etaton-1,2. We review the performance of the ILRS-B combination, in particular with respect to the station coordinates and Earth Orientation Parameters (EOPs).
How to cite: Kuzmicz-Cieslak, M., Evans, K. D., Belli, A., and Lemoiine, F. G.: NASA GSFC/JCET ILRS Analysis Center Contribution to ITRF2020-u2025 Development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15495, https://doi.org/10.5194/egusphere-egu26-15495, 2026.
The contribution of the International Laser Ranging Service (ILRS) to the latest International Terrestrial Reference System (ITRS) realizations is based on Satellite Laser Ranging (SLR) observations of just four spherical satellites (LAGEOS-1/2 and Etalon-1/2). Since 2025, one more spherical satellite (LARES-2) is used by the ILRS to determine global geodetic parameters such as coordinates and velocities of globally distributed SLR stations and Earth Rotation Parameters (ERP), namely x- and y-pole coordinates and length of day (LOD). However, SLR observations to eight more spherical satellites (Starlette, Ajisaj, Stella, GFZ-1, WESTPAC, Larets, BLITS, LARES) and several altimetry satellites are available over an overall time span from 1976 with the total number of their SLR observations exceeding the number of SLR observations of the five presently used satellites by a factor of about five. Orbits of these satellites have various altitudes and inclinations and can be determined at the 1-2 centimeter level of accuracy. The long observational time series and the differing orbital characteristics of the satellites lead to an improved SLR observation geometry.
In this study, we investigate the potential of using SLR observations of seven altimetry satellites (TOPEX/Poseidon, Jason-1/-2/-3, Sentinel-3A/-3B/6A) for the determination of global geodetic parameters mentioned above, as compared to using SLR observations of five and 13 spherical satellites and in combination with them.
How to cite: Rudenko, S., Bloßfeld, M., Seitz, M., and Zeitlhöfler, J.: Determination of an SLR terrestrial reference frame and Earth Rotation Parameters from SLR observations to altimetry and spherical geodetic satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5480, https://doi.org/10.5194/egusphere-egu26-5480, 2026.
As one of the four space geodetic techniques, the Global Navigation Satellite System (GNSS) has been playing an increasingly important role in determining high-quality geodetic parameters, including the Earth rotation parameters (ERPs) and geocenter coordinates (GCCs). In addition to GNSS observations from ground station networks, GNSS observations from low Earth Orbit (LEO) satellites can serve as an important supplement to improve the estimation of geodetic parameters. Over the past decade, with the proposal and validation of the concept of LEO constellation-enhanced GNSS, several LEO navigation-augmentation constellation projects are being planned or constructed. Unlike traditional LEO satellite missions, LEO constellations are not only equipped with onboard receivers but also broadcast downlink navigation signals, establishing a direct link between the LEO satellites/constellations and station fixed on the Earth’s surface. The emergence of LEO navigation-augmentation constellations provides a new technological means for geodetic parameters determination and performance enhancement.
In this study, we focus on the determination of global geodetic parameters using LEO constellation and its potential enhancement to GNSS. We begin with the effect of different orbital configuration on the estimation of ERP and GCC with LEO downlink observations. Different LEO constellations, with different orbital inclination, number of orbital planes, and altitude are designed, and their performance is comparatively analyzed. For LEO orbital inclination, Walker Delta (108/9/0) constellations are designed, with the orbital inclination varying from 45° to 90°. The results indicate that the performance of ERP and GCC estimation is optimal for inclinations 65°-75°. Meanwhile, the increase of the number of orbital planes is demonstrated to be beneficial for geodetic parameters estimation, under scenarios where either the number of satellites per plane or the total number of LEO satellites is fixed. What’s more, when the orbit altitude increases from 500 to 2000 km, the formal errors of ERP and GCC estimates decrease, which is mainly due to the increased number of satellites observed by the ground stations. Nevertheless, the Root Mean Square (RMS) values of length of day (LOD) and GCC reach the minimum at the altitude of approximately 1500 km.
Based on the better-performed LEO constellation (Walker: 144/12/0, orbital altitude: 1500 km), the potential enhancement to GNSS is further investigated. The results indicate that with downlink observations, GNSS and LEO constellation exhibit different capabilities in ERP and GCC estimation, i.e., GNSS performs better in ERP estimation, while LEO constellation is superior in GCC estimation. The GPS+LEO combined solution makes the smallest formal errors, which are 4.21 uas for polar motion, 9.94 uas/d for polar motion rate, 0.64 us/d for LOD, and (0.14, 0.34) mm for the X/Y and Z component of GCC, presenting improvement of 8.1%-75.5% over GPS-only solution. At the same time, the combined solution also improve the accuracy by 10.4%, 56.5%, 62.8%, and 84.7% for polar motion, polar motion rate, LOD, and GCC, respectively, compared with the GPS-only solution.
How to cite: Cheng, Y., Li, X., Zhang, K., Zhao, Y., and Li, Y.: Determination of global geodetic parameters using low Earth orbit constellation: performance analysis and its potential enhancement to GNSS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11970, https://doi.org/10.5194/egusphere-egu26-11970, 2026.
The adjustment of trajectory models to GNSS station position time series is an essential step in the establishment of terrestrial reference frames, but also in a wide range of geophysical studies investigating glacial isostatic adjustment, tectonics, or coastal sea-level change. This trajectory modelling step is complicated by the presence of occasional discontinuities in the time series, including outliers, mean offsets (jumps), and changes in velocity. With the increasing number and longevity of GNSS stations, traditional manual trajectory modelling of position time series by an experienced operator becomes increasingly time-consuming and even impossible for large datasets. For this reason, automatic discontinuity detection approaches are increasingly appealing for many geodetic and geophysical applications.
A central concern with automatic modelling approaches is their reliability. While past studies suggest that automatic approaches are less reliable than human experts, this situation may change with advances in artificial intelligence. One limitation to monitoring progress in automatic trajectory modelling is the absence of a standardized benchmarking approach for discontinuity-detection algorithms. In practice, each research group publishes performance measures based on different data sets of either human-labeled or synthetic time series. Unfortunately, data sets of human-labeled time series are limited in size and may be incomplete because humans are unlikely to detect the smallest discontinuities. Synthetic time series are not necessarily reliable either, as they may lack realism with respect to length, gaps, frequency and amplitude of discontinuities, and noise properties. To address these benchmarking issues, we will present a generator of realistic synthetic GNSS station position time series. Building upon the characterisation of real data sets, this generator will contribute to the development of a standardized benchmarking approach for automatic discontinuity detection algorithms. In the long run, this generator may also be employed to train new machine learning algorithms.
How to cite: Gobron, K., Bouvier, C., De Oliveira, A., Amal, S., and Rebischung, P.: Generating realistic synthetic GNSS station position time series to evaluate automatic discontinuity detectors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14154, https://doi.org/10.5194/egusphere-egu26-14154, 2026.
Accurate estimation of GNSS station velocities requires careful consideration of the stochastic properties of their position time series, which are commonly affected by white and flicker noise. In this study, we propose a non-parametric approach combining Singular Spectrum Analysis (SSA) with an adaptive Monte Carlo SSA (MC-SSA) to estimate station velocities and their uncertainties, explicitly accounting for the noise spectrum. Using SSA, the trend and seasonal components are removed from the analyzed GNSS time series, after which the residual noise is analyzed using Welch’s spectral method to identify its noise type. Monte Carlo simulations are then employed to generate synthetic realizations of white and/or flicker noise according to the detected type, and the trend is reconstructed with SSA for each realization.
The proposed methodology is applied to daily position time series from 28 International GNSS Service (IGS) stations located on the African plate. The data are expressed in the local topocentric reference frame (North, East, Up), referenced to ITRF2020, and cover the period from 1999 to 2026. The results show that the average velocities of the analyzed stations are about 17.625, 19.446, and -0.749 mm/yr in the North, East and Up components, respectively. For stations whose position time series are dominated by white noise, the uncertainties associated with the estimated horizontal and vertical velocities range from 0.001 to 0.027 mm/yr and from 0.010 to 0.086 mm/yr, respectively. In contrast, the velocities affected by flicker noise exhibit a significantly larger uncertainty, varying from 0.045 to 0.260 mm/yr for the horizontal components and from 0.148 to 0.628 mm/yr for the vertical component. The proposed MC-SSA approach was validated using synthetic GNSS position time series generated with prescribed velocities and well-defined noise characteristics, spanning the same time intervals as the used data. The results demonstrate that MC-SSA yields velocity estimates that are very close to the simulated values and provides more realistic uncertainty estimates than ordinary least squares solutions. Moreover, this study provides a consistency assessment of velocities from regional GNSS stations on the African plate through comparison with nearby IGS stations in the ITRF2020 reference frame.
How to cite: Khelifa, S., Dekkiche, H., Allal, S. H., and Ahmed Betchim, Y.: GNSS Velocity Estimation Using Adaptive Monte Carlo SSA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4454, https://doi.org/10.5194/egusphere-egu26-4454, 2026.
The fundamental reliance of GNSS on one-way signal travel time measurements necessitates precise clock synchronization. This introduces high correlations between satellite/receiver clock offsets and nearly all other estimated parameters—such as station coordinates, tropospheric delays, and orbital elements—creating a fundamental bottleneck in modern high-precision geodesy by limiting the independent determinability of these parameters.
Recent breakthroughs in time-frequency technology offer promising pathways to mitigate this issue. Ultra-stable optical clocks and fiber-optic time transfer have emerged as transformative tools. Fiber-optic links can synchronize the clocks of GNSS receivers to a remarkable degree, achieving fractional frequency stability of clock difference at the 10-18 level—several orders of magnitude beyond GNSS-based synchronization. Consequently, receivers connected via fiber can be treated as sharing a common clock. In parallel, highly stable hydrogen masers, already deployed at many permanent GNSS stations, provide another foundation for common-clock processing. When two receivers are each equipped with a hydrogen maser, the stability of their clock offset difference can approach that achievable via fiber links, effectively constituting a "virtual" common clock even in the absence of a physical connection.
To leverage these advancements, we developed and implemented a novel module that incorporates common-clock constraints into the widely used Bernese GNSS Software. This module enforces that multiple receivers share a single common clock parameter per epoch. Initial processing results demonstrate that applying this constraint significantly reduces noise in key estimated parameters, notably in station height time series and high-frequency (e.g., 10 to 30 minutes) tropospheric delay estimates.
The implementation of a common-clock framework opens several avenues for future enhancement of GNSS. Beyond reducing parameter noise through decorrelation, it raises the prospect of establishing a more stable time reference for GNSS networks—potentially realized as a software-generated composite clock. This work represents a critical step toward integrating next-generation timekeeping infrastructure into global geodetic networks, with the goal of improving the stability of the terrestrial reference frame and the precision of all GNSS-derived geodetic products.
How to cite: Wang, Z. and Hugentobler, U.: Implementing a Common Clock Framework in GNSS: Harnessing Fiber-Optic Links and Global Hydrogen Maser Networks for Enhanced Parameter Estimation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12913, https://doi.org/10.5194/egusphere-egu26-12913, 2026.
How to cite: Dumitraschkewitz, P. and Mayer-Gürr, T.: Analysis of estimating PCO/PCV using raw observationa approach in global GNSS processing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12347, https://doi.org/10.5194/egusphere-egu26-12347, 2026.
Accurate satellite phase center offsets (PCOs) are critical for high-precision GNSS data processing. Their pre-launch calibration and on-orbit estimation have long been essential tasks. For the third-generation BeiDou Navigation Satellite System (BDS-3), however, recent studies often derive PCOs from precise orbit determination (POD) using GPS L1/L2 receiver antenna calibrations and adjustable box-wing models for solar radiation pressure (SRP) modeling. Due to differing processing strategies, estimated BDS-3 PCOs vary across studies. Leveraging BDS-3 satellite metadata and BDS-specific receiver antenna calibrations, this study estimates BDS-3 satellite PCOs using long-term data. Results indicate that the X-offset obtained with an empirical SRP model combined with BDS-3 metadata is the most stable. Further analysis shows that the Z-offset is highly sensitive to the type of receiver antenna calibration model used. The relationship can be approximated as follows: a network-averaged bias in the receiver antenna up-direction causes a change of approximately −22.7 times in the MEO Z-offset for BDS-3-only POD, and −28.6 times for combined BDS/GPS processing. This finding aligns with prior studies, despite methodological differences, underscoring the importance of precise receiver antenna calibration. Validation experiments comparing the manufacturer’s model with the newer model show an average improvement of nearly 3% in the RMS of overlapping orbit differences. Additionally, static precise point positioning (PPP) experiments demonstrate coordinate improvements of about 5% for B1I/B3I and 14% for B1C/B2a signals compared to results using the manufacturer’s model.
How to cite: Huang, C.: On-orbit estimation of antenna phase center offsets for BDS-3 satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16386, https://doi.org/10.5194/egusphere-egu26-16386, 2026.
Space-geodetic techniques rely on Earth orientation parameters (EOP) to relate satellite observations to terrestrial reference frames. While their importance for global consistency is well recognized, the sensitivity of satellite-based orbit determination to degraded Earth orientation information remains only partially quantified, particularly for techniques that depend on a combination of externally prescribed and internally estimated parameters.
In this contribution, we present a first assessment of the sensitivity of Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) geodetic products to degraded Earth orientation information. Using a standard DORIS processing configuration, in which UT1–UTC is prescribed from external products while polar motion can be estimated, we analyse how realistic perturbations applied to the Earth orientation time series propagate into observation residuals, orbital parameters, and empirical force modelling.
The study explores the extent to which DORIS solutions can accommodate degraded Earth orientation information through internal parameter adjustments, and examines the respective roles of different components of Earth rotation in this process.
This work provides initial insight into the robustness and limitations of DORIS-based geodetic products with respect to Earth orientation information, and contributes to a broader understanding of the dependence of satellite geodesy on high-quality geodetic products. As such, it provides technical elements relevant to the objectives of the United Nations Global Geodetic Centre of Excellence (UN-GGCE) in assessing the resilience and long-term sustainability of the global geodetic infrastructure.
How to cite: Nahmani, S. and Pollet, A.: Assessing the sensitivity of DORIS precise orbit determination to degraded Earth orientation information, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17706, https://doi.org/10.5194/egusphere-egu26-17706, 2026.
The European Space Agency’s (ESA) Genesis mission has been approved for launch in 2028. Its primary objective is to enhance the terrestrial reference frame by establishing a space tie on board the Genesis satellite that connects all space-geodetic techniques used for its realization.
Concerning the VLBI part of Genesis, new challenges arise from the fact that the VLBI broadband signal will be spread across multiple antennas on the satellite, each emitting in its own bandwidth. If this aspect is not corrected for with sufficient accuracy, the group delays will not refer to a well-defined reference point on the satellite.
In this study, we investigate how large the impact of neglecting such a correction or imperfectly modelling it would be on estimated parameters, such as station positions. We address this question by simulating observations to the Genesis satellite on the group delay level. Based on simulated 24-hour sessions, consisting of quasar and satellite observations, a full geodetic VLBI analysis is carried out, using the software VieVS-VLBI. Here we present our results and discuss the necessity of phase center corrections for VLBI observations to the Genesis satellite.
How to cite: Wolf, H., Jaron, F., and Böhm, J.: On the impact of imperfect models for multiple VLBI antennas on the Genesis satellite on the terrestrial reference frame, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7611, https://doi.org/10.5194/egusphere-egu26-7611, 2026.
The Genesis mission of the European Space Agency (ESA) aims to provide near-continuous space ties among the four major space geodetic techniques. These ties are expected to help improve the accuracy and stability of the International Terrestrial Reference Frame (ITRF) by allowing the determination of inherent inter-technique biases. One of these techniques is Very Long Baseline Interferometry (VLBI). For Genesis, VLBI observations are planned to be made possible by emitting signals with an onboard VLBI transmitter, which can be observed using the VLBI Global Observing System (VGOS).
Many technical and operational challenges are currently being addressed to make sure that VGOS can observe Genesis successfully. This is done through studies that rely on simulations or on experiments using non-Genesis-like satellites. So far, combining real and simulated data has been underutilised, even though it provides both realistic observation conditions and flexible scenario designs, which could be used to answer remaining open questions. Two examples of remaining challenges are the determination of how often Genesis should be observed without degrading the estimation of geodetic parameters and station positions, and the assessment of how and if Genesis observations can contribute to those estimates.
In this study we apply a hybrid approach of combining real and simulated data. The aim is twofold: first, we want to investigate the impact of reducing the number of quasar observations on real 24-hour VGOS sessions as if Genesis was being observed; and second, we want to assess real 24-hour VGOS sessions which include simulated Genesis observations that are partially based on real data. The latter is done by combining real quasar observations and simulated satellite observations that are based on estimates from the real quasar observations. We also investigate the estimation of the geocentre, which is possible due to the added simulated satellite observations.
How to cite: Wolfs, R. and Haas, R.: A Hybrid Approach Using Real and Simulated Data to Assess the Performance of VGOS Sessions with Added Genesis Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18316, https://doi.org/10.5194/egusphere-egu26-18316, 2026.
The BKG/DGFI-TUM IVS Combination Centre (IVS-CC) officially contributes to the realization of the International Terrestrial Reference Frame (ITRF) by incorporating the contributions from the IVS Analysis Centres (ACs).
For the 2025 update of the ITRF 2020 (ITRF2020-u2025), the IVS initiated a reprocessing of the full VLBI observation history since 1979. Besides S/X-band and VGOS sessions, for the first time, K-band VLBI sessions are included in the ITRF contribution. Moreover, on an empirical basis, the IVS-CC provides combined normal equations that include radio source positions as parameters, allowing for the joint and consistent computation of terrestrial and celestial reference frames, and EOPs as the link between them.
This presentation focuses on developments in the framework of the IVS-CC combination setup for the IVS contribution to ITRF2020-u2025. A total of 7613 S/X, 219 VGOS, and 229 K-band VLBI sessions will be used for this study. We begin with a description of our combination setup, followed by validation of the input data provided by the contributing ACs and the combined IVS contribution to ITRF2020-u2025. The investigation focuses on the quality of geodetic products estimated by different session types across eclectic frequency bands, including legacy S/X, VGOS, and K-Band.
How to cite: Raut, S., Kehm, A., Bachmann, S., Bloßfeld, M., Seitz, M., Balidakis, K., Klemm, L., Schneider-Leck, S., and Thaller, D.: BKG/DGFI-TUM IVS Combination Centre's advancements within the framework of the IVS Contribution to ITRF2020-u2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20186, https://doi.org/10.5194/egusphere-egu26-20186, 2026.
