JPL has developed a terrestrial reference frame (TRF) based on combining space geodetic techniques at the observation level. The current version includes observations from the Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI); and it has been shown to be competitive with the international standard (ITRF2020) in terms of fundamental frame parameters (origin and scale) and their temporal evolution, both linear and seasonal. In this work, we build on the current processing infrastructure and add Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) observations to the combination. The four-technique solution strategy uses space ties in low-Earth orbit to connect SLR, GPS and DORIS and ground ties to connect VLBI to GPS. This solution can be viewed as a pathfinder for the upcoming GENESIS mission which will provide a space tie for all 4 techniques. Additionally, we revise parametrization of the SLR range biases to improve retrieval of the scale. Finally, we discuss future enhancements to the TRF realization process. These enhancements include recovering the time-variable gravity field by jointly using observations from the frame realization and GRACE / GRACE-Follow On missions.
How to cite: Peidou, A., Haines, B., Bertiger, W., Conrad, A., Desai, S., Murphy, D., Naudet, C., and Ries, P.: Geodetic Technique Combinations at the Observation Level: Advancements in Terrestrial Reference Frame Recovery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11071, https://doi.org/10.5194/egusphere-egu25-11071, 2025.
To update the ITRS 2020 realizations which are based on observations from the geodetic space techniques VLBI, SLR, GNSS and DORIS until the end of 2020, the ITRS Product Center asked the Technique Centers (TCs) for an extension of these series by as consistent as possible operational series. However, the GNSS input series which formerly realized an own GNSS scale, the full history of data was recomputed by the IGS TC by adopting the ITRF2020 scale based on the VLBI and SLR scale contributions.
DTRF2020, calculated by DGFI-TUM, realizes the scale from VLBI and GNSS contributions and thus needs for its update IGS/GNSS series realizing the GNSS scale. Therefore, the IGS TC provided, in addition, an extension series consistent to the input series for the ITRS 2020 realization. Moreover, the GGFC provided extensions of the previous non-tidal loading (NTL) displacement time series as well as time series for new stations to be used in the DTRF2020 update to reduce non-linear station motions.
We extended the DTRF2020 by using the provided extension series and the NTL input data until 2023. We analyzed the extended station position, datum parameter (origin and scale) and Earth Orientation Parameter time series, introduced additional discontinuities and accounted for post-seismic deformation of stations affected by earthquakes.
We present the DTRF2020 update solution (i.e. DTRF2020-u2023) and discuss the consistency of the former and the extension series. In addition, we discuss the results of comparisons of the updates computed by the three ITRS Combination Centers, which reflect the internal accuracy achieved by today's ITRS realizations.
How to cite: Seitz, M., Bloßfeld, M., Rudenko, S., Zeitlhoefler, J., and Angermann, D.: DTRF2020_u2023: The Update of DTRF2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4041, https://doi.org/10.5194/egusphere-egu25-4041, 2025.
We report on JTRF2020-u2022, the first update of JTRF2020, the most recent terrestrial reference frame (TRF) solution computed at Jet Propulsion Laboratory (JPL). Determined with SREF -a square-root information filter and Dyer-McReynolds smoother algorithm, JPL frame products lend themselves to being easily updated as long as frame inputs from the four space-geodetic technique consistent with the frame-defining data set are available.
Adopting the conceptual framework of Bayesian update inherent to any Kalman filter formulation, SREF uploads the latest estimate of JTRF2020 state and its covariance and updates it by assimilating at daily intervals the extended frame inputs made available by IGS (IGSR3-igr3.atx), IVS (ivs2023b), ILRS (ilrsav86), and IDS (idswd23) from 2021 through the end of 2022 (DOY 330, GPS Week 2237). Afterwards, with SREF running in forecast mode, station position predictions are generated through the end of 2027 (DOY 365, GPS Week 2503).
Discussions will focus on the peculiarities of the extended frame inputs used to compute JTRF2020-u2022 in relation to those adopted to generate JTRF2020, on the data pre-processing itself, and on the way in which the updated frame is constructed . We outline properties of the updated TRF in terms of its frame-defining transformation parameters and present a quality assessment of JTRF2020-u2022.
How to cite: Abbondanza, C., Chin, T. M., Gross, R. S., and Heflin, M. B.: JTRF2020-u2022: The First Update of JTRF2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6631, https://doi.org/10.5194/egusphere-egu25-6631, 2025.
In mid-2024, the IAG-IERS Joint Working Group 1.2.4 was established to complement the evaluation of the International Terrestrial Reference System (ITRS) realizations by the three ITRS combination centres (CC) of IERS with a special focus on the intercomparison of different global Terrestrial Reference Frame (TRF) solutions. The assessment aims at investigating conceptual differences of the three global ITRS realizations based on today’s user and application requirements. The main objectives of the JWG 1.2.4 include (i) the comparison of the combination strategies followed by the IERS ITRS CC; (ii) the assessment/quantification of station position time series differences between the ITRS realizations and w.r.t. geophysical models (e.g., loading displacements): (iii) the development and promotion of alternative rigorous (and independent) methods for the intercomparison of global TRF solutions (e.g., POD of low-, medium- and high-Earth-orbiting satellites); (iv) the development of methods and procedures for the quality control of TRF solutions.
Following a brief presentation of the structure of the JWG, we will give a status of its current activities. Then, we will introduce some of the benchmarks the JWG has identified to assess the quality of both global and regional TRF solutions. Finally, these benchmarks will be illustrated by their use on the latest ITRS 2020 realizations.
How to cite: Susnik, A., Moreaux, G., Ampatzidis, D., Krasna, H., Geisser, L., and Seitz, M.: IAG-IERS Joint Working Group 1.2.4 on the evaluation of the Terrestrial Reference Frames, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16930, https://doi.org/10.5194/egusphere-egu25-16930, 2025.
New realizations of the International Terrestrial Reference System (ITRS) were recently released by the three ITRS combination centers: ITRF2020 by IGN (France), DTRF2020 by DGFI-TUM (Germany) and JTRF2020 by JPL (USA). The three solutions are based on the same reprocessed data from the four space geodetic techniques (DORIS, GNSS, SLR, VLBI). However, the strategies used by the three ITRS centers to combine these input data into their respective solutions differ in several key aspects, such as the modeling of time-varying station trajectories, the connection of the station networks of the four techniques into a unique common frame, and the choices made to define the origin and scale of that frame.
This presentation compares the ITRF2020, DTRF2020 and JTRF2020 solutions and discusses how different aspects of the combination strategies employed by the three ITRS centers affect their solutions in terms of origin, scale and geometry. This comparison and discussion covers two main aspects: (1) individual station trajectories in the three solutions, and their ability to accurately describe the Earth’s time-varying shape, and (2) origins, scales (and orientations) of the station coordinates of each technique in the three solutions.
How to cite: Barnéoud, J., Rebischung, P., Gobron, K., de la Serve, M., Collilieux, X., and Altamimi, Z.: A comparison of ITRF2020, DTRF2020 and JTRF2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11660, https://doi.org/10.5194/egusphere-egu25-11660, 2025.
Genesis is an ESA mission dedicated to Global Navigation Satellite System (GNSS) Science, conducted by the ESA Navigation Directorate. Its primary objective is the contribution to the improvement of the International Terrestrial Reference Frame (ITRF) accuracy (1mm) and long-term stability (0.1mm/year). Secondary objectives include the contribution to a high number of other scientific disciplines (geodesy, geodynamics, earth rotation, geophysics, earth gravity field, atmosphere and ionosphere sciences, metrology, relativity…) [1].
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 a launch date in 2028 [2]. Antwerp Space (B), as the major sub-contractor of OHB-I, oversees the payload and geodetic instruments. Industrial activities were kicked-off in April 2024, the System Requirements Review was successfully closed-out in Q4 2024, and work is on-going towards a Preliminary Design Review in Q4 2025.
In parallel, on the scientific side, after a first successful Genesis Workshop held in February 2024 [3], a Genesis Science Exploitation Team was set-up and members appointed. The Genesis Science Exploitation Team are actively supporting the mission development (in particular consolidation of requirements) and will play a key role in its future exploitation.
The presentation will provide a high-level description of the mission, and provide the programmatic status of Genesis.
[1]: Delva et al. Earth, Planets and Space 75, 5 (2023)
[2]: https://www.esa.int/Applications/Satellite_navigation/ESA_kicks_off_two_new_navigation_missions
[3]: https://www.esa.int/Applications/Satellite_navigation/The_geodetic_community_meets_Genesis
How to cite: Gidlund, S., Fusco, G., Waller, P., Morlet, C., Perez Lissi, F., Sakalauskaite, E., Enderle, W., Schoenemann, E., Berton, J.-C., Gini, F., and Navarro, V.: Overview of Genesis - an ESA mission at the Foundation of Navigation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15776, https://doi.org/10.5194/egusphere-egu25-15776, 2025.
Genesis is an upcoming satellite mission by the European Space Agency (ESA) that will integrate multiple space geodetic techniques on a single satellite at an altitude of 6000 km, including a dedicated Very Long Baseline Interferometry (VLBI) transmitter. This innovative, dynamic space geodetic observatory aims to establish highly accurate and continuous space ties, significantly enhancing the accuracy and stability of Terrestrial Reference Frames (TRFs). Including a VLBI transmitter will enable observations to Genesis using existing VGOS antennas and infrastructure, but several technical challenges must be addressed to ensure the success of VLBI observations.
A key open question is the choice of the satellite’s orbit, whether polar (97°) or inclined (60°). Additionally, the allocation of observation time between satellite and quasar observations must be carefully optimized. While sufficient VLBI observations of Genesis are needed to estimate accurate station positions, maintaining a good sky coverage of quasar observations is essential for precise tropospheric delay modeling, the major error source in VLBI measurements.
This simulation study addresses these points by evaluating various observation scenarios for two VGOS station networks, considering different orbital configurations and observation time distributions. Based on the determination of TRFs from weekly VLBI sessions over a two-year investigation period, we aim to identify the optimal setup for VLBI observations of Genesis.
How to cite: Kern, L., Wolf, H., Steinmetz, S., and Böhm, J.: Evaluating VLBI Scenarios for Genesis: Orbital and Observational Configurations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15312, https://doi.org/10.5194/egusphere-egu25-15312, 2025.
Set for launch in 2028, geodesy’s flagship mission GENESIS is equipped with the instruments of the four space geodetic techniques. The co-location satellite aims to improve the accuracy and stability of future realizations of the ITRF. However, VLBI observations to satellites are not standard and are not performed routinely yet. In the past, observations were limited to specific telescopes and setups. At the moment, most VLBI antennas are not capable of observing currently available satellite signals. This makes testing difficult, although further research on the VLBI component of GENESIS is urgently needed to achieve the accuracy for the mission goals. We present the newly accessible capability of the Australian VGOS telescopes to observe GNSS satellites in L-band. With this new discovery, we are able to generate geodetic delay observables with a full continental-wide telescope array on a routine basis in the style of IVS observations. In particular, we report on a series of successful observations to satellites of the GPS, Galileo and BeiDou constellations with the AuScope 12-m antennas in Hobart, Katherine and Yarragadee using the standard VGOS equipment. We describe the experimental setup, signal chain and key developments enabling these observations. Furthermore, we report on the ongoing efforts in the fringe fitting phase with critical effects on the delay. This crucial development is a valuable opportunity to further develop VLBI observations to satellites in preparation for the GENESIS mission. In addition, such observations could realize the first-ever inter-technique ties between VLBI and GNSS in the Australian region.
How to cite: Schunck, D., McCallum, L., McCallum, J., and McCarthy, T.: Observing GNSS Satellites with the AuScope VLBI Array: A Testbed for the VLBI Component of the GENESIS Mission, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18387, https://doi.org/10.5194/egusphere-egu25-18387, 2025.
The global high-precision Terrestrial Reference Frame (TRF) is determined through the combination of the four space geodetic techniques: VLBI, SLR, GNSS, and DORIS. The multi-technique combination heavily relies on the common objects or parameters, i.e., the ties, which link the different techniques. Current realizations of the International Terrestrial Reference Frame (ITRF) employ local ties and Earth Orientation Parameter (EOP). Additional ties such as tropospheric ties and satellite orbit ties are being explored. Another promising approach is using clock ties, where co-located instruments connected to a common clock enable intra- and inter-technique clock tie modeling.
Clock ties between GNSS and VLBI are of particular interest as (1) GNSS provides dense observations at every epoch, allowing the epoch-wise estimation of clock parameters, and (2) VLBI typically relies on clock modeling due to the insufficient number of observations per epoch. Using the GNSS and VLBI co-location stations during VLBI CONT campaigns, we demonstrate inter-technique clock agreements within 0.1 and 0.2 ns for short (24-hour) and long (15-day) periods, respectively. We further explore the application of clock ties in the GNSS and VLBI integrated solution, focusing on the impact on station coordinates and tropospheric delays. We also address the challenges of modeling deterministic and stochastic components of the clock ties, highlighting their potential to improve the precision of TRF realizations.
How to cite: Wang, J., Balidakis, K., Heinkelmann, R., Ge, M., and Schuh, H.: Applying Clock Ties in GNSS and VLBI Integrated Solution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7460, https://doi.org/10.5194/egusphere-egu25-7460, 2025.
This effort as part of the research unit "Clock Metrology" funded by the German Research Foundation (DFG) focuses on innovative strategies for combining all four space geodetic techniques—DORIS, GNSS, SLR, and VLBI—to significantly enhance the global Terrestrial Reference Frames (TRF) with the goal to achieve the GGOS (Global Geodetic Observing System) requirements of 1 mm accuracy and long-term stability of 1 mm/decade. To achieve this goal, a novel approach of combining the space geodetic techniques is being developed. A common target (CT) will be introduced at the Geodetic Observatory Wettzell (GOW) to combine all the techniques at a common reference point. Additionally, a common clock (CC) will be established at GOW to reference the observations of all techniques to a single time frame. The impact of the CT and CC on the TRF combination is evaluated through simulations involving all four space geodetic techniques. In this study, we exhibit the results of the SLR, GNSS, and VLBI simulations of global station networks as reference solutions for the following implementation of CT and CC. As basis for these simulations, we used current state-of-the-art models and standards based on real observation data to determine realistic accuracy measures for today’s technique-specific observations. We assume a white noise of the observations with an amplitude corresponding to the noise derived from actual data analysis of the real observations for each technique. Subsequently, weekly normal equation systems from the simulated data were accumulated into a combined global TRF solution over a 7-year period to assess the impact on the derived station coordinates and velocities, as well as the Earth Rotation Parameters. The estimated corrections to the station positions remain within a few millimeters, indicating a consistent solution w.r.t a priori. Additionally, in order to perform the combination via a CC, extended software modifications are carried out as in the space geodetic data analysis the clock parameters are usually pre-eliminated and no longer available for further processing. Based on these modifications, first results of the novel combination of intra- and inter-techniques at GOW will be presented.
How to cite: Reinhold, A., Glaser, S., and Seitz, M.: On simulation studies for novel combination strategies of space geodetic techniques, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1646, https://doi.org/10.5194/egusphere-egu25-1646, 2025.
Realizing the terrestrial scale from Global Navigation Satellite System (GNSS) data requires precisely calibrated and highly stable satellite antenna phase centers. The results from the third International GNSS Service (IGS) reprocessing campaign, however, have raised renewed concerns about the long-term stability of the GNSS transmit antenna phase center relative to the spacecraft center of mass. Reevaluation of the satellite radial phase center offsets (z-PCOs) based on SINEX data from multiple IGS analysis centers revealed abrupt changes over time of up to 1 decimeter. Commonly cited reasons for time-varying z-PCO estimates are “aging” of the antenna and its radiation pattern, changing composition of the satellite constellation and ground network, and movement of the center of mass as propellant is consumed for satellite momentum dumps or orbital maneuvers. In this presentation, we shed light on another, yet unknown, effect arising from the drift of the satellite clock that prompts GNSS ground segment operators to adjust the clock frequency to ensure that the timing corrections in the satellite broadcast navigation message remain within the limits specified by the signal-in-space interface. The frequency adjustments are easily detectable in satellite clock bias estimates or broadcast clock correction parameters. However, this is only half the story; changing the clock frequency results in boresight angle-dependent lengthening or shortening of the carrier phase range, which the satellite antenna z-PCO parameter can almost perfectly absorb. As we will demonstrate through simulations and real-world examples from various GNSS spacecraft, a 4 × 10-10 correction applied to the onboard clock fundamental frequency (10.23 MHz) alters the estimated satellite z-PCOs for the standard ionosphere-free linear combination of L1 and L2/E5 by approximately 7 cm. The results indicate that satellite clock adjustments are the cause of the observed z-PCO jumps in the IGS “repro3” time series.
How to cite: Dilssner, F., Springer, T., Gonzalez, F., Schönemann, E., and Gini, F.: The Ticking Truth: How Subtle Clock Adjustments Influence GNSS Satellite Antenna Offset Estimates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19163, https://doi.org/10.5194/egusphere-egu25-19163, 2025.
A Global Geodetic Reference Frame (GGRF) is a fundamental requirement to relate measurements taken from anywhere on the Earth. It provides the basis on which a broad spectrum of scientific and industrial applications rely, and is crucial in any field where precise location information is necessary, including monitoring climate change, agriculture, and changes in groundwater.
The working group Satellite Geodesy at the Institute of Geodesy (IFG), Graz University of Technology (TUG) provide a wide range of of products which are processed and published to the international community such as gravity field ans mass transport solutions, Precise Orbit Data (POD) of Low Earth Orbit (LEO) satellites and Global Navigation Satellite Systems (GNSS) station networks and much more. The products are utilized by various organizations, such as the International Combination Service for Time-variable Gravity Fields (COST-G) of the International Association of Geodesy (IAG), the International GNSS Service (IGS) or the European Copernicus POD Service Quality Working Group (CPOD). A consistent and accurate GGRF is the foundation of all our products and, as such, is essential to ensure the quality of our in-house computed products.
A GGRF is established and maintained by an international community, culminating in the International Terrestrial Reference Frames (ITRF). The latest version, ITRF2020, is based on four space geodetic techniques: GNSS, VLBI, SLR, and DORIS. In ITRF2020, GNSS was ignored in the calculation of the geocenter motion and the estimation of the reference system scale because it was considered too inaccurate.
In this work we present our approach to estimate the geocenter motion and to improve the scale estimation using only GNSS.
We discuss the problems of combined estimation of geocenter motion, reference system scale and satellite antenna center offsets and variations in GNSS only reference frame estimation. We analyze the results and implications for GNSS products and station position time series.
How to cite: Dumitraschkewitz, P., Mayer-Gürr, T., and Süsser-Rechberger, B.: Scale and Geocenter determination by GNSS only, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8525, https://doi.org/10.5194/egusphere-egu25-8525, 2025.
The global geodetic parameters are essential for the realization of an International Terrestrial Reference Frame (ITRF), which has broad geophysical and geodetic applications. With well-distributed global tracking stations and continuous observations, GNSS is suited to providing high quality geodetic parameters, including geocenter coordinates (GCCs) and Earth rotation parameters (ERPs). However, the spurious draconitic signals have been observed in GNSS-based geodetic products. Fortunately, the fast development of multi-GNSS and LEO satellite techniques in recent years provides new opportunity to improve the determination of geodetic parameters by combining observations from constellations with different orbital characteristics. In this study, we perform the integrated precise orbit determination (IPOD) under the ITRF2020 with dual-system GPS/Galileo observations from the Sentinel-6A satellite and 61 ground stations for geodetic parameter estimation. The effects of the LEO solar radiation pressure (SRP) model are analyzed and the contribution of the multi-GNSS combination and the LEO is investigated.
Three Sentinel-6A macro models, from the manufacturer, the German Aerospace Center (DLR) and the University of Colorado and Jet Propulsion Laboratory (UoC/JPL), are used to perform GPS-based IPOD solutions to investigate the impact of LEO SRP model on geodetic parameter estimation. The relationship between the estimated constant SRP scale and sun elevation is first analyzed. The estimated SRP scale based on the UoC/JPL macro model is found to have a weaker correlation with sun elevation compared the other two macro models. By comparing the geodetic parameters obtained using different macro models, we find that the GCC-Z estimates are more sensitive to the LEO priori SRP model than the GCC-X/Y and ERPs, and the best solution with the smallest amplitude in 3 cpy frequency is achieved by UoC/JPL macro model.
Based on the UoC/JPL macro model, we further investigate the performance of the geodetic parameter estimation in IPOD with dual-system GPS and Galileo observations. The introduction of the LEO improves the ERPs estimates, with a reduction in the length of day (LoD) formal error of about 60%, and a reduction in the drift rate of the GNSS-derived dUT1 away from the IERS 20 C04 reference value of over 30%. The introduction of the LEO also improves the GCC estimates with a reduction in GCC-Z formal error and STD value by about 20% and 10% respectively. Compared to single system solution, the combination of GPS, Galileo and the LEO obtains the most stable GCC estimates with the smallest STD values, except for the GCC-Z for the period above 30 days, mainly due to the failure to eliminate the Galileo-induced 3 cpy spurious signal. However, the introduction of Sentinel-6A also induces the spurious annual signal due to its SRP model deficiency. Though this deficiency can be partly compensated by changing the parameterization of SRP scale factor from constant to piece-wise constant, the influence of residual errors of LEO SRP modelling is still visible in the Z component of GCC. These results indicate that refining the a priori macro model of LEO satellite is necessary to obtain accurate geodetic parameters in IPOD with multi-GNSS.
How to cite: Zhao, Y., Zhang, K., Li, X., Fu, Y., and Yuan, Y.: Global geodetic parameter estimation using the combination of GPS, Galileo and LEO satellites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4664, https://doi.org/10.5194/egusphere-egu25-4664, 2025.
To ensure inter-operability and consistency of various geodetic products for Solid Earth science and operational geodesy applications, a long-term global terrestrial reference frame is required, i.e., the International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF). As one of the key parameters in the determination of the ITRF, geocenter motion must be precisely estimated. Space geodetic techniques such as Satellite Laser Ranging (SLR), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and Global Navigation Satellite Systems (GNSS), which connect satellites and ground stations, are capable of determining geocenter motion. However, only the SLR technique is currently included in the realization of the ITRF, despite GNSS being widely regarded as a promising technology. Compared to SLR-based solutions, GNSS exhibits lower accuracy due to various modeling issues, including deficiencies in non-gravitational force models. In recent years, numerous studies have demonstrated the significant potential for improving geocenter coordinate estimation through the integration of ground-based observations and space-based observations from low Earth orbiters (LEOs). Nevertheless, the full contribution of LEOs to geocenter motion estimation remains underexplored, largely due to the limited temporal coverage and the small number of LEOs available..
To evaluate the extent of associated improvements, a network of 150 ground tracking stations and up to 13 LEOs (GRACE-A/B/C/D, SWARM-A/B/C, JASON-1/2/3, SENTINEL-3A/3B, and SENTINEL-6A) was processed over a 20-year period (2004–2024). Three solutions were investigated: (1) a reference solution utilizing only ground-based GNSS observations; (2) a combined ground- and space-based solution employing a reduced-dynamic (DYN) strategy for LEO orbit determination; and (3) a combined ground- and space-based solution employing a kinematic (KIN) strategy for LEO orbit determination. All solutions were implemented in accordance with the processing strategy of the IGS's 3rd reprocessing campaign.
In this contribution, we evaluate contribution of space-based observations to geocenter motion estimation through spectral analysis and external comparisons. Significant improvements are observed in the combined ground- and space-based solutions, particularly in enhancing geocenter motion stability and mitigating certain artificial signals. Among the three solutions, the GNSS/LEO integrated solution employing the KIN strategy for LEOs demonstrates a substantial reduction in draconitic errors compared to the others.
How to cite: Tang, L., Männel, B., Wang, J., Nie, L., and Wickert, J.: The contribution of multi-LEOs to geocenter motion estimation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12120, https://doi.org/10.5194/egusphere-egu25-12120, 2025.
Global Navigation Satellite Systems (GNSS) are based on measurements of signal propagation time, so that clock information is required for both the transmitting satellite and the receiving ground station. In undifferenced GNSS network analyses, synchronization errors of the satellite and station clocks are usually estimated by epoch-wise biases. If, as is common in practice, white noise is assumed as stochastic behavior for the clocks, there are high correlations between the clock estimates and other geodetic parameters. While the satellite clock is correlated with the radial orbit component and geocenter parameters, the station clock shows high correlations with the station height coordinate and the tropospheric zenith delay. These effects can be reduced by introducing proper models for describing the clock characteristics. Especially for global network solutions, deterministic clock modeling is suitable to reduce a substantial number of clock estimates. However, adequate modeling requires a high degree of stability for the corresponding clocks.
In this contribution, we show preliminary results of modeling highly stable GNSS ground and space clocks using piece-wise linear representations. For the satellites, we select the rubidium clocks of the GPS IIF and IIIA blocks as well as the passive hydrogen maser clocks of the Galileo FOC spacecraft for modeling. In addition, a selection of hydrogen maser stations of the International GNSS Service (IGS) is also modeled. Over a period of several weeks, daily network solutions with and without piece-wise linear clock modeling are processed and then compared. We discuss different strategies and show the effects of various modeling options (length of split interval, parameter weighting) on the correlations of the estimated parameters.
How to cite: Widczisk, J. S., Männel, B., and Wickert, J.: Modeling of highly stable GNSS ground and space clocks using piece-wise linear representations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2545, https://doi.org/10.5194/egusphere-egu25-2545, 2025.
Global Navigation Satellite Systems (GNSS) rely on one-way signal travel time measurements from satellites to receivers. To ensure accurate ranging, GNSS must estimate and compensate for clock offsets on at least one end of the transmitter-receiver system. Consequently, clock offsets are highly correlated with GNSS-derived parameters such as station coordinates, tropospheric delay estimates, satellite radial orbit parameters, and apparent geocenter coordinates. Improper handling of clock offsets can lead to their absorption into these parameters, degrading geodetic product accuracy. Traditionally, clocks have been handled within individual techniques without being specially addressed. However, some research efforts and experimental trials have explored using VLBI to synchronize clocks for GNSS and refining clock models to reduce correlations with other estimated parameters in GNSS, thereby improving overall precision.
With recent advancements, high-precision optical clocks and fiber-optic time transfer technologies provide new possibilities for enhancing clock synchronization in GNSS. Optical fiber offers a stable, interference-free medium for time and frequency transfer, eliminating atmospheric effects such as ionospheric and tropospheric delays that impact GNSS-based synchronization. Moreover, fiber-optic time transfer is inherently two-way, removing the need for external clock offset estimation. Thus, fiber-optic clock synchronization represents the most precise timing technique currently available. Establishing a common clock by connecting multiple GNSS receivers via optical fiber could significantly reduce the number of estimated clock parameters in GNSS solutions, leading to improved geodetic measurement precision and a more accurate geodetic reference frame.
Despite its potential, the approach of implementing a common clock with optical fiber for GNSS receivers remains largely untested. Although optical fiber links have been successfully used in clock synchronization, their integration into GNSS receiver clocking is still in an experimental stage. Notable existing efforts include: (1) the Geodetic Observatory Wettzell, where multiple receivers are connected to a single clock via optical fiber, representing a local baseline setup, and (2) the GFZ experiment, where a receiver is linked to the ultra-stable clock of PTB, representing a regional baseline approach.
This study characterizes existing fiber-optic connections among GNSS receivers to identify practical challenges and evaluate their impact on GNSS parameter estimation. We process data from receivers sharing a common clock using Bernese GNSS Software. Initially, PPP will be performed to compare GNSS-derived clock parameters across receivers sharing a common clock, verifying the effectiveness of fiber-optic clock synchronization. Following this validation, we will leverage GNSS-derived clock parameters to evaluate inter-receiver clock differences measured via optical fiber. Subsequently, we will implement a strategy in which only one receiver’s clock parameters are estimated, using fiber-measured clock differences as a priori constraints for other receivers in the PPP solution. This approach reduces the number of estimated clock parameters and serves as a preliminary test of the feasibility of a GNSS common clock framework.
Future developments will focus on refining our analysis framework to enable simultaneous estimation of GNSS receivers operating under a common clock. This research contributes to the broader goal of integrating ultra-stable clocks into global GNSS networks, ultimately enhancing the stability of geodetic reference frames and improving GNSS-derived geodetic products.
How to cite: Wang, Z., Hugentobler, U., Männel, B., and Rodríguez-Villamizar, J.: Common Clock for GNSS Receivers: Characterization of Parameters Estimated with GNSS Receivers Connected to the Same External High-Precision Clock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7197, https://doi.org/10.5194/egusphere-egu25-7197, 2025.
GNSS station operators and network analysers face the challenge of achieving consistent phase center corrections (PCCs), particularly since multi-GNSS calibrations are not available for all antennas. To address this issue, a global initiative involving nine calibration organizations has launched a comprehensive ring calibration campaign. This collaboration aims to enhance the consistency of calibration methods and establish a robust quality assessment framework by sharing six structurally diverse antenna samples for calibration. The recommended methods by the International GNSS Service (IGS), including anechoic chamber and field robot calibration methods, are participating with the aim of defining a global benchmark for the accuracy and reliability of receiver antenna PCCs.
Over the past year, the campaign has made significant progress. Measures and methods to easily compare the PCC patterns and define a benchmark value for consistent PCCs have been established. In this contribution, we present the latest results of this campaign. We demonstrate in the pattern domain that the consistency among the system/frequencies per receiver antenna design varies around an uncertainty level of ±1 mm, with an elevation-dependent effect also needing consideration. In the position domain, we present system-specific PPP results per antenna and facility. For example, the variation among different antennas and facilities for classical GPS ionosphere free linear combination is generally below 2-3 mm for the horizontal component and below 5 mm for the vertical component when comparing calibration sets among the various facilities. We also present comprehensive and effective comparison methods for the pattern domain and evaluation tools for the position domain that are essential for establishing a globally fair and transparent benchmark for receiver antenna PCC calibration and verification processes.
How to cite: Kersten, T., Billich, A., Sutyagin, I., Kröger, J., and Schön, S.: Progress Update on a Global Collaboration for GNSS Receiver Antenna Calibration: Results from the IGS Ring Calibration Campaign (IGS ringCalVal), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9053, https://doi.org/10.5194/egusphere-egu25-9053, 2025.
The International Laser Ranging Service (ILRS) regularly contributes to the maintenance of the reference frame by providing daily and weekly combined time series of station coordinates and Earth Rotation Parameters (ILRSA from the ILRS primary ASI Combination Center) derived from individual Analysis Centers (ACs) solutions, using LAGEOS-1/-2 and Etalon-1/-2 satellite data.
The inclusion of additional satellites in the ILRS official products has been under discussion since years within the ILRS Analysis Standing Committee and the launch of LARES-2 in July 2022 has been considered a real opportunity to improve the product quality. LARES-2 is a LAGEOS-type satellite specifically designed for high-accuracy satellite laser ranging.
The inclusion of LARES-2 as the fifth satellites of the constellation contributing to the routine products foresees a preliminary analysis to model stations' long-term systematic errors related to LARES-2.
The approach to manage the systematic errors is the same used for the ITRF2020 contributions: ACs simultaneously estimate station coordinates and range biases to determine a combined ILRSA set of long-term mean range biases for LARES-2, to be applied in the data analysis.
The identified systematic errors are reported in the ILRS Data Handling File (DHF), which is closely linked to the target signature model.
Preliminary time series of products including LAGEOS/ETALON/LARES-2 are available and an enhanced quality in the estimated station coordinates is evident, particularly in the UP component.
This presentation will address the status of the LARES-2 inclusion to the ILRS official products, emphasizing the quality of estimated parameters.
How to cite: Sarrocco, D., Luceri, V., Basoni, A., Vespe, F., and Blossfeld, M.: LARES-2 in the ILRS official products: analysis and current status, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4085, https://doi.org/10.5194/egusphere-egu25-4085, 2025.
Further development of the Satellite Laser Ranging (SLR) technique is essential not only to achieve the goals defined by the Global Geodetic Observing System (GGOS) but also to meet the growing challenges associated with understanding the increasingly frequent and dynamic processes occurring at the Earth's surface. SLR plays a key role in the realization of the Terrestrial Reference Frames (TRFs). It is also crucial for determining the gravitational potential, as the C20 and C30 coefficients in solutions from dedicated GRACE Follow-On missions are replaced by those derived from laser observations.
This study investigates the optimal orbital parameters to consider for future geodetic satellites. We performed simulations for satellites with different inclination angles ranging from 0° to 180° with 1° interval, and at five different altitudes ranging from 1,500 km to 10,300 km with 1,200 km interval. The analysis was carried out under two different scenarios: (1) optimisation for TRF realisation and (2) optimisation for recovery of the Earth's gravitational potential. The results indicate that the optimal satellite altitude for TRF implementation is about 3,700 km, with inclination angles between 0°-20° or 160°-180°, which minimises formal errors in the determination of geocenter coordinates and Earth Rotation Parameters (ERP). On the other hand, geodetic satellites designed primarily to determine the parameters of the Earth's low gravity potential should operate at an altitude of 1,500 km with inclinations between 30°-40° or 135°-145°.
In particular, none of the current satellites in the SLR constellation have orbital parameters optimised for low-degree gravity recovery. Adding a single satellite with suitable inclination parameters to the existing constellation of ten geodetic satellites would reduce the error in the determination of the Earth's oblateness term, C20, by order of magnitude.
How to cite: Najder, J., Sośnica, K., Zajdel, R., and Kur, T.: Simulation for SLR space segment development to improve global geodetic parameters - different inclination angles & altitudes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20752, https://doi.org/10.5194/egusphere-egu25-20752, 2025.
In the context of its contribution to the second yearly update of the 2020 realization of the International Terrestrial Reference Frame (ITRF2020), the International DORIS Service (IDS) has undertaken the estimation of DORIS station positions and velocities, as well as Earth Rotation Parameters (ERPs), derived from DORIS data. These computations are based on the latest weekly multi-satellite series from the five IDS Analysis Centers and the IDS Associated Analysis Center, covering data from 2024 and 2021 backward.
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) EOPs, and (4) a cumulative position and velocity solution. Additionally, this study examines the benefits of new models as well as the implementation of South Atlantic Anomaly (SAA) mitigation strategies on specific DORIS missions. Particular focus is placed on the enhanced stability of the IDS-derived scale since late 2012.
How to cite: Moreaux, G., Lemoine, F., Capdeville, H., Štěpánek, P., Otten, M., Nahmani, S., Pollet, A., and Schreiner, P.: IDS contribution to the second update of the ITRF2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12833, https://doi.org/10.5194/egusphere-egu25-12833, 2025.
The classical VLBI delay model is built on the assumption that incoming radiowaves are planar, which holds true for observations of distant celestial radio sources due to their immense distances. However, when applied to VLBI observations of satellites in near-Earth orbit, this assumption becomes inadequate, as the curvature of the wavefronts cannot be neglected. Accurately modeling of these delays is crucial for achieving the precision required in satellite-based VLBI studies. To address this challenge, several near-field delay models have been proposed in the literature. In this study, we focus on four near-field VLBI delay models, comparing their methodologies, and resulting accuracy across a range of orbital configurations. By systematically evaluating these models under varying geometric and dynamic conditions, we aim to identify their strengths, limitations, and potential discrepancies.
How to cite: Sert, H., Karatekin, O., and Dehant, V.: Comparison of near-field delay models for Earth-orbiting satellites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12493, https://doi.org/10.5194/egusphere-egu25-12493, 2025.
The upcoming Genesis mission of the European Space Agency (ESA) will allow for the combination of all 4 space geodetic techniques, being GNSS (Global Navigation Satellite Systems), SLR (Satellite Laser Ranging), DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite), and VLBI (Very Long Baseline Interferometry). This promises progress for an improved terrestrial reference frame (TRF) and the determination of inherent biases of each technique. From the VLBI and VGOS (VLBI Global Observing System) point of view, the advantage of adding VLBI observations of satellites into an observing session is that it allows the ability to also estimate the geocenter and the satellite’s orbit to centimetre precision, as shown in previous studies. There is still an opportunity to investigate the effect of the chosen satellite orbit itself and the parameterisation in the analysis stage, on the determined Earth Orientation Parameters (EOP) and the potentially determined satellite orbit. In this work we show the simulation of VGOS observations of a Genesis-like satellite, including scheduling, observations simulation, and analysis. This research will address the impact on the determination of EOPs and the determined satellite orbit, by the chosen initial satellite orbit and the parametrisation in the analysis process. The results of this study will enable future VLBI schedule optimisation that include satellite observations, and serve as a reference for orbital elements selection for VLBI observed geodetic satellites.
How to cite: Wolfs, R. and Haas, R.: Simulating and analysing VGOS observations for Genesis orbits and EOP determination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19542, https://doi.org/10.5194/egusphere-egu25-19542, 2025.
The accuracy of the Terrestrial Reference Frame (TRF) realization is currently constrained by systematic errors among the four main space-geodetic techniques: GNSS, VLBI, SLR, and DORIS. Terrestrial local ties connect physical survey points from local surveys, which will introduce errors in the TRF and transform uncertainties across all geodetic observations. To achieve the GGOS goals of 1 mm accuracy and 0.1 mm/yr stability for TRF realization, space missions equipped with multiple space-geodetic techniques are proposed, such as GRASP (Geodetic Reference Antenna in Space), E-GRASP, and GENESIS. Space co-location will complement ground-based co-location and enhance the TRF.
We are currently developing the simulated space-geodetic observations of various missions and assessing their potential impact on the TRF including station coordinates, Earth Orientation Parameters, and geocenter. The simulations will take into account VLBI tracking GNSS satellites and geodetic satellites, considering three major error sources: measurement noise, clock error, and zenith wet delay. Through these thorough analyses, we will explore the requirements of this new type of observable. The novel measurement concept has the potential for not only solving the inconsistencies and biases between the different geodetic techniques, but also establishing frame ties between the kinematic and dynamic reference frames.
How to cite: Liu, H., Zou, X., Liu, B., Zhao, M., and Pan, J.: Simulation studies on VLBI tracking satellites and the potential to enhance TRF, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5546, https://doi.org/10.5194/egusphere-egu25-5546, 2025.
High precision satellite laser ranging observations to the geodetic spherical satellites are now available for almost five decades, and their analyses are critical to the ongoing realisation of an accurate terrestrial reference frame. Inevitably and importantly the ground-station technologies have improved considerably over time, such that systematic range-measurement errors are now for the major stations at the few mm level. Such hardware improvements, as well as improved analyses procedures instigated by the ILRS, have prompted a review of the measurements made mostly by a number of European network stations in the early 2000s that used time-of-flight equipment known to have systematic, range-dependent errors of up to 10mm. These timers were investigated at the UK Space Geodesy Facility, Herstmonceux in the early 2000s and the range dependencies measured against a highly accurate event timer; however, some of the implications of those results have not yet fully been utilised in data processing for ITRF realisations.
In this poster we review this work and report on our new data analyses that include the range-dependent corrections, commenting on the impact on the quality of the stations’ height time series.
How to cite: Appleby, G. and Susnik, A.: Further progress to improve the accuracy of satellite laser ranging data: impact on geodetic height time series of removal of range-dependent systematic errors at some European stations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10241, https://doi.org/10.5194/egusphere-egu25-10241, 2025.
The NASA GSFC/UMBC JCET ILRS Analysis Center supports the International Laser Ranging Service (ILRS) by operating as an Analysis Center (AC), submitting regular SINEX solutions on a daily and weekly basis, acting as the backup combination center (ILRSB), and conducting validation of ILRS tracking stations. These validations are essential for new stations or stations implementing significant changes. In support of the ILRS Analysis Standing Committee (ASC), the JCET AC processes data to the ILRS “ITRF” satellites (LAGEOS-1, LAGEOS-2, LARES, LARES-2, Etalon-1, and Etalon-2) and submits different SINEX solutions containing Earth orientation parameters and station coordinates daily and weekly. We provide an overview of these analysis activities and present the methods and results of our recent validation efforts, benchmarking the ILRSB results with the results obtained by ILRSA. We summarize the recent contributions of the Analysis Center, including the v85 (ITRF2020 & extension contributions), v80, v180 (LAGEOS1, LAGEOS2, Etalon1-2), as well as v90, v190 (including LARES-2). Additionally, we report on the validation activities that we perform for the ILRS Analysis Standing Committee, where the performance of new stations or stations undergoing system upgrades are evaluated with respect to the quality of their precision of their data and their bias stability. ILRS Stations that have undergone validation in the last six months include Matera (7941), and Yebes (7817).
How to cite: Kuzmicz-Cieslak, M., Evans, K. D., Belli, A., and Lemoine, F. G.: Update on the activities of the NASA GSFC/JCET ILRS Analysis Center, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13490, https://doi.org/10.5194/egusphere-egu25-13490, 2025.
Global Terrestrial Reference Frames (TRFs) are regularly provided by three International Terrestrial Reference System (ITRS) combination centres (CCs) of the International Earth Rotation and Reference Systems Service (IERS), located at the Institut national de l’information géographique et forestière (IGN), at the Jet Propulsion Laboratory (JPL) of the National Aeronautics and Space Administration (NASA), and at the Deutsches Geodätisches Forschungsinstitut (DGFI) of the Technical University of Munich (TUM). All three CCs use different methodologies and assumptions to compute a global TRF.
In the framework of the IAG-IERS Joint Working Group 1.2.4 for the evaluation of the terrestrial reference frames, we analyze the impact of three different 2020 TRF realizations (provided by the CCs) on Satellite Laser Ranging (SLR) data processing using a development version of the Bernese GNSS Software (BSW).
First, to obtain the total effect of the TRF realization on the SLR satellite orbits and the post-fit observation residuals, the station coordinates are fixed to the a priori values. Afterwards, the set of excepted core stations used for a proper datum definition is compared for the different TRFs. Finally, a state-of-the-art SLR data processing is performed, where orbit parameters and range biases along with global geodetic parameters, e.g., Earth rotation parameters and station coordinates, are co-estimated.
How to cite: Geisser, L., Susnik, A., Arnold, D., Dach, R., and Jäggi, A.: Impact of Different TRF Realizations on SLR Data Processing in the Benese GNSS Software, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11575, https://doi.org/10.5194/egusphere-egu25-11575, 2025.
This study outlines the current status of DORIS data processing using the GipsyX software at the IGN-IPGP/JPL analysis center within the International DORIS Service (IDS). We detail the methodological evolution implemented since late 2023 for the ITRF2020-u2024, coinciding with the operational reactivation of the analysis center (AC).
Our analysis focuses on a comparative assessment of precise orbit determination (POD) results against SSALTO orbits, positioning estimates relative to the DPOD2020 reference frame, and Earth Orientation Parameters (EOPs) against the EOPC04 series. This enables a thorough evaluation of the consistency and accuracy of our products relative to established benchmarks.
In addition to describing these advancements, we highlight ongoing and planned developments aimed at enhancing processing capabilities. Among these, we present preliminary results from simultaneous multi-satellite data analysis, which incorporates separate modeling of ground and satellite clocks. These developments are expected to improve the temporal and spatial resolution of DORIS-derived geodetic products, ultimately contributing to the broader geophysical and climate-monitoring goals of the IDS.
How to cite: Pollet, A., Nahmani, S., and Bertiger, W.: DORIS IGN-IPGP/JPL Analysis Center: Current Status and Future Developments , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15635, https://doi.org/10.5194/egusphere-egu25-15635, 2025.
This study investigates the estimation of the Length of Day (LOD) using DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) RINEX data from 2015 to 2023, comparing results with the IERS 20 C04 model. Observations from 10 satellites were analyzed using DORIS-specific modification of the Bernese GNSS software, with varying durations of data availability across the nine years. The analysis explores the variability in Earth's rotation, attributing changes to dynamic factors influencing angular momentum. Various solution versions with different parameter constraints were evaluated. Statistical analysis reveals that the low constrained cross track once per revolution parameters provided less reliable results.
Key findings reveal a close alignment between DORIS-derived LOD values and the IERS 20 C04 model, for satellite combinations, with a weighted mean of 7 µs and a weighted standard deviation of 87 µs . Single-satellite analyses highlight the contributions of specific satellites, such as Cryosat, Saral, and Sentinel-6, in capturing unique geophysical processes. Improved data precision and modeling were observed over the years, reflecting advancements in satellite instrumentation and operational protocols. Statistical analysis emphasizes combining multiple satellite datasets for more reliable LOD estimates, as single-satellite solutions showed higher variability and biases.
Spectral analysis identifies dominant periodic signals, such as annual and semi-annual cycles, and variations induced by tidal and orbital mismodeling. The impact of relativistic effects was evaluated, demonstrating the significant role of Lense-Thirring corrections in precise LOD modeling. A comparison of different subdaily motion models revealed subtle differences in periodic signal amplitudes. This work underscores the possibility of precise LOD estimation from DORIS data, on condition of high-quality satellite data and refined modeling techniques for accurate Earth rotation studies, providing insights into temporal variability in LOD and contributing to geodetic and geophysical research.
How to cite: Stepanek, P., Kumar, V., and Filler, V.: Estimation of the Length of Day (LOD) from recent DORIS Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13470, https://doi.org/10.5194/egusphere-egu25-13470, 2025.
The DORIS Ultra-Stable Oscillators (USO) onboard Sentinel satellites are sensitive to the South Atlantic Anomaly (SAA) effect. While this sensitivity is not particularly significant for the precise orbit determination (POD) of the Sentinel-3A, Sentinel-3B, and Sentinel-6A satellites, it becomes crucial when estimating station positions. Previous studies have shown notable degradation in station position accuracy for stations located within the SAA region when using single-satellite solutions.
This study aims to evaluate the impact of using GPS clock as the modelled DORIS USO, provided by the CNES POD team, on station position estimation derived from single-satellite solutions of Sentinel-3A and Sentinel-6A. Single-satellite solutions were computed both with and without GPS clock corrections and were compared to the SARAL single-satellite solution, which serves as a reference due to its USO being minimally or not at all affected by the SAA. Our analysis investigates whether incorporating GPS clock corrections as a modeled DORIS USO can effectively mitigate the impact of the SAA on station position estimations in the affected regions.
How to cite: Capdeville, H., Mezerette, A., Gravalon, T., Lemoine, J.-M., Moyard, J., Mercier, F., and Couhert, A.: Analyzing the Impact of GPS Clock as the modelled DORIS USO on Station Position Estimation for Sentinel Satellites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11124, https://doi.org/10.5194/egusphere-egu25-11124, 2025.
CODE (Center for Orbit Determination in Europe) acts as one of the analysis centers of the International GNSS Service (IGS). One of the most important products are the final series providing -- among others -- GNSS satellite orbits, satellite clock corrections and station coordinates. Currently it includes GPS, GLONASS, and Galileo satellites. The final solution series shall provide the user community a direct access to the IGS20 reference frame (the IGS-specific realization of the ITRF2020).
Regarding this purpose, the extension of the final products to other systems, in particular BDS and QZSS need a careful consideration not to degrade the access to the reference frame. We present a step-by-step inclusion of BDS (only satellites in MEO orbits) and all BDS satellites (apart from those ones in GEO orbits) using the new combined satellite antenna offsets recently computed by the IGS. Another investigation is related to the QZSS satellites where pre-launch satellite antenna calibrations are available.
As a result of the study, a potential extension of the CODE final solution series to a more complete multi-GNSS product is decided.
How to cite: Dach, R., Brockmann, E., Arnold, D., Kalarus, M., Lasser, M., Schaer, S., Stebler, P., and Jäggi, A.: BDS and QZSS in CODE's final solution -- assessment of the impact , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14680, https://doi.org/10.5194/egusphere-egu25-14680, 2025.
Earth Rotation Parameters (ERPs), including polar motion (PM) and length of day, are crucial for describing the motion of the Earth's axis of rotation and linking the terrestrial and celestial reference system. ERPs can be categorized into long-term components and sub-daily components with periods shorter than two days. For the sub-daily ones, they reveal the impact of ocean tides, atmospheric tides, and other factors on Earth's rotation over short timescales, providing valuable insights into the dynamic process of Earth's motion. Compared to other techniques such as Satellite Laser Ranging, Very Long Baseline Interferometry, and Doppler Orbitography and Radiopositioning Integrated by Satellite, Global Navigation Satellite System (GNSS) technique offers advantages such as a densely distributed global station network, low equipment costs, continuous data tracking and high data sampling rate, making it particularly suitable for studying sub-daily PMs.
Since 2020, the Beidou Satellite Navigation System (BDS) has been officially completed and put into operation. Comparing with GPS, GLONASS, and Galileo, BDS has hybrid constellations with MEO and IGSO satellites which could bring new features into the derived sub-daily PMs. Therefore, this study first focuses on the precision of sub-daily PMs derived from BDS only. All the sub-daily PMs is based on 3-arc-length solutions with a 1-h temporal resolution. The results show that, compared to MEO-only, the addition of IGSO can reduce PMX from 183 to 161μas. For PMY, the addition of IGSO shows a similar improvement, reducing it by approximately 10%. Secondly, we transforme the time series of sub-daily PMs from different systems into the frequency domain by Fast Fourier transform (FFT) to identify and analyze those tidal and non-tidal signals. The results of spectral analysis indicate that the more diverse constellation configuration can effectively reduce the impact of spurious signals especially nearby 28-h term. In addition, more detailed comparisons and analyses with respect to the PMs derived from GPS, GLONASS, and Galileo are also presented. Furthermore, we also analyze the impact of weighting scheme in multi-GNSS combined solutions. Properly adjusting the weights of BDS can effectively improve the accuracy of sub-daily PMs. Finally, we assessed the GNSS-based empirical models with three priori empirical models, IERS2010 model, Gipson model and Desai-Sibois model. Multi-GNSS model with different constellation configurations shows the best consistency with the priori model.
How to cite: Yao, X., Li, X., Yuan, Y., and Zheng, H.: Analysis and Comparison of Sub-daily Polar Motion Derived from BDS, GPS, GLONASS and Galileo, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5417, https://doi.org/10.5194/egusphere-egu25-5417, 2025.
Information about satellite antenna phase center offsets (PCOs) is crucial for high-precision applications of global navigation satellite systems. Pre-launch manufacturer calibrations of the PCOs are available for all individual BDS satellites and three frequencies: B1, B2, and B3. With the imminent retirement of BDS-2 and the superior quality of B1C/B2a signals, the International GNSS Service (IGS) has launched a campaign for BDS-3 and QZSS phase center correction (PCC) calibration. However, only the IF combination of B1C/B2a is required. Considering the upcoming multi-GNSS and multi-frequency applications, the consistency of PCO values across different frequencies and GNSS is important.
We present the estimation of BDS-3 satellite antenna PCCs consistent with the International Terrestrial Reference Frame (ITRF2020) from the ionosphere-free linear combinations of B1I/B3I and B1C/B2a. The results demonstrate that the nadir-angle-dependent phase center variations (PCVs) of the same satellite block type have fairly good consistency. The mean horizontal PCOs of the different frequencies agree at the millimeter level. The X-PCOs show a bias of about 1 cm compared to the manufacturer calibrations, whereas the Y-PCOs are free of such bias. For Z-PCOs, some SECM satellites exhibit unexpected long-term variations and/or abrupt jumps, while all CAST satellites remain stable. The mean estimated values of B1C/B2a and B1I/B3I for BDS-3M-CAST, BDS-3M-SECM, and BDS-3I-CAST are (-15.9, -13.5), (-17.8, -3.0), and (+26.9, +24.0) cm larger than the CSNO values, respectively.
By applying the estimated PCCs instead of the CSNO values, the precise orbit precision can be improved by 3.6-12.2%, and the scale factors determined by BDS solutions exhibit good consistency with the IGS20 frame, with mean scale differences below 0.10 ppb for both frequency combinations.
Furthermore, CSNO values for SECM satellites are excluded from delivering the TRF scale by BDS-3 as they still remain questionable. Although the scale delivered by GPS and Galileo shows good consistency, with +0.84 and +0.73 ppb compared to ITRF2020, the scale difference of BDS-3 with respect to ITRF2020 is -0.84 and -0.92 for B1C/B2a and B1I/B3I. These results demonstrate the consistency of different frequencies for BDS-3 but also highlight the discrepancy within GNSS, specifically between BDS-3 and GPS/Galileo.
How to cite: Li, J. and Guo, J.: Consistency of BDS-3 transmit antenna phase center offsets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12548, https://doi.org/10.5194/egusphere-egu25-12548, 2025.
Obtaining consistent phase center corrections (PCCs) for GNSS receivers remains a significant challenge, as there is currently a lack of benchmarks to consistently evaluate patterns or comparable values between different calibration institutions and methods (anechoic chamber and field robots). To address this problem, a global collaboration with nine calibration institutions known as the IGS Ring Calibration Campaign (IGS ringCalVal) has been launched. This comprehensive initiative aims to compare results from different calibration methods and create a robust framework for quality assessment. Six antennas from different manufacturers were used for calibration in this campaign.
Over the past year, significant progress has been made. We have developed benchmarks and methods that facilitate the comparison of PCC patterns. Our detailed results show that in the pattern domain, the system/frequency consistency per antenna design varies within an uncertainty level of ±1 mm, with an additional elevation-dependent effect. In the positioning domain, system-specific PPP (Precise Point Positioning) results per antenna and GNSS system are presented, which show a deviation of typically less than 2-3 mm for the horizontal coordinate component and less than 5 mm for the vertical component between different systems. But also, special cases will be discussed. Finally, these results are crucial for establishing global standards for PCC calibration and verification
of receiver antennas.
How to cite: Schön, S., Kersten, T., Bilich, A., and Sutyagin, I.: Collaboration in GNSS Antenna Calibration: Insights from the IGS Ring Calibration Campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21229, https://doi.org/10.5194/egusphere-egu25-21229, 2025.
Earth deformation monitoring is an important aspect in the realization and investigation of reference frame. Global Navigation Satellite Systems (GNSS) is well-established technique to estimate the Earth surface velocity field and the deformation rates at the location of permanent stations. We make use of GNSS coordinate time-series to estimate horizontal and vertical velocity fields. However, one of the challenges is the superposition of a variety of signals and the contribution of noise and random processes in the GNSS time-series that adds to the complexities in extraction of the signal of interest in a straightforward manner. Therefore, we need to employ signal processing methods in the analysis of GNSS time-series signal separation or mode decomposition. In addition, the geometry of GNSS positioning and some other effects, e.g., solar radiation pressure-induced draconitic year etc. cannot be neglected. On the other hand, because of unpredictable mechanisms, e.g., earthquakes, coordinate time-series may experience discontinuities. For this reason, we employ mathematical tests to detect, estimate and remove these mechanisms to conclude the velocity field. In addition to signal separation and estimation of a realistic velocity field, the uncertainty estimation is also important for geoscientific applications. For this purpose, we take advantage of the variance and covariance component estimation methods to estimate not only a realistic velocity field, but also for realistic estimation of uncertainties. Studying of uncertainties is of importance and applicable in the sensitivity analysis. In some cases, we would like to know the sensitivity of the GNSS time-series to specific signals, e.g., solid Earth and mantle signals etc. In this study, we will present our work-in-progress approach for GNSS time-series analysis by combining data-driven and analytical approaches to have a better understanding of GNSS time-series with focus on the velocity field of our study area in central Europe.
How to cite: Karimi, H., Hugentobler, U., Abolghasem, A. M., Heydari, M., and Friedrich, A. M.: A new approach for GNSS time-series analysis with focus on uncertainty and sensitivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11796, https://doi.org/10.5194/egusphere-egu25-11796, 2025.
Estimation of Euler pole parameters (EPPs) is a critical step in developing NATRF2022, the upcoming realization of the North American (NA) terrestrial reference frame. These parameters characterize the tectonic motion of the NA plate relative to the ITRF2020/IGS20 reference frame. Improving the accuracy of EPPs reduces residual velocities within the plate, which in turn enhances the stability of geodetic coordinates and extends the validity period of the reference frame. The growing network of consistent, long-term continuously operating GNSS stations provides a robust and reliable source of velocity data for estimating EPPs. Currently, two methods are used for estimating EPPs: (1) solving the classic Euler’s pole theorem in inverse mode, based on the rigid plate assumption, and (2) modeling the deformation field of the tectonic plate to estimate parameters describing the net rotation of the deforming plate, consistent with the deforming plate hypothesis. Both methods are sensitive to the selection of GNSS stations, resulting in slight variations in the estimated EPPs. This sensitivity is further compounded for the NA tectonic plate due to the presence of non-secular and non-stationary deformation induced by glacial isostatic adjustment (GIA) across the plate, as well as the complex dynamics of the diffused boundary zone along its western margin. To address these challenges, a statistical algorithm based on the Maximum Likelihood Estimation (MLE) theory is proposed, offering unbiased parameter estimation for sufficiently large samples. The methodology begins with the selection of stations featuring stable monuments with at least three years of continuous time series. An adaptive grid comprising 50 to 100 cells is considered to ensure a homogeneous spatial distribution of the selected stations. Within each grid cell, one station is randomly selected with place back, and the EPPs are estimated using station velocities. This procedure is repeated many times following the Monte Carlo method to generate a large set of EPP estimates. Histograms of the estimated parameters are then formed to identify the underlying statistical distribution of the EPPs. Finally, the best values corresponding to the maximum likelihood probabilities are selected as the optimized EPPs. The resulting EPPs are then compared with those reported in previous studies, and the significance of the observed differences is evaluated in detail.
How to cite: Goudarzi, M. A.: Statistical determination and analysis of the Euler pole parameters for NATRF2022, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1655, https://doi.org/10.5194/egusphere-egu25-1655, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 1
EGU25-12533 | ECS | Posters virtual | VPS23
Global VLBI ties using mixed-mode sessionsThu, 01 May, 14:00–15:45 (CEST) | vP1.12
Geodetic VLBI (Very Long Baseline Interferometry) currently consists of two observing networks (legacy S/X and broadband VGOS). Heretofore, the two networks have run rather independently, which is non-ideal. There have been several attempts to combine observations from both networks at sites with co-located antennas using either conventional local-tie surveys or VLBI tie-sessions between S/X and VGOS, or both. Unfortunately, the number of sites with co-located VLBI antennas is rather limited, which hampers progress. To overcome this problem, we proposed an approach, the so-called mixed-mode VLBI tie session, that does not require to have co-located VLBI antennas. Instead, mixed-mode sessions have the S/X and VGOS networks observed simultaneously as a single geodetic VLBI technique to thus obtain global ties between the two networks. Two of the sessions observed in 2020 were already included in the ITRF2020 combination. We hypothesize that the global-tie approach helps preserve the geometry of the networks when aligning with the state-of-art ITRF2020 frame. In this presentation, we will describe the observed mixed-mode sessions, detailing scheduling strategies, correlation techniques, and geodetic processing methods used. We will also demonstrate how mixed-mode sessions can help realize a stable global geodetic reference frame such as the ITRF.
How to cite: Mondal, D. R., Elosegui, P., Ruszczyk, C., Lemoine, F., and Behrend, D.: Global VLBI ties using mixed-mode sessions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12533, https://doi.org/10.5194/egusphere-egu25-12533, 2025.
EGU25-5046 | ECS | Posters virtual | VPS23
Initial Findings on Epoch-Wise Realization of a Regional Reference Frame Using Indian CORS Sub-Network ObservationsThu, 01 May, 14:00–15:45 (CEST) | vP1.30
A high-precision Terrestrial Reference Frame (TRF) is essential for accurately monitoring geophysical activities. Currently, India lacks its own Regional Reference Frame (RRF) and relies on the global frame for local applications. With the recent installation of more than 1000 GNSS stations forming the so called CORS (Continuously Operating Reference Stations) network by the Survey of India (SoI), the need for a precise RRF for India has become evident.
The RRF can be realized using either a conventional secular Multi-Year Reference Frame (MRF) or a (geocentric) Epoch-based Reference Frame (ERF). An MRF is realized by aligning the regional network to a global frame such as the ITRF or IGS TRF. However, the accuracy of MRFs diminishes over time as coordinates are extrapolated beyond the observation period using linear velocities. Additionally, MRFs provide limited geophysical information and can’t be utilized with desired accuracy for quasi-instantaneous applications or after large earthquakes.
To address these limitations, this study aims to develop an ERF for the Indian CORS sub-network by adopting the methodology introduced by Kehm (2022) for creating a geocentric ERF in Latin America. The proposed ERF ensures that the frame's origin aligns with the Earth's instantaneous center of mass across all time scales within the observation period.
In this presentation, we will outline the approach to develop the Indian ERF, which involves combining weekly normal equations from global GNSS, SLR, and VLBI networks. Specifically, SLR determines the origin, SLR and VLBI jointly determine the scale, and a homogeneously distributed global GNSS network is used to realise the orientation of the frame. The results will be compared to those obtained using the conventional MRF realization approach. Furthermore, an independent validation strategy will be implemented to evaluate the accuracy of the developed ERF.
How to cite: Kushwaha, R., Bloßfeld, M., Kehm, A., Balasubramanian, N., and Dikshit, O.: Initial Findings on Epoch-Wise Realization of a Regional Reference Frame Using Indian CORS Sub-Network Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5046, https://doi.org/10.5194/egusphere-egu25-5046, 2025.
