We have developed three innovative, empirically-derived all-force radiation pressure models for multi-GNSS, addressing the shortcomings of traditional models that rely on simplified spacecraft geometries and extensive metadata. The models were created using ESA and CODE orbit products with different arc lengths (5-day and 10-day). This presentation will share the findings of a comparative study of these three models, based on a full year of high-precision GNSS data processing.
The results reveal significant variations in model performance across different GNSS constellations. A 5-day ESA-based model with a comprehensive parameter set (including a Z0 term and a Galileo-specific term) showed superior performance for Galileo and GPS. In contrast, a 5-day CODE-based model performed best for BeiDou, underscoring the importance of data source quality. Interestingly, a 10-day ESA-based model demonstrated lower performance, suggesting that longer arcs do not necessarily enhance model accuracy.
Further analysis indicated that while the models effectively reduced the variability in estimated ECOM parameters, consistent non-zero mean values for some parameters—particularly for BeiDou—highlight the presence of unmodeled forces. This is further supported by the anomalous behavior of certain BeiDou satellites, emphasizing the need for dedicated modeling strategies tailored to specific constellations.
This work underscores the critical role of data source quality, arc length selection, and careful parameterization in developing accurate and reliable all-force radiation pressure models for multi-GNSS. To further enhance the models, we will investigate these factors in greater detail, explore alternative parameterizations, and develop strategies to improve performance for challenging constellations, especially BeiDou.
The models developed in this study are freely available to the scientific community to support further research and enhance the accuracy of GNSS precise orbit determination.
How to cite: Springer, T. and Dilssner, F.: Taming the Invisible: A Comparative Study of All-Force Radiation Pressure Models for Multi-GNSS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19120, https://doi.org/10.5194/egusphere-egu25-19120, 2025.
Solar Radiation Pressure (SRP), which plays a crucial role in satellite Precision Orbit Determination (POD), is associated with the satellite’s optical properties and surface structure. The BDS-3 satellites offer a wide range of featured services, which result in complex satellite structures. Significant systematic errors related to solar elevation angles (up to 30 cm) are observed in precision orbit products. To address this issue, we compared the theoretical trend and actual values of acceleration in the Sun-satellite direction, revealing that the satellite antennas may introduce additional SRP perturbations. Consequently, an a priori model that includes antenna illumination was established based on the adjustable box-wing model. The employment of the a priori model shows a notable enhancement in orbit accuracy for the BDS-3 satellites. The mean offset and standard deviation of SLR residuals for C45/C46 are reduced to a level consistent with satellites from the same manufacture. The systematic errors in the residuals are notably reduced, achieving the RMS of 3.85 cm, which represents a 74% improvement over the results obtained using only ECOM1. For IGSO satellites, the 3D OBD is reduced to 18.5 cm, reflecting improvements of 55% and 25% over ECOM1 and ECOM2, respectively. Moreover, the 3-day-arc POD has been demonstrated to markedly enhance the orbit internal consistency of the IGSO satellite, with a 3D OBD reduction to 3.1 cm.
How to cite: Geng, T., Zhang, C., and Xie, X.: Refinement of the solar radiation pressure model for the BDS-3 satellites with considering illuminated antennas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2005, https://doi.org/10.5194/egusphere-egu25-2005, 2025.
The Copernicus Precise Orbit Determination (CPOD) Service is key to the Copernicus Sentinel missions, supporting Sentinel-1, -2, -3, and -6 with critical orbit products and auxiliary data. These products facilitate the operational creation of scientific core outputs at ESA and EUMETSAT, accessible through the Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).
Recent advances have pivoted towards the incorporation of new satellite units, notably Sentinel-1C and Sentinel-2C, launched in late 2024. These additions prompted thorough CalVal activities, ensuring the integrity and accuracy of Precise Orbit Determination. Initial solutions mirrored those of earlier Sentinel models, setting a standard baseline, while performing dedicated verification of Level-0 signal decoding.
A key enhancement is the integration of multiple PODRIX receivers in orbit, routinely tracking both GPS and Galileo signals together with Copernicus Sentinel-6A. GNSS antenna calibration has been pivotal, aiming to reduce multipath errors by creating a Phase Center Variation map. Cross-verification with solutions from the CPOD Quality Working Group (QWG), composed of renowned institutions such as AIUB, CNES, DLR, GFZ, JPL/NASA, PosiTim, TU Munich, and TU Delft, ensures these preliminary orbits meet Copernicus's precision demands.
Building on these innovations, the CPOD Service maintains its commitment to rapid, robust product delivery, achieving 3D RMS consistency below 1 cm with QWG's non-time-critical products and providing near-real-time solutions in under five minutes. Future efforts will focus on refining Sentinel-3's short-time critical products and advancing Sentinel-6 macro-models, as well as consolidating achievements related to the application of the ITRF20 Seasonal Geocenter Motion model.
This presentation will show results from recent satellite commissionings, and explore prospective enhancements within the CPOD service, showcasing the ongoing evolution in support of Copernicus missions' precision and operational efficiency. The contribution will also show the planned evolutions to continue improving and to pave the way for future Copernicus missions.
How to cite: Fernández Martín, C., Fernández Sánchez, J., Peter, H., Pinheiro, M., and Nogueira Loddo, C.: Copernicus POD Service: Status of Copernicus Sentinel Satellite Orbit Determination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2256, https://doi.org/10.5194/egusphere-egu25-2256, 2025.
The Sentinel-6A satellite, launched on November 21, 2020, is equipped with a dual-constellation (Galileo and GPS) onboard receiver for precise orbit determination (POD). Since launch, there have been significant improvements in the force models and data processing strategies. This has resulted in significant improvements to orbit accuracy. The Gravity Recovery and Climate Experiment-Continuity (GRACE-C) mission, which will be launched in 2028, will carry on a similar onboard receiver to Sentinel-6A. The main purposes of this study are to extend our software to process both Galileo and GPS data for preparing GRACE-C and to investigate how well the orbits of the Sentinal-6A satellite can be currently determined using Galileo or/and GPS data based on the current models and approaches. In this study, we present the results of Sentinel-6a POD solutions. The orbit accuracy is assessed using several tests, which include analysis of orbit fits, Satellite Laser Ranging (SLR) residuals, internal and external orbit comparisons. We show that less than one-cm radial orbit accuracy for the Sentinel-6A satellite has likely been achieved through different orbit accuracy evaluations. The precise Sentonel-6A orbits determined based on Galileo and GPS observations can meet the stringent requirement on radial orbit accuracy (1.5 cm).
How to cite: Kang, Z., Nagel, P., Save, H., Bettadpur, S., and Pie, N.: Precise Orbit Determination for Sentinel-6A using Galileo and GPS observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13160, https://doi.org/10.5194/egusphere-egu25-13160, 2025.
Due to mission objective constraints, some low Earth orbit satellites are required to operate in flexible attitude modes, but meanwhile stable Precise Orbit Determination (POD) performances must be guaranteed persistently. In this case, a single zenith-mounting antenna, as most missions have done in the past, will not fulfill POD requirements because its GNSS signal tracking might be significantly downgraded in certain attitude modes. A straightforward solution is carrying two antennas for better receiving geometry. This research investigated PODs for different satellites using GNSS observations from two antennas, which were installed with an angle varying between 45 and 180 degrees in the satellite body-fixed reference frame. The preprocessing and screening of GNSS observations was elaborately done to maximize the continuous arc for ambiguity estimation, in particular for cases when the two antennas tracked the same GNSS satellites alternatively or simultaneously. The potential signal delay between the two antennas and the independent phase patterns need to be evaluated. Afterwards the different GNSS observations were robustly merged referring to the satellite’s center-of-mass. Results indicated that the GNSS observation fusion strategy significantly enhanced the stable POD performances for attitude modes where single antenna was impossible to receive sufficient GNSS observations. The overlapping consistency and internal consistency between the reduced-dynamic orbits and the kinematic orbits were only 1-2 cm in the local orbital reference frame, obtaining a similar level as other renown missions with single zenith-mounting antenna. Besides, such dual-antenna GNSS tracking configuration enabled potential assessments of center-of-mass coordinates as well as other applications.
How to cite: Mao, X., Wang, W., and Gao, Y.: Precise orbit determination for satellites in flexible attitude modes using dual-antenna GNSS observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14826, https://doi.org/10.5194/egusphere-egu25-14826, 2025.
Real-time data processing onboard is increasingly essential for future Low Earth Orbit (LEO) satellites. We propose an ultra-rapid onboard orbit determination (OD) strategy that achieves decimeter-level accuracy, potentially up to centimeter-level. This approach enables high-precision OD and prediction using either precise GNSS products from ground stations or broadcast ephemeris. Consequently, it allows satellite payloads to deliver real-time, high-performance services to ground users, with significant potential for various applications. Experimental results show that using IGS final GNSS products, this method achieves 5 cm accuracy for OD and better than 10 cm for 10-min orbit prediction. With broadcast ephemeris, the accuracies are better than 45 cm for OD and 1 m for 10-min orbit prediction.
How to cite: Luo, P. and Song, Y.: An Onboard Ultra-Rapid Orbit Determination Strategy for LEO Satellite Utilizing GNSS Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5062, https://doi.org/10.5194/egusphere-egu25-5062, 2025.
With the widespread application of precise point positioning (PPP), real-time clock offset products have become a focal point of global navigation satellite system (GNSS). Real-time clock offset estimation offers high accuracy but demands stable data communication and involves significant computational pressure. And the accuracy of ultra-rapid products does not meet the requirements of positioning, navigation and timing (PNT) services. To address this, a short-term clock prediction method based on low sampling rate estimation is proposed. This method provides users with a set of clock model coefficients, enabling them to obtain high sampling rate clock offset at any time. Based on the clock products with 60s intervals estimated by square root information filtering (SRIF) from 80 stations, the most suitable short-term model that the linear model with the same arc length for fitting and prediction is determined by adaptive analysis of the order of polynomial model and data arc lengths. Based on this, short-term predicted parameters for 5min, 10min, 15min, 30min and 60min are obtained. These parameters are then interpolated to 30s interval for detailed accuracy assessment and PPP validation. The results indicate that the clock offset predicting accuracies of BDS-3 are 0.029ns, 0.033ns, 0.037ns, 0.047ns, 0.071ns for 5min, 10min, 15min, 30min and 60min, while the Galileo are 0.023ns, 0.027ns, 0.032ns, 0.039ns, 0.062ns. The predicted clock offsets of Galileo are slightly better than those of BDS-3. The PPP results show that the 2D and 3D positioning accuracies for the 5min prediction are 0.058m and 0.115m, respectively, with positioning accuracy declining as the prediction arc length increases. Overall, the positioning performance of the predicted clock products within 30min are nearly consistent to the real-time estimated clock. Compared to Centre National d’Etudes Spatiales (CNES), the results of PPP performance are similar，and superior to the performance of ultra-rapid clock products. Therefore, short-term predicted products based on low sampling rate estimated clock can serve as a more stable alternative to real-time products in the PPP applications. The updating frequency of the clock offset model coefficients is determined based on the needs of PPP users. The method reduces the sampling rate for estimating clock offset while maintaining high-precision clock offset products. Additionally, it can still offer high-precision real-time clock offset prior information to the PPP users during interruptions in real-time estimation.
How to cite: Cao, Y., Huang, G., Qin, Z., Xie, S., Xie, W., Fan, Y., and Du, S.: Short-Term Clock offset Predicting Products Based on Low Sampling Estimation for Real-time Service, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16653, https://doi.org/10.5194/egusphere-egu25-16653, 2025.
Genesis is ESA's future mission that will contribute to a highly improved Earth reference frame with a target accuracy of 1 mm and a long-term stability of 0.1 mm/year, providing a coordinate system for the most demanding scientific applications on our planet.
The baseline for the Genesis satellite is to combine all four major space-geodetic techniques: Very-Long-Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS). The synchronisation and cross-calibration of these instruments are key to determine the inherent biases of each technique, allowing for a coherent combination of the relevant observations resulting in an improved accuracy of the orbit determination.
In preparation for this mission, which is expected to be launched in 2028, the Navigation Support Office of the European Space Agency will be responsible for the Precise Orbit Determination (POD) of the GNSS satellites and for the Genesis satellite. Hence, the Office is already preparing the tools to be ready for the processing of all the observables coming from these four techniques in a combined and coherent manner.
Real data obtained from ESA’s missions, including the Copernicus Sentinel missions, will serve as the basis for testing, validating, and further developing and enhancing the capabilities of a multi-technique processing, including GNSS, SLR and DORIS. In parallel, the Office is preparing to process the first high precision VLBI observations from a satellite.
A detailed description of the POD methodology that the Navigation Support Office intends to apply for Genesis mission as well as the first results will be presented and discussed at the EGU General Assembly.
How to cite: Berton, J.-C., Bruni, S., Dilssner, F., Otten, M., Sermanoukian Molina, I., Springer, T., van Kints, M., Fusco, G., Gidlund, S., Gini, F., Schoenemann, E., Sakalauskaite, E., Waller, P., and Enderle, W.: A new combined processing for Genesis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20067, https://doi.org/10.5194/egusphere-egu25-20067, 2025.
For the past fifty years, geodetic satellites have contributed to improve our knowledge on various Earth's physical behaviors. The purpose of this paper is to reassess the value of the geocentric gravitational constant (GM), defined by the product of the Earth's universal gravitational constant G and its mass M, from Satellite Laser Ranging (SLR) observations. Indeed, its relatively large uncertainty of 2.0 ppb (Ries et al., 1992) is not compatible with the final goal of the GENESIS MEO (Medium Earth Orbit) mission to realize the Terrestrial Reference Frame with an accuracy of 1 mm. The core of this analysis is based on the simultaneous estimation of the Earth's GM with laser station and satellite biases, taking the most of historical passive geodetic satellites, including three pairs of "twin" satellites to validate independently the accuracy of the newly derived GM value. Furthermore, by combining MEO and LEO (Low Earth Orbit) satellites, a consistent value of GM has been reassessed, this value being higher and less uncertain than the currently used reference value determined in 1992. In particular, the influence of errors in the modeling of the Earth radiation pressure and station coordinates on GM was evaluated.
How to cite: Cherrier, M., Couhert, A., Exertier, P., Mercier, F., and Saquet, E.: Reducing uncertainties in the determination of the Earth's GM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17971, https://doi.org/10.5194/egusphere-egu25-17971, 2025.
Posters on site: Wed, 30 Apr, 10:45–12:30 | Hall X1
Solar Radiation Pressure (SRP) plays a crucial role for Precise Orbit Determination of artificial satellites as it has been proven to be one of its major error sources. An essential parameter used for the calculation of SRP is the eclipse factor. To determine this factor along the orbit of the satellite, various shadow models have been implemented. The aim of this study is to investigate the differences the geometries of the models applied have, in different altitude orbits. To achieve this, we evaluate the results of shadow models used in the bibliography (ECSM, ESCM, Lunar shadow) along various Low Earth Orbits (LEO) and Medium Earth Orbits (MEO) satellites and demonstrate the effect of the geometries used in both cases. The study displays an overview of the results of each implementation and its computational complexity, as to provide an insight to researchers for which model to adopt when implementing an SRP model on LEO and MEO orbits.
How to cite: Krey, V., Papanikolaou, X., and Tsakiri, M.: An overview of shadow models implementations on LEO and MEO orbits., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-814, https://doi.org/10.5194/egusphere-egu25-814, 2025.
Since 2021, GMV has been developing FocusPOD, a new Precise Orbit Determination (POD) and Geodesy software package. Written in modern C++ and Python, FocusPOD is designed around four key pillars:
1. Object-Oriented Programming: Utilizing C++17 and Python3, FocusPOD leverages external libraries and tools to minimize code development, focusing on specific algorithms. The C++ Standard Library (STL) efficiently handles large datasets.
2. Data-Algorithm Separation: This approach allows data reuse for multiple purposes and consistent multi-technique processing with a single algorithm implementation.
3. Data Model: Organizing data in a centralized model, akin to a relational database, facilitates easy navigation through extensive geodesy datasets.
4. Multi-Use Case Support: FocusPOD supports various users, including experts, operators, and machine-to-machine architectures.
The first application of FocusPOD in 2023 was standalone GNSS POD. It is now operational in the Copernicus POD (CPOD) Service, generating millimeter-accuracy orbits for Copernicus Sentinel satellites. SLR processing was added to compute SLR residuals and biases for CPOD quality control with state-of-the-art accuracy. In July 2024, standalone DORIS POD was implemented, achieving centimeter-accuracy orbits for Sentinel-3 and -6 using DORIS only; same was demonstrated with standalone SLR POD. Future steps include integrating state-of-the-art tropospheric models for improving the accuracy of DORIS and SLR POD.
The latest incorporation into FocusPOD is the support to GNSS network processing, handling multiple receivers and GNSS constellations, to estimate orbits, clocks, station coordinates, troposphere, and Earth Orientation Parameters (EOPs). In parallel, advancement have been made to incorporate VLBI, implementing the IERS consensus model for observation reconstruction. These implementations will natively support single- and multi-technique at observation level with the four geodetic techniques. The final pending step is to estimate global solutions through Normal Equation (NEQ) stacking, on which the four techniques could be combined consistently.
This contribution will present the capabilities of FocusPOD, focusing on available models, algorithms, and the results achievable with each technique. It will also outline the current capabilities and maturity level of each technique, along with future development plans.
How to cite: Fernandez Sanchez, J., Fernandez Martin, C., Berzosa Molina, J., Bao Cheng, L., Muñoz de la Torre, M. A., Fernandez Uson, M., Lara Espinosa, S., Terradillos Estevez, E., and Ivanchuk, O.: FocusPOD: A POD and Geodesy SW Package, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2259, https://doi.org/10.5194/egusphere-egu25-2259, 2025.
The NASA-CNES climate science Surface Water and Ocean Topography (SWOT) satellite was successfully launched in December 2022. This mission embodies the longstanding cooperation between CNES and NASA Jet Propulsion Laboratory in space oceanography for 40 years, initiated with TOPEXPoseidon in 1992, subsequently pursued through the Jason series of satellites (1 to 3 between 2001 and 2016) and continued in 2020 with the Copernicus Sentinel-6 mission.
SWOT is the first space mission that will study nearly all of the water on the Earth’s surface. To complete this global survey and mapping of the finer details of the ocean’s surface topography and water bodies over time, the satellite is equipped with a GPS (Global Positioning System) and DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) dual-frequency receivers, as well as a Laser Retroreflector Array (LRA) to support verification of the challenging Precision Orbit Determination (POD) requirements
In this poster, we will present the current results and efforts underway to improve the modeling of Solar Radiation Pressure (SRP). Residual signatures of systematic errors related to the Sun’s elevation angle are observed in-flight when using the current a priori SRP model. To address this issue, we analyze once-per-revolution empirical along-track and cross-track accelerations with respect to the beta prime angle, aiming at reducing this dependency. An updated box-wing model is thus derived for SWOT moving from pre-launch to adjusted data (geometry, surface properties).
How to cite: Blondel, S., Couhert, A., Moyard, J., Mercier, F., and Houry, S.: Refinement of the solar radiation pressure model for the SWOT satellite , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8080, https://doi.org/10.5194/egusphere-egu25-8080, 2025.
A significant contributing error source in the computation of the ITRF is the estimation of terrestrial ties, between geodetic reference points at colocation sites. The discrepancy in the description of the vectors, as determined through space geodetic observations and terrestrial surveying techniques, can be as much as 10 cm at certain sites.
In response, in 2022, the European Space Agency proposed the GENESIS satellite mission which is a specially designed geodetic satellite equipped with the four space geodetic techniques i.e., LRA, GNSS, DORIS and VLBI to achieve an ITRF with a positional accuracy of one mm and a stability of 0.1 mm/year.
Given the increase in the number of LEO satellites that are equipped with multiple geodetic techniques, it is opportune to assess and develop the capability of co-location in space (at the satellite) to achieve these accurate terrestrial ties at sites that are collocated with multiple space geodetic observing techniques.
The aim of the of the study is to determine the feasibility of colocation in space by undertaking multi-technique orbit determination, estimating station coordinates and hence the terrestrial ties between collocated observing techniques using multi-technique data from the Sentinel satellites. This may inform the GENESIS geodetic mission.
Our project estimates orbits for the available techniques on the respective satellites, from 2016 to 2022. The observation network and its categorisation based on collocated systems, the computations standards implemented for each observation type and the subsequent combination method to determine the coordinates for each technique at each site is presented.
The vectors as determined between adjusted station co-ordinates are compared to the official terrestrial ties. This measure may provide insight into the stacking and combining of POD solutions; and station position estimates that may be performed for optimum space co-location results and identify any limitations or potential improvements in the processing strategy.
How to cite: Desai, A., Combrinck, L., and Govind, R.: Precise Multi-Technique Orbit Determination of the Sentinel Satellites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9284, https://doi.org/10.5194/egusphere-egu25-9284, 2025.
Satellite Laser Ranging (SLR) has become an invaluable core technique in numerous geodetic applications. SLR measurements to passive spherical satellites essentially contribute to the determination of geocenter coordinates and global scale in the International Terrestrial Reference Frame (ITRF) realizations. In addition, SLR measurements to active satellites in Low Earth Orbit (LEO) are up to now mostly used for independent validation of orbit solutions, usually derived by microwave tracking techniques based on Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) or Global Navigation Satellite Systems (GNSS). This allows for the analysis of systematic orbit errors (e.g., originating from poorly known non-gravitational perturbations or sensor offsets) not only in the radial direction (key to satellite altimetry missions), but in three dimensions.
It has recently been shown, in Saquet et al. (2023), that the analysis of SLR data to a constellation of active LEO satellites with fixed microwave-derived orbit solutions is a promising approach to exhibit SLR range biases independently from well-known correlation issues and less prone to geographically correlated orbit errors. Clearing systematic range biases from SLR observations is also an essential step to meeting stringent future requirements such as for ESA’s GENESIS mission or enabling the calibration of altimeter range biases for the next generation of altimetry missions.
In this paper, we use geodetic sphere (e.g., LAGEOS-1/2) measurement SLR residuals to assess the quality of the station range biases derived from satellite altimetry compared to ILRS-based range bias values. Systematic differences between the two independent approaches are analyzed, especially for well-performing laser stations with diverse detector types (e.g., single/multi-photon). Finally, relying on multiple years of observations, the contribution of tropospheric delay modeling errors to these biases is estimated.
How to cite: Saquet, E., Couhert, A., Reinquin, F., and Banos Garcia, A.: Clearing systematic range biases from SLR observations: assessment and outlook, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10499, https://doi.org/10.5194/egusphere-egu25-10499, 2025.
The quality of low Earth orbit (LEO) satellite-borne global positioning system (GPS) observation data has an important influence on the precise orbit determination of LEO satellite and the study of the ionosphere. In this contribution, we develop a geometry-free orbit-dynamic-constraint approach to analyze the satellite-borne GPS observations errors, including code errors, carrier phase errors, receiver clock errors, ionospheric delay, to detect and repair cycle slips for satellite-borne dual-frequency carrier phase observations. Different from the traditional methods suitable to satellite-borne GPS observations, we take full advantage of the correlations between the dual-frequency observations, between the satellite orbit variations and the orbit dynamic background models, without a prior precise orbit. The proposed approach can not only remove the geometry variations between GPS satellites and LEO satellite, but also have partial characteristics of other signals separated from GPS observations, such as the receiver clock offset. Then, the performance of the proposed approach is verified by GPS measurement data of GOCE/GRACE satellite with different sampling interval. The results indicate that the proposed approach preforms well on observations error analysis, can effectively detect and fix cycle slips with high success rates, even in real-time applications.
How to cite: Zhu, H., Zou, X., and Wei, H.: Geometry-free error analysis and cycle slips detectionof GPS observations on the basis of dynamic information and its applications on LEO precise orbit determination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21056, https://doi.org/10.5194/egusphere-egu25-21056, 2025.
Low Earth Orbit (LEO) satellites have nowadays shown great potential to enhance the existing GNSSs for better Positioning, Navigation, and Timing (PNT) services. Despite the requirements for high-accuracy real-time orbits, the distribution of various LEO satellite ephemeris is of concern, yet rarely studied for efficient broadcasting of the LEO satellite ephemeris. This is especially important for setting proper thresholds when broadcasting the LEO satellite ephemeris. In this study, the probability distribution of the LEO satellite ephemeris parameters is investigated together with the corresponding fitting accuracies. Twelve LEO satellites flying at different altitudes with different orbital characteristics are tested for 16-, 18-, 20-, and 22-parameter ephemeris fitting. The results reveal that an increase in orbital altitude does not only lead to improved fitting accuracy, but also results in a more concentrated distribution of orbital elements. Reducing the fitting interval and increasing the number of ephemeris parameters contribute positively to improving the fitting accuracy, where an accuracy of 1~2 cm or serval millimeters can be achieved with 10-min fitting interval and 20/22-parameter ephemeris for a 300~1400 km orbital altitude. This, however, comes at the cost of dispersed distribution of the orbital elements, i.e., with wider ephemeris threshold required. It was also found that the mean values of certain crucial ephemeris parameters, e.g., the mean motion correction, the right ascension of ascending node rate, and the second-order harmonic coefficients Cus2 and Crc2, are highly correlated with the orbital altitudes and inclinations.
How to cite: Wei, C. and Wang, K.: Characteristics of Probability Distribution and Fitting Accuracy for LEO Satellite Ephemeris, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3491, https://doi.org/10.5194/egusphere-egu25-3491, 2025.
ESA’s Genesis mission, planned to launch in 2028, aims to contribute to a highly improved International Terrestrial Reference Frame (ITRF) with an accuracy of 1 mm and a stability of 0.1 mm/year. It will combine GNSS, DORIS, SLR and VLBI space geodetic techniques, acting as the first ever space-tie using these four techniques. The satellite will orbit at an altitude of 6000 km and will be equipped with two GNSS antennas, pointing in zenith and nadir direction, in order to counteract the loss of GNSS coverage at those altitudes.
For the mission to provide a strong contribution to the ITRF, dynamic satellite orbit modeling needs to be done as empirical orbit parameters are closely correlated with some geodetic parameters. Thus, the geometry and optical properties of the satellite, expressed as a macro model, should be described as accurately as possible.
During the development of Genesis, different spacecraft designs were considered. We focus on the original box-wing model, consisting of a cuboid body and a single solar panel, and the newer model, which is similar to Sentinel-6. Their respective influence is determined for a Genesis-only precise orbit determination as well as a global combined solution, where the Genesis orbit, GNSS orbits and clocks, ground station coordinates and geodetic parameters are estimated together. In addition, uncertainties to the optical properties of single or multiple surfaces of the spacecraft were introduced in order to test how macro model errors propagate into the global combined solution.
Using simulated pseudo-range and carrier phase GNSS data for Genesis and the ground stations, we reconstruct the orbit and geodetic parameters. A comparison of the solutions to the simulation truth allows for a direct quantification of the impact of different macro models and possible errors.
How to cite: Miller, A., Arnold, D., Jäggi, A., Steigenberger, P., and Montenbruck, O.: The influence of non-gravitational force modeling on Genesis and GNSS orbit and geodetic parameter estimations using two different macro models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16573, https://doi.org/10.5194/egusphere-egu25-16573, 2025.
The atmospheric delay correction of Satellite Laser Ranging (SLR) ground observations depends on the state of the neutral atmosphere. In the state-of-the-art SLR network processing, this delay is an empirical function of local station-based meteorological variables. We propose an alternative modelling approach commonly used in Global Navigation Satellite Systems (GNSS). Here, the slant delay (SD) is estimated via ray tracing (RT) with atmospheric information provided by Numerical Weather Prediction (NWP). We compare the default processing of the atmospheric correction using the Mendes-Pavlis (M-P) model supplied with station meteorological data and the alternative processing using the Least Travel Time version 2 (LTT v2) ray tracer coupled with the Open Integrated Forecasting System (OpenIFS) NWP model of European Centre for Medium-Range Weather Forecasts (ECMWF). Additionally, we employ a hybrid approach where the M-P model is supplied with interpolated weather forecast data. Our SLR processing setup is a position determination of 10 satellites using only the SLR observations from December 2016, done using the Gravity Recovery Object Oriented Programming System (GROOPS) toolkit. We compare three atmospheric modelling approaches by employing their slant delay estimates in the SLR processing and performing residual analysis.
How to cite: Vasiuta, M., Süsser-Rechberger, B., Mayer-Guerr, T., and Järvinen, H.: Employing the numerical weather prediction for direct modelling of SLR atmospheric corrections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15720, https://doi.org/10.5194/egusphere-egu25-15720, 2025.
Precise Orbit Determination (POD) of Global Navigation Satellite Systems (GNSS) satellites relies on precise satellite attitude data to accurately model satellite dynamics and observation geometry. Errors in the attitude control, such as biases, and periodic signals, have the potential to propagate into orbit estimates and derived geodetic parameters, thereby influencing the accuracy required for high-precision geodetic applications. Furthermore, accurate attitude determination plays a critical role in Next-Generation GNSS, particularly for the implementation of inter-satellite range links. This study presents a simulation framework to analyse the impact of such effects on GNSS attitude data and their implications for POD.
A Galileo-like constellation is simulated over a three-year period, employing state-of-the-art methods and datasets, including ITRF2020. The basis of the simulation are realistic assumptions concerning satellite geometry and attitude control. Systematic orientation biases and periodic signals, such as misalignments in solar panel orientation or inaccuracies in yaw steering, are applied to the attitude data to emulate potential errors in real systems. The simulation then examines the propagation of these errors into POD solutions, including their effects on orbit errors and clock estimates.
Particular attention is given to systematic effects arising from solar radiation pressure (SRP) modelling in combination with systematic attitude errors. The results obtained demonstrate the sensitivity of GNSS POD to precise attitude knowledge, thereby providing valuable insights for the design and calibration of future GNSS. This study emphasises the critical role of attitude control in achieving the accuracy objectives outlined by the Global Geodetic Observing System (GGOS) for subsequent reference frame determination.
How to cite: Schreiner, P., Glaser, S., König, R., Neumayer, K. H., Raut, S., and Schuh, H.: On the Impact of Attitude Data Deviations for GNSS Precise Orbit Determination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18031, https://doi.org/10.5194/egusphere-egu25-18031, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 1
EGU25-15238 | ECS | Posters virtual | VPS23
Real-time high-precision joint orbit determination of GPS and LEO using SRIFThu, 01 May, 14:00–15:45 (CEST) | vP1.11
Low Earth Orbit (LEO) satellites have the advantages of high flight velocity and minimal influence from external environmental factors on onboard observation. Integrating LEO satellite observations with ground observations can improve the accuracy and convergence performance of GPS and LEO real-time orbit determination, which can simultaneously meet the prerequisites for real-time Positioning, Navigation, and Timing (PNT) services for both GPS and LEO systems. Therefore, this study employs the Square Root Information Filter (SRIF) for GPS and LEO satellites real-time joint orbit determination (RTJOD). Based on observations from eight existing scientific LEO satellites, a detailed study on RTJOD was conducted under two scenarios: one using observations from 100 global stations and the other using observations from 9 regional stations in Australia. The results show that, with 100 global stations, incorporating LEO observations can significantly improve the convergence performance and GPS satellite orbit accuracy. The convergence times in the Along-track, Cross-track, and Radial components are reduced from 3.5, 5.8, and 10.3 h to 0.9, 1.0, and 10.3 h, respectively. The accuracy improves from 5.8, 3.6, and 2.8 to 4.0 cm, 2.5 cm, and 2.5 cm. Additionally, the ambiguity resolution (AR) performance is significantly enhanced. The time required to achieve a 90% narrow-lane ambiguity fixing rate is reduced from 4.9 to 0.7 h. After AR, the orbit accuracy further improves to 3.1 cm, 2.3 cm, and 2.4 cm. In the case of the 9 regional stations in Australia, after incorporating LEO, the orbit accuracy of the float solution after convergence is comparable to that of the 100 global stations without LEO, with accuracies of 6.0, 4.8, and 2.9 cm in the three components. It is important to note that, due to insufficient observations in this case, AR does not result in any further improvement in accuracy. In addition, LEO can achieve orbit determination accuracy better than 5 cm within a short time in both station distribution scenarios. This ensures that RTJOD enables LEO and GPS to generate high-precision real-time orbits simultaneously. Finally, the processing time for each epoch in all scenarios is less than 5 seconds, ensuring that the GPS and LEO RTJOD can provide timely orbit updates.
How to cite: Lai, W., Huang, G., Wang, L., She, H., Xie, S., Xie, W., and Wang, Q.: Real-time high-precision joint orbit determination of GPS and LEO using SRIF, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15238, https://doi.org/10.5194/egusphere-egu25-15238, 2025.
