What a priori weightings should be applied to the observations used is a recurring question faced by anyone making estimates based on real observations. In the field of space geodesy, this issue has been extensively examined, particularly with GNSS techniques, to account for the elevation-dependent uncertainties inherent in observational data. This study explores the application of this question to the DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) technique. The precision of geodetic products derived from DORIS data is similarly influenced by the a priori weighting of measurements, as their uncertainty varies with satellite elevation. Despite the existence of several weighting schemes currently employed by International DORIS Service (IDS) Analysis Centers and Precise Orbit Determination (POD) services, no consensus has been reached regarding an optimal approach. Here, we propose a novel station-specific weighting model derived from DORIS observation residuals and optimized using the Bayesian Information Criterion. Its performance is evaluated against five established models, including those routinely adopted by IDS analysis centers. We assess the impact across all primary geodetic outputs: DORIS post-fit residuals, satellite orbits, reference frame stability, station position accuracy, and polar motion estimates. The results are promising, with improvements observed in nearly all processed products. Notably, pole coordinate WRMS values are reduced by up to 30 % compared to results obtained using uniform weighting strategies. These results demonstrate the feasibility and value of incorporating station-specific elevation-dependent weightings in DORIS processing chains. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The main goal of this paper is to introduce a new ensemble-based Multi-Criteria Decision-Making (MCDM) strategy to rank multiple orbit configurations and identify those that maximize the objectives of a satellite mission. The strategy combines five diverse MCDM methods with five objective weighting techniques to determine orbit regions that maximize the performance across a set of selected criteria. As an example, we apply this strategy to the recently ESA-approved Genesis mission. Genesis, approved by ESA in 2022, is designed to co-locate the four space geodetic techniques (DORIS, GNSS, SLR and VLBI) on board a single satellite. Its main goal is to improve the accuracy of the International Terrestrial Reference Frame (ITRF) by overcoming systematic biases in the four techniques and replacing ground-based ties with continuous space ties. The effectiveness of this mission depends, among other factors, on the selection of a proper orbit configuration, as it directly influences the visibility, tracking geometry, thermal conditions and calibration capabilities. This study aims to thoroughly assess and identify orbit configuration regions by applying the new ensemble MCDM strategy, with the objective of maximizing the mission's geodetic contribution and strengthening the realization of the ITRF. This was accomplished by evaluating 6700 circular orbit configurations, with keplerian parameters ranging from 1000 to 10000 km for altitude and 0 to 180 in inclination, based on eleven criteria. These criteria are related to orbital constraints, GPS visibility, ground network tracking distribution and multi-technique visibility. In order to ensure a robust ensemble MCDM application, multicollinearity and distribution analyses of the criteria were performed. In addition, extensive comparisons among the MCDM and weighting methods were conducted to evaluate their consistency, sensitivity, and influence on the final orbit rankings. This paper presents a comprehensive orbit design framework for Genesis-like satellites, where the ensemble MCDM strategy is applied to identify orbit configuration regions that are optimal under the applied criteria and the assumptions made in each criterion of this study. In support of this strategy, single-criterion analyses were first carried out to assess the consistency and structure of the applied criteria, while also revealing best-and poor-performing regions for each criterion individually. To our knowledge, this is the first application of an ensemble MCDM approach to orbit design in space geodesy. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Abstract We evaluate the quality of zenith tropospheric delay (ZTD) estimates from four IGS Analysis Centres (ACs) – COD, GFZ, GRG, and TUG – participating in the third IGS reprocessing campaign (repro3). This study focuses on outliers, defined as estimates outside the 1–3 meter range. A small yet significant fraction of estimates fall outside this range for three ACs that did not constrain this parameter. Most outliers originate from a limited number of stations and frequently occur in clusters or during specific periods (e.g., 2000–2003). We find that 95% of outliers are unique to individual ACs, indicating dependence on their specific processing procedures. Outliers are typically linked to poor data quality, including large multipath effects, cycle slips, and/or strong data editing during pre-processing or processing. They often coincide with suboptimal ambiguity fixing statistics. Other parameters, such as station positions, may also be poorly estimated. outliers can be mitigated through robust screening of estimates. Screening based solely on formal errors may be insufficient, as some datasets processed with a zero-difference network strategy contain outliers despite small formal errors. As an alternative, screening using an independent reference ZTD data from atmospheric reanalysis is recommended.

For the second yearly update of the 2020 realization of the International Terrestrial Reference Frame ITRF2020, i.e., ITRF2020-u2024, the International DORIS Service (IDS) submitted to the International Earth Rotation and Reference Systems Service (IERS) a set of 209 weekly solution files including station coordinates and Earth Orientation Parameters, covering the time period from 2021.0 to 2025.0. Three of the five IDS Analysis Centers (ACs) contributing to the new IDS combined solution delivered new series. These new series have been derived using new models and processing strategies for almost all of the current DORIS missions: Cryosat-2, HY2C, HY2D, Jason-3, Saral, Sentinel-3A, Sentinel-3B, and Sentinel-6A. In this paper, we present both the IDS AC and the IDS 25 combined solutions released for the ITRF2020-u2024. Then, we evaluate these series in terms of scale, geocenter and station positions with respect to (w.r.t.) ITRF2020-u2023 and in terms of Earth Orientation Parameters (EOPs) w.r.t. the IERS C04 series. The evaluation shows that, over the four-year time span, the IDS 25 scale values lie in a range of ± 2.5 mm with a trend of -0.10 mm/yr . Thanks to an improved modeling of the surface forces on the satellites, especially on Sentinel-6A, compared to the first IDS contribution to the ITRF2020, the new IDS 25 combined solution depicts smaller annual and 118-day signals in the geocenter coordinate time series. The evaluation also showed that the IDS 25 has an internal position consistency in North-East-Up components better than 6 mm per component. The EOPs from the IDS 25 combination were compared with the IERS C04 time series and the RMS agreement between these two time series is about 200 μ as for the x- and y- pole coordinates.

Abstract The Surface Water and Ocean Topography (SWOT) satellite, developed by the National Aeronautics and Space Administration (NASA, USA) and Centre National d’Études Spatiales (CNES, France), with contributions from the Canadian Space Agency (CSA, Canada) and UK Space Agency (UKSA, United Kingdom), is a groundbreaking mission aimed at providing the first comprehensive global survey of Earth’s surface water. By measuring fine details of ocean surface topography and monitoring changes in water bodies over time, SWOT will enhance our understanding of global hydrological and oceanic processes. For SWOT to fulfill its primary mission, precise orbit determination is essential. To achieve this, the satellite is equipped with a DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) instrument, enabling highly accurate positioning and geodetic measurements. This study presents the first results of SWOT DORIS data processing by the IDS IGN-IPGP/JPL Analysis Center (IGN AC), focusing on orbit quality and its impact on geodetic products.We assess the accuracy of SWOT orbit solutions through internal consistency checks (overlap analysis) and external comparisons with SSALTO Precise Orbit Determination (POD) products, developed by CNES in collaboration with Collecte Localisation Satellites (CLS, France), for precise orbit computation and altimetry data processing. After verifying the quality of SWOT DORIS data processing through these orbit comparisons, we further evaluated the impact of including or excluding SWOT data in the multi-satellite solutions generated by the IGN AC and delivered to the IDS. This assessment provides insights into the contribution of SWOT to the robustness of combined geodetic products and highlights its potential role in future IDS solutions. The results show that SWOT significantly improves the weighted root mean square (WRMS) of station coordinates, with reductions of about 15 $$\%$$ % for East and Up components and 25 $$\%$$ % for North, compared to solutions without SWOT. Improvements are also observed for Earth Orientation Parameters, with WRMS reductions of approximately 7.5 $$\%$$ % for both X-pole and Y-pole. SWOT further contributes to the definition of the terrestrial reference frame, particularly along the X-origin, although slight degradations are noted in the Z-origin and scale (around 0.2 ppb). These findings highlight the positive contribution of SWOT to IDS geodetic products, while also pointing to potential calibration issues related to the antenna Phase Center Offset that warrant further investigation.

The growing interest of the GNSS community in computing GNSS series using the iPPP (Precise Point Positioning with integer ambiguity resolution) mode with the GINS software and the products of the CNES/CLS analysis center (GRG products) culminated in 2022 with the SPOTGINS project. This initiative enables several research laboratories to cooperate in processing a global network of stations, benefiting from the expertise of the IGS analysis center and the advanced quality of the GRG products.This standardization and collaboration require a unified computational strategy, involving the same version of the GINS software, identical configurations (products, corrections, models, constellations), and consistent metadata. Currently, daily station positions are computed using GPS and Galileo constellations, using the “G20” orbits and clocks from the IGS CNES-CLS based on ITRF2020, FES2014b ocean tidal loading and VMF1 mapping functions.SPOTGINS started in 2022 with the collaboration between the OMP in Toulouse, the EOST in Strasbourg and the LIENSs in La Rochelle, whose massive calculations with GINS were already being done for several years. In 2023 and 2024, other groups expressed interest in joining SPOTGINS: the GeF/Cnam in Le Mans, the IPGP/IGN in Paris and the OSUG/ISTerre in Grenoble. Each member pursues different scientific objectives, but all contribute collectively to the dissemination of PPP series for the community through the Geodesy Plotter of the FormaTerre data and service hub.

In anticipation of the first update of the 2020 realization of the International Terrestrial Reference Frame (ITRF2020), the International DORIS Service (IDS) Combination Center is participating in the estimation of DORIS stations positions/velocities as well as Earth Orientation Parameters (EOPs), using DORIS data. These computations are based on the latest weekly multi-satellite series from all four IDS Analysis Centers and two IDS Associated Analysis Centers, from January 2021 to December 2023. The primary objectives of this study are to analyze the DORIS contribution to this first update of the ITRF2020 in terms of: (1) geocenter and scale solutions, (2) station positions and week-to-week repeatability, and (3) Earth Orientation Parameters (EOPs). Comparisons with the IDS 19 series time extension (contributing to ITRF2020) will highlight the benefits of the new models, including the latest DORIS missions (e.g. HY-2C, HY-2D, Sentinel-6A MF), and the addition of two new IDS contributors. Additionally, this study will assess the impact of new strategies designed to mitigate perturbations caused by the South Atlantic Anomaly (SAA) on certain DORIS missions.

A distributed Global Navigation Satellite System analysis center, designated SPOTGINS, has been established by several research groups that utilize the GINS software and the CNES-CLS precise products. Despite the heterogeneity in their research objectives, the SPOTGINS members apply the same configuration and metadata. The computed global ambiguity-fixed precise point positioning time series are fully consistent among the members, and are subsequently published as a single product (https://doi.org/10.24400/170160/20250414, Santamaría-Gómez et al., 2025). At the time of writing (August 2025), the SPOTGINS dataset includes 5768 daily series from May 2000 to present. This product facilitates a range of research activities, including but not limited to the precise monitoring of the Earth's deformation. A comparison of the SPOTGINS series with published series from the Nevada Geodetic Laboratory solution shows no significant difference in quality.

In 2009, the geoscience community has fixed an objective of 1 mm accuracy and 0.1 mm/yr stability for the terrestrial reference frame (TRF) realization (Global Geodetic Observing System, GGOS, Meeting the Requirements of a Global Society on a Changing Planet in 2020, Plag and Pearlman in Global geodetic observing system: meeting the requirements of a global society on a changing planet in 2020. Springer, Berlin, 2009. ). This accuracy and stability are needed for diversified studies like climate change, tectonic sciences and more generally any geoscience requiring the use of an accurate and precise TRF. Unfortunately, they are still not reached by the last International Terrestrial Reference Frame. To reach this goal, the use of "multi-technique" satellites as "space-ties" has been studied since 2011 and a few proposals have been made in response to different space agency calls: the Geodetic Reference Antenna in Space (GRASP) mission-NASA Earth Venture 2 call, Eratosthenes-GRASP (E-GRASP)-ESA Earth Explorer 9 (EE9) call, MOBILE-ESA EE10 call, MARVEL-CNES Seminaire de Prospective Scientifique 2019). In this article, we present the numerical simulations carried out by the French Groupe de Recherche de Geodesie Spatiale (GRGS) for the E-GRASP proposal in response to the ESA EE-9 call and their improvements carried out afterwards. These simulations aim to answer three different questions:Is it possible to reach the GGOS requirements for the TRF with the measurements of a GRASP-like satellite like E-GRASP alone?If it is possible, which level of accuracy for the positioning of the on-board antennas is needed?What is the minimal lifetime of a E-GRASP mission to reach the GGOS requirements?The results of these simulations show that a E-GRASP satellite can allow us to reach, after five years, an accuracy close to 1 mm and a stability better than 0.1 mm/yr for the TRF. However, it is necessary to ensure a positioning better than 1 mm for the on-board antennas. We therefore encourage the new ESA GENESIS mission proposal, accepted during the ESA last Ministerial meeting on 23rd November 2022, which takes up the concept of a GRASP-type satellite.

In space geodetic data analysis, improving tropospheric delay modelling is motivated by the correlation between tropospheric zenith total delay (ZTD) and the station height. The gradients are correlated with the horizontal displacements. In the microwave techniques such as GPS, DORIS, and VLBI, the tropospheric delay effects are correlated over the collocation sites. This correlation allows for the estimation of common tropospheric parameters, often referred to as tropospheric ties. These tropospheric ties provide valuable complementary information for the computation of the terrestrial reference frame (TRF) and have been the subject of investigation in many studies. In this study, we investigate the effects of tropospheric ties on the daily TRF combination at the observation level using a batch least-squares estimation. The observations of GPS, DORIS, and VLBI were collected from 06 May 2014 to 20 May 2014 during the CONT14 campaign of VLBI. The tropospheric delay and gradient ties are computed using different numeric weather prediction (NWP) data sets provided by ECMWF and NCEP. We examined different levels of tropospheric ties 0.01, 5, and 10 mm for ZTD and 0.001, 0.5, and 1.0 mm for gradients in the combination of techniques. The results show that the combined solution with tropospheric ties derived from the four NWP data sets does not exhibit significant differences. For VLBI, the repeatability of station coordinates and network scale were found to be improved by around 20% and 30%, respectively. The stronger tropospheric ties show a higher improvement in VLBI baseline repeatability. However, applying tropospheric ties at GPS-DORIS collocation sites does not significantly affect the repeatability of station coordinates and network scale. Both ZTD and gradient ties enhance the repeatability of polar motion components in EOPs, while no observable contribution is observed for dUT1 and celestial pole offsets.

In 2009, the geoscience community has fixed an objective of 1 mm accuracy and 0.1 mm/yr stability for the terrestrial reference frame (TRF) realization (Global Geodetic Observing System, GGOS, Meeting the Requirements of a Global Society on a Changing Planet in 2020, Plag and Pearlman in Global geodetic observing system: meeting the requirements of a global society on a changing planet in 2020. Springer, Berlin, 2009. https://doi.org/10.1007/978-3-642-02687-4 ). This accuracy and stability are needed for diversified studies like climate change, tectonic sciences and more generally any geoscience requiring the use of an accurate and precise TRF. Unfortunately, they are still not reached by the last International Terrestrial Reference Frame. To reach this goal, the use of “multi-technique” satellites as “space-ties” has been studied since 2011 and a few proposals have been made in response to different space agency calls: the Geodetic Reference Antenna in Space (GRASP) mission—NASA Earth Venture 2 call, Eratosthenes-GRASP (E-GRASP)—ESA Earth Explorer 9 (EE9) call, MOBILE—ESA EE10 call, MARVEL—CNES Séminaire de Prospective Scientifique 2019). In this article, we present the numerical simulations carried out by the French Groupe de Recherche de Géodésie Spatiale (GRGS) for the E-GRASP proposal in response to the ESA EE-9 call and their improvements carried out afterwards. These simulations aim to answer three different questions: The results of these simulations show that a E-GRASP satellite can allow us to reach, after five years, an accuracy close to 1 mm and a stability better than 0.1 mm/yr for the TRF. However, it is necessary to ensure a positioning better than 1 mm for the on-board antennas. We therefore encourage the new ESA GENESIS mission proposal, accepted during the ESA last Ministerial meeting on 23rd November 2022, which takes up the concept of a GRASP-type satellite.

The Standing Committee on Performance Simulations and Architectural Trade-Offs (PLATO) was established by the Bureau of Networks and Observations of the Global Geodetic Observing System (GGOS) in order to support – by prior performance analysis – activities to reach the GGOS requirements for the accuracy and stability of the terrestrial reference frame. Based on available data sets and simulated observations for further stations and satellite missions the committee studies the impact of technique-specific improvements, new stations, and additional co-locations in space on reference frame products. Simulation studies carried out so far show the importance of the individual station performance and additional stations for satellite laser ranging, the perspectives for lunar laser ranging assuming additional stations and reflectors, and the significant impact of the new VGOS antennas. Significant progress is achieved in processing VLBI satellite tracking data. New insights in technique-specific error sources were derived based on real data from short baselines. Regarding co-location in space PLATO members confirmed that E-GRASP could fulfill the GGOS requirements with reaching a geocenter and scale accuracy and stability of 1 mm and 0.1 mm/year, respectively.