Second release of combined monthly gravity fields of the GRACE and GRACE-FO satellite missions in spherical harmonic representation (Level-2 product) generated by the Combination Service for Time-variable Gravity Fields (COST-G; Jäggi et al., 2020), a product center for time-variable gravity fields of IAG's International Gravity Field Service (IGFS).
COST-G RL02 is a combination of gravity field time series provided by the following analysis centers (ACs) and partner analysis centers (PCs) of COST-G:
ACs:
- GFZ Helmholtz Centre for Geosciences: GFZ RL06 (GRACE), GFZ RL06.3 (GRACE-FO)
- Graz University of Technology, Institute of Geodesy: ITSG-Grace2018 (GRACE), ITSG-Grace_op (GRACE-FO)
- Centre National d’Etudes Spatiales, Groupe de Recherche de Geodesie Spatiale: CNES_GRGS_RL05_CHOL (GRACE & GRACE-FO)
- Astronomical Institute University of Bern: AIUB-RL03 (GRACE), AIUB-GRACE-FO_rl02op (GRACE-FO)
- Leibniz Universität Hannover: LUH-GRACE-2020 (GRACE), LUH-GRACE-FO-2020 (GRACE-FO)
- Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences: APM-SYSU (GRACE)
- HuaZhong University of Science and Technology: HUST-Grace2024 (GRACE & GRACE-FO)
- Southern University of Science and Technology, Department of Earth and Space Sciences: SUSTech2025 (GRACE)
- Tongji University, College of Surveying and Geo-informatics: Tongji-Grace2022 (GRACE)
PCs:
- Center for Space Research at University of Texas: CSR RL06 (GRACE), CSR RL06.3 (GRACE-FO)
- NASA Jet Propulsion Laboratory: JPL RL06 (GRACE), JPL RL06.3 (GRACE-FO)
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Version History:
4 July 2025:
Release of Version 2.1. This is an update of Version 2.0 of the same data set including the following changes: Replacement of Tongji-Grace-Costg (nonofficial release) by Tongji-Grace2022; replacement of HUST-Grace2023 (nonofficial release) by HUST-Grace2024 (currently also not yet officially released); use of GFZ RL06.3, CSR RL06.3, JPL RL06.3 and CNES_GRGS_RL05_CHOL for the entire GRACE-FO period.
25 April 2025:
Initial release of the data (Version 2.0).
Combined monthly gravity fields of the GRACE satellite mission in spherical harmonic representation (Level-2 product) generated by the Combination Service for Time-variable Gravity Fields (COST-G; Jäggi et al. (2020):http://dx.doi.org/10.1007/1345_2020_109), a product center for time-variable gravity fields of IAG's International Gravity Field Service (IGFS). COST-G GRACE RL01 is a combination of AIUB-RL02, GFZ-RL06, GRGS-RL04 (unconstrained solution), ITSG-GRACE2018, and CSR-RL06. The original time-series were provided by the analysis centers (ACs) and partner analysis centers (PCs) of COST-G.
Operationally combined monthly gravity fields of the GRACE-FO satellite mission in spherical harmonic representation (Level-2 product) generated by the Combination Service for Time-variable Gravity Fields (COST-G; Jäggi et al. (2020):http://dx.doi.org/10.1007/1345_2020_109), a product center for time-variable gravity fields of IAG's International Gravity Field Service (IGFS). COST-G_GRACE-FO_RL01_OP is a combination of AIUB-GRACE-FO_op, GFZ-RL06 (GFO), GRGS-RL05 (unconstrained solution), ITSG-Grace_op, LUH-GRACE-FO, CSR-RL06 (GFO) and JPL-RL06 (GFO). The original time-series were provided by the analysis centers (ACs) and partner analysis centers (PCs) of COST-G.
Although the knowledge of the gravity of the Earth has improved considerably with CHAMP, GRACE and GOCE satellite missions, the geophysical community has identified the need for the continued monitoring of its time-variable component with the purpose of estimating the hydrological and glaciological yearly cycles and long-term trends. Currently, the GRACE-FO satellites are the sole provider of this data, while previously the GRACE mission collected these data for 15 years. Between the GRACE and GRACE-FO data periods lies a gap spanning from July 2017 to May 2018, while the Swarm satellites have collected gravimetric data with its GPS receivers since December 2013.
This project aims at providing high-quality gravity field models from Swarm data that constitute an alternative and independent source of gravimetric data, which could help alleviate the consequences of the 10-month gap between GRACE and GRACE-FO, as well as the short gaps in the existing GRACE and GRACE-FO monthly time series.
The geodetic community has realized that the combination of the different gravity field solutions is superior to any individual model. This project exploits this fact and delivers to the highest quality monthly-independent gravity field models, resulting from the combination of 4 different gravity field estimation approaches. All solutions are unconstrained and estimated independently from month to month.
Preliminary comparison with GRACE data has demonstrated that the signal in the Swarm gravity field models is restricted to degrees 12-15 and below, while the temporal correlations decrease considerably above degree 10. The 750km smoothed models are suitable to retrieve the global annual temporal variations of Earth's gravity field and the agreement with GRACE over large basins (e.g. Amazon, Congo-Zambezi, Ganges-Brahmaputra) is within 1cm RMS in terms of Equivalent Water Height. The global RMS relative to a bias, trend, an annual and semi-annual model derived from GRACE over deep ocean areas (those roughly 1000km from shorelines) is under 1mm geoid height during periods of low ionospheric activity.
More information about this project can be found at https://www.researchgate.net/project/Multi-approach-gravity-field-models-from-Swarm-GPS-data and ESA's Swarm DISC (the Data, Innovation and Science Cluster) Website (https://earth.esa.int/web/guest/missions/esa-eo-missions/swarm/activities/scientific-projects/disc#MAGF). This project is funded by ESA via the Swarm DISC, Sub-Contract No. SW-CO-DTU-GS-111.