Monitoring Terrestrial Mass Changes: The CNES's Level-2 and Level-3 Gravimetry Products

by Lecomte, H., Blazquez, A., Meyssignac, B., Zawadzki, L., Lemoine, J.-M. and Bonniface, C.
ESA Living Planet Symposium 2025
(poster) June, 2025

The Centre National d’Etudes Spatiales (CNES) is actively contributing to the development and distribution of space gravimetry Level-2 and Level-3 products. These products are essential for the study of mass repartition within the Earth’s system. Mass changes products enable study of various physical processes such as tides, sea-level change, post-glacial rebound, terrestrial water storage change, co-seismic deformation, atmospheric/oceanic circulation, Earth’s core processes and others. As an analysis center for the processing of Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, CNES distributes Level-2 spherical harmonics coefficients that are the combination of Satellite Laser Ranging data with GRACE data at the normal equation level inverted with the use of truncated singular value decomposition. CNES also contributes to the combined solution produced by the International Combination Service for Time-variable Gravity Fields (COST-G). This presentation highlights the different Level-3 products developed and distributed by CNES. The Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS) and CNES have developed a processing chain based on GRACE(-FO) Level-2 spherical harmonics products from various analysis centers. This processing chain generates Level-3 products, corrected for low-degree and solid Earth signals  (including earthquakes and post-glacial rebound), filtered, and comes with an uncertaintiy estimation. These L3 products are designed to study water mass transfers with a spatial resolution of a few hundreds kilometers. The Level-3 total water storage changes data product is distributed via the Data Terra/Theia inland water thematic hub hydroweb.next (hydroweb.next.theia-land.fr). The terrestrial water storage is the addition of groundwater, surface water, soil moisture, snow and glaciers water contents. This information can be associated with other satellites observations to study particular components of the land water budget. It is essential for freshwater resource management, drought and flood forecasting. Level-3 Barystatic sea-level product is distributed via the DaTa Terra/ODATIS hub. This oceanography product is combined with sea-level change estimates from satellite altimetry, ocean temperature profiles from in-situ measurements to generate a Level 4 Ocean Heat Content product also distributed at the same portal. This product places a strong constraint on the Earth’s energy imbalance and is crucial to monitor the oceans’ role in the climate system. The Level-3 Ice-sheets and glacier mass changes products will be distributed via the Data Terra/ForMaTerre hub. This cryosphere product relies on gravimetry to estimate ice sheet and glacier mass changes within the framework of the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) project. This product follows the glaciers and ice-sheets dynamics and serves as an estimation of the cryosphere component of the sea-level budget rise. These different products exemplify the key role of CNES in developing innovative services based on satellite gravimetry missions. These products will make use of futur gravimetry mission data  including the MAGIC mission, where they will be further enhanced through continuous development and the improved spatial and temporal resolution provided by MAGIC

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