Theia SAGSA Gravimetry Total Water Storage Anomalies

GRACE and GRACE-FO spatial missions

The GRACE (Gravity Recovery And Climate Experiment; Tapley et al., 2004) and GRACE-FO (GRACE-Follow On; Landerer et al., 2020) missions enable the measurement of spatial and temporal variations in the Earth's gravity field with a spatial resolution of a few hundred kilometers and a temporal resolution ranging from weeks to months. To derive variations in continental water stocks, a few post-processing steps must be applied. The latter aim at reducing the instrumental noise, at estimating the very long wavelength components (degree 1 and 2) of the gravitational field to which satellites are not very sensitive, and at removing signals related to the deformation of the solid Earth (glacial isostatic adjustment and co-seismic deformations). The uncertainties associated with the processing and post-processing of GRACE and GRACE-FO data are estimated using an ensemble approach developed by Blazquez et al. (2018).

Data description

The products distributed in this collection are assessments of monthly Terrestrial Water Storage nomalies (TWSA), estimated from GRACE and GRACE-FO measurements. TWSA includes all water stocks from the Earth surface to deep aquifers: surface water (rivers, lakes, floodplains), water retained by vegetation, water under snow form, soil moisture, and groundwater. TWSA is the volume anomalies for each position expressed in water cubic kilometers and are calculated relative to the temporal average of the series over the period January 2005 - December 2014.

TWSA are derived from SAGSA Level 3 ensemble products, available on GEODES and documented at the following link: GEODES SAGSA Project. The gridded ensemble products, expressed in meters of equivalent water height (m EWH), are multiplied by each ellipsoidal surface to obtain water volumes in cubic kilometers. Final hydrogravimetry products are generated by applying a landmask to the data. This land mask, that also includes drainage basins’ masks, is distributed through the variable “land_mask” in the hydrogravimetry products of this collection as well as in the ensemble products available on GEODES. For more details, a User Manual describes the processing steps for converting the Level 3 gravimetric dataset to the equivalent water volumes covered by this collection.

Different versions of the dataset

The Level 3 gravimetric dataset is updated twice a year to complete the time series with the most recent products and to incorporate software updates that refine and improve the processing of Level 2 GRACE and GRACE-FO data. Version 2.1 of “Theia SAGSA GRACE Terrestrial Water Storage Anomalies” collection is the most recent version of this dataset and is recommended for use.

The versions’ history of the “Theia SAGSA GRACE Terrestrial Water Storage Anomalies” collection is presented below:
- Version 2.0.1. Available upon request. Covers April 2022 to September 2023.
- Version 2.1. Published in March 2026. Covers April 2022 to August 2025. Produced from input GEODES SAGSA Project. Product User Manual. DOI: https://doi.org/10.24400/329360/SAGSA_TWSA_ENS_1MONTH_V2.1

The previous versions are available upon request by contacting Alejandro Blazquez at alejandro.blazquez@cnes.fr.

How to cite

If you use the data, please cite: “The hydrological products from satellite gravimetry were produced by Magellium/CNES/LEGOS (Blazquez et al, 2018, doi: 10.1093/gji/ggy293)
and distributed by hydroweb.next DOI: https://doi.org/10.24400/329360/SAGSA_TWSA_ENS_1MONTH_V2.1 "

Contacts

For any technical issues or additional information related to the spatial gravimetry hydrological products, users are advised to contact Judith Garnier: judith.garnier@magellium.fr