Groundwater and terrestrial water storage covers large-scale changes in aquifers, soil moisture, snow, rivers, lakes, and other land-water stores. GRACE and GRACE-FO are the direct EO route for total terrestrial water-storage change: NASA/JPL describes the missions as tracking surface mass anomalies and water movement, including underground water storage, on at least a monthly cadence.^[1]

Groundwater itself is not usually observed as a clean standalone satellite signal. NASA groundwater and soil-moisture maps combine GRACE observations with modelling and other observing systems to estimate wetness and drought conditions.^[2] SMAP, Copernicus Surface Soil Moisture, and ESA CCI Soil Moisture products serve the surface-soil-moisture component of the water budget rather than deep aquifer storage.^[3]^[4]^[5]

InSAR is a strong local proxy where groundwater withdrawal causes aquifer-system compaction and land subsidence; USGS notes that repeat-pass radar images are used to monitor subsidence and uplift at high spatial detail.^[6] Inland-water altimetry can constrain surface-water storage, but it does not replace gravimetry for basin-scale terrestrial water storage.