Launched 17 March 2002, Gravity Recovery and Climate Experiment (GRACE) twin satellites made detailed measurements of Earth's gravity field and improved investigations about Earth's water reservoirs over land, ice and oceans. GRACE was a collaboration of the US and German space agencies (NASA and DLR). The key partners were the University of Texas Center for Space Research (CSR), the GeoForschungsZentrum (GFZ) Potsdam, and the Jet Propulsion Laboratory (JPL).
GRACE measured gravity by relating it to the distance between the twin satellites. For example, an increase in gravity ahead of the pair caused the front satellite to speed up and increase the distance between the pair. Alternately, increased gravity in between the pair decreased their relative distance. The satellites were separated by 220 km and could detect changes smaller than a micrometer per second in relative velocity. These measurements, in conjunction with other data and models, provided observations of terrestrial water storage changes, ice-mass variations, ocean bottom pressure changes and sea-level variations.
GRACE ended its science mission in 12 October 2017.
The GRACE Tellus webpage at JPL is an excellent first introduction to GRACE and related projects, the measurements, FAQ's, and which product is best suited for a specific use case. From there, the User Guides should be consulted. A general rule of thumb for choosing which data set to use: most non-expert users interested in hydrology, ice mass, and ocean bottom pressure mass change should look at the MASCON gridded data products (e.g. 10.5067/TEMSC-3MJ634, 10.5067/TEMSC-3JC634) and the globally averaged Level 4 time series products (10.5067/TEMSC-AT634, 10.5067/TEMSC-GT634, 10.5067/TEMSC-OT634). These products combine the records from GRACE and GRACE-FO into a longer time series and are added to monthly. Advanced users wanting gridded fields based on the traditional spherical harmonic basis functions, or users looking at gravity field analysis, sensitivity studies, and solid Earth processes, should consult the Level 2 spherical harmonic gravity field products and Level 3 Tellus products (note there are different solutions provided from each of the three GRACE project partners, JPL, CSR, and GFZ).
GRACE / GRACE-FO Bibliography >>
