Gravity Recovery and Climate Experiment

Gravity Recovery and Climate Experiment The Gravity Recovery and Climate Experiment was a joint National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR) mission consisting of twin satellites to map Earth's gravity field and monitor mass transport. The mission provided monthly gravity solutions that informed studies of ice sheet mass balance, terrestrial water storage, ocean circulation, and sea level, enabling cross-disciplinary work across Jet Propulsion Laboratory, University of Texas at Austin, University of Bonn, GeoForschungsZentrum Potsdam, and Massachusetts Institute of Technology researchers.

Background and Objectives

Conceived in collaboration between NASA and DLR, the mission aimed to improve on predecessors such as the Lageos laser geodynamics efforts and complement gravity field models like those produced by GRACE-FO planners. Primary objectives included quantifying mass changes in the Greenland ice sheet, Antarctic ice sheet, major river basins such as the Amazon River and Ganges River, and ocean mass redistribution associated with events like the 2004 Indian Ocean earthquake and tsunami. Secondary goals targeted improvements to geoid models used by NOAA and integration with altimetry records from TOPEX/Poseidon and Jason-1.

Mission Design and Instruments

The two satellites, often called "twin" craft, flew in a polar, near-circular formation following launch aboard a Rockot/Delta II-class launcher from Vandenberg Air Force Base. Core hardware included a high-precision inter-satellite K-band microwave ranging instrument derived from work at JPL and a three-axis electrostatic accelerometer developed with contributions from CNES. Attitude and positioning combined data from Global Positioning System receivers, star cameras influenced by designs used on Hubble Space Telescope guidance systems, and preflight calibration at facilities such as European Space Agency test centers. The spacecraft design utilized lessons from missions like CHAMP and incorporated thermal controls informed by International Space Station thermal models.

Operations and Data Processing

Operational control was shared between NASA centers and DLR mission operations teams, with science processing led by consortia at University of Texas at Austin, University of Bonn, GFZ Potsdam, and JPL. Level-1 telemetry passed through ground stations including Wallops Flight Facility and Kiruna Space Center before conversion to Level-2 gravity field solutions employing spherical harmonic analysis and parameter estimation methods developed in the tradition of EIGEN and ITG-Grace. Data assimilation integrated GRACE-derived mass anomalies into models run by groups at National Centre for Atmospheric Research and NOAA to improve hydrological forecasts and glaciological mass budgets. Validation campaigns referenced in situ observations from GRACE-complementary missions and networks such as GLACIERS field campaigns, Permanent Service for Mean Sea Level, and UNESCO hydrometric stations.

Key Scientific Findings

Analyses revealed significant mass loss from the Greenland ice sheet and West Antarctica contributing to observed sea level rise quantified alongside altimetry from Jason-2. The mission detected seasonal and long-term terrestrial water storage variations in basins like the Amazon River basin, Murray–Darling basin, and Ganges River basin, improving drought and flood assessments tied to events such as the 2010 Pakistan floods and 2015–16 El Niño. GRACE data captured postseismic mass redistribution associated with the 2004 Indian Ocean earthquake and tsunami and the 2011 Tōhoku earthquake and tsunami, informing studies of solid Earth deformation and glacial isostatic adjustment investigated in the context of Plate tectonics models developed at Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory. Ocean mass trend detection refined estimates of steric versus mass-driven sea level change, complementing work from Argo float datasets and satellite altimeters from Envisat.

Legacy and Successor Missions

The mission established a new paradigm for satellite gravimetry and directly motivated the GRACE Follow-On program, international collaborations among agencies including NASA, DLR, and partners such as CNES and CSA. Techniques pioneered influenced subsequent missions like GOCE and operational services at ESA and NOAA that use gravity products for geodesy, hydrology, and climate monitoring. The GRACE data archive continues to underpin research by institutions including Columbia University, ETH Zurich, Imperial College London, and Australian National University, and has informed policy dialogues at Intergovernmental Panel on Climate Change and basin management practices in regions such as the Colorado River Basin and Nile Basin.

Category:Earth observation satellites Category:NASA missions Category:Satellite gravimetry