GOCE

GOCE, ESA’s Gravity field and steady-state Ocean Circulation Explorer, flew from 17 March 2009 to its reentry on 11 November 2013, mapping Earth’s gravity field at the highest resolution then achieved. It carried a three-axis electrostatic gradiometer in a drag-free orbit as low as 224 to 255 km, sustained by an ion engine, to recover the geoid to about 1 to 2 cm at 100 km scales. That geoid is the reference surface altimetry needs: subtract it from the measured sea surface height and the remainder is the mean dynamic topography, which gives the geostrophic surface current. GOCE sharpened ocean-circulation estimates and the marine gravity field used in bathymetry inversion.