The Radar Altimeter (RA) onboard the ERS-1 and ERS-2 missions was a Ku-band (13.8 GHz) nadir-pointing active microwave sensor designed to measure the time return echoes from ocean and ice surfaces. Functioning in one of two operational modes (ocean or ice) the RA provided information on significant wave height; surface wind speed; sea surface elevation, which relates to ocean currents, the surface geoid and tides; and various parameters over sea ice and ice sheets.

The ERS-1 mission launched on 17 July 1991 and ended on 10 March 2000. ERS-2 was launched on 21 April 1995 and retired on 5 September 2011.