Radar altimetry is a technique to measure height or altitude above a surface using an instrument called a radar altimeter. The principle is that the radar altimeter emits a radar wave and analyses the return signal that bounces off of a surface. NSIDC archives and distributes data from the following radar altimeters:

• Radar Altimeter (RA) on ERS -1 and -2: A Ku-band (13.8 GHz) radar altimeter launched on board the European Remote Sensing satellite 1 and 2 on 17 July 1991 and 21 April 1995, respectively.
• Radar Altimeter on GEOSAT: A Ku-band (13.5 GHz) radar altimeter launched on board GEOSAT on 12 February 1985.
• Radar Altimeter (ALT) on Seasat: A Ku-band (13.5 GHz) radar altimeter launched on board Seasat on 27 June 1978.
• Dual-Frequency Topex Radar Altimeter (ALT) on TOPEX/Poseidon: A Ku-band (13.6 GHz) and C-band (5.3 GHz) radar altimeter launched on board TOPEX/Poseidon on 10 August 1992.

The radar altimeters provide measurements of the altitude of the Earth's surface to determine ice sheet topography, small-scale ocean roughness, and wind speed.

NSIDC archives and distributes radar altimeter data in the form of Digital Elevation Models (DEMs). To access this data, see the Polar Ice Sheet DEMs and Elevation Data Web page.