An example of a radar altimetry instrument that is already flying: Envisat’s Radar Altimeter-2 (RA-2) has a special tracking mode to measure topographic features such as ice edges and sea-ice thickness. On 14 March 2002, two days after the RA-2 was switched on, the Radar Altimeter observed the large iceberg, seen in the ASAR image, and measured its emerged height (about 25 meters), as can be seen in this along-track measurement profile. This iceberg is about 200 meters high, including its submerged part. CryoSat should deliver improved resolution over sea ice and heightened performance over the irregular topography found at the edge of land ice sheets.