Cryosat-2 is an altimetry satellite built by the European Space Agency dedicated to polar observation. It embarks on a three-and-a half-year mission to determine variations in the thickness of the Earth's continental ice sheets and marine ice cover, and to test the prediction of thinning arctic ice due to global warming.

The Cryosat-2 satellite studies continental and sea ice. Its orbit -at an inclination of about 92 degrees and an altitude of 717 kilometers- covers almost all polar regions. Cryosat-2 carries an altimeter/interferometer called Siral and a Doris instrument, but no radiometer. Siral is a Ku-band instrument (13.575 GHz) operating in three modes :

• Low-resolution, nadir-looking altimeter mode, provides conventional pulse-width limited altimetry over central ice caps, oceans and land,
• SAR mode improves along-trackresolution (~250 m) over sea ice by significantly increased pulse repetition frequency and complex ground processing,
• SAR interferometric mode adds a second receive chain to measure the cross track-angle of arrival of the echo over topographic surfaces at the margins of ice caps.

Cryosat-2 was initially designed for studying the cryosphere but it is also an opportunity mission for oceanographic studies as it operates over the oceans for validation purposes in low-resolution mode, and in SAR mode over some specific zones. That means that the ground segments are able to process oceanic altimetry measurements acquired by Siral. Direct radiometric corrections, however, are not possible given the lack of onboard dedicated instrument.

Even if the dynamic topography data of Cryosat-2 are of reduced quality compared to those from the dedicated altimetry missions, they are collected on a different and new orbit, and therefore, are of a particular interest in the combination with the measurements from these missions.

One first satellite Cryosat was lost on launch, on October 8, 2005, due to an anomaly in the launch sequence.

More information on the <link http: www.esa.int esalp lpcryosat.html _blank external-link-new-window>mission (Esa website)