CryoSat-2 will carry a sophisticated radar altimeter to meet two principal challenges.
The first will acquire accurate measurements of the thickness of floating sea ice so that annual variations can be detected. The second will survey the surface of ice sheets accurately enough to detect small changes.
CryoSat-2's radar altimeter is based on heritage from existing instruments, but with several major enhancements designed to improve measurements of icy surfaces. Because of its operations in SAR and Interferometric modes, the altimeter is called SIRAL (SAR Interferometric Radar Altimeter). CryoSat-2 will orbit at an unusually high inclination, reaching latitudes of 88° North and South.
CryoSat-2 will determine the thickness of floating sea ice by measuring the freeboard of ice floes; that is the height by which the ice extends above the water surface. This technique has been demonstrated with the ERS-1 radar altimeter, but this instrument, as with all conventional radar altimeters, is hampered by its relatively low spatial resolution of about 5 km. CryoSat-2 will achieve improved spatial resolution of 250 m in the along-track direction using the Synthetic Aperture technique.
The first returning energy in the radar echo comes from the part of the Earth's surface closest to the satellite.
Over sea ice (and ocean) this point is directly below the satellite, but on sloping surfaces, such as those found
around the edges of ice sheets, this nearest point can be anywhere. CryoSat-2 will be able to pin down the
location of the echo in the fore- and aft-direction by using its SAR capability, but to resolve left and right an
additional feature is needed. Over these sloping surfaces CryoSat-2 will operate in the SAR-Interferometry mode,
which provides the key measurements of the angle of arrival and thus the pin-pointed source of the echo.
More information can be found in the Cryosat Mission and Data Description document