The go-ahead to build and launch the CryoSat-2 mission came in February 2006 after the loss of the first CryoSat in October 2005 due to a launch failure. The mission's objectives remain the same as before – to measure ice thickness on both land and sea very precisely to provide conclusive proof as to whether there a trend towards diminishing polar ice cover, furthering our understanding of the relationship between ice and global climate. CryoSat-2 is due for launch in 2009.

It is now generally agreed that the Earth's atmosphere is getting warmer, and although the impact of climate change is expected to be amplified at the poles, it is extremely difficult to predict what effect this is having on the polar ice cover. On one hand, recent years have already seen record summer reductions, in extent and concentrations, of sea ice in the Arctic. In Antarctica, giant icebergs have calved and part of the Larsen ice shelf has disintegrated. However, on the other hand, ships have recently been trapped for weeks in unusually heavy Antarctic pack ice conditions.  
 

	Artist's impression of CryoSat in orbit

From an altitude of just over
700 km and reaching latitudes of 88°, CryoSat-2 will monitor precise changes in the thickness of the polar ice sheets and floating sea ice. The observations made over the three-year lifetime of the mission will provide conclusive evidence of rates at which ice cover may be diminishing.
 
 
Fundamentally, there are two types of polar ice – the ice that floats in the oceans and the ice that lies on land. Not only do these two forms of ice have different consequences for our planet and its climate, they also pose different challenges when trying to measure them from space.
 
 

Floating sea ice

Sea ice is relatively thin – up to a few metres thick, but, it influences regional temperature and the circulation of ocean currents, and consequently the Earth's climate. CryoSat-2 will acquire precise measurements of the thickness of floating sea ice so that annual variations can be detected.
 
 

	Ice-shelf break up

In contrast, the ice sheets that blanket Antarctica and Greenland are several kilometres thick. It is the growth and shrinkage of these ice masses that have a direct influence on sea level. The chosen approach to measuring these vast thicknesses is to determine the height of the surface accurately enough to detect small changes.
 
 
To meet the challenges of measuring ice, CryoSat-2 will carry a sophisticated radar altimeter called SIRAL (Synthetic Aperture Radar Interferometric Radar Altimeter). It is based on heritage from existing instruments, but with several major enhancements designed to overcome the difficulties intrinsic to the precise measurement of ice surfaces.
 
 
Last update: 6 February 2008