This video highlights the calibration and validation campaigns carried out on the ground ahead of the Cryosat mission (a year before Cryosat-1 was set to launch). Scientists must endure living in harsh conditions for months in order to measure and assess snow pack conditions so that this ground information can be compared to airborne radar altimeter instrument data. These analyses provide ESA with the guarantee that the measurements provided by Cryosat will be accurate and ensure that the thickness of Earth's polar ice can be determined with unprecedented accuracy over a period of three years -- the lifetime of Cryosat. This 3-year-long record of centimetre precision will allow scientists to answer whether the polar ice has started to melt due to climate change and, if so, where it is happening.