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The launch of the first Cryosat satellite in 2005 ended in failure, but the mission rose from the ashes and in 2010 Cryosat-2 was sent into a 717-km polar orbit from the Baikonur Cosmodrome in Kazakhstan atop a Russian-Ukrainian Dnepr launcher. For the first time ever, it would measure the thickness of sea and land ice (the ice caps of the Antarctic and Greenland) from space with centimetre accuracy.
Cryosat-2 is carrying an innovative radar altimeter instrument called SIRAL. Built in France by Thales Alenia Space, SIRAL continuously measures the distance or range from the satellite to the ice surface and employs an interferometric mode to map the rugged relief of the polar ice caps.
But to determine ice thickness, we need to establish another parameter: the satellite’s orbital position. This is measured—also with centimetre accuracy—by the DORIS1 system. Developed by CNES and the French mapping and survey agency IGN, DORIS consists of an instrument on Cryosat-2 that communicates with 60 ground stations transmitting signals to the satellite.
Without DORIS, Cryosat-2 would have been unable to achieve its objectives and answer many of the questions raised by global warming. For example, is polar ice melt gaining pace? Is ice melting faster in Antarctica than in the Arctic? Does it reform completely every year? And to what extent is polar ice melt contributing to rising sea level?