Interferometric radar mapping of ice velocity in Antarctica and Greenland

Satellite radar interferometry is revolutionizing our knowledge of ice motion in the polar regions. With ERS-1 launched in 1992, ERS-2 in 1995 and Radarsat-1 in 1997, we have accumulated 14 years of experience mapping ice motion in Greenland and Antarctica. A nearly complete map of the velocity of Greenland glaciers was assembled using Radarsat-1 data from year 2000, and the results were employed to calculate ice discharge and mass balance of the Greenland Ice Sheet. By tracking changes in ice dynamics over time, one can precisely measure changes in mass balance. Those results indicate that the mass loss from the Greenland Ice Sheet has doubled in the last decade. In Antarctica, we employed both ERS-1/2 and Radarsat-1 data to map 85 percent of the velocity along the coastline. Interferometry is also key to infer the position of grounding lines, either from ERS-1/2 or Radarsat-1 double difference interferometry. The results are providing a major step forward in our knowledge of mass discharge, and the relative importance of various glaciers to the mass balance of ice sheets. By tracking velocity changes over time, a picture of the most dynamic sectors of Antarctica is now emerging. The results reveal a very complex and dynamic landscape which changes faster than anticipated. Key to these advances have been the availability of data from the European Space Agency (ERs, and now Envisat) and the Canadian Space Agency (Radarsat-1, distributed either by ESA or the Alaska Satellite Facility. Sustained and growing access to these data, with more satellites to come, and despite the fact that none of these satellites were designed to do this work, promises further important and timely advances in our understanding of the evolution of ice sheets in a warming climate.