Elevation of Antarctic ice sheets, computer artwork. The red band shows that the western side of Antarctica (towards the left) is lower than the east. It is feared that glacial flow has accelerated on the west of the continent and the West Antarctic ice sheet is thinning. This artwork is based on data from the Geoscience Laser Altimeter System (GLAS) on NASA's Ice, Cloud, and Land Elevation Satellite (ICESat). This device is designed to measure the mass balance of Earth's ice sheets, to determine whether the processes that produce ice are balanced by the processes that remove it. An imbalance would have implications for global sea levels.