Polar Clouds—Early Observations from the Geoscience Laser Altimeter System

The Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud, and Land Elevation Satellite (ICESat) was launched in January 2003, and early atmosperic observations from this mission are presented. GLAS provides global cloud and aerosol profiles from space-based lidar, the first time such a comprehensive measurement is available. Observations of polar clouds from satellites must overcome two significant problems. First, the ice- and snow-covered high latitude surfaces underlying the clouds appear very similar to the clouds themselves, both at visible wavelengths and in the infrared. Clouds could be brighter or darker than the snow-surface, making it difficult to distinguish them from clear-sky observations. Second, passive imagery does not reveal the structure of the clouds from which it is recorded. Accurate characterization of cloud radiative properties measured by passive sensors will be improved by knowledge of cloud-layering; the active profiling of atmospheric layers by GLAS provides this information routinely. Also of interest to the polar climate research community, measurements from GLAS will provide high precision surface laser altimetry for study of the balance of precipitation and ice loss on the Antarctic and Greenland ice sheets, and other surface applications.