ICESat's Laser Measurements of Polar Ice, Atmosphere, Ocean, and Land

NASA's Ice, Cloud and Land Elevation Satellite (ICESat) mission is designed to measure changes in elevation of the Greenland and Antarctic ice sheets beginning in January 2003. Time-series of elevation changes will enable determination of the present- day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and estimation of the present and future contributions of the ice sheets to global sea level rise. Other scientific objectives of ICESat include: global measurements of cloud heights and the vertical structure of clouds and aerosols; precise measurements of land topography and vegetation canopy heights; and measurements of sea ice roughness, sea ice thickness, ocean surface elevations, and surface reflectivity. The Geoscience Laser Altimeter System (GLAS) on ICESat has a 1064 nm laser channel for surface altimetry and dense cloud heights and a 532 nm lidar channel for the vertical distribution of clouds and aerosols. Differences between the characteristics of laser and radar altimetry, such as effective depth of the backscattered signal, elevation accuracy, and footprint location, and their relevance to inter-relating measurements from ERS, Envisat, ICESat, and Cryosat are discussed. Preliminary ICESat results obtained during the calibration and validation period of ICESat are described. ICESat is designed to operate for 3 to 5 years and should be followed by successive missions to measure ice changes for at least 15 years.