Measurements and Status of the First Satellite Lidar for Atmospheric Science

GLAS (the Geoscience Laser Altimeter System) was successfully launched aboard the Ice, Cloud and Land Elevation Satellite (ICESat) into a near-polar orbit (inclination 94 degrees) on January 12th 2003. Since that time, GLAS has been acquiring data in 5-6 week-long observation periods 3 times per year. It has obtained almost 8 months of data in total, providing the first global views of the vertical structure of clouds and aerosols by an orbiting lidar. GLAS is an important part of NASA's Earth Science Enterprise (ESE) which includes a series of satellites beginning in 1999 to measure Earth's atmosphere, oceans, land, ice, and biosphere for a period of 10 to 15 years. The main goal of ESE is to measure changes in the earth-atmosphere system which are indicative of climate and environmental change.

GLAS uses one of three 40 Hz, frequency-doubled ND:YAG lasers to obtain backscatter profiles of the atmosphere from 40 km to the surface at 532 nm and 20 km to the surface at 1064 nm with a vertical and horizontal resolution of 76 and 175m, respectively. ICESat has the ability to accurately point to ground targets which greatly facillitates the validation and calibration of the data.