The Geoscience Laser Altimeter System (GLAS) is the sole instrument on the Ice, Cloud, and land Elevation Satellite (ICESat). It is part of NASA's Earth Observing System (EOS) and was launched on 12 January 2003 into a near-circular and near-polar 91-day orbit with a 33-day repeat cycle. At an altitude of approximately 600 km, GLAS provides global coverage between 86° N and 86° S. The GLAS laser transmits short pulses (4 nanoseconds) of infrared light at 1064 nm and visible green light at 532 nm 40 times per second. The spatial resolution of the disk illuminated by the laser is 70 meters in diameter and spaced at 170-meter intervals along the Earth's surface.

The main objective of the GLAS instrument is to measure ice sheet elevations and changes in elevation through time. Secondary objectives include measurement of cloud and aerosol height profiles, land elevation and vegetation cover, and sea ice thickness. This data will enable scientists to study the Earth's climate, and ultimately predict how ice sheets and sea level will respond to future climate change.

NSIDC archives and distributes 15 products, including Levels 1A, 1B, and 2 laser altimetry and atmospheric lidar data. Please see the ICESat/GLAS Data at NSIDC Web site for tools to order and work with the data, information regarding the availability of data products, how to obtain guide documentation, FAQs, and other related GLAS information. NSIDC also archives and distributes GLAS Digital Elevation Models (DEMs). To access the GLAS DEMs, see the Polar Ice Sheet DEMs and Elevation Data Web site.