EO·Atlas
Geoscience Laser Altimeter System (GLAS)
Full-waveform laser altimeter on NASA ICESat (2003-2010), 1064 nm and 532 nm, 40 Hz PRF, 66 m footprint, 170 m along-track spacing.
The Geoscience Laser Altimeter System (GLAS) was a full-waveform lidar altimeter that flew aboard NASA's ICESat satellite from January 2003 until the mission's retirement in August 2009. GLAS was built at NASA Goddard Space Flight Center; the ICESat spacecraft was built by Ball Aerospace.
GLAS carried three independent Nd:YAG lasers operating at 1064 nm for surface altimetry, with a 532 nm channel for cloud and aerosol profiling. Only one laser was active at a time, with the others held in reserve as the operational laser degraded. Pulse repetition rate was 40 Hz. Pulse energy figures in the literature span a range: 75 mJ [1], 70 mJ on-orbit initial [2], and 100 mJ in early design documentation [3], reflecting design, on-orbit initial, and nominal values at different phases of the mission. Energy declined progressively over each laser's operational period. Footprint diameter was 66 m, along-track shot spacing 170 m, and beam divergence approximately 0.11 mrad [1] [2]. Waveforms were digitised by a 1 GHz analogue-to-digital converter, yielding vertical precision better than 5 cm on flat surfaces [3].
The three-laser configuration addressed the laser reliability constraints of the era; each unit carried a limited pulse-life budget. Laser 1 failed after 37 days; Laser 2 operated across multiple campaign periods through 2007; Laser 3 carried the mission to its end in 2009. Campaigns were time-limited and non-continuous, so the global coverage pattern differs from continuously operating altimeters.
GLAS demonstrated spaceborne lidar for ice-sheet elevation change, sea-ice freeboard, vegetation canopy height, and cloud-top height retrieval, establishing the scientific and technical foundation that ICESat-2 ATLAS continued with its photon-counting architecture.
Supported methodologies
| Methodology | Evidence class | Mission context |
|---|---|---|
| Spaceborne LiDAR Altimetry and Canopy Structure | Demonstrated | ICESat [3] [2] [1] |
Compositional position
- Spaceborne LiDAR altimetryvia ICESat
GLAS on ICESat (2003-2009) demonstrated spaceborne lidar altimetry for ice sheets, land topography, and vegetation canopy height; full-waveform approach with 66 m footprint and 170 m along-track spacing.
- Atmospheric backscatter profiling lidarvia ICESat
GLAS 532 nm channel used for cloud/aerosol backscatter profiling alongside primary 1064 nm altimetry
None on record.
- [1]GLAS Instrument Overview, NASA GSFC ICESat Projectagency doc2026-06-02
- [2]ICESat (GLAS) Mission Overview, ESA eoPortalcommunity2026-06-02
- [3]ICESat/GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction, PMCpeer reviewed2026-06-02