NASA launched the Ice, Cloud, and land Elevation Satellite (ICESat) to begin precise, global elevation measurements with a space-based laser altimeter. The mission aimed to track changes in ice sheets and sea ice over time, supporting better estimates of ice loss and sea-level rise. Its key instrument was the Geoscience Laser Altimeter System (GLAS).
ICESat’s GLAS instrument was activated to start collecting elevation data by timing how long laser light took to travel to Earth and back. This marked the start of routine laser altimetry observations from space for polar ice monitoring. Early measurements helped prove the mission concept and calibrate data processing methods.
GLAS Laser 1 unexpectedly stopped working after only weeks of operation, reducing the mission’s ability to collect continuous measurements. The failure forced NASA to adjust operations and rely on backup lasers to extend the overall measurement record. This event shaped how the mission was run for the rest of its lifetime.
After engineering review, ICESat resumed elevation measurements using GLAS Laser 2. Returning to science operations restored the ability to monitor polar ice sheets, sea ice, and land elevation changes. The mission’s stop-and-start approach helped conserve the remaining lasers and extend the time series.
ICESat entered a planned operational period designed to collect consistent elevation data over a repeat ground track. This type of scheduled observing supports “change detection,” where scientists compare repeat measurements to see how ice height changes from season to season and year to year. These campaign-style operations became a practical way to keep the mission productive despite limited laser lifetime.
When ICESat’s laser system began reaching end-of-life, NASA started Operation IceBridge using aircraft-mounted sensors to maintain annual measurements of polar ice. Airborne surveys provided detailed elevation and thickness observations while a successor satellite was being developed. This helped keep the record of ice change more continuous than satellites alone could.
ICESat ended science observations when its final functioning laser stopped working. This effectively closed the satellite portion of the first ICESat measurement record, increasing the importance of airborne campaigns and planning for a next-generation satellite. The event highlighted a key engineering risk for laser altimetry missions: limited laser lifetime in space.
NASA formally decommissioned ICESat after completing end-of-mission steps, and the spacecraft reentered Earth’s atmosphere later that month. The mission left a valuable baseline record of ice-sheet elevation and sea-ice surface height. That baseline became a key reference for later comparisons with airborne surveys and ICESat-2 data.
NASA launched ICESat-2 to restore space-based laser measurements of ice, land, and vegetation. Its instrument, the Advanced Topographic Laser Altimeter System (ATLAS), was designed to collect many more measurements than ICESat by firing rapidly and detecting individual photons. This enabled denser coverage and improved change detection for polar ice.
ICESat-2 fired its laser for the first time and soon returned its first elevation measurements, including early tracks across Antarctica. These initial results confirmed that the satellite, pointing, and photon detection were working together as designed. Early “first light” is an important milestone before routine science data collection begins.
ICESat-2’s ATLAS splits its laser into six beams arranged as three pairs, improving ground coverage and helping estimate surface slope. Each pair includes a strong and a weak beam, allowing measurements over surfaces with different reflectivity (how much light they return). This multi-beam approach is a major technical step beyond ICESat’s single-beam design.
ICESat-2 data products became broadly accessible through the National Snow & Ice Data Center (NSIDC), supporting both research and public use. The product set includes photon-level data (ATL03) and higher-level ice and sea-ice height products (such as ATL06 and ATL07). Easier access and standard products helped expand the number of users and applications.
Operation IceBridge wound down after ICESat-2 was in orbit and producing data, completing its role as a bridge between the two satellite missions. The combined record—ICESat, IceBridge aircraft surveys, and ICESat-2—supports longer-term comparisons of ice elevation and thickness change. This transition improved continuity for monitoring polar ice in a changing climate.
By the mid-2020s, ICESat-2 remained a core mission for repeated, high-density elevation measurements over ice sheets and sea ice. Its repeat-orbit approach supports tracking seasonal and multi-year changes by comparing measurements along similar ground tracks. The mission’s continuing data stream underpins modern satellite-based polar ice altimetry and related research tools.
ICESat and ICESat-2 polar ice altimetry missions (2003–present)