Using ICESat/GLAS to Detect Changes in Arctic Sea Ice

Abstract

Arctic sea ice is currently in a state of change. Observations suggest that, over the past few decades, a substantial decline in Arctic sea ice extent and thickness has occurred. Monitoring sea ice thickness is a more difficult task than measuring sea ice extent; our understanding of the variability of ice thickness is limited due to a lack of large-scale spatial and temporal observations. Spaceborne altimeters are however beginning to provide improved coverage of the Earth's poles. Their use has resulted in a major enhancement in our ability to measure sea ice thickness from Earth orbit over the past decade. NASA's Ice, Cloud and land Elevation Satellite (ICESat) utilises laser altimetry to provide high-resolution topographic data over the Arctic and Antarctic. Together with knowledge of the position of the sea surface, altimetric data can be used to estimate the portion of sea ice above water, known as the sea ice freeboard. The Geoscience Laser Altimeter System (GLAS) onboard ICESat extends satellite altimetric coverage of sea ice to 86 degrees latitude for the first time. Using GLAS altimetry data products, we outline a new method to accurately determine sea surface elevation in the sea-ice covered regions of the Arctic Ocean. These data enable us to construct maps of sea ice freeboard during a period in March 2003 corresponding to the initial phase of spacecraft operations. Comparisons are made between GLAS sea ice freeboard measurements and coincident data from the radar altimeter onboard ESA's ERS-2 satellite. Initial analysis shows good agreement between these datasets, whose mean difference is ∼12cm ± 20cm. Such comparisons illustrate both the potential to estimate other key climatic parameters, such as snow loading on sea ice, by combining laser and radar altimetric measurements over sea ice, as well as the importance of continuous observation of the Earth's polar regions by coincident laser and radar altimeters.