Laser Targeting Performance in the ICESat Mission

On June 22, 2010, NASA initiated the decommissioning of the Ice, Cloud and land Elevation Satellite (ICESat), marking the end of first laser altimetry mission dedicated to surveying the Earth. Despite numerous technical challenges encountered after launch - including shortened laser lifetimes, photo-darkening of the frequency doubler, limited use of the Stellar Reference System, and higher-than-anticipated laser-targeting errors - ICESat has produced a rich topographic record, and provided our first large-scale assessments of elevation change and mass balance of the polar ice sheets. Pre-launch performance estimates suggested that the ICESat observatory would be able to meet its requirement to target the reference ground tracks in the polar regions with an accuracy of ±35 meters. Here, we summarize, for the first time, the actual targeting performance achieved during the ICESat mission, which varied between operational campaigns. The RMS cross-track offset ranged from a minimum of 56 meters (during Winter 2007) to a maximum of 111 meters (during Fall 2008). We examine the underlying causes of these offsets, and their impact on the recovery of elevation change rates from ICESat data. Furthermore, we discuss the potential implications for the planned ICESat-2 mission.