A New Methodology for Detecting Ice Sheet Surface Elevation Changes From Laser Altimetry Data

The integrated program Surface Elevation Reconstruction And Change detection (SERAC) was specifically designed and developed for detecting surface elevation and elevation changes from the Ice Cloud and land Elevation Satellite (ICESat). ICESat carried geoscience laser altimeter system (GLAS) with the primary goal of measuring elevation changes of the polar ice sheets to sufficient accuracy to assess their impact on global sea level. GLAS had three lasers that operated sequentially, with two to three campaigns per year. The footprint size was about 70 m and the point-to-point spacing between neighboring laser points reached 170 m. SERAC copes with different scenarios. Originally developed for calculating surface elevation changes of crossover areas, it was extended to along-track areas and the inclusion of non-ICESat laser data, such as Airborne Topographic Mapper (ATM), an airborne laser scanning system developed by NASA Wallops Flight Facility. The adjustment system of SERAC simultaneously computes the shape of surface patches containing laser points of the same time epoch, estimates surface elevation changes, and approximates the time series of elevation changes by a polynomial after removing the seasonal cycle. Results shown in the second part of the paper demonstrate the potential of SERAC for calculating detailed ice sheet elevation and volume change histories. Greenland Ice Sheet volume changes, calculated from a combined ICESat/ATM data set, show good agreement with previously published results and provide improved sampling in the rapidly thinning coastal regions of southern Greenland. Moreover, the polynomial approximation of the time series of surface elevation changes is taken to advantage in the last example of Northwest Greenland, illuminating the intricate thinning/thickening patterns that often vary considerably over short spatial scales.