Precision and accuracy of satellite radar and laser altimeter data over the continental ice sheets

The unprecedented accuracy of elevations retrieved from the Ice Cloud and Land Elevation Satellite (ICESat) laser altimeter is investigated and used to characterize the range errors in the Environmental Satellite (Envisat) and European Remote Sensing 2 Satellite (ERS-2) radar altimeters over the continental ice sheets. Cross-mission crossover analysis between time-coincident ERS-2-, Envisat-, and ICESat-retrieved elevations and comparisons to an ICESat-derived digital elevation map are used to quantify the radar elevation error budget as a function of surface slope and to investigate the effectiveness of a method to account for the radar altimeter slope-induced error. The precision and accuracy of the elevations retrieved from the ICESat Geoscience Laser Altimeter System and the European Space Agency radar altimeters on ERS-2 and Envisat are calculated over the Greenland and Antarctic ice sheets using a crossover analysis. As a result of this work, the laser precision is found to vary as a function of surface slope from 14 to 59 cm, and the radar precision varies from 59 cm to 3.7 m for ERS-2 and from 28 cm to 2.06 m for Envisat. Envisat elevation retrievals when compared with ICESat results over regions with less than 0.1 degrees surface slopes show a mean difference of 9 +/- 5 cm for Greenland and -40 +/- 98 cm over Antarctica. ERS-2 elevation retrievals over these same low surface slope regions differ from ICESat results by -56 +/- 72 cm over Greenland and 1.12 +/- 1.16 m over Antarctica. At higher surface slopes of 0.7 degrees to 0.8 degrees, the Envisat/ICESat differences increase to -2.27 +/- 23 m over Greenland and to 0.05 +/- 26 m over Antarctica.