ICE SHEET TOPOGRAPHY FROM ERS RADAR ALTIMETRY

摘要

Before the launch of ERS-1, only sparse, terrestriallyderived elevation data, with generally poor accuracy, were available for much of Antarctica and the northern half of Greenland. Elevation errors in excess of 200 m existed for these regions, severely limiting the utility of ice sheet topography for glaciological applications (Figure 1). ERS-1 extended the limit of useful data to 81.5° providing almost complete coverage of Greenland and ～80% of Antarctica (Figure 1). Initially digital elevation models (DEMs) were produced at relatively course, 20 km, resolution [1]. However, the geodetic phase of ERS- 1, between April 1994 and March 1995, provided dense across-track spacing over the ice sheets. As a result, new (DEMs) of both ice sheets were produced with unprecedented accuracy and spatial resolution [2-4]. Most recently, ERS-1 geodetic phase data have been combined with ICESat laser altimeter measurements to provide both unparalleled vertical accuracy with high spatial resolution (Figure 2). These various DEMs have been used in a wide range of glaciological and geodetic applications and have provided insights into many important processes and glaciological features. Here, I consider some of the main applications they have been used for. One of the most important for understanding ice dynamics has been determining the pattern of flow over the ice sheets by modelling ice particle paths down-slope and integrating snow accumulation along flow to determine a parameter known as the balance flux [5]. Dividing fluxes by the ice thickness gives an estimate of the depth averaged velocity needed to keep the ice sheet in steady state, known as balance velocities.