Evaluating a satellite altimeter-derived digital elevation model of Antarctica using precision kinematic GPS profiling

The Radarsat Antarctic Mapping Project Digital Elevation Model (RAMP DEM) represents the best currently available compilation of Antarctic surface topography. Satellite altimeter data provide the foundation for most of the DEM, augmented where available with other mapping and survey information. We use precision global positioning system (GPS) data collected continuously along several profiles 150-320 km long in West and East Antarctica to independently assess the performance of the DEM in capturing the shape of the ice sheet surface. Overall, the DEM performs well at representing the gross morphology of the ice sheet north of 81.4degreesS. South of this latitude, where the DEM is unconstrained by high-resolution altimeter data, the DEM is less capable of capturing surface topographic detail, and elevation accuracy degrades. The comparison with GPS data indicates that the horizontal resolution of the DEM over well-constrained inland portions of the ice sheet is approximately 8 km. This resolution is larger than initial estimates, meaning that many of the important topographic details of the ice sheet surface are omitted. This omission has implications for applications using the DEM to understand patterns of local accumulation rate variability or for mapping ice flow features. There also appear to be some errors in the absolute elevations, especially in regions of relatively rugged inland topography where GPS elevations differ by up to 50 m from DEM elevations. (C) 2004 Published by Elsevier B.V