Refined analysis of radar altimetry data applied to the region of the subglacial Lake Vostok/Antarctica

Satellite altimetry is a powerful tool to map the ice sheet elevation as well as a number of other parameters linked to geometrical and geophysical properties of ice sheets. Irrespective of new instrumental developments like the laser altimeter on ICESat (Ice, Cloud and land Elevation Satellite) the well-established radar altimeter (RA) missions ERS-1,2 (European Remote Sensing satellites) and ENVISAT (ENVIronment SATellite) are unique in their temporal coverage over more than a decade and in their temporal and spatial sampling. Therefore, the full exploitation of these RA data by improved methods is imperative. Here we develop improved techniques to correct for topographically induced errors by a refined consideration of the relevant topographic conditions. Furthermore we improve the gridding procedure by adapting it to local conditions and thus preserving smaller-scale features. We apply our methods to the region of the subglacial Lake Vostok/Antarctica and derive digital elevation models (DEMs) for this region with the aim of improving/resolving smaller scales. The effect of our improvements is demonstrated in detail by comparing our DEMs and previously published DEMs to the ICESat laser measurements which are taken as a reference here. Due to our improvements, the standard deviation of the difference between RA-based DEMs of the Lake Vostok region and ICESat data decreases from more than 1.1 m to 0.5 m. This remaining error is chiefly the error inherent in the RA observations. Our RA-ICESat comparisons, supported by Fourier analyses, also reveal the presence and importance of small-scale features that can be detected by laser but not by the RA measurements.