Evaluation and application of GPS and altimetry data over central Dronning Maud Land, Antarctica: annualelevation change, a digital elevation model, and surface flow velocity

Abstract

The polar ice sheets are unique paleoclimatic archives and play an important role in recent and future climate. The melting of the big freshwater reservoirs will not only increase the global sea level, but will also influence the ocean currents. Therefore, it will be of particular interest to improve the currently available numeric climate models to achieve more accurate statements about climatic change and its consequences.In this work, the evaluation and the different applications of GPS and altimetry data will be described in respect to enhance models. The antarctic area of investigation, Dronning Maud Land (DML), is of particular interest for German polar research, because both the overwintering station Neumayer and the summer station Kohnen are located within it. In the surroundings of these two stations, highlyaccurate kinematic GPS measurement were made, which will be the basis for the digital elevation model presented here. Because these data are spatially limited, they are supplemened with remotely sensed data. For this purpose, two airborne altimetry data sets and spaceborne laser altimetry data of the Ice, Cloud, and land Elevation Satellite (ICESat) are used. The basic tool for the combination of these data sets is the crossover-point analysis. In this process, the elevation differences at equal positions (crossover points) of two different data sets are determined. On the basis of this process, the vertical accuracy of the different data sets and the elevation differences to the ground-based kinematic GPSdata are determined. These differences are used to shift the remotely sensed data to the highly accurateground-based GPS data. With the aid of the geostatistical interpolation method "Ordinary Kriging" an improved digital elevation model with a resolution of 2.5 km x 2.5 km of the region within 20°W to 20°E and 69° S up to 86°S was generated. A comparison with commonly used digital elevation models, covering the whole continent, shows high elevation differences up to several 100m in the coastal region.Due to the use of ground-based highly accurate GPS data, the elevation model could be significantlyimproved above all for the coastal region of DML.An application of this elevation model is the re-locating of the ice divides in the area of investigation.Ice divides are the lines between two neighboring catchment areas. Their location is determined by the aspect of the topography. Additionally, static GPS measurements are processed to determine the surface flow velocity of the ice, which is further used for the calculation of the strain rate in the vicinity of Kohnen station. These results will improve the interpretation of climate proxies of the deep ice core (EDML), which was drilled between 2001 and 2006 at Kohnen station within the European Project for Ice Coring in Antarctica (EPICA).On the basis of ICESat ice sheet altimetry data from different measurement periods between 2003 and2007, the mean annual elevation change trend was calculated. From crossover-point analyses meanannual elevation change was determined for the coastal region and the plateau. The mean annual elevation change trend shows decreasing elevations in the coastal region (0.06 m) as well as at the plateau (-0.02 m).The data sets presented here give an explanation about the natural facts in the area of investigation and may be used as input parameter, to improve numeric modeling.