Abstract:
All these data over the Astrolabe Glacier have been collected in the framework of a better understanding of the specific dynamics of outlet glaciers in Antarctica.
The major set is represented by the bedrock subglacial topography, most of which has been obtained from airborne radar soundings covering the entire drainage basin (roughly 200 x 40 km) at the average resolution of 5 km. The
... radargramms actually provide the ice thickness, which substracted from either a DEM (icesat) or from accurate positioning of the aircraft, provide the bedrock topography.
2 campaigns have actually been caried out with 2 different radar systemes (Wise 5-20 MHz radar of the Jet Propulsion Laboratory, and that of the University of Texas operating at 60 Mhz frequency). A new survey is planned for the forthcoming (2009/10 season) in order to increase the resolution, especially close to the 'dynamicall-sensitive' zones (vicinity of the grounding line for instance).
One second set of data consists of the proper localization of the grounding line (line where the ice starts to float on its way to the sea). This grounding line is crucial in the sense that it gives rise to a marked change in the ice flow regime (mainly due to drastic changes in basal conditions). The method is based on detecting the presence of tidal motion or not from differential GPS measurements (cm-accuracy required). Despite some problems in solving cycles ambiguities in the differential GPS post-processing) these data allowed to locate areas respectively undergoing tidal motion or not, and therefore to precise the actual position of the grounding line.
Surface velocity as well as surface mass balance have also been measured from repeated accurate GPS positioning and emergence of stakes set up in the ice (12 stakes across glacier). Mass balance data, and more specifically their spatial variability have been also investigated from some GPR surface profiles (isochrons measurements) 
