WADFW Puget Sound Ambient Monitoring Program Winter 96Entry ID: seamap246
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)
(Click for Interactive Map)
Start Date: 2007-12-15
Quality Radar data on an irregular grid. Given the apparently rough topography, final results may be fairly sensitive tothe interpolation scheme.. which makes comparison of the 2 data sets (The 2 US campaigns) sometimes difficult.
Differential GPS accuracy not systematically attained due to strong ionospheric perturbations over the area (vicinity of the south magnetic pole). Some alternative processing is still under way. Some of these measurements will have to be reconsidered and/or repeated during the forthcoming season (2009/10).
Access Constraints Some of these data are still under processing and have not been entirely published yet. Also, due to technical problems, some of these data will have to be acquired again with updated devices (GPS with longer range radio communications allowing for Real Time Kinematic measurements over longer distances) .
Last, data relative to the deformation network will only be available after revisiting the remote GPS devices left on the glacier last season (a real time data transfer system will be installed on these GPSs next season). The network comprising 5 GPS stations so far will be completed (normally to a total of 12) during the 2009/10 field season.
Role: TECHNICAL CONTACT
Role: DIF AUTHOR
Phone: + 33 4 76 82 42 22
Fax: + 33 4 76 82 42 01
Email: manu at lgge.obs.ujf-grenoble.fr
LGGE Rue Molière BP 96 Domaine Universitaire
City: Saint Martin d'Hères, Cedex
Postal Code: 38402
Creation and Review Dates
DIF Creation Date: 2009-11-16
Last DIF Revision Date: 2012-01-27