Application of synthetic aperture techniques to radar echosoundings of the Pine Island Glacier, Antarctica
In this PhD I have developed a Synthetic Aperture Radar (SAR) processing algorithm and applied it to airborne radar sounding data collected during the 2004/05 austral summer season over Pine Island Glacier (PIG) West Antarctica. The SAR processing algorithm is one-dimensional and non-symmetrical and is applied in MATLAB® . Phase corrections are calculated and applied on a trace-by-trace basis, and are based on pre-calculated lookup tables. The section of the survey that I concentrated on was that of the main PIG glacier trunk, which was flown at a terrain clearance of between 110 m and 260 m. The flights over the trunk were sub-divided into 4 along-flow flight sections (L 1 -L4) and 13 cross-flow flight sections (X1-X13). After SAR processing the levels of surface clutter are reduced allowing for the imaging of englacial layering and the bed-interface, even in areas of heavy surface crevassing. In addition the SAR processor improves the along-track resolution from hundreds of metres to metres allowing for the imaging of small-scale subglacial and englacial features. Using SAR processed data in proximity to the grounding line I constrained the grounded ice interface material by inverting the radar equation. 0n the PIG ice shelf I observed bottom crevassing extending from the base of the ice shelf into the ice mass. By performing a stress analysis using published velocity fields I estimated the maximum height a bottom crevasse can reach and the strain rates required for their formation. I also observed undulations on the ice shelf base and using spectral analysis techniques I show these undulations to have a dominant periodicity of around a year. I therefore link the genesis of these undulations to localised melting at the grounding line forced by an annual influx of circumpolar deepwater into the ice shelf cavity. These undulations decrease in amplitude away from their grounding line formation site which I attribute to a combination of melting by modified circumpolar deep water escaping the cavity and viscous relaxation of ice operating on a decadal timescale.