SUBGLACIAL STRUCTURE OF ANTARCTICA

In 1997, we completed the first, high-resolution radar mapping of Antarctica using the Canadian RADARSAT-1. Those data have now been assembled into a radiometrically and geometrically accurate mosaic that depicts the surface of the continent at scales as fine as 25 m. Important glaciological boundaries are evident in the mosaic including: the position of the seaward ice sheet margin, the location of ice divides; and regions of fast glacier flow including ice streams. Perhaps most remarkably, there is considerable qualitative evidence for the transfer of information about subglacial structures and processes through several kilometers of ice, to the surface of the ice sheet and its ultimate capture in the mosaic. For example, Lake Vostok, now buried beneath over 4 km of ice is clearly delineated in the mosaic. There are also indications that 100's of km long lineaments in the subglacial crust are also manifest as tonal patterns in the radar image. In this paper, we present a quantitative analysis of why information about the subglacial structure of Antarctica should appear in this image of the ice sheet surface. We present experimentally derived transfer functions that link subglacial topography to ice sheet surface topography and to SAR backscatter properties. The transfer functions, constructed using newly available data from the Greenland Ice Sheet, agree very well with theoretical predictions developed by previous researchers studying longitudinal flow in glaciers. We conclude with a discussion of features in the mosaic, which we believe have their origins in the subglacial crust.