Shuttle imaging radar (SIR‐C/X‐SAR) reveals near‐surface properties of the South Patagonian Icefield

Abstract

Shuttle imaging radar C/X band synthetic aperture radar (SIR‐C/X‐SAR) views of the South Patagonian Icefield in southern Chile and Argentina demonstrate the ability of spaceborne multiparameter radar to detect climatically driven, intra‐annual changes in the snow and ice conditions on glaciers. The SIR‐C/X‐SAR system aboard space shuttle Endeavor acquired images during two 11‐day missions in April and October 1994. The radar signatures of differing snow and ice conditions are distinctive and homogeneous over large areas of the ice fields. The signatures are characterized mainly by (1) backscatter amplitude levels, (2) relative amplitudes of the C and L bands (wavelengths of 5.7 and 24 cm, respectively), and (3) polarization properties indicative of volumetric or surface scattering. The radar signatures are interpreted by correlating the radar characteristics with elevation of the snow and ice surfaces and with changes in the meteorological conditions. We are able to define four “radar glacier zones”: (zone A) a relatively dry snow zone with dominant C band returns; (zone B) a moderately wet snow zone with dominant L band returns; (zone C) a wet snow zone with weak returns in all bands; and (zone D) bare ice and/or heavily crevassed surfaces with strong returns in all bands. The spatial changes in the radar glacier zones between April and October are consistent with colder temperatures recorded in October, producing drier snow conditions at lower elevations than in April.