SYNTHETIC APERTURE RADAR (SAR) CHANGE DETECTION ON SOIL AND ICE SURFACES, MCMURDO DRY VALLEYS, ANTARCTICA

The McMurdo Dry Valleys are the largest ice-free region in Antarctica. Polar alpine glaciers, perennially ice-covered lakes, ephemeral streams, and exposed soil dominate the landscape. Summer climate is delicately balanced around the melting point. Small variations in climate conditions have a dramatic effect on the amount of melt water produced, which in turn has a significant impact on the ecosystem.

Synthetic Aperture Radar (SAR) is an ideal instrument for studying this region because it is an active system and unaffected by the 6 months of darkness in winter or by clouds in summer. We acquired weekly RADARSAT images from a typical summer climate -- August to December of 1999 and developed color composites to spatially and temporally map changes in the backscatter signal for defined areas of interest. Mean backscatter values from these areas were correlated with locally measured meteorological variables and the surficial processes causing the changes were inferred. Surface roughness measurements were also taken to aid in interpreting the backscatter signal. We compared our results with RADARSAT images from the abnormally warm 2001-2002 summer.

Results indicate that the changes in backscatter from the perennially frozen lakes, the sandy soils, and from the glacier surfaces are all due to different processes. For the lakes, the backscatter significantly drops with the initial onset of melt. Changes in soil backscatter are due to moisture changes in sandy soils. Where rough boulders are present, which is most of the valley floor, the backscatter from the rough surfaces mask any signal from moisture differences. Although the glaciers melt somewhat during the summer, we believe the changes in backscatter are due to increased surface roughness due to sun cup formation. Comparison of the normally cool 1999-2000 summer with the 2001-2002 abnormally warm summer illustrated the dramatic rise in elevation of the melt limit on the glaciers and the expansive areas subject to melt.

By understanding how these meteorological variables affect the spatial distribution of melt, the impact of past and future climate changes on this landscape can be estimated. The detection and spatial distribution of melting continues to help in the study of the ecosystem. This study provides a terrestrial analog for the search for water and life on Mars.