Glacier snow line mapping using ERS-1 SAR imagery

This article paper evaluates the effectiveness of ERS-1 synthetic aperture radar (SAR) imagery for mapping movement of the transient snow line in a temperate glacier basin during an ablation season. The two primary objectives of this study are to normalize the topographically induced distortions (radiometric and geometric) inherent in SAR imagery of rugged terrain and to delineate the snow line in the normalized imagery. The radiometric distortions are normalized with a cosine correction, and the image texture is enhanced to take advantage of the spatial distribution of tonal variations within each image. To minimize geometric distortions and georeference the imagery, each cosine corrected/texture enhanced SAR image is orthorectified to an error of approximately 60 m using a DEM and satellite orbital and ephemeris data. A supervised classification is performed on the orthorectified imagery to map the spatial distribution of snow and glacial ice within the basin. The visual boundary between the wet snow and glacier ice surfaces on the orthorectified images is within 75 m horizontally of the snow line obtained from field data. The glacier boundary is also discernible to within 75 m of the surveyed glacier outline. Several isolated bare ice areas on the lower glacier give a low return, similar to wet snow, resulting in some confusion between glacier ice and wet snow. It is speculated that the incident wave is lost within the crevasses and surface runoff runnels due to specular reflection within the features. Despite the localised confusion between glacier ice and wet snow, the wet-snow line and can be mapped reasonably well and in a timely manner using ERS-I SAR imagery.