GLACIER SNOW LINE MAPPING USING ERS-1 SAR IMAGERY

This article paper evaluates the effectiveness of ERS-1 synthetic aper ture radar (SAR) imagery for mapping movement of the transient snow li ne in a temperate glacier basin during an ablation season. The two pri mary objectives of this study are to normalize the topographically ind uced distortions (radiometric and geometric) inherent in SAR imagery o f rugged terrain and to delineate the snore line in the normalized ima gery. The radiometric distortions are normalized with a cosine correct ion, and the image texture is enhanced to take advantage of the spatia l distribution of tonal variations within each image. To minimize geom etric distortions and georeference the imagery, each cosine corrected/ texture enhanced SAR image is orthorectified to an error of approximat ely 60 m using a DEM and satellite orbital and ephemeris data. A super vised classification is performed on the orthorectified imagery to map the spatial distribution of snow and glacial ice within the basin. Th e visual boundary between the wet snow and glacier ice surfaces on the orthorectified images is within 75 m horizontally of the snow line ob tained from field data. The glacier boundary is also discernible to wi thin 75 m of the surveyed glacier outline. Several isolated bare ice a reas on the lower glacier give a low return, similar to wet snow, resu lting in so me confusion between glacier ice and wet snow. It is specu lated that the incident wave is lost within the crevasses and surface runoff runnel due to specular reflection within. the features. Despite the localised confusion between glacier ice and wet snore, the wet-sn ow line and can be mapped reasonably well and in a timely manner using ERS-1 SAR imagery. (C) Elsevier Science Inc., 1997.