ANALYSIS OF ERS-1 SYNTHETIC-APERTURE RADAR DATA FROM NORDAUSTLANDET, SVALBARD

Study of the Earth's terrestrial ice masses (glaciers, ice caps and ic e sheets), especially the seasonal variation of different surface cond itions such as dry snow, wet snow and bare ice, is of particular impor tance in relation to possible climatic change. Synoptic monitoring tec hniques using visible and near-infrared satellite imagery are severely limited by the prevalence of cloud cover in the polar regions, and wi nter observations are impossible as a result of the absence of solar r adiation. Consequently, considerable attention is now being focused on the use of imaging radar in the study of large ice masses. In this pa per, we present and interpret a time-series of C-band synthetic apertu re radar images acquired using the ERS-1 satellite from the Austfonna ice cap in eastern Svalbard. Winter imagery shows little variability, most of the ice cap having a uniform and high (approximately -3 dB) ba ckscatter attributed to ice lenses or to a large effective grain size. Summer imagery shows considerable topographically-related detail, and backscatter values typically 5 to 10 dB less than in winter, which ca n be explained on the basis of surface scattering from wet snow. Howev er, the marginal areas of the ice cap show a clearly defined zone of h igh (-5 dB) backscatter in mid- to late-August. It is proposed that th is corresponds to the bare ice zone, the high backscatter values being due to scattering from crevasses and meltwater channels, and that the inner boundary of the zone of enhanced backscatter indicates the posi tion of the transient snow line.