Remote Sensing Studies of Svalbard Glaciers
The study uses remotely sensed data from (1) air borne altimetry and radio echo sounding, (2) Landsat satellite imagery, and (3) aerial photography, to investigate aspects of the morphology and dynamics of the ice caps of Nordaustlandet, Svalbard. Data collection, methods of reduction and errors are discussed. Three principal topics are examined. First, as a preliminary to comprehensive radio echo sounding operations over Nordaustlandet, the ability of 60 MHz radar equipment to sound ice at or near its melting point was tested over a number of glaciers in Spitsbergen. Ice thickness data were obtained from 38 glaciers. The results are compared with previous geophysical investigations of ice thickness on Spitsbergen, revealing problems concerning existing Soviet radio echo sounding data obtained at higher frequencies. An internal layer echo was interpreted as the bed by Soviet workers. Second, the ice caps of Nordaustlandet, about which little glaciological information was previously available, are described and mapped. The coastline and ice margins are located using corrected satellite imagery. The surface of the ice caps is described in detail, and ice divides and drainage basins are mapped. Synoptic data on relative surface elevations from digitally enhanced Landsat imagery is calibrated using accurate airborne altimetric information available only along flight lines. The morphology of the underlying bedrock, and the thickness of the ice cover above it, is recorded. Ice thickness on Austfonna-Sorfonna reaches 583 m and 28% of the bed is below present sea level. Third, several aspects of the regional glaciology of the Nordaustlandet ice caps are examined. Digital analysis of ice cap surface radiance characteristics provides data on snow line position and mass balance. The spatial and temporal pattern of detector saturation in each band of the Landsat MSS over snow in the polar regions is predicted from analysis of the influence of sun elevation. Regions of ice cap basal melting are identified from enhanced Landsat imagery by the presence of suspended sediment plumes off shore. No plumes are observed off Brasvellbreen, which is probably stagnant and frozen to its bed after a recent surge. The recent fluctuations of 20 outlet glaciers are recorded from enhanced imagery, a method accurate to +150 m. Three groups of basins, with distinctive dynamic behaviour, are defined from an analysis of variations in long profiles and the pattern of driving stresses within the ice caps. First, basins which have surged and are now in the quiescent period between such activity are relatively stagnant. They typically have low surface profiles and driving stresses. Second, several outlet glaciers of southern Vestfonna have marked shear zones separating them from the surrounding ice and also have low surface slopes . They are interpreted as flowing fast over a lubricated bed on a continuous basis and may provide a small scale analogue for ice streams in the large ice sheets. Third, other basins in Nordaustlandet have high marginal driving stresses and relatively steep surface profiles and are interpreted as being frozen to their beds near the margins at least. Although three dynamic classes of basin have been identified, field data from them do not support the analysis and modelling of Budd (1975).