Abstract The overall aim of this Thesis is to emphasise how Ground Penetrating Radar (GPR) can be used in different glaciological studies: in mapping the inner structure, determining accumulation rates, estimating water contents, mapping drainage channels and superimposed ice. The Thesis also aims to improve current knowledge on Svalbard polythermal glaciers: their hydrothermal properties, drainage and behaviour in the changing climate. Six glaciers were studied: four tidewater glaciers, one ice-field and one valley glacier. The hydrothermal structure of Hansbreen was mapped with GPR at high lateral and vertical resolution. The hydrothermal structure of the glacier is highly variable and complex. In general the temperate ice contains 1-2% water, but water contents of about 4% are associated with englacial water channels or water-filled near surface crevasses or moulins. Hydrothermal properties determined from detailed GPR surveys of Hansbreen, Werenskioldbreen, Nordenskjöldbreen and Kongsvegen show similar structures such as foliations and superimposed ice in the firn-ice transition area, though with different emphasis on each glacier. The overall extent of superimposed ice was difficult to measure accurately because of the limited resolution and the sporadic nature of the reflections. However there is encouraging similarity between GPR and satellite imagery of superimposed ice extent. Hydraulic geometry models of the subglacial hydrology of Hansbreen and Werenskioldbreen suggest that the water pressure is generally close to ice-overburden pressure but varies greatly depending on local conditions. GPR data and data from three ice-cores were used to determine spatial and temporal variation of snow accumulation on a longitudinal profile of Nordenskjöldbreen. Spatial variations of 40-60% in snow accumulation over short distances along the profile were observed. The results indicate a 12% increase in accumulation rate during the late 1980s and 1990s. Hornbreen and Hambergbreen and several surrounding glaciers in southern Svalbard were mapped with GPR together with a DGPS (Differential Global Positioning System) in 2000. The data were compared to glacier surface height and glacier front length data from 1936 and 1901. The results show that the low-lying glaciated valley filled with Hornbreen and Hambergbreen may become a partially inundated ice-free isthmus within the next 100-150 years.

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