Determination of Ice-thickness Using GPR at Brandner Glacier in Vorarlberg, Austria - Case Study

The discharge of the Brandner glacier (Austria) is being caught for electricity generation. As the glacier has been rapidly shrinking in the last few years the existing and now dry gallery should be replaced. Therefore a geophysical survey with ground penetrating radar and reflection seismic was carried out in 2009 to determine the thickness of the glacier and the lowest level of the bedrock. A 40MHz antenna was used for GPR and 4m geophone spacing for the seismic. The depth of the bedrock from GPR and seismic data correlates very well. Reflections in the GPR data down to 100m depth are identified. The seismic velocity for ice is about 3700m/s, the bedrock velocity 4600m/s. The GPR data show that moraine material and stones lie within the ice body. A 2D map was made with kriging-technique based on the line data identifying two troughs. The estimated ice-volume is 14 million m³. The thickest part of the glacier is in the upper trough and goes down to 80 m. In the lower trough the main thickness is around 20 m. The lowest elevation of the bedrock surface is situated at the eastern end of the glacier.