F Paul

Strong spatial variability of snow accumulation observed with helicopter-borne GPR on two adjacent Alpine glaciers

The spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers. Traditional point measurements (snow pits and-probes) are labour intensive and interpolation in-between the points causes uncertainties.Airborne radar measurements have already been used for snow mapping innon-glacierized terrain, but not on Alpine glaciers. To enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations,we have conducted high-resolution helicopter-borne radar measurements on the temperatedglacier Findel and neighbouring Adler Glacier in southwestern Switzerland.The radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 MHz with a bandwidth of 400 MHz. The results were validated withextensive ground-based profiling of the snow cover. The radar data allows a clearrecognition of the snow cover (6% of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering) and agreed well with the groundbased measurements (R2 = 0.85). Reduced accumulation has been observed in allcrevassed zones. Statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a GIS environment, revealing differingaccumulation patterns: On the lower part of Findel Glacier accumulation showsa clear altitudinal trend, while the upper part is dominated by strongly varying snowdepth without an altitudinal trend. The accumulation characteristic on Adler Glacieris similar to the upper part of Findel Glacier, but despite of their close vicinity, accumulationis reduced by 40% compared to the same elevation on Findel Glacier. Thisstudy reveals a large potential of helicopter-borne snow profiling for measurements ofaccumulation distribution on alpine glaciers.