Lidar snow cover studies on glaciers in the Ötztal Alps (Austria): comparison with snow depths calculated from GPR measurements

Abstract

Abstract. The storage of water within the seasonal snow cover is a substantial source of runoff in high mountain catchments. Information about the spatial distribution of snow accumulation is necessary for calibration and validation of hydro-meteorological models. Generally, only a small number of precipitation measurements deliver precipitation input for modelling in mountain areas. The spatial interpolation and extrapolation of measurements of precipitation is still difficult. Multi-temporal application of lidar techniques from aircraft, so-called airborne laser scanning (ALS), provides surface elevations changes even in inaccessible terrain. These ALS surface elevation changes can be used to derive changes in snow depths of the mountain snow cover for seasonal or subseasonal time periods. However, since glacier surfaces are not static over time, ablation, densification of snow, densification of firn and ice flow contribute to surface elevation changes. ALS-derived surface elevation changes were compared to snow depths derived from 35.4 km of ground penetrating radar (GPR) profiles on four glaciers. With this combination of two different data acquisitions, it is possible to evaluate the effect of the summation of these processes on ALS-derived snow depth maps in the high alpine region of the Ötztal Alps (Austria). A Landsat 5 Thematic Mapper image was used to distinguish between snow covered area and bare ice areas of the glaciers at the end of the ablation season. In typical accumulation areas, ALS surface elevation changes differ from snow depths calculated from GPR measurements by −0.4 m on average with a mean standard deviation of 0.34 m. Differences between ALS surface elevation changes and GPR derived snow depths are small along the profiles conducted in areas of bare ice. In these areas, the mean absolute difference of ALS surface elevation changes and GPR snow depths is 0.004 m with a standard deviation of 0.27 m. This study presents a systematic approach to analyze deviations from ALS generated snow depth maps to ground truth measurements on four different glaciers. We could show that ALS can be an important and reliable data source for the spatial distribution of snow depths for most parts of the here investigated glaciers. However, within accumulation areas, just utilizing ALS data may lead to systematic underestimation of total snow depth distribution.

Mass balance observations and reconstruction for Batysh Sook Glacier, Tien Shan, from 2004 to 2016

“…A good estimate of the accumulation gradient seems to be very difficult because of insufficient data to better constrain the spatial distribution of snow. Several studies (e.g., Sold et al, 2016;Helfricht et al, 2012Helfricht et al, , 2014 show that an improvement in the mass balance determination is possible through the combination of conventional mass balance data and data obtained by new methods such as helicopter-borne Ground Penetrating Radar or Light Detection And Ranging (LiDAR) measurements. Such data also enables an improvement in the interpolation of the accumulation distribution.…”

“…We assume that the spatial snow distribution does not change significantly from one year to another (e.g. Helfricht et al, 2014). Observations in May 2014 are thus used for all years without extensive winter surveys.…”

Projected cryospheric and hydrological impacts of 21st century climate change in the Ötztal Alps (Austria) simulated using a physically based approach

“…Due to the generally small vertical ice flow contribution for the majority of the glaciers in the study region (Helfricht et al, 2014) this is a reasonable approach for shorter simulation periods. However, when performing simulations on multidecadal scales the effect of ice flow dynamics must be considered in glaciohydrological models.…”

Projected cryospheric and hydrological impacts of 21st century climate change in the Ötztal Alps (Austria) simulated using a physically based approach

“…Due to the generally small vertical ice flow contribution for the majority of the glaciers in the study region (Helfricht et al, 2014) this is a reasonable approach for shorter simulation periods, however when performing simulations on multidecadal scales, the effect of ice flow dynamics must be considered in glaciohydrological models. Otherwise, systematic errors in the simulated ice distributions (and 20 subsequently in glacier runoff) are introduced as the glaciers thicken in their accumulation areas and retreat too quickly in the tongue parts.…”