Abstract
Abstract. Using sparsely glaciated southern Norway as a case study, we assess the potential and limitations of ICESat laser altimetry for analysing regional glacier elevation change in rough mountain terrain. Differences between ICESat GLAS elevations and reference elevation data are plotted over time to derive a glacier surface elevation trend for the ICESat acquisition period 2003–2008. We find spatially varying biases between ICESat and three tested digital elevation models (DEMs): the Norwegian national DEM, SRTM DEM, and a high-resolution lidar DEM. For regional glacier elevation change, the spatial inconsistency of reference DEMs – a result of spatio-temporal merging – has the potential to significantly affect or dilute trends. Elevation uncertainties of all three tested DEMs exceed ICESat elevation uncertainty by an order of magnitude, and are thus limiting the accuracy of the method, rather than ICESat uncertainty. ICESat matches glacier size distribution of the study area well and measures small ice patches not commonly monitored in situ. The sample is large enough for spatial and thematic subsetting. Vertical offsets to ICESat elevations vary for different glaciers in southern Norway due to spatially inconsistent reference DEM age. We introduce a per-glacier correction that removes these spatially varying offsets, and considerably increases trend significance. Only after application of this correction do individual campaigns fit observed in situ glacier mass balance. Our correction also has the potential to improve glacier trend significance for other causes of spatially varying vertical offsets, for instance due to radar penetration into ice and snow for the SRTM DEM or as a consequence of mosaicking and merging that is common for national or global DEMs. After correction of reference elevation bias, we find that ICESat provides a robust and realistic estimate of a moderately negative glacier mass balance of around −0.36 ± 0.07 m ice per year. This regional estimate agrees well with the heterogeneous but overall negative in situ glacier mass balance observed in the area.
Highlights
The role of mountain glaciers and snow as sources for drinking water, irrigation, and hydropower is getting increasing attention, not least due to the significant population increase and economic development in a number of mountain regions and surrounding lowlands (Jansson et al, 2003; Viviroli et al, 2007)
Vertical offsets to ICESat elevations vary for different glaciers in southern Norway due to spatially inconsistent reference digital elevation models (DEMs) age
After application of cH, ctile and cglac correction terms, 94 and 95 % of the ice, and land autumn samples respectively, but only 80 % of ice border autumn samples show less than 10 m absolute elevation difference between ICESat and the Kartverket 10 m DEM elevations (Fig. 2, right)
Summary
The role of mountain glaciers and snow as sources for drinking water, irrigation, and hydropower is getting increasing attention, not least due to the significant population increase and economic development in a number of mountain regions and surrounding lowlands (Jansson et al, 2003; Viviroli et al, 2007). Regional estimates of ice loss recently gained importance, not least for assessing the current and future contribution of water stored in land ice masses to sea level rise (Gardner et al, 2013; Jacob et al, 2012; Marzeion et al, 2012; Radicet al., 2014; Radicand Hock, 2011) and for quantifying current run-off contribution from glacier imbalance (Kääb et al, 2015) or changes in the upstream cryosphere Elevation data from the Geoscience Laser Altimeter System (GLAS) on board the NASA Ice, Clouds, and Land Elevation Satellite (ICESat) provides what is likely the most consistent global elevation measurement currently available (Nuth and Kääb, 2011). The use of this data to derive thick-
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