Abstract
Abstract. Glacier mass balance has been estimated on individual glacier and regional scales using repeat digital elevation models (DEMs). DEMs often have gaps in coverage (“voids”), the properties of which depend on the nature of the sensor used and the surface being measured. The way that these voids are accounted for has a direct impact on the estimate of geodetic glacier mass balance, though a systematic comparison of different proposed methods has been heretofore lacking. In this study, we determine the impact and sensitivity of void interpolation methods on estimates of volume change. Using two spatially complete, high-resolution DEMs over southeast Alaska, USA, we artificially generate voids in one of the DEMs using correlation values derived from photogrammetric processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes. We then compare 11 different void interpolation methods on a glacier-by-glacier and regional basis. We find that a few methods introduce biases of up to 20 % in the regional results, while other methods give results very close (<1 % difference) to the true, non-voided volume change estimates. By comparing results from a few of the best-performing methods, an estimate of the uncertainty introduced by interpolating voids can be obtained. Finally, by increasing the number of voids, we show that with these best-performing methods, reliable estimates of glacier-wide volume change can be obtained, even with sparse DEM coverage.
Highlights
Glacier mass balance responds directly to climatic influences, and long-term records of glacier mass balance reflect changes in climate
Using digital elevation models (DEMs) derived from radar of different bands, especially those acquired in different seasons such as the Shuttle Radar Topography Mission (SRTM) (February) and interferometric synthetic-aperture radar (IfSAR), would require a consideration of the effects of differential radar penetration in snow and ice, as well as a temporal correction accounting for the difference in season, before converting elevation changes to a mass balance value (Haug et al, 2009; Kronenberg et al, 2016)
A question arises: when using noisy, “real-world” data such as ASTER DEMs, is it better to keep only the most reliable values for a given DEM, potentially producing large voids that must be interpolated, or is it better to have a more complete DEM? Given the results presented and the results shown in Sect. 4.5, we suggest that on-glacier areas with relatively low correlation can still have usable data
Summary
Glacier mass balance responds directly to climatic influences, and long-term records of glacier mass balance reflect changes in climate. Traditional estimates of glacier mass balance have involved in situ seasonal or annual measurements of accumulation and ablation at select locations and the extrapolation of these sparse measurements to the entire glacier (the glaciological method; see, e.g., Cogley, 2009) This can provide a temporally dense time series for an individual glacier, but for very large glaciers or at regional scales, it is neither practical nor even possible. Glacier mass balance has been calculated over longer time spans and with larger spatial coverage by differencing remotely sensed surface elevation measurements of glaciers (e.g., Bamber and Rivera, 2007) Integrating these differences over the glacier produces an estimate of volume change. With the current increase in the number of available, accurate digital elevation models (DEMs) derived from airborne and in particular spaceborne sensors, measurements
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