Abstract
TanDEM-X digital elevation model (DEM) is a global DEM released by the German Aerospace Center (DLR) at outstanding resolution of 12 m. However, the procedure for its creation involves the combination of several DEMs from acquisitions spread between 2011 and 2014, which casts doubt on its value for precise glaciological change detection studies. In this work we present TanDEM-X DEM as a high-quality product ready for use in glaciological studies. We compare it to Aerial Laser Scanning (ALS)-based dataset from April 2013 (1 m), used as the ground-truth reference, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) V003 DEM and SRTM v3 DEM (both 30 m), serving as representations of past glacier states. We use a method of sub-pixel coregistration of DEMs by Nuth and Kääb (2011) to determine the geometric accuracy of the products. In addition, we propose a slope-aspect heatmap-based workflow to remove the errors resulting from radar shadowing over steep terrain. Elevation difference maps obtained by subtraction of DEMs are analyzed to obtain accuracy assessments and glacier mass balance reconstructions. The vertical accuracy (± standard deviation) of TanDEM-X DEM over non-glacierized area is very good at 0.02 ± 3.48 m. Nevertheless, steep areas introduce large errors and their filtering is required for reliable results. The 30 m version of TanDEM-X DEM performs worse than the finer product, but its accuracy, −0.08 ± 7.57 m, is better than that of SRTM and ASTER. The ASTER DEM contains errors, possibly resulting from imperfect DEM creation from stereopairs over uniform ice surface. Universidad Glacier has been losing mass at a rate of −0.44 ± 0.08 m of water equivalent per year between 2000 and 2013. This value is in general agreement with previously reported mass balance estimated with the glaciological method for 2012–2014.
Highlights
Monitoring of changing ice masses worldwide is presently an important topic due to their significance as climate change indicators [1] and relevance as a water source to millions of people in the world [2]
The 30 m Digital Elevation Models (DEM) generated from TanDEM12 keeps the good alignment, but all three DEMs initially supplied at 30 m resolution had to be shifted by an order of magnitude greater than the horizontal and vertical vectors to achieve low median ∆Z
TanDEM-X DEM (TanDEM) depicts a multi-year average of ice elevation, in our case it approximated well the glacier surface in April 2013, which was close to the midpoint of the intermediate DEM acquisition period, and with an accuracy sufficient for change detection studies
Summary
Monitoring of changing ice masses worldwide is presently an important topic due to their significance as climate change indicators [1] and relevance as a water source to millions of people in the world [2]. An established tool for glacier change detection is the analysis of Digital Elevation Models (DEM), which are computer representations of surface relief. Geometric changes of ice masses reflect the condition of a glacier with prolonged negative mass balance manifesting itself as frontal retreat and overall thinning, while advance of the front may be a symptom of mass gain or surging [5]. Multi-temporal analyses, using DEMs from different times, can be used to track these changes and provide valuable estimates of ice mass state. The elevation models themselves can be acquired with different methods. Radar imaging and photogrammetric analysis of optical stereoimagery are common ways of creating DEMs
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