Validation of digital elevation models (DEMs) and comparison of geomorphic metrics on the southern Central Andean Plateau

Other literature type English OPEN
Purinton, Benjamin ; Bookhagen, Bodo (2017)

We validate and compare elevation accuracy and geomorphic metrics of the current generation of satellite-derived digital elevation models (DEMs) on the southern Central Andean Plateau. The plateau has an average elevation of 3.7&thinsp;km, and is characterized by diverse topography and relief, lack of vegetation, and clear skies that create ideal conditions for remote sensing. At 30&thinsp;m resolution, the SRTM-C, ASTER GDEM2, stacked ASTER L1A stereopair DEM, ALOS World 3D, and TanDEM-X have been analyzed. The higher resolution datasets include 12&thinsp;m TanDEM-X, 10&thinsp;m single-CoSSC TerraSAR-X / TanDEM-X DEMs, and 5&thinsp;m ALOS World 3D. We assessed vertical accuracy by comparing standard deviations (SD) of the DEM elevation versus 307,509 differential GPS (dGPS) measurements across 4,000&thinsp;m of elevation. Vertical SD for the 30&thinsp;m DEMs were 9.48&thinsp;m (ASTER GDEM2), 6.93&thinsp;m (ASTER Stack), 3.33&thinsp;m (SRTM-C), 2.81&thinsp;m (ALOS World 3D), and 2.42&thinsp;m (TanDEM-X). Values were generally lower for higher resolution DEMs at 2.02&ndash;3.83&thinsp;m (10&thinsp;m single-CoSSC TerraSAR-X / TanDEM-X), 1.97&thinsp;m (12&thinsp;m TanDEM-X), and 1.64&thinsp;m (5&thinsp;m ALOS World3D). Analysis of vertical uncertainty with respect to terrain elevation, slope, and aspect revealed the high performance across these attributes of the 30&thinsp;m SRTM-C, 30&thinsp;m and 12&thinsp;m TanDEM-X, and 30&thinsp;m and 5&thinsp;m ALOS World 3D DEMs. Single-CoSSC TerraSAR-X / TanDEM-X 10&thinsp;m DEMs and the 30&thinsp;m ASTER GDEM2 displayed slight aspect biases, which were removed in their stacked counterparts (TanDEM-X and ASTER Stack). Based on high vertical accuracy and visual inspection of minimal hillslope artifacts alongside optical satellite data, we selected the 30&thinsp;m SRTM-C, 12&ndash;30&thinsp;m TanDEM-X, 10&thinsp;m single-CoSSC TerraSAR-X / TanDEM-X, and 5&thinsp;m ALOS World 3D for geomorphic metric comparison in a 66&thinsp;km<sup>2</sup> catchment with a distinct river knickpoint. For trunk channel profiles analyzed with chi plots, consistent <i>m/n</i> values of 0.49&ndash;0.57 were found regardless of DEM resolution or SD. Hillslopes were compared through slope and curvature calculations to assess basin-wide differences in their distributions and in the hillslope-to-valley transition related to the knickpoint feature. We find 0.1&ndash;0.2&thinsp;m/m higher slopes downstream of the knickpoint, related to the over-steepened baselevel. While slope and hillslope length measurements vary little between datasets, curvature displays higher magnitude measurements with fining resolution. This is especially true for the optical 5&thinsp;m ALOS World 3D DEM, which demonstrated high-frequency noise in 2&ndash;8 pixel steps through a Fourier frequency analysis. The improvements in accurate space-radar DEMs (e.g., TanDEM-X) for geomorphometry are promising, but airborne or terrestrial data is still necessary for meter-scale analysis.
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