Benchmarking Elevation Plus Land Surface Parameters Finds FathomDEM and Copernicus DEM Win as Best Global DEMs

Highlights What are the main findings? Digital elevation models with one-arc-second are still the best free scale available globally. When compared to a lidar-derived reference digital terrain model, FathomDEM consistently performs best but has a restrictive license. The Copernicus DEM is the best free option, with the ALOS AW3D30 only in rugged and steep mountainous areas. We also evaluated FABDEM and GEDTM v1.2. The capability of global DEM to represent land surface parameters, such as slope, curvatures, and roughness changes in relation to land cover and morphology. Parameters computed with the second order partial derivatives show a range of correspondence, and those computed with third order partial derivatives show extremely low correspondence. What is the implication of the main finding? The procedures for creating a bare earth digital elevation from a digital surface model are a black box that can hallucinate, and the results must be checked carefully. The creators should check derived land surface parameters as well as the raw elevation values, as a good digital surface model can be better than a poor digital terrain model. Geomorphometry workers must carefully assess the land surface parameters they use. First derivative parameters perform best; second derivative parameters, like curvature, vary in their signal-to-noise ratio; the third derivative parameters, like change of curvature, might be all noise.Highlights What are the main findings? Digital elevation models with one-arc-second are still the best free scale available globally. When compared to a lidar-derived reference digital terrain model, FathomDEM consistently performs best but has a restrictive license. The Copernicus DEM is the best free option, with the ALOS AW3D30 only in rugged and steep mountainous areas. We also evaluated FABDEM and GEDTM v1.2. The capability of global DEM to represent land surface parameters, such as slope, curvatures, and roughness changes in relation to land cover and morphology. Parameters computed with the second order partial derivatives show a range of correspondence, and those computed with third order partial derivatives show extremely low correspondence. What is the implication of the main finding? The procedures for creating a bare earth digital elevation from a digital surface model are a black box that can hallucinate, and the results must be checked carefully. The creators should check derived land surface parameters as well as the raw elevation values, as a good digital surface model can be better than a poor digital terrain model. Geomorphometry workers must carefully assess the land surface parameters they use. First derivative parameters perform best; second derivative parameters, like curvature, vary in their signal-to-noise ratio; the third derivative parameters, like change of curvature, might be all noise.Abstract We evaluated six global digital elevation DEMs at 1-arc-sec resolution: CopDEM and AW3D30, which are digital surface models (DSMs), and EDTM, GEDTM, FABDEM, and FathomDEM, which are digital terrain models (DTMs). We compared them to reference DTMs created by mean aggregation from 1-2 m lidar-derived DTMs from national mapping agencies, using 1510 approximately 10 x 10 km test tiles from the United States and western Europe. Our criteria used the grids for elevation and derived land surface parameters (LSPs), including characteristics of the difference distributions and the fraction unexplained variance derived from grid correlations.The best DEM depends on the LSP used and the characteristics of the test tile, especially average slope, barrenness, and forest coverage. FathomDEM emerged as the best among the DEMs, with CopDEM the best overall for the DEMs with unrestricted licenses. GEDTM performed poorly. This is especially important for LSPs like curvature measures, which require higher-order partial derivatives for computation, and which should be used very cautiously.