Global digital elevation models for terrain morphology analysis in mountain environments: insights on Copernicus GLO-30 and ALOS AW3D30 for a large Alpine area

This study focuses on the quality evaluation of two of the best 1 arc-second public global digital elevation models (DEMs), Copernicus GLO-30 DEM and ALOS AW3D30 DSM, from the perspective of their capability to represent the terrain fine-scale morphology of a complex alpine landscape, located in the Italian Trentino Province. The analysis is performed on an area of 6210 km(2), considering a reference DEM derived from a high resolution and accurate airborne Lidar survey. The quality assessment goes beyond a conventional approach based on elevation differences statistics, computed on a pixels-by-pixel basis. An ad hoc approach for evaluating the capability to represent fine-scale morphology, including surface roughness, is adopted. Moreover, the quality analysis is performed considering the influence of local morphology and of the different land covers. The findings show that although the two global DEMs have comparable overall quality, their relative performances change according to local landscape characteristics. Copernicus DEM performance is on average better than ALOS in correspondence of urbanized areas as well as in areas without vegetation cover, with gentle slopes and relatively low short-range roughness. Meanwhile, ALOS DEM performance is slightly better than Copernicus in rougher terrain and steeper slopes. In general, both DEMs have poor performances in steep slopes, with a limited capability to describe fine-scale morphology. The adoption of these global DEMs for terrain analysis and modelling of earth surface processes should be performed carefully, considering the impact of different land covers and of local morphology, including surface roughness

Digital Elevation Models: Terminology and Definitions

Digital elevation models (DEMs) provide fundamental depictions of the three-dimensional shape of the Earth’s surface and are useful to a wide range of disciplines. Ideally, DEMs record the interface between the atmosphere and the lithosphere using a discrete two-dimensional grid, with complexities introduced by the intervening hydrosphere, cryosphere, biosphere, and anthroposphere. The treatment of DEM surfaces, affected by these intervening spheres, depends on their intended use, and the characteristics of the sensors that were used to create them. DEM is a general term, and more specific terms such as digital surface model (DSM) or digital terrain model (DTM) record the treatment of the intermediate surfaces. Several global DEMs generated with optical (visible and near-infrared) sensors and synthetic aperture radar (SAR), as well as single/multi-beam sonars and products of satellite altimetry, share the common characteristic of a georectified, gridded storage structure. Nevertheless, not all DEMs share the same vertical datum, not all use the same convention for the area on the ground represented by each pixel in the DEM, and some of them have variable data spacings depending on the latitude. This paper highlights the importance of knowing, understanding and reflecting on the sensor and DEM characteristics and consolidates terminology and definitions of key concepts to facilitate a common understanding among the growing community of DEM users, who do not necessarily share the same backgroun