Digital elevation models
Figure: Hillshade of a high-resolution digital elevation model created from aerial laser scanning data showing the tracks of debris-flows and the deposits of a rock avalanche (Figure: T. Oppikofer, NGU).
Digital Elevation Models (DEMs) are digital representations of the topography, generally as rasters (grids of square cells with a constant cell size). DEMs are extensively used as elevation datasets in Geographical Information Systems (GIS). Nowadays, DEMs are frequently generated from remote sensing data, such as Interferometric Synthetic Aperture Radar (InSAR), like the Shuttle Radar Topography Mission (SRTM), but also from stereoscopic pairs of aerial photographs taken from different viewpoints during the same flight pass (photogrammetry), as well as from Light Detection and Ranging (LiDAR) techniques that include Aerial Laser Scanning (ALS) and Terrestrial Laser Scanning (TLS).
The altitude information provided by a DEM can be used for numerous applications and allows the creation of many derivatives, such as contour lines, slope angle, slope aspect and hillshade. Hillshade maps of the DEM reveal morphologies related to landslides, especially if the DEM has a high resolution (created by ALS or TLS). The topographic expression of landslides, i.e. head scarps, head depressions, toe accumulations, debris-flow tracks etc., are visible and can be mapped on hillshade maps. The main geomorphologic features of an unstable rock slope, i.e. its back-scarp, lateral release surface, sliding surfaces and eventual deposits, can also be easily mapped using hillshades. The combination of DEM hillshades and orthophotos is particularly useful for the detection and mapping of landslides.