LARGE-SCALE TERRAIN VISUALIZATION USING SRTM DIGITAL ELEVATION MODELS: AN EXAMPLE FROM THE INDIAN HIMALAYA

This poster demonstrates the kind of terrain visualization that can be done using freely available Shuttle Radar Topography Mission (SRTM) 3 arc-second digital elevation models (DEMs) and the open source GIS software GRASS 6. In the low to middle latitudes, 3 arc-second DEM postings correspond to approximately 90 m. Techniques illustrated using SRTM data for a 5 x 5 degree DEM covering the Indian Himalaya are the generation of 1) a series of shaded relief images with varying illumination direction and inclination and 2) geomorphic derivative maps depicting attributes such as slope angle, residual topography, and topographic roughness. Shaded relief images with varying illumination angles allow linear features with different orientations to be effectively visualized and mapped. Geomorphic derivative maps are based only on the data in the DEM and do not add or create any new information, but are instead used to enhance or accentuate aspects of the topography useful for landform identification. Functions for such derivatives as slope angle and curvature are available in a number of GIS programs. There is, however, no universally accepted definition of topographic roughness. The approach described here was originally developed as a computationally quick, simple, and robust method useful for large LiDAR DEMs consisting of many millions of points. First, residual topography is calculated by creating a smoothed DEM using an n x n moving average. Then, topographic roughness is calculated as the moving standard deviation of the residual topography using the same size moving window, where the window size n is chosen based on the scale of the landforms being visualized. Preliminary inspection of the results and comparison with a very generalized tectonic map of the region suggests that the combination of a suite of shaded relief images and geomorphic derivative maps may provide an effective tool for delineating continental-scale morphotectonic units or terranes.