Morphological Processing of Severely Occluded Digital Elevation Images to Extract and Connect Stream Channels

Recent advances in technology have enabled the acquisition of high-resolution topographic data by means of airborne laser swath mapping (ALSM), which can yield digital elevation models (DEMs) with horizontal resolutions of 1m. A DEM is a grayscale image wherein pixel value corresponds to elevation. Using ALSM imaging systems over forested terrain, we filter out the laser returns from the occluding foliage and estimate bare-surface DEMs. Extracting stream networks from DEMs is important for modeling many hydrological processes. We apply a sequence of morphological operations to an ALSM DEM to detect stream channels in forested terrain. We verify the accuracy of the results using a set of error measures over simulated terrain and also using GPS ground truth over real terrain. For linking disconnected stream segments, a measure of pixel connectivity is used.