Morphological segmentation of Lidar Digital Elevation Models to extract stream channels in forested terrain

Our paper proposes an approach for the extraction of stream channels from Airborne Laser Swath Mapping (ALSM) data. Recent advances in technology have led to high-resolution topographic data acquisition by means of airborne lidar (i.e. ALSM), which can yield Digital Elevation Model (DEM) datasets with horizontal resolutions of 1 m and vertical rms errors in the range of 10 - 15 cm. The extraction of a stream network from a DEM plays a fundamental role in modeling spatially distributed hydrological processes and flow routing. We apply morphological filtering to an ALSM DEM to detect and characterize stream channels in forested terrain. Since the size and shape of morphological Structuring Elements (SEs) is known to strongly affect filtered results, we test for accuracy by developing a set of error measures over simulated terrain. We subsequently apply the filter to actual ALSM data. For linking disconnected stream segments, a measure of pixel connectedness known as the Connectivity Number is used. The method presented is shown to enable systematic characterization and comparisons of streams, even in heavily forested terrain.