Scan Line Void Filling of Airborne LiDAR Point Clouds for Hydroflattening DEM

Abstract

Generation of LiDAR-derived digital elevation model (DEM), particularly for hydrologic and shore environments, poses a continuous challenge. The presence of laser dropouts found on the water bodies causes data voids/holes in the airborne LiDAR data point clouds. Unnatural huge triangular artifacts may appear in these regions when a DEM is generated, resulting in not only unpleasant visual effect but also inaccurate terrain analyses. The United States Geological Survey (USGS) has stressed the need of having a hydro-flattened DEM in the LiDAR Base Specification. Different forms of water bodies should be represented by a flat surface. Existing approaches mainly rely on the use of ancillary data or manual intervention during the hydro-flattening process. In this study, an automatic data processing workflow is proposed to 1) classify land and water data points collected by a topographic airborne LiDAR system based on the scan line intensity-elevation ratio (SLIER), 2) perform scan line void filling of data points in close-to-nadir region and at both swath edges, 3) generate a virtual water surface based on the classified water data points, and 4) perform hydro-flattening on the DEM. The proposed workflow was examined using five datasets collected by topographic airborne LiDAR on the inland ponds and lakes, inland rivers, non-tidal boundary water bodies, tidal water bodies, and islands, as addressed in the LiDAR Base Specification. The results showed that the proposed workflow can successfully generate hydro-flattened DEMs and overcome the drawback of existing approaches.

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