Bidirectional DEM relief shading method for extraction of gully shoulder line in loess tableland area. (4th July 2018) - Na, Jiaming
Abstract: The gully shoulder line, one of the most important topographical features, reveals the erosional process and reflects the geomorphological evolution of a loess area. Existing shoulder-line extraction methods are based on local window-filter or image-edge detection, which are sensitive to image noises and algorithm parameters, causing unsatisfactory accuracy and efficiency. This paper proposes a bidirectional relief-shading (BRS) method for loess shoulder-line extraction based on a 5-m Digital Elevation Model (DEM). First, two hill-shaded images are simulated with appropriate altitude and symmetric direction of the light. Second, the grey value difference between inter-gully and inner-gully area can be easily identified by fusing the two images with the mean method. Finally, the shoulder line can be derived by image segmentation using a threshold determined by an empirical equation. Experiments in three areas of loess tableland in Shaanxi Province validated the method, which has the advantages of being a simple operation with relatively high accuracy, 89.7% compared with manual digitalization, and high efficiency. We discuss three parameters in this method: zenith angle, azimuth angle, and segment threshold. Results suggest that the method is applicable for broad-scale gully shoulder line extraction in loess tablelands.