Bidirectional DEM relief shading method for extraction of gully shoulder line in loess tableland area |
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Authors: | Jiaming Na Wen Dai Min Li Liyang Xiong Rui Zhu |
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Institution: | 1. Key Laboratory of Virtual Geographic Environment, Ministry of Education, Nanjing Normal University, Nanjing, China;2. Jiangsu Centre for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing Normal University, Nanjing, China;3. State Key Laboratory Cultivation Base of Geographical Environment Evolution, Nanjing Normal University, Nanjing, China;4. Department of Land Surveying and Geo-Informatics, Hong Kong Polytechnic University, Hong Kong, Hong Kong |
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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. |
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Keywords: | Loess shoulder lines hillshade Digital Elevation Model terrain-feature extraction gully |
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