Bidirectional DEM relief shading method for extraction of gully shoulder line in loess tableland area. (4th July 2018)

• Record Type: Journal Article
• Authors: Na, Jiaming; Yang, Xin; Dai, Wen; Li, Min; Xiong, Liyang; Zhu, Rui; Tang, Guoan
• Is Part Of: Physical geography. Volume 39:Number 4(2018)
• Page Start: 368
• Page End: 386
• Publication Date: 2018-07-04
• Subjects: Loess shoulder lines -- hillshade -- Digital Elevation Model -- terrain-feature extraction -- gully; Physical geography -- Periodicals; 910.02
• DOI: 10.1080/02723646.2017.1410974
• Languages: English
• ISSNs: 0272-3646

Abstract

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.