Abstract
For identification of forested landslides, most studies focus on knowledge-based and pixel-based analysis (PBA) of LiDar data, while few studies have examined (semi-) automated methods and object-based image analysis (OBIA). Moreover, most of them are focused on soil-covered areas with gentle hillslopes. In bedrock-covered mountains with steep and rugged terrain, it is so difficult to identify landslides that there is currently no research on whether combining semi-automated methods and OBIA with only LiDar derivatives could be more effective. In this study, a semi-automatic object-based landslide identification approach was developed and implemented in a forested area, the Three Gorges of China. Comparisons of OBIA and PBA, two different machine learning algorithms and their respective sensitivity to feature selection (FS), were first investigated. Based on the classification result, the landslide inventory was finally obtained according to (1) inclusion of holes encircled by the landslide body; (2) removal of isolated segments, and (3) delineation of closed envelope curves for landslide objects by manual digitizing operation. The proposed method achieved the following: (1) the filter features of surface roughness were first applied for calculating object features, and proved useful; (2) FS improved classification accuracy and reduced features; (3) the random forest algorithm achieved higher accuracy and was less sensitive to FS than a support vector machine; (4) compared to PBA, OBIA was more sensitive to FS, remarkably reduced computing time, and depicted more contiguous terrain segments; (5) based on the classification result with an overall accuracy of 89.11% ± 0.03%, the obtained inventory map was consistent with the referenced landslide inventory map, with a position mismatch value of 9%. The outlined approach would be helpful for forested landslide identification in steep and rugged terrain.
Highlights
The Yangtze Three Gorges area of China has more than 2500 unstable slope localities, and often suffers from landslide events [1,2,3]
According to Stumpf and Kerle [28], this study mainly focused on the automated selection of object features for classification rather than the automated selection of scale parameters for segmentation
Using an object-based image analysis (OBIA) method with only Light detection and ranging (LiDar) data, a semi-automatic forested landslide identification process was implemented in areas of dense vegetation, bedrock cover and rugged terrain, within the
Summary
The Yangtze Three Gorges area of China has more than 2500 unstable slope localities, and often suffers from landslide events [1,2,3]. The Three Gorges area is characterized by steep and rugged terrain with heavy vegetation cover, often obscuring or subduing morphologic features indicative of landslides [12,13]. Light detection and ranging (LiDar) technology can obtain high resolution topographic data and penetrate vegetation, measuring features subdued by the rugged and forested terrain [11]. A range of LiDar derivatives, including DTMs, shaded relief, slope, aspect, and surface roughness, have been widely used for qualitative visual interpretation and quantitative statistical analysis of landslides [12,32,41,42,43,44,45,46,47]
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