Detection and analysis of landslide geomorphology based on UAV vertical photogrammetry

High-resolution landslide images are required for detailed geomorphological analysis in complex topographic environment with steep and vertical landslide distribution. This study proposed a vertical route planning method for unmanned aerial vehicles (UAVs), which could achieve rapid image collection based on strictly calculated route parameters. The effectiveness of this method was verified using a DJI Mavic 2 Pro, obtaining high-resolution landslide images within the Dongchuan debris flow gully, in the Xiaojiang River Basin, Dongchuan District, Yunnan, China. A three-dimensional (3D) model was constructed by the structure-from-motion and multi-view stereo (SfM-MVS). Micro-geomorphic features were analyzed through visual interpretation, geographic information system (GIS), spatial analysis, and mathematical statistics methods. The results demonstrated that the proposed method could obtain comprehensive vertical information on landslides while improving measurement accuracy. The 3D model was constructed using the vertically oriented flight route to achieve centimeter-level accuracy (horizontal accuracy better than 6 cm, elevation accuracy better than 3 cm, and relative accuracy better than 3.5 cm). The UAV technology could further help understand the micro internal spatial and structural characteristics of landslides, facilitating intuitive acquisition of surface details. The slope of landslide clusters ranged from 36° to 72°, with the majority of the slope facing east and southeast. Upper elevation levels were relatively consistent while middle to lower elevation levels gradually decreased from left to right with significant variations in lower elevation levels. During the rainy season, surface runoff was abundant, and steep topography exacerbated changes in surface features. This route method is suitable for unmanned aerial vehicle (UAV) landslide surveys in complex mountainous environments. The geomorphological analysis methods used will provide references for identifying and describing topographic features.