Investigation and Risk Assessment of a Loess Landslide Based on UAV Tilt Photogrammetry

[Objective] The tilt photogrammetry of single landslide was carried out by a flexible light rotary-wing UAV in order to explore a method that can meet the needs of geological disaster investigation and assessment in loess region under complex terrain conditions. [Methods] The study was conducted for the Zhaojiaan landslide in Yan’an City, Shaanxi Province. Multi-view, high-overlapping, and high-resolution landslide images were obtained by using UAV tilt photogrammetry technology to generate a digital elevation model (DEM), a digital orthophoto map (DOM), and a real-world 3D model. Spatial geometric information of the landslide body was then acquired, and the Zhaojiaan landslide risk was evaluated by combining the analytic hierarchy procedure (AHP) and the hazard calculation method. [Results] ① By interpreting the high-resolution DEM, DOM, and multi-level real-world 3D model, the fine topographic and micro-geomorphic features of the landslide were extracted, thereby improving the accuracy of geological hazard interpretation and effectively reducing the labor intensity, time cost, and operational risk of manual geological hazard investigation; ② The hazard value (R) of the Zhaojiaan landslide was 0.635, designating it as a high hazard slope. It is therefore necessary to strengthen professional monitoring work. [Conclusion] The method of landslide investigation and risk assessment based on UAV tilt photogrammetry technology is especially suitable for landslide investigations in loess areas with steep valley slopes, deep river valleys, and sparse vegetation. This technology appears to be a promising method for risk assessment of single landslide hazards in loess areas.