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The primary objective of this research is to better understand the movement characteristics and patterns of a sudden landslide that occurred in the Three Gorges Reservoir, China (the Sept. 2, 2014 Shanshucao landslide) by using three periods of multi-source remote sensing images in combination with a field survey. A georeferenced, aerophotographic orthomosaic and corresponding 1:2000 topographic map of the pre-landslide area was referenced to rectify the micro-unmanned aerial vehicle (UAV) based orthomosaic, digital surface model (DSM) and Google Earth satellite image of the post-landslide area. By using orthomosaics of the post-landslide area, especially the very high spatial resolution micro-UAV based orthomosaic, the landslide boundaries were accurately delineated. By comparing the images of the area both pre- and post-landslide, three landslide subzones were identified, and two boundaries between the three subareas were divided more precisely than in previous studies. Based on the digital elevation model (DEM) of the pre-landslide area and DSM of the post-landslide area, the change in altitude and volume of the landslide were quantified. Then, the movement pattern of the landslide was proposed. The results showed the rocky, southern sliding part was the main sliding zone with the longest distance and deepest sliding surface, and the northern soil mass did not experience any overall movement. However, loose soil mass collapse and features of counterclockwise rotation were observed under the traction of the rocky, southern sliding part. Additionally, more accurate knowledge has been obtained including the location of the original lateral boundary, shear outlet altitudes, and main triggering factors of the rocky sliding mass. This study has demonstrated that the use of multi-source remote sensing images, which include both pre- and post-landslide images, can effectively describe the characteristics, patterns, and even the mechanism of a sudden landslide. [ABSTRACT FROM AUTHOR]

Monitoring has been considered to be the most effective means of preventing and mitigating geo-hazards. Unmanned aerial vehicle (UAV) based remote sensing has been proven to be a viable method for monitoring relatively flat areas, but has typically encountered challenges on steep mountainous slopes. The Qinglingou Slope, which is located at the head of the Three Gorges Reservoir, China, was selected as a case study, and a UAV-based remote sensing method was applied to monitor this steep mountainous slope. The UAV, which was equipped with a camera, was used to acquire images on May 10 and Sept. 13, 2015. At the same time, a plan for establishing and measuring a detailed network of ground control points (GCPs) and check points was carefully designed and implemented, according to the local conditions. Georeferenced digital surface models (DSMs) and digital orthophotos were obtained by photogrammetric processing. Based on the results, a simple and quick method that identified and quantified slope deformation by calculating and analyzing the changes in the DSMs was developed. The results showed that the UAV-based remote sensing method was rapid, safe and effective, and it could be valuable for monitoring a large number of steep mountainous slopes in the Three Gorges Reservoir. [ABSTRACT FROM AUTHOR]