Deformation monitoring of high and steep slopes with UAV LiDAR technology assisted by oblique images

Aiming at the problem of low accuracy of DEM reconstruction and deformation analysis due to the lack of data during the scanning of high and steep slope point cloud based on light and small unmanned airborne LiDAR in the topographic environment of high-altitude gorge, this paper proposed an optimized data acquisition scheme using UAV image/point cloud data acquisition of high and steep slope flying perpendicular to the ridge, and DEM reconstruction scheme using UAV LiDAR point cloud with the aid of dense point cloud derived from multi-view oblique images. The accuracy and integrity of DEM reconstruction of high and steep slope and the accuracy of landslide deformation measurement in different periods have been improved. This method uses the point cloud data generated from the collected tilted image and the LiDAR point cloud data of the same period, in order to compensate the LiDAR point cloud missing data based on the iterative nearest neighbor point algorithm. Then, high-precision DEM products of landslides are constructed using the compensated LiDAR point cloud; Finally, the deformation of the landslides in elevation direction is obtained by comparing the current DEM with the DEM generated from the oblique images acquired in the past. Taking the landslides located at high and steep slopes of Qinghai Longyangxia Hydropower Station as the study area, an experiment is carried out and verified using the measured GNSS ground control points. It is concluded that the accuracy of LiDAR point cloud after fusion is 0.063 m, which is 0.018 m higher than that before fusion. The elevation accuracy of the reconstructed DEM of three typical landslides is 0.08 m, which improves the completeness and accuracy of DEM of slopes. The deformation results of typical landslides in the area are obtained by a comparison of DEM from two different epochs. The conclusions can be drawn that many slopes in the landslide group have different degrees of soil sliding, and the deformation in the elevation direction is up to more than 50 m, heavy deformations happened to the landslides.