A photogrammetry application to rockfall monitoring: the Belca, Slovenia case study

UAV aerial photogrammetry offers a powerful and cheap methodology to reconstruct the terrain geomorphology. The purpose of this study is the application of a generic Structure-from-Motion workflow to properly elaborate different set of images from multitemporal surveys in order to perform a surface and volume change detection by meaning of a cloud-to-cloud comparison. The complex geomorphology of the site of interest, characterized by niches, asperities, flat rock walls with different orientation, debris deposits and isolated rock blocks, challenges the accurate reprojection of the points into a 3D space. The chronological comparison of the point cloud offers a qualitative and quantitative estimation of distances and volume change between sequential models. For the distance computation, a level of accuracy accounting for different sources of uncertainty was estimated. The data sets available for this study was 7 and they were acquired by two different faculties of the University of Ljubljana, BF and FGG. Many surveys were performed with different approaches, leading to different accuracy in the final reconstruction of the terrain. The data post-processing has been performed with the latest versions of Agisoft Metashape and CloudCompare.