Studying landslide deformations using Remote Sensing and field surveys. A raster and point cloud approach for the Charonnier landslide, France

Landslides are among the most widespread hazards in the word, with special relevance in mountainous regions. In January 1994, a rainfall-triggered rotational landslide mobilised about 28000m3 of material from the hillslopes of the Charonnier basin, in the French department of Hautes-Alpes. Hydrological and geotechnical surveys are classic approaches for stability studies, built upon in situ observation and soil parameterization. Nevertheless, the introduction of remote sensing systems for landslide mapping and monitoring in the last decades yields intersecting results, yet their possibilities are not fully exploited and remains nowadays a promising area of study. Reconstruction of landslide topography and its evolution throughout the years is achievable with the help of photogrammetry techniques. In the present study, historical aerial pictures from 1993 and 1999 are used to generate elevation information of the Charonnier landslide area in raster (DTM) and point cloud (DPC) format. Resolution of the available historical photographs appears to be a crucial factor for the accuracy of the derived products, decreasing their RMSE from 3.4m to 0.14m (900dpi vs. 2400dpi images). With the help of a UAV, which captures on demand, high-resolution images, elevation models for 2016 and 2017 are built with errors around 10cm. 1993, 1999, 2016 and 2017 products are compared to distinguish morphodynamic processes in the short and long term. DTMs corresponding to different dates are subtracted one from the other, to detect areas where terrain elevation has varied. This way, the location of the source area and volume of the displaced mass are drowned. The distance between DPCs for different dates is computed with the M3C2 algorithm. The main outcome of the computation is the delimitation of areas subjected to erosion in the flanks of the Charonnier creek, in the form of gullies, and of riverbed incision of around 10cm/year. A soil sampling campaign and material characterization wer