Photogrammetry and in situ observations to produce high detailed geo-information of the Charonnier landslide

Abstract

Remote sensing techniques have made major improvements in the fields of photogrammetry and the acquisition of high resolution geographical data which makes it possible to produce highly detailed and accurate results. The techniques are promising, but it is still a challenge to gain high quality and quantity results in remote mountainous areas like the Alps. Large parts of the southern France Alps consist of a black marl top layer formation which is highly erodible. Together with the Mediterranean climate it is a perfect environment for mass movements to take place. Mass movements can have major impacts on its surroundings, both natural and economical. Due to a wet winter in 1993 – 94 and an extreme rainfall event on the 6th of January 1994, the hillslope of the Charonnier valley collapsed, causing a rotational landslide. Different remote sensing techniques are used to understand the dynamics of the Charonnier landslide, both quantitative and qualitative. With the use of LPS Project Manager various orthophoto´s and DEMs with a RMSE of 3.5 meter, are produced of aerial photographs both prior and after the landslide took place. The differences between the DEMs are used to calculate an estimation of the moved mass. The displaced mass at the source area is 21,600 m3. The estimate volume of the toe is 20,450 m3. Based on the produced DEMS, in situ observations, aerial images, field notes and dGPS measurements a detailed geomorphological map of the landslide is produced. Two photogrammetry software’s are used to create an orthomosaic and DEM with aerial images taken from an UAV. Both the photogrammetry software’s Drone2Map and Agisoft use the Structure from Motion technique and have results with centimetre resolution and accuracy. Drone2Map has a slightly better resolution and accuracy, where Agisoft is more stable, controllable and reliable in its results. Together with the analysis of precipitation data and the calculation of the recurrence time, it is possible to gain qualitative information about the dynamics of the Charonnier landslide.