Investigating an active rockslide by long-range laser scanner: alignment strategy and displacements identification

Landslides are considered one of the major natural hazards in mountain regions. Nowadays landslides monitoring has become a central issue for Authorities to be able to anticipate hazards. For this reason, several examples exist about landslides monitoring; they may be installed in different configurations depending on purposes and economic resources.The heart of this research is to detect an efficient methodology for the reliable acquisition and interpretation of Terrestrial Laser Scanning (TLS) data: the final purpose is a proposal for a methodology which is based on TLS technology for identifying displacements and extracting geomorphological changes. The approach is clearly based on a multi-temporal analysis which is computed on several repetitions of TLS surveys performed on the area of interest. To achieve best results and optimize the processing strategy, different methods about point clouds alignment have been tested, together with algorithms both for filtering and post- processing. The final aim is also to provide a sort of guidelines about a suitable way for planning and properly carrying out TLS surveys.The case study is the Col Piagneto landslide, located in the North Apennines (Reggio Emilia, Italy) on the right flank of Biola torrent. The large scale composite landslide area is made both by a wide rock slide sector and a more limited earth slide sector. An integrated monitoring system is installed since 2009 and comprises both point-based technologies (extensometers, total station and global positioning system), as well as area-based ones (airborne laser scanner, long-range TLS and ground-based radar). This choice combines the advantages of both approaches.The research focuses on TLS surveys for trying to detect displacements which might be considered responsible for instability. By sequentially analyzing TLS surfaces, displacement maps have been obtained for the rockslide area. Confirmation can be achieved by comparing results with movements of reflectors located on the slope and continuously measured by total station. Such validation strengthens the idea that TLS may be successfully used for analyzing instability.