Application of Tls for Change Detection in Rock Faces

The paper describes some experiences carried out in monitoring of two rock faces in Italian Prealps in order to detect changes due to rock detachments. Since the forecasting of possible rockfall events is the main aim of this research, terrestrial laser scanning application was investigated for high precision deformation monitoring in this context. Firstly, problems concerning the data acquisition and the reduction of georeferencing errors are analyzed by comparing results obtained from different approaches. A method including the use of a removable steel pillar to constrain the 3D shifts of the instrumental reference system, and of ICP surface matching algorithm to solve for rotations gave the best results. Secondly, some techniques for filtering vegetation from pointclouds of cliffs are presented and discussed here. These are mainly based on 3D spatial filters. The use of an infrared camera integrated to terrestrial laser scanner is also proposed. Finally, results on the comparison of multi-temporal laser scans are presented, showing somehow the proposed pipeline can be successfully applied to detect small rock detachments of the size of a few cube centimetres.