Contribution of UAS to the monitoring at the Lärchberg-Galgenwald landslide (Austria)

ABSTRACTIn April 2001, a rock fall occurred at the landslide Larchberg-Galgenwald, Austria. The movement of this landslide has been under observation for decades, but the methods used so far have several disadvantages. This article aims to show that unmanned aerial systems (UAS) provide a reasonable alternative in terms for monitoring the landslide. At the landslide, we focused on the most active area to (i) record changes of the landslide’s surface, (ii) assess the accuracy of the resulting data, (iii) assess whether the number of ground control points (GCPs) could be reduced in subsequent UAS surveys, and (iv) conclude whether UAS-based recording is favourable compared to common terrestrial methods. UAS imagery, acquired under challenging site conditions in November 2015 and May 2016, were processed to digital elevation models and orthophotos with a ground sampling distance of 0.04 m, which should display expected changes of up to ~0.17 m (relating to previously reported movements of up to 30 cm a−1) fo...