Monitoring mass movements using georeferenced time-lapse photography: Ritigraben rock glacier, western Swiss Alps

An automatic method was developed to monitor rock glacier kinematics. Displacements derived from monoscopic time-lapse images were scaled and projected into the Swiss Coordinate System CH1903. We tested this method at the front of the rapidly creeping Ritigraben rock glacier, where time-lapse pictures of the rock glacier front were taken by an automatic camera with a temporal resolution of 3 h. The images were automatically processed using a Matlab algorithm. The output data were spatially resolved creep velocities between successive images and mean relative velocities over time. The digital elevation model used for the projection of the time-lapse data was acquired using terrestrial laser scanning (TLS). The resulting horizontal displacement velocities and accelerations were validated against GPS data measured at one point on the rock glacier front. The high temporal resolution of the time-lapse image velocities provided new insights on the kinematics of the rock glacier front, which could not have been discerned with the GPS or TLS measurements applied. The Ritigraben study site is particularly suitable for our approach due to the temporally constant movement directions. Snow coverage and fog are disturbing factors which can lead to failure of the method.