Historical aerial image photogrammetry for tracking past deformation of Reissenschuh deep-seated rock slide in Tyrol, Austria

The Reissenschuh deep-seated rock slide in the Schmirn valley (Tyrol, Austria) is one of the most active in the region. In this study, historical aerial images were used to photogrammetrically reconstruct past topography, to analyse spatio-temporal rock slide kinematics and extend differential global navigation satellite system (DGNSS) monitoring time series established in 2016. The computed 3D point clouds and their 2.5D digital surface models (DSMs) were analysed with a novel feature-tracking image-correlation technique (IMCORR-FT), resulting in a 4D displacement reanalysis covering a time span of 67 years. The quality of the registration of photogrammetrically derived topographies to the reference airborne laser scan differs according to the data source. The three-dimensional uncertainty of point clouds created from scanned aerial imagery is approximately $\pm$ 1.3 m (95% percentile), whereas that of digital sources is markedly lower, around 0.3 m. This study provides unique insights into the spatio-temporal surface changes that occurred over more than six decades, highlighting significant displacements of up to 50 metres in the central rock slide part and in recent years, an acceleration. The reconstructed spatially distributed displacement time series reveals the variability of the rock slide’s kinematics, and allows for the delineation of landslide subunits. It also reveals acceleration trends in the last two decades, potentially linked to increased precipitation and pore water pressure. This study shows the importance of long-term terrain reconstruction to aid process understanding and model development related to deep-seated rock slides valorising the extensive historical aerial image archives.