Time for change: quantifying landslide evolution using historical aerial photographs and modern photogrammetric methods

A sequence of historical aerial photographs captures morphological change, which can only be unlocked by using appropriate photogrammetric methods. There are several challenges: initially it is necessary to trace and acquire suitable imagery in an appropriate format; typically there is a lack of precise photo-control available at the time of photography and similarly, it is rare to have access to the original camera calibration certificate. Furthermore, it is essential to assess the quality of the extracted morphological data. Once these challenges have been overcome, such morphological change data can be used to develop landslide evolutionary models, which can be related to localised climate change. This paper describes the use of modern digital photogrammetric methods to extract high-resolution digital elevation models (DEMs) and orthophotographs using historical photography. Initial results from a case study at Mam Tor (Derbyshire, UK) show the potential of the methods to quantify past landslide movements. Photographs from four different epochs (1953, 1971, 1973 and 1990), of varying scale and quality, were processed. Difficulties caused by limited ground control and limited camera calibration data were solved by differential GPS and self-calibrating bundle adjustment methods. The quality of the data was at an adequate level to extract ground movements that were consistent with observations by other authors. A more detailed analysis of the displacements in both vertical and horizontal directions is expected to increase the understanding of the mechanics of the landslide. This is an ongoing research project in which these dated spatial data will be used to relate landslide evolution to climate change.