Application of archival aerial photogrammetry to quantify climate forcing of alpine landscapes

Recent and future climate change may lead to landscape changes in geomorphic processes and process rates. Such modifications are likely to be widely distributed, making their direct measurement difficult and there are almost no such measurements at decadal intervals. Aerial imagery has been acquired by many national agencies since the 1950s and significant archives remain. Unlocking the information from these data sources is important because their timescale may inform significant unresolved hypotheses regarding the impact of rapid climate change on Alpine environments. However, such photogrammetric applications are challenging because of topographic complexity (including occlusions and large elevation ranges) and variations in image texture. A complete workflow is described from raw data to the treatment and interpretation of results. This is applied to imagery of Val d'Héréns, Switzerland, a landscape containing an assemblage of glacial, periglacial, hillslope and fluvial landforms across a height range of 1800 to 3600 m from the 1960s to the present. These changes reveal important characteristics of landscape scale erosion and deposition at the decadal scale.