Combining Structure-from-Motion with high and intermediate resolution satellite images to document threats to archaeological heritage in arid environments

For millennia, humans have lived in regions which have been and/or are today characterised by arid environmental conditions. Many archaeological sites are therefore located in deserts where they are subjected to specific conditions regarding their preservation, vulnerability, visibility and accessibility. The aim of this paper is to show how data from high and intermediate resolution satellite sensors and ground-based multi-image photogrammetry (Structure-from-Motion) can be combined to document damage to spatially extensive archaeological heritage in arid environments. In this approach, high-resolution satellite images (QuickBird) are used to locate archaeological sites and to verify the type of disturbance. Multiple sequential intermediate resolution satellite images (Landsat 7 ETM+) are used to document the spatial extent and temporal development of surface disturbances at the site and in the surrounding area. Structure-from-Motion (SfM) is used to document damage to a small segment of the archaeological site by creating a very high resolution DEM and orthophoto which are used for detailed damage assessment. The approach is exemplified using damage by off-road vehicles to a large Nasca period geoglyph in the coastal desert of southern Peru. It can be applied to document threats to spatially extensive archaeological sites in arid environments, such as large-scale looting, agricultural expansion or urban and industrial sprawl.