Innovative Strategies and Use of UAVs to Survey and Monitor Archaeological Sites in Conflict/Post Conflict Zones. The Case Study of the Fortified Citadel of Shahr-i Zohak in Bamiyan (Afghanistan)

Abstract. Although unmanned aerial vehicle (UAV) mapping and photogrammetry have become common and relatively accessible for surveying and mapping cultural heritage sites, conducting surveys to model sites in conflict/post conflict zones remains challenging. This is particularly true for sites in a country like Afghanistan, where limited accessibility, the presence of Unexploded ordnance (UXOs), portability of the equipment, cost efficiency, as well as absence of data connectivity and Ground Control Point establishment pose major challenges. In this paper, we discuss the adopted strategy and implemented methodology to create a 3D model from both inside and outside of a section of the fortified citadel of Shahr-e Zohak which is part of the UNESCO World Heritage Property of the Cultural Landscape and Archaeological Remains of the Bamiyan Valley in Afghanistan. In particular, we examine in this paper what acquisition strategy was set for this site by going through the reasoning for selecting specific equipment and drones, the flight parameters, the camera settings, as well as how we prepared the dataset at the flight planning stage to allow merging GPS referenced data from the external flights of the UAV with non-GPS referenced data from the flights inside the domes and built structures. Succinctly, we go through the modelling strategy and parameters that have generated optimal results using both Agisoft Metashape and Bentley Itwin Capture.
Our results show that using Skydio’s X10 and S2 drones and setting a low Ground to surface distance (between 1 and 5 meters) and high overlap (75%-95%) allowed us to achieve 3D models with an average accuracy of 1 millimetre per pixel for a 120m long and 30m wide section of the fortified citadel of Shahr-i Zohak. These results also show that it is indeed possible to use UAV based photogrammetry to generate 3D models that can be used for damage assessments which is particularly useful in areas where it is difficult or impossible to bring international experts or institutions to conduct this work on site. Finally, this research highlights the capabilities as well as limitations of this method and provide practical guidelines for future works in comparably challenging environments.