Method for photogrammetric surveying of archaeological sites with light aerial platforms

In this paper, we describe a complete methodology for performing photogrammetric surveying of archaeological sites using light aerial platforms or unmanned aerial vehicle (UAV) systems. Traditionally, the main problem with using these platforms is the irregular geometry of the photographs obtained. These irregular image block patterns are occasioned by uncontrolled circumstances (e. g. effect of wind, lack of flight control, etc.) which generate high imprecision in the positioning of camera stations. The method proposed here allows the execution of the photogrammetric flight following the predicted parameters determined in mission planning (camera focal length, photo scale, ground sample distance -GSD-, overlaps, etc.) so we can obtain regular flight geometries. Our method allows the use of conventional photogrammetric data reduction methods based on the use of stereoscopic photogrammetric workstations. Although flights with irregular patterns can allow the formation of stereo pairs within certain limits, conventional photogrammetric procedures often have great difficulty in processing these irregular image blocks. For this reason this system raises the staking out of the camera positions by using a robotized total station and a mini prism situated on the platform. This method is applied to a real photogrammetric survey of an archaeological site of the Tartessic epoch in Southern Spain. The results obtained, confirmed by a quality control of the photogrammetric flight, have demonstrated the viability of this methodology even when moderate wind effects appear.