Photogrammetric Documentation of an Archaeological Site (palpa, Peru) Using an Autonomous Model Helicopter

In this paper we describe a new system for the recording of archaeological sites based on an autonomous UAV (unmanned aerial vehicle) that has recently been employed in the framework of the Nasca-Palpa Archaeological Project on the south coast of Peru. In the vicinity of Palpa, the prehispanic site of Pinchango Alto is an attractive, yet difficult target for archaeological research. On the one hand, its well preserved stone architecture, abundant surface finds, and richly furnished graves dating to the Late Intermediate Period (AD 1000-1400) offer many opportunities to study this still poorly understood pre-Inkaic period. On the other hand, access to and working on the site is rather difficult. The recording of the preserved surface remains therefore required a highly mobile and flexible documentation system. In the 2004 field campaign we used a model helicopter carrying a CMOS camera to acquire a series of vertical aerial images for a photogrammetric recording and 3D modeling of the site and the surrounding terrain. The system used in Pinchango Alto is based on a commercial low cost model helicopter. It features an integrated GPS/INS based stabilizer. While the GPS/INS unit enables semiautomated navigation along a predefined flight path, the stabilizer ensures a stable flight attitude and thus a highly reliable image acquisition. The processing and analysis of the acquired images encompassed image pre-processing, semiautomatic triangulation, and DTM generation. The inhouse software used for automatic DSM generation is here described in detail. A virtual 3D model of the site was produced and visualized. The resulting data were analyzed concerning in particular the potential of DSM generation from model helicopter images as compared to laser data. In this paper we present the first results of our ongoing work in Pinchango Alto and discuss the strengths and weaknesses of the UAV-based documentation system for archaeological research.