Empleo de UAV para la documentación efectiva y de bajo coste de espacios arqueológicos. Una experiencia en sistemas agricolas prehispánicos en Atacama (N. Chile)

The paper summarizes the contribution of UAV to the archaeological documentation, through the case of a vast group of late Prehispanic agrarian elements (fields, irrigation canals) in the arid Atacama area (northern Chile). Taking advantage of the extraordinary preservation and visibility of fields, canals and other constructions, the general mapping of the area was based on a combination of visual interpretation of high resolution satellite images (GeoEye 1) and fieldwork. However, despite their high resolution, satellite images did not provide sufficient detail in some areas. A more detailed approach was needed to produce an adequate documentation of fields, settlement areas and singular constructions. An Structure From Motion-based computer vision approach was carried out, based on the use of a low cost UAV (Dji Phantom) and a consumer-grade compact digital camera for the acquisition of low altitude aerial images that allowed the generation of 3D models and orthoimages of great detail. The main result has been the construction of a highly detailed and accurate map of a complex group of archaeological structures, which has been used since for the analysis and interpretation of the area, and also for the design of new fieldwork seasons. In this paper we describe the workflow and assess the ratio between working time, tools and quality of the results. Besides, we compare the workflow and results of two different instruments.