Low-height aerial imagery and digital photogrammetrical processing for archaeological mapping

In the framework of the Joint Archaeological Mission of the Universities of Bologna and Lecce at the ancient town of Soknopaiou Nesos (Fayyum, Egypt) a wide-range of geomatic methodologies were experimented (GPS, total station surveys, low-height aerial and close-range photogrammetry, Visual Reality, high resolution satellite imagery, etc.). The surveys were conducted with the aim of recording metrical and non-metrical information inside a common reference system for the development of a GIS for the archaeological area. The paper deals in particular with the acquisition and processing of low-height aerial imagery to provide very large-scale mapping of the area in support of archaeological researches. A remote controlled system, ad hoc developed for cultural heritage applications, permits to operate both semi-metric and non-metric cameras, lifted by balloon or kites with specific arrangements, in order to systematically take pictures over the study area. The images acquired during the 2002 campaign by a non-metrical camera, calibrated by field calibration procedure, were processed within a Socet Set digital photogrammetric workstation: aero-triangulation, digital orthoimage generation and mosaicing were realized. The external orientation was established through kinematic GPS-derived ground control points, surveyed within the International Terrestrial Reference Frame ITRF2000; the same kinematic survey provided also a DTM for the entire site. After a description of the overall approach to the survey of the site by the integration of different techniques, the paper describes the results obtained by this photogrammetric campaign, pointing out specifically the aspects concerning the non-standard image arrangement within the photogrammetric block, the problems arised by the geometrical structure of the buildings (e.g. the presence of very high mud-bricks walls in the temenos), and the use and comparison of DTMs derived from image-matching techniques or from GPS surveys.