COMPARISON OF LOW ALTITUDE PHOTOGRAMMETRIC METHODS FOR OBTAINING DEMS AND ORTHOIMAGES OF ARCHAEOLOGICAL SITES

Abstract. In this work it is performed a comparison of two methods for obtaining digital elevation models (DEMs) and orthoimages of medium-sized archaeological sites (500-5000 m²). The photogrammetric methods analyzed consist in the use of a light aerial platform applying the normal case of photogrammetry (vertical photographs and regular blocks), and the second one is based on a network of oblique photographs, taken from a telescopic mast, using a DEM obtained from a terrestrial laser scanner (TLS) survey. The main goal is to analyze the more efficient method for these studies taking into account variables such the working time, the accuracy obtained in the final products, the visual analysis of final orthoimages, etc. This study has been applied to the same archaeological site in two different epochs. The image acquisition was performed before and after a conservation intervention at the archaeological site. The results have shown similar characteristics for both products (DEMs and orthoimages) and accuracies but the density of DEMs and the visual analysis of orthoimages have shown differences that allows us to select the more adequate method taking into account the characteristics of each case. Thus the DEMs obtained using the TLS survey has shown more density of points while the visual analysis of orthoimages has shown a better behaviour (radiometrically and visually) in the case of vertical photographs.