Use of UAV's and geophysical prospection as a way to promote prehistorical archaeological heritage

Abstract

The Northwest of Portugal is a mountainous region with hundreds of funerary megalithic mounds dating back from the Middle / Later Neolithic (between the end of the 5th to the end of the 4th millennia BCE) (Jorge, 1982; Sousa, 2012). It is an heritage that is not fully inventoried and therefore susceptible of destruction due to the forest advances, constructions or enlargements of road networks in rural and urban context and. The systematic excavation of this type of monuments is time consuming and its conservation or later valorisation for didactic and tourist purposes becomes an impossible task. Thus, the objective of this work is to demonstrate that, through the use of new non-invasive technologies, it is possible to obtain relevant information about this type of monuments, which can be used scientifically and integrated into tourist-didactic projects. The methodology used combines the inventory and the cleaning of the vegetation covering funerary megalithic monuments, with geophysical prospection (Ground-penetrating Radar) (Fig. 1) and remote sensing for the production of high-resolution colour orthophotography and digital surface models (DSMs) obtained from an unmanned aerial vehicle (UAV) (Fig. 2). The case studies correspond to 5 megalithic mounts in the Serra do Corno do Bico, Ponte de Lima municipality, Viana do Castelo district, and 1 monument in Tojal, in the municipality of Póvoa de Lanhoso, Braga district. The results obtained with GPR enabled us to know some constructive aspects, such as determining intermediate or peripheral lithic rings in the artificial mounds that cover the funeral chambers, as well as determining the degree of destruction of the chambers and stone corridors. This is very clear in the case study of the Tojal Mound (Fig. 3). Photogrammetry by UAV enables 3D modeling of monuments and areas of envelopment, giving them volume and greater visibility. In summary, the information obtained, besides being an important auxiliary of the archaeological investigation, enables the selection of better conserved monuments for future archaeological excavations and can and should be used for recreational and tourist purposes, through its reproduction in informative plates and on-line information with high resolution 3D models, accompanied by explanatory texts intended for both local populations and visitors. The combination of the methodologies expressed corresponds to a praxis that is inexpensive and quick to perform in the field and can be systematically applied in the knowledge, safeguard and valorisation of the most sensitive prehistoric archaeological heritage, such as funerary megalithic mounds.