UAV Data and GPR Prospection for the Study of a Pre-Historic Necropolis in NW Portugal

Over past decade, different remote sensing methodologies have been widely used in the detection, exploration and documentation of archaeological sites. Geophysical prospection, photogrammetric surveys and archaeological prospection and excavation are increasingly combined in several archaeological projects that serve both site investigation and dissemination of results. In this work, we present the results of Unmanned Aerial Vehicle (UAV) based survey and its integration with geophysical survey data from Ground Penetrating Radar (GPR), and some results from subsequent archaeological excavation, that were conducted in the study of Chã da Mourisca necropolis located in Ponte de Lima, NW Portugal. In this study photogrammetry by UAV enabled the accurate mapping of the necropolis area, with the production of high-resolution RGB orthomosaics and DSM's (Digital Surface Models). The GPR survey was conducted, over some selected areas, in a grid based prospection with parallel profiles acquired with 20 cm of separation. The equipment used was the GSSI SIR 3000 with a 400 MHz antennae. The data enabled the definition of the local stratigraphy and the detection of probable cists and ditches/trenches and a semi circular structure. This data was used to select areas for archaeological excavation and, afterwards, the UAV was used to register different phases of the archaeological works. The data obtained is an important auxiliary for the archaeological investigation, as resulting maps and other images, can be used to direct excavations, or to digitally reconstruct the archaeological structures, without the need of excavation, and therefor test ideas about the past. The combination of these methodologies is inexpensive, and quick to perform in the field, and can be systematically applied in the knowledge, safeguard and valorisation of other prehistoric archaeological heritage.