Marine geo-archaeological mapping using Unmanned Surface Vehicle (USV). Case study: ancient semi-submerged settlement of Grotta Naxos, Greece

The surveying, exploration and documentation of underwater cultural heritage (UCH) sites are rapidly entering a new era with the evolution of technology. Marine remote sensing techniques enable an adapted approach to the study area, overcoming the difficulties and limitations of conventional means and acting in a non-intrusive, non-destructive manner. This research is a marine geo-archaeological survey the case study of which is the semi-submerged site of Grotta, the north coastal zone of the ancient city of Naxos, Cyclades, in Greece. To meet the peculiar needs of the site with the presence of antiquities in ultra-shallow waters (0 to −5 m), a catamaran Unmanned Surface Vehicle (USV) was employed for the concurrent retrieval of shallow geoacoustic data and visual footage, equipped with acoustical and optical sensors. The collected acoustic datasets were processed to create bathymetric view and georeferenced mosaics of high-resolution and metric precision to map and investigate the submerged residential remains. Additionally, photogrammetric methods was applied for creation of 3D models and orthophotomosaics of the ancient structures located on the seabed, facilitating a better record of their individual characteristics. Both acoustic datasets were incorporated into GIS Software, where diverse spatial information was utilized to generate conclusive maps of the study area. This field research aims to demonstrate the adaptive use of USV’s in challenging environments for the exploration and documentation of underwater archaeological sites and the simultaneous acquisition of multi-level information without damaging the marine antiquities.