Assessment of Deep Water Archaeological Sites with Autonomous Underwater Vehicles

Deep submergence vehicle technology has recently enabled significant advances in the rapid assessment of marine archaeological sites. Precisely navigated vehicles equipped with high resolution digital cameras and high-frequency multibeam sonar systems can be used to assess not only the distribution of wreckage, but to quantify the size, distribution, and condition of individual artifacts contained within the wreck. This information is critical to deriving new knowledge of ancient civilizations based on shipwreck sites. The Woods Hole Oceanographic Institution in collaboration with the Hellenic Ministry of Culture and the Hellenic Centre for Marine Research is conducting an ongoing program to document ancient shipwrecks and refine underwater archaeological survey methods. The first project took place in 2005 near the Aegean island, Chios, when the team deployed an Autonomous Underwater Vehicle to investigate a 4th century BC wreck in 70 m water depth. Multiple low speed (20 cm/sec) digital imaging and acoustic mapping surveys were conducted at an altitude of 2.5 m yielded 200+% coverage of the wreck. Multibeam data provide centimeter resolution of the site's bathymetry, and a subset of 6000+ overlapping digital images were used to generate a continuous photomosaic of the entire wreck at sub-centimeter resolution. The full survey of the 20 m x 7 m wreck took approximately 18 hours. The second season in 2006 resulted in the survey of a historic period warship. The combination of digital imagery and sonar data reveal information about these wrecks that would otherwise be difficult to quantify. For instance, the orientation, location, number, and preservation state of amphora cargo elements observed in high-resolution imagery can be used to determine the vessel's origin and order of lading. Additionally, first-order archaeological questions can be answered: age of the wreck, cultural origin of the vessel, dimensions of the site, computation of three-dimensional cargo estimates, and possibly cause for the vessel's loss.