SS: Multibeam Backscatter: Utilization of Multibeam Bathymetry and Backscatter For Documenting and Planning Detailed Investigations of Deepwater Archaeological Sites

Abstract

Abstract In the past, planning detailed visual investigations of deepwater archaeological sites has primarily been done with side scan sonar and subbottom profiler data. Advancements in multibeam bathymetry acquisition and processing, especially of backscatter data, now provide additional ways to view these sites. Deepwater archaeologists have begun to utilize bathymetry and backscatter data to develop better understandings of overall site conditions and attributes. As a result, they are able to develop more cost and time effective investigation plans to detail deepwater sites with increased accuracy. This paper will examine several deepwater shipwreck sites to demonstrate how use of the backscatter and bathymetry data has advanced the investigation methodologies used on deepwater archaeological sites. Introduction Underwater archaeology has long relied on technology to locate and initially document inundated archaeological sites or shipwrecks. For years, side scan sonars, subbottom profilers, and magnetometers have been the primary documentation tools for archaeologists studying sites in both shallow and deep water environs. Within the past decade, with access to new technologies, archaeologists added multibeam systems to their archaeological investigative tool kit. Multibeam bathymetry and backscatter provide high resolution, accurately positioned data that can be easily quantified, repeated, and integrated (Lawrence and Oxley, 2004). Using multibeam data with visualization software now allows three-dimensional (3D) views of archaeological sites from the shallowest lagoons to the deepest ocean reaches. Several innovative projects, including ScapaMap and RASSE, at the beginning of this century resulted in the increased use of multibeam data for archaeological investigations. These cutting edge studies proved the viability of multibeam bathymetry and backscatter for archaeology; they also influenced many areas of underwater archaeology, including deepwater archaeology. Deepwater archaeologists, many in oil and gas related fields, building upon these earlier studies have adopted multibeam data as part of a larger investigation methodology for deepwater shipwreck documentation and interpretation. This paper explores the role multibeam bathymetry and backscatter play within deepwater shipwreck investigation methodologies. Early Projects Using Multibeam on Shipwreck Sites At the beginning of the 21st century, several underwater archaeological projects employed multibeam systems for site documentation. Investigations on the Normandy Coast documented submerged features associated with the D-Day Landings. The project documented diverse submerged features including lost vehicles, vessels sunk as artificial breakwaters, and Mayberry Dock remnants originally used to hasten the supply flow to the beachheads (Mayer, et al., 2003). In Italy, high resolution multibeam surveys mapped the inundated Roman City at Baia and the Roman harbor at Porto Guilio (Wille, 2005). Two projects in the United Kingdom, ScapaMap and RASSE, were the most influential in illustrating the potential for multibeam in archaeology and the most pertinent to multibeams use for deepwater shipwreck studies.