Geophysical Techniques for Maritime Archaeological Surveys

Over the last ten years, the high-resolution marine geophysical survey field has witnessed significant advances in survey investigation equipment. New equipment is based on acoustic, optical, electrical, and magnetic sensors. This paper will focus on the use of quantitative acoustic methods for the high-resolution mapping of the seafloor for archaeological heritage management. In particular multibeam sonar and acoustic ground discrimination sonar (agds) were tested at two historic wreck sites on the UK shelf, namely the Stirling Castle, Goodwin Sands, England and the SMS Cöln, Scapa Flow, Scotland. At both sites, acoustic reflection amplitude values were mapped using the single beam sonar over each wreck site and in the immediate wreck vicinity. The amplitude values were analysed with respect to the 3D topography of the site obtained mapped from very high resolution bathymetric surveying using the multibeam sonar. Subsequent ground truth inspection based on the maps produced from the agds and multibeam sonar was carried out using both diver and ROV observations. Correlations obtained between the remote geophysical surveying and the ground truth observations provided new insight into the current state of the wrecks and the wreck site stability. With increasing pressure on the near shore zone from leisure activities, the extraction industry and environmental changes, there is a great need for rapid mapping and evaluation techniques. Thus the information provided by remote geophysics can be of great benefit not only for mapping what is in these zones today but also for future long-term management of the archaeological heritage.