True 3D High Resolution imagery of a Buried Shipwreck: the Invincible (1758)

This paper will present the first true 3D high resolution acoustic imagery of a wreck site buried in the marine environment. Using a 3D Chirp system developed at the University of Southampton, a marine seismic survey of the mid-eighteenth century wreck site has been undertaken. The Invincible was a 74 gun warship built by the French in 1744, captured by the British in 1747 and subsequently lost off Portsmouth, UK in February 1758. The wreck was re-discovered by divers in 1979, partially buried on the margins of a mobile sandbank in approximately 8 metres of water. In 2004 the system was surveyed using a 60 channel, rigid framed 3D Chirp (1.5-13 kHz source sweep) system with integral RTK GPS and attitude systems. An area of 160 m x 160 m, centered over the wreck site, was surveyed with a total of 150 Gb data being acquired. The data was processed, using 3D Promax, to produce 25 cm bins with typical 3-6 fold coverage. The stacked traces have been visualized and interpreted using Kingdom Suite software. The final imagery shows at unprecedented resolution the full three-dimensional buried form of the wreck and it's relationship to the surrounding sedimentary sequences, enabling the full evolution of the site to be discussed. Further, the data is compared to previously acquired swath bathymetry and 2D seismic data in order to illustrate the impact of such a device for underwater cultural heritage management.