3D reconstruction of a shallow archaeological site from high-resolution acoustic imagery - a case study

This paper compares a 2D and 3D-Chirp geophysical investigation of a buried shipwreck: the Grace Dieu (1418). The site, covered by 2-5m of water, is buried within muddy inter-tidal sediments. At exceptionally low tides, a few of the marginal timbers are exposed. The marine survey utilised a 2D-Chirp systems with a DGPS navigational system, and a 3-Chirp system with RTK-positioning capability. In both cases, the source was towed over the site by divers. Close survey line spacing, accurate navigation and decimetre scale resolution data enabled the construction of a pseudo- and full 3D-image of the site, which were calibrated against an RTK-GPS-terrestrial survey. The exercise demonstrated the improved spatial resolution provided by the 3D-Chirp system and the ability of a well-constrained 2D survey to produce a pseudo-3D reconstruction of the gross ship structure.