3D reconstruction of a shallow archaeological site from high-resolution acoustic imagery: The Grace Dieu

Acoustic imaging and characterisation of buried objects (and in particular archaeological materials) in shallow-water (<5 m) is often unsuccessful owing to problems related to vessel-induced bubble turbulence and the restricted acoustic geometry of the system. A 2D surveying method that tackles these problems has been tested on the known wreck of the Grace Dieu (1418), Henry V’s flagship, currently buried within the inter-tidal sediments of the Hamble River. The wooden hull is recognisable in the seismic sections as a high amplitude anomaly underlain by an acoustic blanking zone. Close survey line spacing (ca. 1 m) allowed the construction of time slices, identifying the ovate plan of the hull. High, predominantly negative, reflection coefficients suggest this anomaly corresponds to degraded oak timbers buried within the sediment. Combining the data enabled the construction of a (pseudo)-3D image, revealing the dimensions and shape of the hull remains for the first time.