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

Abstract

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.

Decimeter-resolution 3D seismic volume in shallow water: A case study in small-object detection

“…Given the low density and thin covering of overbearing sediments, it is difficult to correlate it with a possible source/trap. Similar acoustic signatures have been observed in archaeological sites, where they commonly have been associated with low-density material such as wood/rope and peat layers ͑Quinn et al, 1997a; Quinn et al, 1997b;Arnott et al, 2005;Plets et al, 2007͒. However, the postsurvey dredging failed to identify any material.…”

“…As with target 15, it is not flat; rather, it dips from south to north at a 0.5°angle from horizontal. The vertical sections ͑Figure 10b and c͒ provide a better indication of the size and shape of the migrated horizon, and its reversed polarity suggests that it is a wooden object, probably degraded ͑Quinn et al, 1997a;Quinn et al, 1997b;Arnott et al, 2005;Plets et al, 2007͒. At this location, a wooden railway sleeper 4.0ϫ 0.36ϫ 0.08 m was found ͑Figure 10d and e͒. Heavily degraded, the sleeper broke apart when it landed in the hopper and again when transferred to a skip.…”

The use of a high-resolution 3D Chirp sub-bottom profiler for the reconstruction of the shallow water archaeological site of the Grace Dieu (1439), River Hamble, UK

“…A previous study by Plets et al (2008) demonstrated that a well-constrained 2D Chirp survey managed to image the remains of the Grace Dieu. The site was revisited with a high-resolution 3D Chirp sub-bottom profiling system in order to:…”

“…During the exceptionally low tides of the spring equinox in 2005, the surviving timbers protruding from the mud were surveyed with a terrestrial RTK-GPS system (Fig 4), a procedure which has been described in detail by Plets et al (2008).…”

Detecting submerged objects: The application of side scan sonar to forensic contexts

“…A compressed high intensity radar pulse, also known as a CHIRP, is a sub-bottom profiler used to map the sub-seabed and underwater archeological sites [25][26][27][28][29][30]. This system uses known and repeatable frequency-modulated (FM) acoustic pulses with a desired frequency bandwidth to produce vertical seismic reflection crosssections of the sub-seabed according to their acoustic reflectivity [6,25,26].…”