Maritime archaeologists are increasingly required to investigate important sites in a nondestructive manner. Therefore, this thesis aimed to adapt and apply sub-bottom acoustic techniques to shallowly buried shipwrecks and submerged palaeo-landsurfaces. The imaging of archaeological sites requires a geophysical source with high resolving power. A model was developed to determine the vertical resolution of the Chirp sub-bottom profiler, the source used throughout this thesis. The horizontal resolution, on the other hand, was determined by modelling the directivity pattern of an array of Chirp transducers. The results were then used to choose a suitable Chirp sweep to image shallowly buried objects. Three sites were selected to test the ability of the system to image, reconstruct and characterize archaeological material. The first site comprised of a shipwreck buried within muddy riverine sediments: the Grace Dieu (1418). The survey utilized both a 2D- and 3D-Chirp system. In both cases, the source was pushed over the site by divers. Close survey line spacing, accurate navigation and decimeter-scale resolution data enabled the construction of a pseudo- and full 3D-image of the site. In the second site, the Yarmouth Roads Wreck (16th century), an acoustic blanking zone, a consequence of the highly attenuating character of degraded wood, was detected and used to create maps of the buried remains. The final site concentrated on the detection of peat layers in the English Channel, which are crux to palaeo-landscape reconstructions. Results suggest that peat buried in fine to medium grained sediments has an easily identifiable acoustic signature. The seismic data acquired for the aforementioned case studies was subsequently used for quantitative studies of the buried material. Firstly, reflection coefficients were calculated and used to determine the degradation state of the hull remains. Secondly, the Quality factor was calculated for the Yarmouth Roads Wreck site to objectively demonstrate the highly attenuating character of degraded wood buried in sediments in comparison to the surrounding sediments. Overall, this PhD has demonstrated the potential of the Chirp sub-bottom system for archaeological purposes, by creating (pseudo-) 3D reconstructions and making object characterization possible.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:440603 |
| Date | January 2007 |
| Creators | Plets, Ruth Mieke Karen |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/48831/ |
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