Optimising protocols for high-definition imaging of historic shipwrecks using multibeam echosounder
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ORIGINAL PAPER
Optimising protocols for high-definition imaging of historic shipwrecks using multibeam echosounder Kieran Westley 1 & Ruth Plets 1 & Rory Quinn 1 & Chris McGonigle 1 & Fabio Sacchetti 2 & Mekayla Dale 1,2 & Rory McNeary 3 & Annika Clements 4 Received: 7 June 2018 / Accepted: 19 March 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract Conservation of historic shipwrecks is prohibitively expensive and in situ preservation and recording are the preferred archaeological approaches. Non-destructive high-definition 3D imaging is therefore essential for recording and managing submerged historic shipwrecks. Multibeam echosounders (MBES), the standard tool for hydrographic survey, can produce point clouds to image complex 3D structures. However, wreck imaging is often done using MBES in traditional survey mode optimised for morphological characterisation of the seafloor. This does not necessarily provide high-definition imagery required by archaeologists. This study demonstrates key factors influencing high-definition MBES imaging of wrecks through a controlled field experiment. Results show that optimal high-definition 3D imaging is achieved through maximising the pulse rate, narrowing the angular sector, using the highest frequency and shortest pulse lengths, applied to at least 3 to 5 overlapping centreline-parallel and offset passes with additional perpendicular/oblique lines. Variations in survey design are demonstrated to exert strong controls on sounding density and distribution, with high-density on horizontal and vertical wreck surfaces enabled by a combination of overlapping passes and offset lines. Adoption of this method would result in more widespread high-definition 3D imaging of wrecks to benefit archaeological research and develop effective mitigation strategies to minimise loss of the fragile underwater resource. Keywords Multibeam echosounder . Shipwreck . Marine geoarchaeology . Point cloud . High-definition imaging . Best practice
Introduction Shipwrecks are recognised for their cultural and archaeological significance, providing empirical evidence of past trade and migration, technological change, and both shipboard and wider society (Adams 2001; Gibbins and Adams 2001; * Kieran Westley [email protected] 1
School of Geography & Environmental Sciences, Ulster University, Coleraine, Northern Ireland BT52 1SA, UK
2
Marine Institute, Oranmore, Co. Galway H91 R673, Republic of Ireland
3
Historic Environment Division, Department for Communities, Causeway Exchange, 1-7 Bedford Street, Belfast, Northern Ireland BT2 7EG, UK
4
Agri-Food and Biosciences Institute, Fisheries and Aquatic Ecosystems Branch, Newforge Lane, Belfast, Northern Ireland BT9 5PX, UK
Flatman 2003). In some instances, they are monuments to historic events ranging from individual disasters like the sinking of Titanic (Ballard and Archbold 1987) to global conflicts such as the First and Second World Wars (McCartney 2016). Researching and managing historic shipwrecks are linked by the need
