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Abstract
Creating photo‐mosaics and plans of submerged archaeological sites quickly, cost‐effectively and, most importantly, to a high level of geometric accuracy remains a huge challenge in underwater archaeology. This paper describes a system that takes geo‐referenced stereo imagery from a diver‐propelled platform and combines it with mapping techniques widely used in the field of robotic science to create high‐resolution 2D photo‐mosaics and detailed 3D textured models of submerged archaeological features. The system was field tested on the submerged Bronze Age town of Pavlopetri off the coast of Laconia, Greece, in 2010. This paper outlines the equipment used, data collection in the field, image processing and visualization methodology.
Acknowledgements
This work was supported by the Australian Research Council Centre of Excellence programme, the Institute of Aegean Prehistory, The University of Nottingham, The British School at Athens, The Hellenic Ministry of Culture and The Municipality of Voiai. Special thanks to Dr Angeliki Simosi (Director of the Ephorate of Underwater Antiquities), Elias Spondylis (the Greek Director of the Pavlopetri Project), Aggelos Mallios, Dimitris Sakellariou and the Hellenic Centre for Maritime Research for their help in facilitating operations at Pavlopetri. Without the support of Professor Cathy Morgan, Tania Gerousi, Chrysanthi Gallou and the diver‐rig field team (Gemma Hudson, Peter Campbell, Kirsten Flemming, Ariell Friedman, Robin Harvey, Derek Irwin and Stefan Williams) the work could not have taken place.
Notes
1. The biggest difference from an AUV configuration, apart from lack of propulsion, was the absence of a Doppler Velocity Log (DVL) which provides very accurate motion estimates in real‐time for automated vehicles so they can follow a desired trajectory. This data can be used to complement image‐based motion calculations. A swath bathymetry unit, such as an Imagenex DeltaT 260-kHz, can also be used to complement the data. However, it was felt that this extra cost was not necessary in terms of achieving further accuracy or outputs. In this application the detailed bathymetric maps produced depend on the visual maps because in the process of creating the 3D mosaic we estimate the camera poses (using SLAM). If swath bathymetry was also carried out it would be these camera poses that we would then ‘hang’ the multibeam range data/swaths to create a cloud of 3D acoustic soundings. These could then be turned into a Digital Elevation Model (DEM) by binning.