Techniques for Underwater Archaeological Research
An important aspect of project design is likely to be managing the logistics of operating from a boat and of managing diving operations. Archaeological techniques and equipment applicable to underwater sites include:
Position fixing. Marine sites are typically located using GPS. Historically, sites within sight of the shore would have been located using transects. A site may also be located by visual surveying some form of marker (such as a buoy) from two known (mapped) points on land.
Remote sensing. Sensitive sonar, especially side-scan sonar may be used to image an underwater site. Magnetometry can be used to locate metal remains such as metal shipwrecks, anchors and cannons. Sub-bottom profiling utilises multi-beam sonar to detect structures buried beneath sediment.
Remotely Operated Vehicle (ROV). Where it is not practical or safe for divers to physically visit a site, video cameras can be steered from the surface.
3D survey[1]. Three dimensional surveying is typically undertaken using depth gauges and tape measurements.
Photography and Photomontage or Photomosaic. Cameras, including video cameras can be provided with special housings that enables them to be used underwater. A series of photographs can be taken at adjacent points and then combined into a single image of the whole site.
Underwater Excavation. Where intrusive excavation is appropriate, silts and sediments can be removed from an area of investigation using a water dredge or air lift. When used correctly, these devices have an additional benefit in tending to improve the visibility in the immediate vicinity of the investigation.
Scale drawing can be undertaken underwater. Pencils will write underwater on permatrace, plastic dive slates, or matt laminated paper.
Archaeological Science. Dendrochronology is an important technique for dating the timbers of wooden ships. It may also provide additional information, including the area where the timber was harvested (i.e. likely to be where the ship was built) and whether or not there are later repairs or reuse of salvaged materials. Because plant and animal material can be preserved underwater, archaeobotany and archaeozoology have roles in underwater archaeology. For example, identification of pollen samples from sedimentary or silt layers can provide information on the plants growing on surrounding land and hence on the nature of the landscape. Information about metal artefacts can be obtained through X-ray of concretions. Geology can provide insight into how the site evolved, including changes in sea-level, erosion by rivers and deposition by rivers or in the sea.
Conservation [2]. Artefacts recovered from underwater sites need stabilisation to manage the process of removal of water. The artefact either needs to be dried carefully, or the water replaced with some inert medium (as in the case of The Mary Rose). Artefacts recovered from salt water, particularly metals and glass need to be stabilised following absorption of salt or leaching of metals. In-situ conservation of underwater structures is possible, but consideration needs to be given to the dynamic nature of the site. Changes to the site during intrusive investigation or removal of artefacts may result in scouring which exposes the site.
Interpretation and Presentation of Underwater Archaeology
Diver trails can be used to allow scuba-divers to visit and understand archaeological sites that are suitable for scuba-diving. Otherwise presentation will typically rely on publication (book or journal articles, web-sites and electronic media such as CD-ROM). Television programmes can attempt to provide an understanding of underwater archaeology to a broad audience.
http://en.wikipedia.org/wiki/Underwater_archaeology 