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A Life on the Ocean Wave...

The sun is out, the weather is good (mostly), and here at Wessex Archaeology’s GeoServices department we are well into this year’s marine geophysical survey season.  As a major provider of maritime archaeological services in the UK we undertake a number of such surveys every year, at sites located from Cornwall to the Shetland Islands.
 
2445 Marine Magnetometer Deployment
 
As with the more familiar terrestrial ’Geophys’ techniques, marine geophysical surveys are a good way to determine the overall extent of a site and are quicker than intrusive investigations.  This is especially the case for the marine environment, as maritime excavations carry additional complications relative to terrestrial digs – not least the lack of oxygen on site!
 
A number of methods can be used for such surveys.  Multibeam bathymetry and sidescan sonar systems both use sound waves to image the seabed, and can produce 3-D models of a site and detailed images of individual features respectively.  Magnetometers are also commonly used to identify any iron material, either on the seabed or buried beneath.  Other equipment, such as parametric sonar, can be used to ‘see’ beneath the seabed for any buried material.  This equipment can either be towed behind the vessel or attached – either on poles over the side or directly to the hull.
 
2447 Sidescan Sonar Image of a Shipwreck (© Historic Scotland. Prepared by Wessex Archaeology)
 
These surveys can be used in different ways, such as:

Site-specific monitoring of known wreck sites to assess any changes, such as degradation or damage, and the investigation of new potential sites;

Area investigations to ensure areas are free from features of archaeological interest in advance of developments (eg, port extensions and dredging areas);

Investigations of larger sites, such as submerged settlements and old ports.
The results of the surveys can then be used to provide our dive team with possible targets for further investigation and excavation.
 
So, why the sun and good weather?  Well, accurate site investigations need high quality data and, since the equipment is in the water, high quality data needs good weather conditions.  It’s all just a happy coincidence!
They say worse things happen at sea – but hopefully not for at least another year…
 
 
By Dave Howell, Senior Marine Geophysicist
 
 
 
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