Page 106 - Manual for Activities directed at the Underwater Cultural Heritage

A survey is usually conducted today using a combination of four techniques:
• Side-Scan Sonar
• Magnetometer
• Swath Bathymetry (Multibeam Echo Sounder)
• Diver (in shallow water) or video/ROV (in deep
water) ground truthing
It is important to train the operating staff well. The time for the project depends on the area covered.
Data collecting should be integrated with GPS- positioning.
A side-scan sonar survey should include overlapping lanes and cross-angles in sufficient redundancy to warrant discovery.
A magnetometer is of no use for submerged sites and of limited use for wooden wrecks predating the use of iron guns.
Multibeam sonar and visual inspection can be deployed to get a better image of an identified irregularity.
A multibeam area survey, also called Swath Bathymetry can be highly revealing, especially at high resolution. It is still, however, an expensive technique, requiring an expert operator. Besides being attractive for archaeology, it is preferred by more and more water and harbour authorities. This means it is useful to try and combine objectives and seek cooperation.
A survey will only detect objects on the surface of the seabed, so always include depth of sedimentation and prediction of potential in a report.
Seismic techniques are generally not finegrained enough to enable the direct location of archaeological sites. The integration of cumulative seismic data in a regional analysis, however, produces fascinating and informative images of submerged palaeolands capes. Large amounts of seismic data have been produced by industry during exploration for mineral resources. This applies to all water regions of the world. Although produced for other purposes, their analysis on the basis of archaeological research questions is highly informative, both in inventory and impact assessment. Hence, also, the importance of desk- based work, using data collected for other purposes.
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Preliminary work