summarizes a range of geophysical instruments and

techniques that can be useful in an underwater archae-

ological project, including:

• acoustic systems (see below);


• magnetometers;


• submersibles – remotely operated vehicles (ROVs),
  autonomous underwater vehicles (AUVs).

SEARCH PATTERNS, NAVIGATION AND

POSITIONING

The search patterns appropriate to diver investigations of

the sea-bed (see chapter 12) are also appropriate to larger

scale investigations, the differences being in the scale

of operations and the method of location control. For a

marine geophysical survey it is essential to plan the track

of the vessel so that there is total coverage of the search

area. This usually involves the survey boat following

parallel lines at set distances apart, the distance propor-

tional to the coverage of the instrument and any overlap

required. For intensive work, the overlap is often more than

100 per cent and, to guarantee total coverage and provide

a different viewpoint, two corridor search patterns at

90 degrees, or even three at 60 degrees, to each other may

be considered. Any decisions regarding line spacing and

line direction will depend on the type of equipment

S

ince the 1960s a variety of marine geophysical tech-

niques have been used to investigate a range of sub-

merged archaeological sites, with the principal aim

of site prospection. More recently the emphasis of archaeo-

logical research has moved away from pure prospection

towards a fuller understanding of individual sites in terms

of detailed site mapping, the wrecking event, site-formation

processes, and ultimately the development of heritage-

management strategies for conservation and protection.

A significant advantage of geophysical surveying is the

ability to collect large amounts of information quickly, often

at some distance from the target. This allows search pat-

terns to be much more widely spaced and undertaken

at a greater ‘speed over the ground’ than could ever be

achieved by divers. Some types of equipment can detect

certain classes of information that are buried and out of

the sight of divers. Furthermore, restricted underwater

visibility and strong currents are less of a problem for

geophysical survey instruments and, in many instances,

they can be deployed in sea conditions worse than those

in which divers can safely operate. However, these tech-

niques should not be seen as ways of removing divers from

underwater archaeological investigation, but as tools

which can both enhance the effectiveness of diver inves-

tigation and extend the range of environments in which

underwater survey can be undertaken.

Geophysical survey in archaeology is generally con-

cerned with research and/or site management. This chapter

Geophysical and

Remote-Sensing Surveys

Contents

u Search patterns, navigation and positioning

u Acoustic systems

u Bathymetric survey

u Echo-sounders

u Multibeam swath systems

u Bottom-classification systems

u Sidescan sonar

u Sub-bottom profiling

u Magnetometry

u Integrated surveys

u Submersibles: ROVs and AUVs

u Aerial photography

13

Underwater Archaeology: The NAS Guide to Principles and Practice Second Edition Edited by Amanda Bowens
© 2009 Nautical Archaeological Society ISBN: 978-1-405-17592-0