Page 81 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

60 Maritime Archaeology: A Technical Handbook, Second Edition
(Bass and Joline, 1968), although they are somewhat difficult to use in locat- ing sites. Obviously these systems are unlikely to be effective in deep-water searches over large areas of the seabed due to their limited field of view, the difficulty in controlling a search pattern in deep water, and the limited range. Such systems are more likely to be useful in the final location and inspection phase of a deep-water search and in the survey of these deep- water sites.
The use of the ROV is also an interesting development for maritime archaeology. In the majority of cases video cameras are placed onboard an ROV and used in deep-water site inspection. Recent examples of the use of this type of system were with the discovery of the Titanic (Ballard and Crean, 1988), the Bismark (Ballard and Archbold, 1991), HMS Hood (Means, 2002) in the mid-Atlantic, and the discovery of HMS Breadalbane (McInnis, 1982) in northern Canada. Not only can deep-water sites be inves- tigated in a nonlife-threatening situation, but the instrument also can be deployed for long periods of time allowing leisurely inspection of sites. Obviously, there would be little justification to use a large-scale ROV in very shallow water, but from depths beyond 20 m, depending on the nature of the work, such systems could be very useful. It seems that the ROV is most likely to be used in the predisturbance survey of a site, because they usually have limited mechanical ability. In these searches, a towed acoustic and visual vehicle (Argo) was used to produce detailed information about the seabed.
The advent of the autonomous underwater vehicle (AUV) ROV is a new development. AUVs are unmanned, untethered submersible ROVs that are capable of carrying out work autonomously. Examples of AUVs include: the EAVE-III vehicles of the Marine Systems Engineering Laboratory (part of the Autonomous Undersea Systems Institute), the Ocean Voyager and Ocean Explorer vehicles of Florida Atlantic Univer- sity, the Odyssey vehicles at MIT Sea Grant, and the Phoenix AUV at the Naval Postgraduate School. These vehicles are capable of being pro- grammed to conduct an autonomous search of the seabed, gathering a range of data, and then returning to the mother vessel where the unit is recov- ered and these data downloaded and analyzed. A recent technical problem with the AUV system has been described by Hocker (personal communi- cation 2002). He indicated that during the time taken to conduct an exten- sive AUV survey, there is generally no feedback of data from the unit to the operator, consequently, targets of interest that need to be re-examined have to undertaken after the survey. Where one is looking for a particular site or where the AUV produces a poor quality image, the system has to be reprogrammed and sent on a further mission, all of which is time consum- ing and expensive.