underwater vehicles

underwater vehicles are used by those studying oceanography and marine archaeology, and they also have application in the offshore oil and gas industries, and for marine salvage and military surveillance. Free-swimming divers can only reach depths of 100 metres (300 ft) with any degree of safety, so if humans are to observe what is deeper than that they either need to descend in pressure-protected containers like a submarine, or send down devices that can ‘see’ into the depths, either on an umbilical, like remotely operated vehicles (ROVs), or free-ranging robotic devices known as autonomous underwater vehicles (AUVs). Early versions had limited manoeuvrability and carried simple sonar and cameras, but modern devices are more manoeuvrable and sophisticated, for example carrying ‘Television and Search and Salvage System’, or TVSS. These have made the use of manned underwater vehicles for commercial and defence applications all but redundant.

The first attempts to make first-hand observations in water as deep as 300 metres (1,000 ft) were by William Beebe who in 1934 had himself sealed in a bathysphere. Then Auguste Piccard (1884–1962), one of the pioneers of underwater vehicles, built the bathyscaphe Trieste, in which his son Jacques, together with Don Walsh, dived to the bottom of the Marianas Trench in January 1960; an achievement repeated in 1995 by a Japanese ROV. In the early 1960s deep submersibles, often referred to as deep submergence vessels (DSVs), began to be developed.

The best known of these DSVs is the Alvin. Funded by the US Navy, it first came into operation in 1964. Among its many achievements, it found a hydrogen bomb lost in the sea off Spain and discovered the rich biological communities that live around hydrothermal vents. Alvin can carry three people, a pilot and two observers, to a maximum depth of 4,500 metres (14,850 ft) from its catamaran support vessel, Lulu. Other underwater vehicles have much shallower depth capabilities, but in the case of the Johnson Sea Link, run by the Harbor Branch oceanographic institute, its Plexiglas compartment gives far better facilities for scientific observation and sample collection.

During the 1980s the Deep Submergence Laboratory at the Woods Hole Oceanographic Institution developed two underwater vehicles, Argo and Jason. They were designed to be used simultaneously from the same support vessel. The Argo was a towed survey vehicle capable of scanning large areas of the ocean bed with sonar, film, and video, but also functioned as the mother ship of the much smaller ROV Jason. When Argo detects something on the seabed that merits closer inspection, Jason is sent to look at it. During an expedition led by Dr Ballard, it was these two vehicles that discovered the Titanic in 1985. They and similar ROVs have also explored the remains of the German battleship Bismarck, ocean liners Lusitania and Britannic, and numerous other shipwrecks of interest to those working in marine archaeology.

Manned underwater vehicles are not only more expensive to run but also, for safety reasons, can only be operated in good sea conditions. So as technology has improved sensors design, information storage, battery power, propulsion, underwater navigation, and the streamlining of the hulls, the ranges of AUVs have increased to hundreds of kilometres with depth capabilities of over a thousand metres. The stimulus for their development has come from the exploitation of deep-water hydrocarbons, science, and military requirements. AUVs can undertake pre-programmed tasks without the need for communication, so they are ideal instruments for seabed surveys, covert surveillance, deep-water inspections, and cable-laying tasks, as well as making scientific observations. The cost of conducting an AUV survey may be a third less than a conventional research ship, and AUVs reach regions that are otherwise inaccessible, such as beneath ice sheets. Robotics will probably have the same sort of impact in revolutionizing our understanding of the ocean as did the development after the Second World War (1939–45) of electronics, sonars, and computers.
www.diveweb.com/rovs/features/mayjune2000.01.htmhttp://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/oceanography_how_deep.html

M. V. Angel