Underwater closed-circuit television has been in use for some years. It first achieved a notable success in locating a sunken submarine on the bottom of the English Channel in 1951. Underwater television has found some applications in biological work, having advantages over photography in allowing immediate, continuous observation. The apparatus is more complex and costly than photographic cameras, and there are greater difficulties in its use at very deep levels (Barnes, 1963). As yet, it is not often used in the deep sea because of the very heavy power drain from the cables connecting the camera to the surface ship. Fibre optics may help to resolve this problem in the future.
Television cameras can be mounted on towed underwater sledges along with still cameras. The television signals give a continuous record of the strip of sea bottom traversed by the sledge, and colour photographs show greater detail of particular areas (Holme and Barrett, 1977). If the distance travelled by the sledge is measured, then quantitative estimates of fauna can be made.
In recent years, high-resolution video cameras have been developed and used attached to submersibles or free vehicles. This system was used to survey the remains of the Titanic after she was discovered in 1985. In biology, such video footage has proved of great use in studying the behaviour of deep-sea animals such as those around deep-sea vents (see Section 6.4.4).
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