Acoustic Telemetry Of Video Information

Increasing use of underwater instrumentation packages and remotely operated submersibles is giving rise more frequently to applications where availability of an acoustic link for telemetry of video information would be useful. Such links are very sensitive to multipath interference which is an often present property of underwater sound propagation. Successful operation is normally limited to certain ideal situations which minimize multipath such as near vertical links in deep water. However, by using narrow beam transducers, alignment of the link with the most direct or robust path between two underwater points will reduce or eliminate any multipath interference common in coastal waters. This paper documents the use of a narrow beam (\simeq 1\deg) acoustic link to transmit slow-scan video frames underwater for distances up to 300 metres. The transudcer projected the beam at an angle of10\degdown from horizontal with a source level of 234.5 dB re1 \muP at 1m. Very good quality frames could be received continuously at 8.5s intervals when the receiving hydrophone was properly located in the beam. Attempts were made to relate the video quality to pulse modulated carrier measurements.