Digital Acoustic Telemetry of Color Video Information

High-speed. and reliable telemetry of color video information from an underwater submersible to a support-ship has been developed for real-time deep-sea viewing. Narrow transmission bandwidth caused by low carrier frequency and comparative bandwidth of ultrasonic transducer make it difficult to transfer enormous color video information over long distances in a short time. Moreover, unsteady acoustic channel and Doppler shift make its reliability lower. High-speed and reliable acoustic telemetry with 4-PSK at 20kbitsisec for 25kHz carrier was realized through development of (i) Wideband Transducer with a single matching plate that more than doubles the bandwidth, (ii) Image Coding based on Discrete Cosine Transform(DCT) that reduce color video information to 2bits/pixel, and (iii) Adaptive Equalizer with Phase Controller that removes the intersymbol interference and compensates for the Doppler shift. A field experiment with the test system, beamwidth 35" for source, and 40" for receiver, has sucessfully achieved a 7 second transmission of 256x256 pixels color image at the range of 3,500m.