Digital acoustic video image transmission system for deep‐sea research submergence vehicle ‘‘SHINKAI 6500.’’

High‐speed video image transmission from a research submersible to the mother ship is desirable to facilitate effective deep‐sea research by a submersible. Therefore, a digital acoustic image transmission system was developed, and was installed in the manned deep‐sea research submergence vehicle ‘‘SHINKAI 6500’’ of the Japan Marine Science and Technology Center. This system which adopts 4‐DPSK modulation with a carrier frequency of 20 kHz, has a communication capability of 16 kbit/s and is able to transmit a color‐still image of 256×240 pixels in 8 s. Its communication range is more than 6800 m. In order to transfer a high‐quality color image in a short time, (a) a wide band transducer, that doubles the transmission band, (b) a DCT‐ (discrete cosine transform) based image coding technique that reduces transmission data volume, and (c) an adaptive equalizer and phase controller, that improve communication quality and Doppler compensation, are employed. Results of a performance test (various video images) w...