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SUMMARY The main subject of this investigation is to perform research and development and verification experiments on underwater communications (underwater visible light communications; VLCs) under the assumption that VLC can be used for tourism and environmental protection under the ocean conditions of the Okinawa region (Zamami village), which is one of the most popular diving spots, with the most transparent water and abundant coral and fish. Radio is rarely used as a communications tool underwater because the attenuation rate of radio signals is high. The only communications tool now available under water is sonic (ultrasonic) communications, although it has not spread among divers because it is subject to noise from reflections of the water surface or the sea floor, and its use is not simple. Another disadvantage of this mode of communication is that it is very difficult to identify the speaker when several divers are present in the same area. With the underwater VLC device, most of the underwater communications problems are already solved, for the following reasons: (1) the device is easy to move and does not involve cables; (2) it is much easier to capture another person's words because communication does not diverge as sonic communication does; (3) conversation is much easier since the other party can recognize the speaker visually. [ABSTRACT FROM AUTHOR]