Underwater Audio Communication

communication established in an aqueous medium by the radiation and reception of modulated audio-frequency or ultrasonic oscillations. It is used for two-way contact between ships, between ships and shore installations, and between surface ships and deep-water apparatus, divers, and scuba divers. In addition to the complicated, heavy shipboard apparatus for underwater communication, light, portable transceivers that are mounted directly on the equipment of a diver or scuba diver, as well as sound ranging stations, are also used for underwater audio communication.

The use of underwater sound signals for communication has long been known (for example, the natives on the New Guinea islands used special drums for underwater communication). Its intensive development began with the appearance of submarines, when it became necessary for them to communicate with each other or with surface ships during long periods of submersion. The development of underwater audio communication was greatly facilitated by the advent of atomic submarines capable of remaining submerged for lengthy periods, by the broad investigation of the depths of the ocean, and by the conduct of important research and rescue work in the oceans.

The principle of operation and the equipment of an underwater communication station are analogous to sonar. How-ever, unlike the sonar, the audio-frequency or ultrasonic oscillations radiated by the station are modulated (using a microphone, telegraph key, or special coding device) by signals that contain the information. At the receiving station of the system the modulated oscillations are again decoded into electrical signals containing the information. The oscillations are most commonly modulated with single-sideband telephone signals. Directional signal transmission and reception, various types of coding of the transmitted information, or masking of the radiated signals with acoustic noise are used for privacy in underwater communications. Under favorable hydrological conditions communications can be maintained at distances of dozens of kilometers. The distance is affected by the radiated frequency (the distance increases with decreasing frequency), the speed of the ship receiving the signals (as the speed increases, the distance decreases, since the noise of the ship’s motion increases), and the hydrological conditions in the communication area.