Sound Ranging Observation Post

the receiving (shore) portion of an oceanic hydroacoustic system for the determination of the location of a ship or airplane that produces acoustic signals propagating in an underwater sound channel over very great distances (thousands of kilometers). In the Atlantic Ocean the sound channel is at a depth of about 1,200–1,500 m, and in the Pacific it is at about 500–700 m.

A sound ranging observation post consists of an acoustic antenna (a system of hydrophones), which is placed on the continental slope at the depth of the sound channel’s axis; a submarine cable to connect the antenna with the apparatus on the shore; amplifiers; indicating and recording equipment; timing instruments; data transmission facilities; and electric power sources. In case of emergency, a special small bomb weighing 1–2 kg is dropped from the ship or airplane and explodes at the depth of the sound channel’s axis. The acoustic wave that propagates after the explosion is received by several pairs of sound ranging posts (no fewer than two pairs, of which one station can be common). According to the difference in the time of arrival of the acoustic signal at the pairs the site of the explosion or emergency is determined to an accuracy of about 5 miles (about 10 km) at distances of 2,000 miles (about 4,000 km).

Sound ranging observation posts can also be used to receive conventional signals from a submarine, to permit a submarine to fix its position according to the arrival time of acoustic signals, and to give warnings of an approaching storm or tsunami by means of the infrasonic vibrations created by such phenomena.