Sonar

The term is an acronym for SOund Navigation And Ranging. The technique is a means of underwater echolocation developed by the military for locating submarines. Brief pulses of sound, ranging from 5 to 50 kHz, are emitted in narrow, intense beams. The echoes of these pulses, returning at different time intervals depending on the speed of sound in the medium and the distance they travel before striking a reflective surface, are converted into audible signals and images on a cathode ray screen. The information received defines the objects or surfaces according to their shape and distance from the source.

The technique has been modified for use in underwater mapping and salvage, as well as for location of foreign matter in the human body prior to surgery. The possibility of a sonar substitute for X-rays using ultrasound in the megahertz range has recently been developed.

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