ASDIC

n. device used for underwater detection of submarines

SONAR (SOund NAvigation and R anging) — or sonar — is a technique that uses  sound propagation under water (primarily) to navigate, communicate or to detect other vessels. There are two kinds of sonar — active and passive. Sonar may be used as a means of  acoustic location.Acoustic location in air was used before radar. Sonar may also be used in air for robot navigation while SODAR (an upward looking in-air sonar) is used for atmospheric investigations.The term sonar is also used for the equipment used to generate and receive the sound. The frequencies used in sonar systems vary from infrasonic to ultrasonic.
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Noun
1. a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return; sonar is an acronym for sound navigation ranging; asdic is an acronym for anti-submarine detection investigation committee
(synonym) sonar, echo sounder
(hypernym) measuring instrument, measuring system, measuring device
(part-holonym) submarine, pigboat, sub, U-boat
(part-meronym) pinger

asdic /'æzdik/
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