Sonar (originally an
acronym for
SOund
Navigation
And
Ranging) is a technique that uses
sound propagation (usually underwater, as in
submarine navigation) to
navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar":
passive sonar is essentially listening for the sound made by vessels;
active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of
acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of
radar. Sonar may also be used in air for robot navigation, and
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 acoustic frequencies used in sonar systems vary from very low (
infrasonic) to extremely high (
ultrasonic). The study of underwater sound is known as
underwater acoustics or
hydroacoustics.
