Sonar

Sonar, acronym for Sound Navigation and Ranging, technique used at sea for detecting and determining the position of underwater objects (e.g., submarines, shoals of fish) and for finding the depth of water under a ship's keel. Sonar works on the principle of echolocation. High-frequency sound pulses are beamed from the ship, and the direction of and time taken for any returning echoes are measured to give the direction and range of the reflecting objects.