sonar = sound navigation and ranging ultrasound . error.

Sonar(originally anacronymforsoundnavigationranging) is a technique that usessoundpropagation (usually underwater, as insubmarine navigation) tonavigate, communicate with or detect objects on or under the surface of the water, such as other vessels.[2]Two types of technology share the name "sonar":passivesonar is essentially listening for the sound made by vessels;activesonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means ofacoustic locationand of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction ofradar. Sonar may also be used in air for robot navigation, andSODAR(an upward-looking in-air sonar) is used for atmospheric investigations. The termsonaris 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 asunderwater acousticsorhydroacoustics.The first recorded use of the technique was byLeonardo da Vinciin 1490 who used a tube inserted into the water to detect vessels by ear.[3]It was developed during World War I to counter the growing threat ofsubmarine warfare, with an operationalpassive sonarsystem in use by 1918.[2]Modern active sonar systems use an acoustictransponderto generate a sound wave which is reflected back from target objects.[2]