Sonar

A technique that uses sound propagation to navigate, communicate with or detect other vessels is sonar, originally an acronym for Sound Navigation And ranging. There are two technologies that share the name sonar. Passive sonar is essentially listening for the sound made by vessels, active sonar is emitting pulses of sound and listening for echo’s. As a historical evidence of sonar we take Leonardo da Vinci who recorded a ultrasonic sound by inserting a tube in 1940.

          Sonar may be used as a means of acoustic location and the 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 radar is used for atmospheric investigations. The acoustic frequencies used in sonar system vary from very low (infrasonic) to extremely high (ultrasonic). In 1930s American engineers developed there own underwater sound detection technology and important inventions like thermo clines were made. After technical information was exchanged between two countries during the Second World War, Americans began to use the term "sonar" for their system, coined as the equivalent of radar. The detection classification and localization performance of sonar depends upon the environment and the receiving equipment.

          Sonar operation is affected by variation in sound speed, which is determined by the waters bulk modulus and mass density. The sonar technology is very much useful and the well practiced technology in the recent days.