Sonar (originally an acronym for sound navigation 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 essential 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. 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.
The first recorded use of the technique was by Leonardo da Vinci in 1490 who used a tube inserted into the water to detect vessels by ear. It was developed during World War I to counter the growing threat of submarine warfare, with an operational passive sonar system in use by 1918.[2] Modern active sonar systems use an acoustic transponder to generate a sound wave which is reflected back from the target object
Prior to the advent of sonar, mariners used lead lines to take systematic ‘soundings’ of the seafloor, which enabled them to produce early depth charts and bathymetric maps. Sonar was first used during World War I to detect submarines. By the 1920s, the U.S. Coast and Geodetic Survey—the precursor to NOAA’s National Ocean Service—was using it to map deep-water areas. The technology steadily improved, and by World War II, was used once again for military purposes.
In the 1960s, the development of digital computer technology made plotting of sonar data much easier, but this technology was not available to the civilian scientific community until the U.S. Navy declassified it in the 1970s.
NOTE: Text based and compiled from Wikipedia, Urick, and NOAA