Left to right: 424 CHIRP, sidescan sonar towfish, and Applied Acoustic boomer plate represent three sonar technologies. [larger version]
Sonar is an acronym for SOund NAvigation and Ranging. Sonar methods rely on bouncing sound waves off a target and intercepting the return signal. The outgoing signal is called a 'ping' and the return signal is called an 'echo'. Transducers and hydrophones transmit and receive the sound waves. Distance or target characteristics are determined by measuring the time and strength of the returning echo. Several types of sonar devices are used to map water depths and characteristics of the seafloor bottom.