SONAR – an abbreviation for “Sound, Navigation, And Ranging” – can be passive or active. 

A passive SONAR system consists of a sound receiver, signal processor, and display unit; an active SONAR system adds a sound transmitter. (In some active systems the sound transmitter and sound receiver are combined into a component referred to as a "transducer" or "echo sounder.") A SONAR operation sometimes is referred to as “sounding.”

A passive SONAR system listens, processes, and displays detected sound, while an active system also creates pulses of sound (often called “pings”) and transmits them into the water. When transmitted sound waves strike objects or surfaces, they rebound or echo. As echoes strike the SONAR receiver, they are converted back into electrical signals, amplified by the receiver, processed, and sent to a display unit.  Pulses of sound can be created electronically with a SONAR “projector” (a signal generator, power amplifier, and electro-acoustic transducer), with mechanical or air driven equipment, and with explosives.

To determine the distance to an object (called “echo sounding”), the time from transmission of a pulse of sound to the reception of that pulse’s echo is measured and used to calculate the range (the speed of sound in water is approximately 4,800 feet per second). See Single-Beam SONAR.

See projects where Substructure used SONAR technology.