The History of Sonar

Sonar is a system that uses transmitted and reflected underwater sound waves to detect and locate submerged objects or to measure distances underwater. It has been used for submarine and mine detection, depth detection, commercial fishing, diving safety and communication at sea.

The Sonar device will send out a subsurface sound wave and then listens for returning echoes. The sound data is then relayed to the human operators by a loudspeaker or through a display on a monitor.

The Inventors

As early as 1822, Daniel Colloden used an underwater bell to calculate the speed of sound underwater in Lake Geneva, Switzerland. This early research led to the invention of dedicated sonar devices by other inventors.

Lewis Nixon invented the very first Sonar type listening device in 1906 as a way of detecting icebergs. Interest in Sonar increased during World War I when there was a need to be able to detect submarines.

In 1915, Paul Langévin invented the first sonar type device for detecting submarines called an "echolocation to detect submarines" by using the piezoelectric properties of the quartz. His invention arrived too late to help very much with the war effort, though Langévin's work heavily influenced future sonar designs.

The first Sonar devices were passive listening devices, meaning no signals were sent out. By 1918, both Britain and the U.S had built active systems (in active Sonar, signals are both sent out and then received back). Acoustic communication systems are Sonar devices where there is both a sound wave projector and receiver on both sides of the signal path. It was the invention of the acoustic transducer and efficient acoustic projectors that made more advanced forms of Sonar possible.

Sonar - SOund, NAvigation, and Ranging

The word Sonar is an American term first used in World War II. It is an acronym for SOund, NAvigation, and Ranging. The British also call Sonar "ASDICS," which stands for Anti-Submarine Detection Investigation Committee. Later developments of Sonar included the echo sounder or depth detector, rapid-scanning Sonar, side-scan Sonar, and WPESS (within-pulseectronic-sector-scanning) Sonar.

Two Major Kinds of Sonar

Active sonar creates a pulse of sound, often called a "ping" and then listens for reflections of the pulse. The pulse may be at a constant frequency or a chirp of changing frequency. If it's a chirp, the receiver correlates the frequency of the reflections to the known chirp. The resulting processing gain allows the receiver to derive the same information as if a much shorter pulse with the same total power were emitted.

In general, long-distance active sonars use lower frequencies. The lowest has a bass "BAH-WONG" sound. To measure the distance to an object, one measures the time from emission of a pulse to reception.

Passive sonars listen without transmitting. They are usually military, although a few are scientific. Passive sonar systems usually have large sonic databases. A computer system frequently uses these databases to identify classes of ships, actions (i.e. the speed of a ship, or the type of weapon released) and even particular ships.