Seeing Underwater - Sonar Explained

If you've ever watched a movie with a submarine

, the chances are you'll be familiar with the word synonymous with navigation underwater sonar. On the other hand though you're less likely to be familiar with how the technology actually works.

Originally developed by the British anti-submarine division in World War One, sonar technology has become widely used in a wide range of fields outside of the original military application. Amazingly, it's actually an example of 'bio-mimetic' technology - basically, nature got their first. Millions of years ahead of humans in fact - sonar is how bats navigate in the dark despite having terrible vision, as well as being used by dolphins for communicating and hunting.

Basically, sonar is a means of acoustic location - locating things via sound. Sonar systems effectively use very low (infrasonic) or very high (ultrasonic) waves to locate objects underwater. Broadly speaking, there are two types of sonar technology: passive and active.

Passive sonar systems simply listen for the sounds and echoes made by other vessels or forms of undersea life. These systems can rarely of use in finding inanimate objects, though the echo from another source of sound can sometimes be used to give some indication of their shape and location. More commonly these systems are used by ships - particularly in warfare; if you don't make sound, you're much harder to see by sonar.

Active sonar systems emit pulses of sounds on the ultrasonic or infrasonic frequencies and can be used to provide a near-real time image of where objects are underwater and their physical characteristics. The pulse is often called a 'ping' (you may remember this noise from the movies) and aside from providing an idea of the position of other vessels and large shoals of fish, it also provides a clear idea of the position of the ocean floor.

The technology may have been developed for military purposes - and indeed still plays a huge part in naval warfare - but it has also proven extremely useful for many civilian maritime applications. Fisheries use sonar to locate their catch, or to locate the position of their nets in the water; sonar devices are used to locate aircraft in case they crash at sea; ships use the technology to navigate shallow waters; and in a field fairly related to its original purpose, its also used as a security measure to counter the threat of sabotage and terrorism at naval bases, commercial ports and oil platforms.

by: Joel Boness

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