Marine researchers and animals use sonar in many different ways, but all methods fall into one of two categories: active or passive. Passive sonar Passive sonar simply listens to sound in the ocean environment using an array of receivers. Background sound provides ‘acoustic daylight’, but sources such as ships or calling whales are easily detected. Active sonar Active sonar uses underwater electronic sound generators spaced in an array to produce a beam of pulsed sound that can be swept from side to side like a searchlight: a similar array of receivers detects the echo signals. These echoes can be from the sea floor, from objects such as ships, shipwrecks or submarines, or from animals. Using computers it is then possible to produce maps of the sea floor and to highlight particular sorts of echoing objects, such as rocks, sand, or vegetation. Applications of sonar These sonar techniques are being used for many purposes around Australia, producing maps of the sea floor to determine areas to be set aside as marine park reserves, for studies of the behaviour of marine creatures, to search for ancient wrecks and to assess the numbers or variety of fish in an area for harvesting. Both passive and active sonar are also important in ship navigation and in the surveillance operations of the Australian Navy. Related sites:
Other boxes Box 1. Comparison of the properties of sound in air and water Box 2. Measurement of sound levels Box 4. Disturbing beaching events
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Posted August 2007.
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