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Equipment Class: Fishing technologyEquipment Type: Wheelhouse
Sonar is an apparatus that uses sound waves to detect objects underwater by measuring or classifying the echoes received from them. An echosounder is a sonar that transmits vertically. In practice, a sonar is an apparatus other than an echosounder, i.e., a sonar transmits horizontally.
The electronics industry has rapidly developed other forms of echosounders such as sonar, which is based on a manoeuvrable transducer capable of being directed like a torch around the vessels to search for fish. Modern versions of sonar are able to electronically sweep the area around the vessel, rather than by mechanically manipulating the transducer. This increases the area scanned, improves reliability and reduces the cost of the equipment.

Sonar detection instrument
Sonar detection instrument
Courtesy of JRC

Because of difficulties in displaying a three-dimensional image on a two-dimensional screen, modern sonars show "slices" of the area around the vessel. These "slices" can be in any direction because they are manipulated electronically, and the display is similar to that of a radar. Coloured displays linked to navigational equipment give the true track and speed of the targets. Used primarily for detecting midwater targets such as pelagic fish, the modern version can also be used for navigating or fishing with trawls in areas where there is limited knowledge of the bottom strata.

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