Facts And History About Sonar
Single-beam sonar usually consist of a combined transmitter / receiver element which usually is mounted pointing straight down toward the bottom. It occurs also other applications, such as forward mounted to detect obstacles or up mounted in underwater vehicles, for example, to detect water or for operations under the ice. Such sonar has a relatively large opening angle, preferably 15-30 °, which leads to the footprint of the base is large, and one loses when details of the terrain. These these units can operate on different frequencies, and 38 KHz have been a common frequency, combining good range with relatively small transducers. Low frequencies causes the sound needs something into the ground. This is exploited by special sonar that is designed to look down in the first few meters below the bottom. These are called bottom penetrating sonar.
Multi-beam sonar
Depth Acquisition of multi-beam sonar.A further development of the sonar is multi-beam sonar, which sends out simultaneous audio signals from the seabed in a fan shape across the vessel's course. For each pulse sent out, scanned thus a certain sector of the sea floor. The data is stored electronically for further processing and possibly the production of bathymetric maps. How broad sector as measured, varies with the type of equipment and water; up to 120 ° are not uncommon. The Norwegian firm Kongsberg Maritime has been a world leader in the development of multi-beam sonar, but also the Danish firm Reson is the market leader in parts of the market.
Modern multi-beam sonar is usually constructed by the sender and receiver are separated and mounted as a cross or a "T". By using a "far" element, in relation to the wavelength that provides a wave front spreading in a narrow beam from the transmitter element. This is usually mounted along the vehicle so that the fan spread out perpendicular from the item. The receiver element is mounted 90 ° in relation to sending the item and each consists of many smaller elements that are managed and picks up the signal separately. By detect time differences between the arrival of the various the elements in the receiver, one can calculate where the beam came from. In order to place a depth of the bottom must of course have control of all parameters that affect the measurements: The vessel's position and orientation (training, HIV, roll and stamp) in sending and receiving time is important because these provide the basis for calculations. But the speed of sound in the entire water column is necessary to have knowledge of, because sound waves are broken / suspend in accordance with Snell's law. All this makes a multi-beam sonar to a very complicated system that typically costs several million Norwegian kroner.
Uses
Sonar can be used to identify schools of fish. For trawl fisheries and other sea meant sonar therefore a technological revolution during the 1900s. Today, the fishing boat and other small fishing vessels fish finder on board. Some larger recreational vessels may also be equipped with sonar.
Sonar meant a revolution in surveying the seabed, so-called bathymetry. While the one measurement at greater depths with a plumb line could take much of a day, could now make several measurements in minutes. In shallow water can modern multi-beam sonar collect up to depths of 40,000 per second.
NHS (Norwegian Hydrographic Service) Operating in 2009, four multi-beam sonar, all delivered by Kongsberg Maritime: Two Em3002D, one Em710 and one Em1002 (spare)
History
Titanics loss in 1912 gave impetus to the research on underwater measurements. In 1914, the American Reginald A. Fessenden, Who had previously worked with Thomas Edison, Prepare a "Iceberg Detector and Echo Depth Sounder". Fessenden detector sent out an ultrasonic pulse in front of the vessel to listen for echoes from underwater section of the icebergs provided.
During World War Fessenden engaged in work on systems for localization of submarines. After the war began with attempts to correct soundings down for the measurement of the sea floor, and in 1922, Fessenden detector first used to produce a continuous profile of the seabed, on board the U.S. naval vessel USS Stewart.