Asonobuoy (aportmanteau ofsonar andbuoy) is a small expendable sonar buoy dropped from aircraft or ships foranti-submarine warfare orunderwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on the water, sonobuoys have both aradio transmitter above the surface andhydrophone sensors underwater. Sonobuoys are mission-critical platforms for enhancing Undersea Domain Awareness (UDA), providing an effective means to detect, locate, and track submarines and other underwater threats. Playing a key role in anti-submarine warfare (ASW) and other naval operations, they support in maintaining naval security and in protecting naval carrier strike groups.
Sonobuoys are ejected from aircraft in canisters and deploy upon water impact. An inflatable surface float with aradio transmitter remains on the surface for communication with the aircraft, while one or morehydrophone sensors and stabilizing equipment descend below the surface to a selected depth that is variable, depending on environmental conditions and the search pattern. The buoy relaysacoustic information from its hydrophone(s) viaUHF/VHF radio to operators on board the aircraft.
With the technological improvement of thesubmarine in modern warfare, the need for an effective tracking system was born. Sound Navigation And Ranging (SONAR) was originally developed by the British—who called itASDIC—in the waning days ofWorld War I. At the time the only way to detect submarines was by listening for them (passive sonar), or visually by chance when they were on the surface recharging theirbattery banks. Air patrols (the British mostly used smallairships which had the advantage of long endurance) could spot surfaced submarines and occasionally, when conditions were right, even submerged ones as the diving depth of submarines of the era was so limited. If contact was made, they would follow the submarine while summoning surface ships by radio to attack it.
Sonar saw extremely limited use and was mostly tested in theAtlantic Ocean with few naval officers seeing any merit in the system. With the end of World War I came the end to serious development of sonar in the United States, that fact was to be reinstated in the early days ofWorld War II. While the United Kingdom pursued the development of sonar during the interwar period, theUnited States Coast and Geodetic Survey during the 1920s developed theradio acoustic ranging method of fixing the position ofsurvey ships duringhydrographic survey operations by detonating a small explosive at the location of the ship, recording the time it took for the sound of the explosion to reach distanthydrophones mounted at shore stations or aboard crewed station ships, and radioing the time of receipt of the sound to the ship, allowing the crew to make precise position fixes by usingtriangulation. In 1931, the Coast and Geodetic Survey proposed the replacement of crewed station ships with "radio-sonobuoys", and placed the new buoys in service beginning in July 1936. These buoys weighed 700 pounds (320 kg), could be deployed or recovered by Coast and Geodetic Survey ships in five minutes, and were equipped with subsurface hydrophones, batteries, and radio transmitters that automatically sent a radio signal when their hydrophones detected the sound of a ranging explosion. These "radio-sonobuoys" were the ancestors of the sonobuoys that began to appear in the 1940s.[1][2][3][4]
The damage inflicted upon the Allies by GermanU-boats during World War II made the need for sonar a priority. With millions of tons of shipping being sunk in the Atlantic,[5] there was a need to locate submarines so that they could be sunk or prevented from attacking. Sonar was installed on a number of ships along withradar andhigh-frequency direction finding ("Huff-Duff") to detect surfaced submarines. While sonar was a primitive system, it was constantly improved.
Modern anti-submarine warfare methods evolved from the techniques devised for the movement of convoys and battle groups through hostile waters during World War II. It was imperative that submarines be detected and neutralized long before the task group came within range of an attack. Aircraft-based submarine detection was the obvious solution. The maturity of radio communication and sonar technology made it possible to combine a sonar transducer, batteries, a radio transmitter and whip antenna, within a self-contained air-deployed floating (sono)buoy.
Early sonobuoys had limited range, limited battery life and were overwhelmed by the noise of the ocean. They first appeared during World War II, in which they first were used in July 1942 byRAF Coastal Command under the code name 'High Tea', the first squadron to use them operationally beingNo. 210 Squadron RAF, operatingSunderlands. They were also limited by the use of human ears to discriminate man-made noises from the oceanic background. However, they demonstrated that the technology was viable. With the development of better hydrophones, thetransistor and miniaturization, and the realization that very low frequencysound was important, more effective acoustic sensors followed. The sonobuoy went from being an imposing six-foot (1.8 m) tall, two-foot (0.61 m) diameter sensor to the compact suite of electronics it is today.
The advancement in sonobuoy technology were to be later used to aid anti-submarine aircraft such as theP-2 Neptune,S-2 Tracker,S-3B Viking andP-3 Orion.
Sonobuoys are classified into three categories: active, passive and special purpose.
This information is analyzed by computers, acoustic operators andtactical coordinators to interpret the sonobuoy information.
Active and/or passive sonobuoys may be laid in large fields or barriers for initial detection. Active buoys may then be used for precise location. Passive buoys may also be deployed on the surface in patterns to allow relatively precise location bytriangulation. Multiple aircraft or ships monitor the pattern either passively listening or actively transmitting to drive the submarine into the sonar net. Sometimes the pattern takes the shape of a grid or other array formation and complexbeamformingsignal processing is used to transcend the capabilities of single, or limited numbers of, hydrophones.
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 The Sonobuoy Indicator Group AN/AQA-1: Operation |
