A sonobuoy (a portmanteau of sonar and buoy) is a relatively small buoy – typically diameter and long – expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research.
Sonobuoys are ejected from aircraft in canisters and deploy upon water impact. An inflatable surface float with a radio transmitter remains on the surface for communication with the aircraft, while one or more hydrophone 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 relays acoustic information from its hydrophone(s) via UHF/VHF radio to operators on board the aircraft.
With the technological improvement of the submarine 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 it ASDIC—in the waning days of World 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 their battery banks. Air patrols (the British mostly used small airships 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 the Atlantic 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, a fact that was to be fatal in the early days of World War II. However, considerable development of ASDIC took place in the United Kingdom, including integration with a plotting table and weapon.
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Anti-submarine warfare (ASW, or in the older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations are typically carried out to protect friendly shipping and coastal facilities from submarine attacks and to overcome blockades. Successful ASW operations typically involved a combination of sensor and weapon technologies, along with effective deployment strategies and sufficiently trained personnel.
A hydrophone () is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a sound wave. A hydrophone can detect airborne sounds, but will be insensitive because it is designed to match the acoustic impedance of water, a denser fluid than air. Sound travels 4.3 times faster in water than in air, and a sound wave in water exerts a pressure 60 times that exerted by a wave of the same amplitude in air.
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We present high-precision experiments conducted with the aim to better characterise weak deformations of single cavitation bubbles. Using two needle hydrophones and a high-speed photodetector, we record the timings of shock waves and luminescence emitted a ...