NationMaster - Encyclopedia: SONAR

SONAR (SOund NAvigation and Ranging) — or sonar — is a technique that uses sound propagation under water to navigate, communicate or to detect other vessels. There are two kinds of sonar — active and passive. Sonar may be used as a means of acoustic location. SODAR (sonic detection and ranging) - meteorological instrument which priciple of operation is based on sound waves scattering by atmosheric turbulence. ... Sonar could refer to: Sonar, underwater sound propagation. ... Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... The Georges Leygues class (F70 type) is a type of anti-submarine frigates of the French Navy. ... The La Motte-Picquet is a F70 type anti-submarine frigates of the French Marine Nationale. ... This article is about audible acoustic waves. ... Table of geography, hydrography, and navigation, from the 1728 Cyclopaedia. ... Acoustic location is the art and science of using sound to determine the distance and direction of something. ...

Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation while SODAR (an upward looking in-air sonar) is used for atmospheric investigations. Acoustic location is the art and science of using sound to determine the distance and direction of something. ... For other uses, see Radar (disambiguation). ... SODAR (sonic detection and ranging) - meteorological instrument which priciple of operation is based on sound waves scattering by atmosheric turbulence. ...

The term sonar is also used for the equipment used to generate and receive the sound. The frequencies used in sonar systems vary from infrasonic to ultrasonic. Infrasound is sound with a frequency too low to be detected by the human ear (less than approximately 20 hertz). ... Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ...

The study of underwater sound is known as underwater acoustics or sometimes hydroacoustics. Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ... Hydroacoustics is a general term for the study and application of sound in water. ...

History

Although some animals have probably used sound for communication and object detection for millions of years, the use by humans is initially recorded by Leonardo Da Vinci in 1490. A tube inserted into the water was said to be used to detect vessels by placing an ear to the tube. In the 19th century an underwater bell was used as an ancillary to lighthouses to provide warning of hazards. (NHL ) The use of sound to 'echo locate' underwater in the same way as bats use sound for aerial navigation seems to have been prompted by the Titanic disaster of 1912. The world's first patent for an underwater echo ranging device was filed at the British Patent Office by English meteorologist Lewis Richardson, one month after the sinking of the Titanic, and a German physicist Alexander Behm obtained a patent for an echo sounder in 1913. Canadian Reginald Fessenden, while working for the Submarine Signal Company in Boston, built an experimental system beginning in 1912, a system later tested in Boston Harbor, and finally in 1914 from the U.S. Revenue (now Coast Guard) Cutter Miami on the Grand Banks off Newfoundland Canada. In that test, Fessenden demonstrated depth sounding, underwater communications (Morse Code) and echo ranging (detected an iceberg at two miles (3 km) range). The so-called Fessenden oscillator, at ca. 500 Hz frequency, was unable to determine the bearing of the berg due to the 3 meter wavelength and the small dimension of the transducer's radiating face (less than 1 meter in diameter). The ten Montreal-built British H class submarines launched in 1915 were equipped with a Fessenden oscillator.^[1] â€œDa Vinciâ€ redirects here. ... The Peggys Point lighthouse in Nova Scotia, Canada An aid for navigation and pilotage at sea, a lighthouse is a tower building or framework sending out light from a system of lamps and lenses or, in older times, from a fire. ... For other uses, see Titanic (disambiguation). ... For other uses, see Patent (disambiguation). ... The UK Intellectual Property Office, or UK-IPO, formerly known as The Patent Office,[1] is the lead United Kingdom government agency responsible for developing and administering policy in most areas of intellectual property, under the overall aegis of the Department of Trade and Industry. ... Lewis Fry Richardson (October 11, 1881 - September 30, 1953) was a mathematician, physicist and psychologist. ... Alexander Behm (born 11 November 1880 in Sternberg (Mecklenburg); died 22 January 1952 in Tarp (Schleswig-Flensburg)) was a German physicist. ... Reginald Fessenden (October 6, 1866 â€“ July 22, 1932) was a Canadian inventor, best known for his work in early radio. ... Map showing the Grand Banks Historic map of the Grand Banks. ... Newfoundland may refer to: Newfoundland and Labrador, a Canadian province (known simply as Newfoundland until 2001) Dominion of Newfoundland, an independent country (from 1907 to 1934) Colony of Newfoundland, a British colony prior to 1907 Newfoundland (island), a Canadian island that forms part of the province of Newfoundland and Labrador... Nickname: Motto: Concordia Salus (well-being through harmony) Coordinates: , Country Province Region MontrÃ©al Founded 1642 Established 1832 Government - Mayor GÃ©rald Tremblay Area [1][2][3] - Total 365. ... Length: Beam: 15. ...

During World War I the need to detect submarines prompted more research into the use of sound. The British made early use of underwater hydrophones, while the French physicist Paul Langevin, working with a Russian émigré electrical engineer, Constantin Chilowski, worked on the development of active sound devices for detecting submarines in 1915 using quartz. Although piezoelectric and magnetostrictive transducers later superseded the electrostatic transducers they used, this work influenced future designs. Lightweight sound sensitive plastic film and fibre optics have been used for hydrophones (acousto-electric transducers for in-water use), while Terfenol-D and PMN (lead magnesium niobate) have been developed for projectors. Piezoelectric composite materials are available from several manufacturers including Morgan Electro Ceramics. â€œThe Great War â€ redirects here. ... For other uses, see Submarine (disambiguation). ... Paul Langevin (January 23, 1872 â€“ December 19, 1946) was a prominent French physicist who developed Langevin dynamics and the Langevin equation. ... Year 1915 (MCMXV) was a common year starting on Friday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Thursday[1] of the 13-day-slower Julian calendar). ... Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. ... Electrostatics (also known as static electricity) is the branch of physics that deals with the phenomena arising from what seem to be stationary electric charges. ... A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... Terfenol-D is an alloy of the formula Tb(0. ... Morgan Electro Ceramics (MEC) is a subsidiary of The Morgan Crucible Company plc, MEC forms part of the Morgan Technical Ceramics (MTC) group. ...

In 1916, under the British Board of Invention and Research, Canadian physicist Robert Boyle took on the active sound detection project with A B Wood, producing a prototype for testing in mid-1917. This work, for the Anti-Submarine Division, was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy no mention of sound experimentation or quartz was made - the word used to describe the early work ('supersonics') was changed to 'ASD'ics, and the quartz material 'ASD'ivite. From this came the British acronym ASDIC. In 1939, in response to a question from the Oxford English Dictionary, the Admiralty made up the story that the letters stood for 'Allied Submarine Detection Investigation Committee', and this is still widely believed, though no committee bearing this name has ever been found in the Admiralty archives.^[2] Robert Boyle (Irish: Robaird Ã“ Bhaoill) (25 January 1627 â€“ 30 December 1691) was an Irish natural philosopher, chemist, physicist, inventor, and early gentleman scientist, noted for his work in physics and chemistry. ... Dr Albert Beaumont Wood OBE DSc (1890 - 19 July 1964) was a British physicist, known for his pioneering work in the field of underwater acoustics and sonar. ... The Oxford English Dictionary print set The Oxford English Dictionary (OED) is a dictionary published by the Oxford University Press (OUP), and is the most successful dictionary of the English language, (not to be confused with the one-volume Oxford Dictionary of English, formerly New Oxford Dictionary of English, of...

By 1918, both the U.S. and Britain had built active systems, though the British were well in advance of the US. They tested their ASDIC on HMS Antrim in 1920, and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school, HMS Osprey, and a training flotilla of four vessels were established on Portland in 1924. The U.S. Sonar QB set arrived in 1931. 1918 (MCMXVIII) was a common year starting on Tuesday of the Gregorian calendar (see link for calendar) or a common year starting on Wednesday of the Julian calendar. ... For other uses of terms redirecting here, see US (disambiguation), USA (disambiguation), and United States (disambiguation) Motto In God We Trust(since 1956) (From Many, One; Latin, traditional) Anthem The Star-Spangled Banner Capital Washington, D.C. Largest city New York City National language English (de facto)1 Demonym American... For other ships with the same name, see HMS Antrim. ... A flotilla (from Spanish, meaning a flota of small ships, and this from French flotte), or naval flotilla, is a formation of small warships that may be part of a larger fleet. ... The Isle of Portland is a long by wide limestone island in the English Channel. ...

By the outbreak of World War II, the Royal Navy had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine attack system. The effectiveness of early ASDIC was limited by the use of the depth charge as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in the moments prior to attack. The hunter was effectively firing blind, during which time a submarine commander was able to take evasive action. This situation was remedied by using several ships cooperating and by the adoption of "ahead throwing weapons", such as Hedgehog and later Squid, which projected warheads at a target ahead of the attacker and thus still in ASDIC contact. Developments during the war resulted in British ASDIC sets which used several different shapes of beam, continuously covering blind spots. Later, acoustic torpedoes were used. Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki TÅjÅ Casualties Military dead: 17,000,000 Civilian dead: 33,000... This article is about the navy of the United Kingdom. ... Depth Charge used by U.S. Navy later in World War II The depth charge is the oldest anti-submarine weapon. ... Hedgehog anti-submarine weapon, British WWII Hedgehog anti-submarine mortar with full load of practice bombs, circa 2002. ... Squid was a World War II ship-mounted anti-submarine weapon. ...

At the start of WWII British ASDIC technology was transferred for free to the US. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed. These included sonobuoys, first developed by the British in 1944, dipping/dunking sonar and mine detection sonar. This work formed the basis for post war developments related to countering the nuclear submarine. Work on sonar had also been carried out in the Axis counties, notably in Germany, which included countermeasures. At the end of WWII this German work was assimilated by Britain and the US. Sonars have continued to be developed by many countries, including Russia, for both military and civil uses. In recent years the major military development has been the increasing interest in low freqency active systems.

In World War II, the Americans used the term SONAR for their systems, coined as the equivalent of RADAR. In 1948, with the formation of NATO, standardisation of signals led to the dropping of ASDIC in favor of SONAR for all NATO countries. For other uses, see Radar (disambiguation). ... This article is about the military alliance. ...

Performance factors

The detection, classification and localisation performance of a sonar depends on the environment and the receiving equipment, as well as the transmitting equipment in an active sonar or the target radiated noise in a passive sonar.

Sound propagation

Sonar operation is affected by variations in sound speed, particularly in the vertical plane. Sound travels more slowly in fresh water than in sea water, though the difference in speeds between fresh and salt water is small. In all water sound speed (sometimes called velocity though this is incorrect) is determined by its bulk modulus and mass density. The bulk modulus is affected by temperature, dissolved impurities (usually salinity), and pressure. The density effect is small. The speed of sound (in feet per second) is approximately equal to: The speed of sound varies depending on the medium through which the sound waves pass. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... Sea water is water from a sea or ocean. ... The bulk modulus (K) of a substance essentially measures the substances resistance to uniform compression. ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... Annual mean sea surface salinity for the World Ocean. ... This article is about pressure in the physical sciences. ... This page is about the physical speed of sound waves in a medium. ...

This is an empirically derived approximation equation that is reasonably accurate for normal temperatures, concentrations of salinity and the range of most ocean depths. Ocean temperature varies with depth, but at between 30 and 100 meters there is often a marked change, called the thermocline, dividing the warmer surface water from the cold, still waters that make up the rest of the ocean. This can frustrate sonar, for a sound originating on one side of the thermocline tends to be bent, or refracted, through the thermocline. The thermocline may be present in shallower coastal waters. However, wave action will often mix the water column and eliminate the thermocline. Water pressure also affects sound propagation. Increased pressure increases the sound speed, which causes the sound waves to refract away from the area of higher sound speed. The mathematical model of refraction is called Snell's law. A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. ... The thermocline is a layer within a body of water where the temperature changes rapidly with depth. ... For the property of metals, see refraction (metallurgy). ... This article is about pressure in the physical sciences. ... Refraction of light at the interface between two media of different refractive indices, with n2 > n1. ...

Sound waves that are radiated down into the deep ocean bend back up to the surface in great arcs due to the increasing pressure (and hence sound speed) with depth. The ocean must be at least 6000 feet (1850 meters) deep, or the sound waves will echo off the bottom instead of refracting back upwards, and the reflection loss at the bottom reduces performance. Under the right conditions these sound waves will then be focused near the surface and refracted back down and repeat another arc. Each focus at the surface is called a convergence zone (CZ). This CZ forms an annulus about the sonar. The distance and width of the CZ depends on the temperature and salinity of the water. In the North Atlantic, for example, CZs are found approximately every 33 nautical miles (61 km), depending on the season. Sounds that can be heard from only a few miles in a direct line can therefore also be detected hundreds of miles away. With powerful sonars the first, second and third CZ are fairly useful; further out than that the signal is too weak, and thermal conditions are too unstable, reducing the reliability of the signals. The signal is naturally attenuated by distance, but modern sonar systems are very sensitive, i.e. can detect despite low signal-to-noise ratios. A nautical mile or sea mile is a unit of length. ...

If the sound source is deep and the conditions are right, propagation may occur in the 'deep sound channel'. This provides extremely low propagation loss to a receiver in the channel. This is because of sound trapping in the channel with no losses at the boundaries. Similar propagation can occur in the 'surface duct' under suitable conditions. However in this case there are reflection losses at the surface.

In shallow water propagation is generally by repeated reflection at the surface and bottom, where considerable losses can occur.

Sound propagation is also affected by absorption in the water itself as well as at the surface and bottom. This absorption is frequency dependent, with several different mechanisms in sea water. Thus sonars required to operate over long ranges tend to utilise low frequencies to minimise absorption effects. Absorption refers to the absorption of sound waves by a material. ...

The sea contains many sources of noise that interfere with the desired target echo or signature. The main noise sources are due to waves and shipping. The motion of the receiver through the water can also cause low frequency noise, which is speed dependent. A WAVES Photographer 3rd Class The WAVES were a World War II era division of the U.S. Navy that consisted entirely of women. ... Damaged package The Panama canal. ...

Reverberation

When active sonar is used, scattering occurs from small objects in the sea as well as from the bottom and surface. This can be a major source of interference but does not occur with passive sonar. This scattering effect is different from that in room reverberation which is a reflection phenomenon. An analogy for reverberation is the scattering of a car's headlights in fog or mist. A high-intensity pencil beam will penetrate the fog; main headlights are less directional and result in "white-out" where the returned reverberation dominates. Similarly, to overcome reverberation, an active sonar needs to transmit in a narrow beam.

Target characteristics

The target of a sonar, such as a submarine, has two main characteristics that influence the performance of the sonar. For active sonar it is its sound reflection characteristics, known as its target strength. For passive sonar the target's radiated noise characteristics are critical. The radiated spectrum in general will consist of an unresolved continuum of noise with spectral lines in it, the lines being used for classification.

Echoes are also obtained from other objects in the sea such as whales, wakes, schools of fish and rocks.

Countermeasures

Active (powered) countermeasures may be launched by a submarine under attack to raise the noise level and/or provide a large false target. Passive (ie non-powered) countermeasures include mounting noise generating devices on isolating devices and coating the hull of submarines.

Active sonar

Active sonar uses a sound transmitter and a receiver. When the two are in the same place it is monostatic operation. When the transmitter and receiver are separated it is bistatic operation. When more transmitters (or more receivers) are used, again spatially separated, it is multistatic operation. Most sonars are used monostatically with the same array often being used for transmission and reception, though when the platform is moving it may be necessary to consider a single transmitter/receiver as being operated bistatically. Active sonobuoy fields may be operated multistatically. Image File history File links Sonar_Principle_EN.svg Beschreibung Description: Principle of a sonar or radar distance measurement Source: Self drawn with Inkscape Date: created 3. ... Image File history File links Sonar_Principle_EN.svg Beschreibung Description: Principle of a sonar or radar distance measurement Source: Self drawn with Inkscape Date: created 3. ...

Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections (echo) of the pulse. This pulse of sound is generally created electronically using a Sonar Projector consisting of a signal generator, power amplifier and electro-acoustic transducer/array, possibly with a beamformer. However, it may be created by other means, eg chemically using explosives or by using heat sources in thermoacoustics. ËŒ For other uses, see Pulse (disambiguation). ... The reflection of a bridge in Indianapolis, Indianas Central Canal. ... In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. ... Sonic or thermoacoustic refrigeration is a technology that uses high-amplitude sound waves in a pressurised gas to pump heat from one place to another. ...

To measure the distance to an object, the time from transmission of a pulse to reception is measured and converted into a range by knowing the speed of sound. To measure the bearing, several hydrophones are used, and the set measures the relative arrival time to each, or with an array of hydrophones, by measuring the relative amplitude in beams formed through a process called beamforming. Use of an array reduces the spatial response so that to provide wide cover multibeam systems are used. The target signal (if present) together with noise is then passed through various forms of signal processing, which for simple sonars may be just energy measurement. It is then presented to some form of decision device that calls the output either the required signal or noise. This decision device may be an operator with headphones or a display, or in more sophisticated sonars this function may be carried out by software. Further processes may be carried out to classify the target and localise it, as well as measuring its velocity. In navigation, a bearing is the clockwise angle between a reference direction (or a datum line) and the direction to an object. ... A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... Beamforming is a signal processing technique used with arrays of transmitting or receiving transducers that control the directionality of, or sensitivity to, a radiation pattern. ... Multibeam or Swathe or Swath echosounders originated in the late 1950s, developed by the US Navy and General Instruments in the 1970s to map large swaths of the ocean floor to assist with underwater navigation of its submarine force. ... Signal processing is the processing, amplification and interpretation of signals, and deals with the analysis and manipulation of signals. ...

The pulse may be at constant frequency or a chirp of changing frequency (to allow pulse compression on reception). Simple sonars generally use the former with a filter wide enough to cover possible Doppler changes due to target movement, while more complex ones generally include the latter technique. Today, pulse compression is usually achieved using digital correlation techniques. Military sonars often have multiple beams to provide all-round cover while simple ones only cover a narrow arc. Originally the latter was often scanned around mechanically but this was a slow process. For other uses, see Frequency (disambiguation). ... This article does not cite any references or sources. ... Pulse Compression Pulse compression or chirp radar, also known as pulse coding, is a signal processing technique designed to maximise the sensitivity and resolution of radar systems. ...

Particularly when single frequency transmissions are used, the Doppler effect may be used to measure the radial speed of a target. The difference in frequency between the transmitted and received signal is measured and converted into a velocity. Since Doppler shifts can be introduced by either receiver or target motion, allowance has to be made for the radial speed of the searching platform. This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

One useful small sonar looks roughly like a waterproof flashlight. One points the head into the water, presses a button, and reads a distance. Another variant is a "fishfinder" that shows a small display with shoals of fish. Some civilian sonars approach active military sonars in capability, with quite exotic three-dimensional displays of the area near the boat. However, these sonars are not designed for stealth. Cabin display of a commercial or oceanographic fathometer sonar A fishfinder is a type of Fathometer, both being specialized types of echo sounding systems, a type of Active SONAR. (Sounding is the measurement of water depth, a historical nautical term of very long usage. ... Look up Shoal in Wiktionary, the free dictionary. ...

When active sonar is used to measure the distance from the transducer to the bottom, it is known as echo sounding. Similar methods may be used looking upward for wave measurement. Illustration of echo sounding. ...

Active sonar is also used to measure distance through water between two sonar transducers or a combination of a hydrophone (underwater acoustic microphone) and projector (underwater acoustic speaker). A transducer is a device that can transmit and receive acoustic signals ("pings"). When a hydrophone/transducer receives a specific interrogation signal it responds by transmitting a specific reply signal. To measure distance, one transducer/projector transmits an interrogation signal and measures the time between this transmission and the receipt of the other transducer/hydrophone reply. The time difference, scaled by the speed of sound through water and divided by two, is the distance between the two platforms. This technique, when used with multiple transducers/hydrophones/projectors, can calculate the relative positions of static and moving objects in water.

In wartime, emission of an active pulse is so compromising for a submarine's stealth that it is considered a very severe breach of tactics.

A very directional, yet low-efficiency type of sonar (used by fisheries, military, and for port security) makes use of a complex nonlinear feature of the water known as non-linear sonar, the virtual transducer being known as a parametric array. The parametric array is a nonlinear transduction mechanism that generates narrow, nearly sidelobe free beams of low frequency sound, through the mixing and interaction of high frequency sound waves, effectively overcoming the diffraction limit (a kind of spatial uncertainty principle) associated with linear acoustics [1]. Parametric arrays can be formed...

Transponder

This is an active sonar device that receives a stimulus and immediately (or with a delay) retransmits the received signal or a predetermined one.

Performance prediction

A sonar target is small relative to the sphere, centred around the emitter, on which it is located. Therefore, the power of the reflected signal is very low, several orders of magnitude less than the original signal. Even if the reflected signal was of the same power, the following example (using hypothetical values) shows the problem: Suppose a sonar system is capable of emitting a 10000 W/m² signal at 1m, and detecting a 0.001 W/m² signal. At 100 m the signal will be 1 W/m² (due to the inverse-square law). If the entire signal is reflected from a 10 sq m target, it will be at 0.001 W/m² when it reaches the emitter, ie just detectable. However, the original signal will remain above 0.001 W/m² until 300 m. Any 10 sq m target between 100 and 300 m using a similar or better system would be able to detect the pulse but would not be detected by the emitter. The detectors must be very sensitive to pick up the echoes. Since the original signal is much more powerful, it can be detected many times further than twice the range of the sonar (as in the example). For other uses, see Sphere (disambiguation). ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... This diagram shows how the law works. ...

In active sonar there are two performance limitations, due to noise and reverberation. In general one or other of these will dominate so that the two effects can be initially considered separately.

where SL is the source level, TL is the transmission loss (or propagation loss), TS is the target strength, NL is the noise level, DI is the directivity index of the array (an approximation to the array gain) and DT is the detection threshold. Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ... Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ... Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ... In telecommunication, noise level is the noise power, usually relative to a reference. ... In MIMO communication systems, array gain means a power gain of transmitted signals that is achieved by using multiple-antennas at transmitter and/or receiver. ...

In reverberation limited conditions at initial detection (neglecting array gain):-

Marine animals

Adverse effects

High-powered sonar transmitters may harm marine animals, although the precise mechanisms for this are not well understood. Some marine animals, such as whales and dolphins, use echolocation systems similar to active sonar to locate predators and prey. It is conjectured that sonar transmitters could confuse these animals and cause them to lose their way, perhaps preventing them from feeding and mating. This article is about the animal. ... For other uses, see Dolphin (disambiguation). ... Echolocation, also called Biosonar, is the biological sonar used by several mammals such as bats (although not all species), dolphins and whales (though not baleen whales). ...

It has been suggested that military sonar may induce whales to panic and surface too rapidly leading to a form of decompression sickness. This was first raised by a paper published in the journal Nature in 2003. It reported acute gas-bubble lesions (indicative of decompression sickness) in whales that beached shortly after the start of a military exercise off the Canary Islands in September 2002.^[3] Decompression sickness (DCS), the diverâ€™s disease, the bends, or caisson disease is the name given to a variety of symptoms suffered by a person exposed to a decrease (nearly always after a big increase) in the pressure around his body. ... Anthem: ArrorrÃ³ Capital Las Palmas de Gran Canaria and Santa Cruz de Tenerife Official language(s) Spanish Area â€“ Total â€“ % of Spain Ranked 13th 7,447 kmÂ² 1. ...

In the Bahamas in 2000, a sonar trial by the United States Navy of transmitters in the frequency range 3–8 kHz at a source level of 223–235 decibels re 1 μPa (scaled to a distance of 1 m) resulted in the beaching of seventeen whales, seven of which were found dead. The Navy accepted blame in a report, which found the dead whales to have experienced acoustically-induced hemorrhages around the ears. The resulting disorientation may have led to the stranding.^[4] USN redirects here. ... This article is about the SI unit of frequency. ... For other uses, see Decibel (disambiguation). ... A subconjunctival hemorrhage is a common and relatively minor post-LASIK complication. ...

A kind of sonar called mid-frequency sonar has been correlated with mass cetacean strandings throughout the world's oceans, and has therefore been singled out by environmentalists as causing the death of marine mammals.^[5] A lawsuit filed by the Natural Resources Defense Council in Santa Monica, California on 20 October 2005 contended that the U.S. Navy has conducted sonar exercises in violation of several environmental laws, including the National Environmental Policy Act, the Marine Mammal Protection Act, and the Endangered Species Act.^[6] The Natural Resources Defense Council (NRDC) [1] is a leftist, New York City-based, non-profit, non-partisan environmental advocacy group, with offices in Washington, D.C., San Francisco, and Los Angeles. ... For other uses, see Santa Monica (disambiguation). ... is the 293rd day of the year (294th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... The National Environmental Policy Act (or, NEPA) was signed into law on January 1, 1970 by US President Richard Nixon. ... The Marine Mammal Protection Act of 1972 prohibits, with certain exceptions, the take of marine mammals in U.S. waters and by U.S. citizens on the high seas, and the importation of marine mammals and marine mammal products into the U.S. Congress defines take as â€œharass, hunt, capture... The Endangered Species Act (, et seq. ...

On November 13, 2007, a United States appeals court restored a ban on the U.S. Navy's use of submarine-hunting sonar in upcoming training missions off Southern California until it adopts better safeguards for whales, dolphins and other marine mammals. is the 317th day of the year (318th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ...

Mitigation methods

Environmental impacts of the operation of active sonar are required to be carried out by US law. Procedures for minimising the impact of sonar are developed in each case where there is significant impact.

Hand-held sonar for use by a diver

Remotely operated vehicles (ROV) are mobile tools used in environments too dangerous for humans. ... For the Wizard of Oz series character, see Frogman (Oz character). ... Clearance Diver is the British Navys official name for the usual sort of general-purpose naval work diver. ... A naval mine is a stationary self-contained explosive device placed in water, to destroy ships and/or submarines. ... In Meteorology, ability is a measure of the nothingness at which an object or light can be seen. ... For other uses, see SPIE (disambiguation). ... Space Shuttle Columbia (NASA Orbiter Vehicle Designation: OV-102) was the first spaceworthy space shuttle in NASAs orbital fleet. ... Pool-and-weir fish ladder at Bonneville Dam on the Columbia River Fishways, most commonly called fish ladders but also known as fish passes and in Australia they are referred to as fish steps, are structures on or around artificial barriers (such as dams and weirs) to facilitate diadromous fishes... Undershot water wheels on the Orontes River in Hama, Syria Saint Anthony Falls Hydropower is the capture of the energy of moving water for some useful purpose. ... Image File history File links Aa_INSS_01. ... Image File history File links Aa_INSS_01. ... Early ideas of autonomous under-water systems appear in Twenty Thousand Leagues Under the Sea Scuba Diving is the use of independent breathing equipment to stay underwater for long periods for recreational diving and professional diving. ...

Passive sonar

Passive sonar listens without transmitting. It is often employed in military settings, although it is also used in science applications, e.g. detecting fish for presence/absence studies in various aquatic environments - see also passive acoustics and passive radar. In the very broadest usage, this term can encompass virtually any analytical technique involving remotely generated sound, though it is usually restricted to techniques applied in an aquatic environment. Passive acoustics is the action of listening for sounds, often at specific frequencies or for purposes of specific analyses. ... Passive radar systems (also referred to a passive coherent location and passive covert radar) encompass a class of radar systems that detect and track objects by processing reflections from non-cooperative sources of illumination in the environment, such as commercial broadcast and communications signals. ...

Identifying sound sources

Passive sonar has a wide variety of techniques for identifying the source of a detected sound. For example, U.S. vessels usually operate 60 Hz alternating current power systems. If transformers or generators are mounted without proper vibration insulation from the hull or become flooded, the 60 Hz sound from the windings can be emitted from the submarine or ship. This can help to identify its nationality, as most European submarines have 50 Hz power systems. Intermittent sound sources (such as a wrench being dropped) may also be detectable to passive sonar. Until fairly recently, the identification of a signal was carried out by an operator using experience and training. Now computers may be utilised in this process. This article is about the SI unit of frequency. ... City lights viewed in a motion blurred exposure. ... For other uses, see Transformer (disambiguation). ... This article is about machines that produce electricity. ... Look up vibration in Wiktionary, the free dictionary. ... A hull is the body or frame of a ship or boat. ... For other uses, see Submarine (disambiguation). ... Combination wrench, or combination spanner (left: box-end/ring, right: open-end) A wrench or spanner is a tool used to provide a mechanical advantage in applying torque to turn bolts, nuts or other hard-to-turn items. ...

Passive sonar systems may have large sonic databases, however final classification is generally performed manually by the sonar operator. A computer system frequently uses these databases to identify classes of ships, actions (i.e., the speed of a ship, or the type of weapon released), and even particular ships. Publications for classification of sounds are provided by and continually updated by the U.S. Office of Naval Intelligence. A database is an information set with a regular structure. ... This article or section is in need of attention from an expert on the subject. ... The Office of Naval Intelligence (ONI) was established in the United States Navy in 1882. ...

Noise limitations

Passive sonar on vehicles is usually severely limited because of noise generated by the vehicle. For this reason, many submarines operate nuclear reactors that can be cooled without pumps, using silent convection, or fuel cells or batteries, which can also run silently. Vehicles' propellers are also designed and precisely machined to emit minimal noise. High-speed propellers often create tiny bubbles in the water, and this cavitation has a distinct sound. Core of a small nuclear reactor used for research. ... Convection in the most general terms refers to the movement of currents within fluids (i. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... A battery is of one or more electrochemical cells, which store chemical energy and make it available in an electrical form. ... For other uses, see Propeller (disambiguation). ... Cavitating propeller model in a water tunnel experiment High speed jet of fluid impact on a fixed surface. ...

The sonar hydrophones may be towed behind the ship or submarine in order to reduce the effect of noise generated by the watercraft itself. Towed units also combat the thermocline, as the unit may be towed above or below the thermocline. A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... The thermocline is a layer within a body of water where the temperature changes rapidly with depth. ... The thermocline is a layer within a body of water where the temperature changes rapidly with depth. ...

The display of most passive sonars used to be a two-dimensional waterfall display. The horizontal direction of the display is bearing. The vertical is frequency, or sometimes time. Another display technique is to color-code frequency-time information for bearing. More recent displays are generated by the computers, and mimic radar-type plan position indicator displays. It has been suggested that this article or section be merged with periodogram. ... For other uses, see Radar (disambiguation). ... An annotated picture of one of the first Plan Position Indicator images - Pembroke and Milford Haven as seen on the PPI of an early H2S screen The Plan Position Indicator, known as PPI, is the most common way to represent radar data. ...

Performance prediction

Unlike active sonar, only one way propagation is involved. Because of the different signal processing used, the minimum detectable signal to noise ratio will be different. The equation for determining the performance of a passive sonar is given by Urick as :-

where SL is the source level, TL is the transmission loss, NL is the noise level, DI is the directivity index of the array (an approximation to the array gain) and DT is the detection threshold. Urick defines the figure of merit of a passive sonar as FOM = SL + DI - (NL + DT). A Figure of merit is a quantity used to characterize the performance of a device relative to other devices of the same type. ...

Warfare

Modern naval warfare makes extensive use of sonar. The two types described before are both used, from various platforms, i.e. water-borne vessels, aircraft and fixed installations. The usefulness of active versus passive sonar depends on the radiated noise characteristics of the target, generally a submarine. Although in WWII active sonar was mainly used, except by submarines, with the advent of noisy nuclear submarines passive sonar was preferred for initial detection. As the submarines have become quieter, active operation is now more used. This article does not cite any references or sources. ...

Active sonar is extremely useful, since it gives the exact position of an object. Active sonar works the same way as radar: a signal is emitted. The sound wave then travels in many directions from the emitting object. When it hits an object, the sound wave is then reflected in many other directions. Some of the energy will travel back to the emitting source. The echo will enable the sonar system or technician to calculate, with many factors such as the frequency, the energy of the received signal, the depth, the water temperature, etc., the position of the reflecting object. Using active sonar is somewhat hazardous however, since it does not allow the sonar to identify the target, and any vessel around the emitting sonar will detect the emission. Having heard the signal, it is easy to identify the type of sonar (usually with its frequency) and its position (with the sound wave's energy). Moreover, active sonar, similar to radar, allows the user to detect objects at a certain range but also enables other platforms to detect the active sonar at a far greater range. For other uses, see Radar (disambiguation). ...

Since active sonar does not allow an exact identification and is very noisy, this type of detection is used by fast platforms (planes, helicopters) and by noisy platforms (most surface ships) but rarely by submarines. When active sonar is used by surface ships or submarines, it is typically activated very briefly at intermittent periods, to reduce the risk of detection by an enemy's passive sonar. As such, active sonar is normally considered a backup to passive sonar. In aircraft, active sonar is used in the form of disposable sonobuoys that are dropped in the aircraft's patrol area or in the vicinity of possible enemy sonar contacts. Sonarbuoy loaded on aircraft A sonobuoy (a portmanteau of sonar and buoy) is a relatively small (typically 4 7/8 inches, or ~124 mm, in diameter and 36 inches, or ~914 mm, long) expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater...

Passive sonar has several advantages. Most importantly, it is silent. If the target radiated noise level is high enough, it can have a greater range than active sonar, and allows an identification of the target. Since any motorized object makes some noise, it may be detected eventually. It simply depends on the amount of noise emitted and the amount of noise in the area, as well as the technology used. To simplify, passive sonar "sees" around the ship using it. On a submarine, the nose mounted passive sonar detects in directions of about 270°, centered on the ship's alignment, the hull-mounted array of about 160° on each side, and the towed array of a full 360°. The no-see areas are due to the ship's own interference. Once a signal is detected in a certain direction (which means that something makes sound in that direction, this is called broadband detection) it is possible to zoom in and analyze the signal received (narrowband analysis). This is generally done using a Fourier transform to show the different frequencies making up the sound. Since every engine makes a specific noise, it is easy to identify the object. In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ...

Another use of the passive sonar is to determine the target's trajectory. This process is called Target Motion Analysis (TMA), and the resultant "solution" is the target's range, course, and speed. TMA is done by marking from which direction the sound comes at different times, and comparing the motion with that of the operator's own ship. Changes in relative motion are analyzed using standard geometrical techniques along with some assumptions about limiting cases. Mathematically the term trajectory refers to the ordered set of states which are assumed by a dynamical system over time (see e. ...

Passive sonar is stealthy and very useful. However, it requires high-tech components (band-pass filters, receivers) and is costly. It is generally deployed on expensive ships in the form of arrays to enhance the detection. Surface ships use it to good effect; it is even better used by submarines, and it is also used by airplanes and helicopters, mostly to a "surprise effect", since submarines can hide under thermal layers. If a submarine captain believes he is alone, he may bring his boat closer to the surface and be easier to detect, or go deeper and faster, and thus make more sound. The frequency axis of this symbolic diagram would be logarithmically scaled. ... USS Los Angeles A submarine is a specialized watercraft that can operate underwater. ...

Examples of sonar applications in military use are given below. Many of the civil uses given in the following section may also be applicable to naval use.

Anti-submarine warfare

Until recently, ship sonars were usually with hull mounted arrays, either amidships or at the bow. It was soon found after their initial use that a means of reducing flow noise was required. The first were made of canvas on a framework, then steel ones were used. Now domes are usually made of reinforced plastic or pressurised rubber. Such sonars are primarily active in operation. An example of a conventional hull mounted sonar is the SQS-56.

Because of the problems of ship noise, towed sonars are also used. These also have the advantage of being able to be placed deeper in the water. However, there are limitations on their use in shallow water. These are called towed arrays (linear) or variable depth sonars (VDS) with 2/3D arrays. A problem is that the winches required to deploy/recover these are large and expensive. VDS sets are primarily active in operation while towed arrays are passive.

An example of a modern active/passive ship towed sonar is Sonar 2087 made by Thales Underwater Systems. Sonar 2087 is a new towed sonar system for Royal Navy Type 23 frigates maufactured by Thales Underwater Systems. ... Thales Underwater Systems (TUS), formerly known as Thomson Marconi Sonar, is a defence manufacturer specialising in Sonar for Submarines and Surface Ships, as well as Airborne sonar systems, and communications masts and systems for Submarines. ...

Torpedoes

Modern torpedoes are generally fitted with an active/passive sonar. This may be used to home directly on the target, but wake following torpedoes are also used. An early example of an acoustic homer was the Mark 37 torpedo. The Mark 37 torpedo is a torpedo with electrical propulsion, developed for US Navy. ...

Torpedo countermeasures can be towed or free. An early example was the German Sieglinde device while the Pillenwerfer was a chemical device. A widely used US device was the towed Nixie while MOSS submarine simulator was a free device. A post war US diagram of a Pillenwerfer. ... The word nixie has four different meanings, depending on context: The mythical water creature known as the Nix (aka Näcken / Nøkken), appearing in Scandinavian folk tales Another word for Melusine Nixie tubes, a special form of vacuum tubes formerly used as numerical indicators Mail returned as undeliverable or... For other uses, see Moss (disambiguation). ...

Mines

Mines may be fitted with a sonar to detect, localise and recognise the required target. Further information is given in acoustic mine and an example is the CAPTOR mine. An acoustic mine is a type of naval mine which monitors audio activity in its vicinity. ... A captor mine is an American naval mine. ...

Mine countermeasures

Mine Countermeasure (MCM) Sonar, sometimes called "Mine and Obstacle Avoidance Sonar (MOAS)", is a specialised type of sonar used for detecting small objects. Most MCM sonars are hull mounted but a few types are VDS design. An example of a hull mounted MCM sonar is the Type 2193 while the SQQ-32 Mine-hunting sonar and Type 2093 systems are VDS designs. The AN/SQQ-32 is a mine-hunting sonar system. ...

Submarines

Submarines rely on sonar to a greater extent than surface ships as they cannot use radar at depth. The sonar arrays may be hull mounted or towed. Information fitted on typical fits is given in Oyashio class submarine and Swiftsure class submarine. SS590 Oyashio, navigates through Pearl Harbour. ... The Royal Navys Swiftsure-class of nuclear fleet submarines (SSNs) is the older of the two classes of attack submarine in service with the RN. It originally contained six boats, but HMS Swiftsure was decommissioned in 1992 due to damage suffered to the pressure hull during trials. ...

Aircraft

Helicopters can be used for antisubmarine warfare by deploying fields of active/passive sonobuoys or can operate dipping sonar, such as the AQS-13. Fixed wing aircraft can also deploy sonobuoys and have greater endurance and capacity to deploy them. Processing from the sonobuoys or dipping sonar can be on the aircraft or on ship. Helicopters have also been used for mine countermeasure missions using towed sonars such as the AQS-20A Sonarbuoy loaded on aircraft A sonobuoy (a portmanteau of sonar and buoy) is a relatively small (typically 4 7/8 inches, or ~124 mm, in diameter and 36 inches, or ~914 mm, long) expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater... The AQS-20A is an airborne mine countermeasure detection system, developed by Raytheon. ...

Image File history File links Download high-resolution version (2946x1935, 3345 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Sonar ... Image File history File links Download high-resolution version (2946x1935, 3345 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Sonar ... The Sikorsky SH-3 Sea King (company designation S-61) is a twin-engined anti-submarine warfare (ASW)helicopter. ...

Underwater communications

Dedicated sonars can be fitted to ships and submarines for underwater communication. See also the section on the underwater acoustics page. Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water and its boundaries. ...

Ocean surveillance

For many years, the United States operated a large set of passive sonar arrays at various points in the world's oceans, collectively called Sound Surveillance System (SOSUS) and later Integrated Undersea Surveillance System (IUSS). A similar system is believed to have been operated by the Soviet Union. As permanently mounted arrays in the deep ocean were utilised, they were in very quiet conditions so long ranges could be achieved. Signal processing was carried out using powerful computers ashore. With the ending of the Cold War a SOSUS array has been turned over to scientific use. SOSUS, an acronym for SOund SUrveillance System, is a chain of underwater listening posts located across the northern Atlantic Ocean near Greenland, Iceland and the United Kingdomâ€”the so-called GIUK gap. ...

In the United States Navy, a special badge known as the Integrated Undersea Surveillance System Badge is awarded to those who have been trained and qualified in its operation. Officer and enlisted versions of the Integrated Undersea Surveillance System Badge The Integrated Undersea Surveillance System Badge is a military badge of the United States Navy which has been existence since the 1970s. ...

Underwater security

Sonar can be used to detect frogmen and other scuba divers. This can be applicable around ships or at entrances to ports. Active sonar can also be used as a deterrrent and/or disablement mechanism. One such device is the Cerebus system. For the Wizard of Oz series character, see Frogman (Oz character). ... Early ideas of autonomous under-water systems appear in Twenty Thousand Leagues Under the Sea Scuba Diving is the use of independent breathing equipment to stay underwater for long periods for recreational diving and professional diving. ... This article is about protecting craft and bases and installations and other places and areas in water or accessible from water, from intrusion by frogmen or other divers that may be a threat to security or property. ...

See Underwater Port Security System and Anti-frogman techniques#Ultrasound weapon. // See UIS and IAS for other meanings of these initials. ... This article is about protecting craft and bases and installations and other places and areas in water or accessible from water, from intrusion by frogmen or other divers that may be a threat to security or property. ...

Hand-held sonar

Limpet Mine Imaging Sonar (LIMIS) is a hand-held or ROV-mounted imaging sonar designed for patrol divers (combat frogmen or clearance divers) to look for limpet mines in low visibility water. Image File history File links Aa_INSS_01. ... Image File history File links Aa_INSS_01. ... Early ideas of autonomous under-water systems appear in Twenty Thousand Leagues Under the Sea Scuba Diving is the use of independent breathing equipment to stay underwater for long periods for recreational diving and professional diving. ... Remotely operated vehicles (ROV) are mobile tools used in environments too dangerous for humans. ... For the Wizard of Oz series character, see Frogman (Oz character). ... Clearance Diver is the British Navys official name for the usual sort of general-purpose naval work diver. ... Polish wz. ... In Meteorology, ability is a measure of the nothingness at which an object or light can be seen. ...

Integrated Navigation Sonar System (INSS) is a small flashlight-shaped handheld sonar for divers that displays range.^[8]^[9]

Intercept sonar

This is a sonar designed to detect and locate the transmissions from hostile active sonars. An example of this is the Type 2082 fitted on the Vanguard class submarines. The Vanguard class are the Royal Navys current nuclear ballistic missile submarines (SSBN), each armed with up to 16 Trident II SLBMs. ...

Civil applications

Fisheries

Fishing is an important industry that is seeing growing demand, but world catch tonnage is falling as a result of serious resource problems. The industry faces a future of continuing worldwide consolidation until a point of sustainability can be reached. However, the consolidation of the fishing fleets are driving increased demands for sophisticated fish finding electronics such as sensors, sounders and sonars. Historically, fishermen have used many different techniques to find and harvest fish. However, acoustic technology has been one of the most important driving forces behind the development of the modern commercial fisheries. Fishing is the activity of hunting for fish by hooking, trapping, or gathering. ... The Earth Day flag includes a NASA photo. ...

Sound waves travel differently through fish than through water because a fish's air-filled swim bladder has a different density than seawater. This density difference allows the detection of schools of fish by using reflected sound. Acoustic technology is especially well suited for underwater applications since sound travels farther and faster underwater than in air. Today, commercial fishing vessels rely almost completely on acoustic sonar and sounders to detect fish. Fishermen also use active sonar and echo sounder technology to determine water depth, bottom contour, and bottom composition. The gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming. ...

Companies such as Raymarine UK, Marport Canada, Wesmar, Furuno, Krupp, and Simrad make a variety of sonar and acoustic instruments for the deep sea commercial fishing industry. For example, net sensors take various underwater measurements and transmit the information back to a receiver onboard a vessel. Each sensor is equipped with one or more acoustic transducers depending on its specific function. Data is transmitted from the sensors using wireless acoustic telemetry and is received by a hull mounted hydrophone. The analog signals are decoded and converted by a digital acoustic receiver into data which is transmitted to a bridge computer for graphical display on a high resolution monitor. Fishfinder sonar From: National Oceanic and Atmospheric Administration/Department of Commerce Image ID: fish0021, Fisheries Collection Photo Date: 1995 Photographer: Captain Robert A. Pawlowski, NOAA Corps File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Fishfinder sonar From: National Oceanic and Atmospheric Administration/Department of Commerce Image ID: fish0021, Fisheries Collection Photo Date: 1995 Photographer: Captain Robert A. Pawlowski, NOAA Corps File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The term deep sea refers to those areas of oceans to which little or no light penetrates (the aphotic zone). ... An analog or analogue signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. ... ...

Echo sounding

An echo-sounder sends an acoustic pulse directly downwards to the seabed and records the returned echo. The sound pulse is generated by a transducer that emits an acoustic pulse and then “listens” for the return signal. The time for the signal to return is recorded and converted to a depth measurement by calculating the speed of sound in water. As the speed of sound in water is around 1,500 metres per second, the time interval, measured in milliseconds, between the pulse being transmitted and the echo being received, allows bottom depth and targets to be measured.

The value of underwater acoustics to the fishing industry has led to the development of other acoustic instruments that operate in a similar fashion to echo-sounders but, because their function is slightly different from the initial model of the echo-sounder, have been given different terms.

Net location

The net sounder is an echo sounder with a transducer mounted on the headline of the net rather than on the bottom of the vessel. Nevertheless, to accommodate the distance from the transducer to the display unit, which is much greater than in a normal echo-sounder, several refinements have to be made. Two main types are available. The first is the cable type in which the signals are sent along a cable. In this case there has to be the provision of a cable drum on which to haul, shoot and stow the cable during the different phases of the operation. The second type is the cable less net-sounder – such as Marport’s Trawl Explorer - in which the signals are sent acoustically between the net and hull mounted receiver/hydrophone on the vessel. In this case no cable drum is required but sophisticated electronics are needed at the transducer and receiver.

The display on a net sounder shows the distance of the net from the bottom (or the surface), rather than the depth of water as with the echo-sounder's hull-mounted transducer. Fixed to the headline of the net, the footrope can usually be seen which gives an indication of the net performance. Any fish passing into the net can also be seen, allowing fine adjustments to be made to catch the most fish possible. In other fisheries, where the amount of fish in the net is important, catch sensor transducers are mounted at various positions on the cod-end of the net. As the cod-end fills up these catch sensor transducers are triggered one by one and this information is transmitted acoustically to display monitors on the bridge of the vessel. The skipper can then decide when to haul the net. A transducer is a device, usually electrical or electronic, that converts one type of energy to another. ...

Modern versions of the net sounder, using multiple element transducers, function more like a sonar than an echo sounder and show slices of the area in front of the net and not merely the vertical view that the initial net sounders used.

The sonar is an echo-sounder with a directional capability that can show fish or other objects around the vessel.

Ship velocity measurement

Sonars have been developed for measuring a ship's velocity either relative to the water or to the bottom.

ROV and UUV

Small sonars have been fitted to Remotely Operated Vehicles (ROV) and Unmanned Underwater Vehicles (UUV) to allow their operation in murky conditions. These sonars are used for looking ahead of the vehicle. The Long-Term Mine Reconnaissance System is an UUV for MCM purposes. The Long-Term Mine Reconnaissance System (LMRS) is a torpedo tube-launched and tube-recovered underwater search and survey unmanned undersea vehicle (UUV) capable of performing autonomous minefield reconnaissance as much as 200 kilometers (120 miles) in advance of a host Los Angeles-, Seawolf-, or Virginia-class submarine. ...

Vehicle location

Sonars which act as beacons are fitted to aircraft to allow their location in the event of a crash in the sea. Short and Long Baseline sonars may be used for carring out the location, such as LBL. The Berkeley Lab is perched on a hill overlooking the Berkeley central campus and San Francisco Bay. ...

Scientific applications

Biomass estimation

Biomass estimation uses sonar to detect fish, etc. As the sound pulse travels through water it encounters objects that are of different density than the surrounding medium, such as fish, that reflect sound back toward the sound source. These echoes provide information on fish size, location, and abundance. Bioacoustics is a cross-disciplinary science that combines biology and acoustics. ...

Wave measurement

An upward looking echo sounder mounted on the bottom or on a platform may be used to make measurements of wave height and period. From this statistics of the surface conditions at a location can be derived.

Water velocity measurement

Special short range sonars have been developed to allow measurements of water velocity.

Bottom type assessment

Sonars have been developed that can be used to characterise the sea bottom into, for example, mud, sand, and gravel. Relatively simple sonars such as echo sounders can be promoted to seafloor classification systems via add-on modules, converting echo parameters into sediment type. Different algorithms exist, but they are all based on changes in the energy or shape of the reflected sounder pings.

Bottom topography measurement

Side-scan sonars can be used to derive maps of the topography of an area by moving the sonar across it just above the bottom. Low frequency sonars such as GLORIA have been used for continental shelf wide surveys while high frequency sonars are used for more detailed surveys of smaller areas. Diagram of sidescan sonar Side scan sonar (also sometimes called side-scan sonar, sidescan sonar, side looking sonar and side-looking sonar) is a category of sonar system that is used to efficiently create an image of large areas of the sea floor. ...

Sub-bottom profiling

Powerful low frequency echo-sounders have been developed for providing profiles of the upper layers of the ocean bottom.

Synthetic aperture sonar

Various synthetic aperture sonars have been built in the laboratory and some have entered use in mine-hunting and search systems. An explanation of their operation is given in synthetic aperture sonar. Synthetic aperture sonar (SAS) is a form of sonar in which sophisticated post-processing of sonar data are used in ways closely analogous to synthetic aperture radar. ...

Parametric sonar

Parametric sources utilise the non-linearity of water to generate the difference frequency between two high(er) frequencies. A virtual end-fire array is formed. Such a projector has advantages of broad bandwidth, narrow beamwidth and when fully developed and carefully measured it has no obvious sidelobes.

Its major disadvantage is very low efficiency of only a few percent.^[10]. P.J. Westervelt's seminal (and brief!) 1963 JASA paper summarizes the trends involved.

In theory, a parametric receiver is possible but there is no known implementation.

Sonar manufacturers

Kongsberg Gruppen (KOG) (lit. ... Thales Underwater Systems (TUS), formerly known as Thomson Marconi Sonar, is a defence manufacturer specialising in Sonar for Submarines and Surface Ships, as well as Airborne sonar systems, and communications masts and systems for Submarines. ...

Contents

History GA_googleFillSlot("encyclopedia_square");

Performance factors

Sound propagation

Reverberation

Target characteristics

Countermeasures

Active sonar

Transponder

Performance prediction

Marine animals

Adverse effects

Mitigation methods

Hand-held sonar for use by a diver

Passive sonar

Identifying sound sources

Noise limitations

Performance prediction

Warfare

Anti-submarine warfare

Torpedoes

Mines

Mine countermeasures

Submarines

Aircraft

Underwater communications

Ocean surveillance

Underwater security

Hand-held sonar

Intercept sonar

Civil applications

Fisheries

Echo sounding

Net location

Ship velocity measurement

ROV and UUV

Vehicle location

Scientific applications

Biomass estimation

Wave measurement

Water velocity measurement

Bottom type assessment

Bottom topography measurement

Sub-bottom profiling

Synthetic aperture sonar

Parametric sonar

Sonar manufacturers

See also

Notes

References

Bibliography

External links

History