NationMaster - Encyclopedia: Active sonar

Sonar (sound navigation and ranging) is a technique that uses sound propagation under water to navigate or to detect other watercraft. There are two kinds of sonar, active and passive. 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. ... A schematic representation of auditory signaling Sound is vibration, as perceived by the sense of hearing. ... There are several traditions of navigation. ...

History

In 1906, Lewis Nixon invented the very first sonar-type listening device, as a way of detecting icebergs. During World War I, with the need to detect submarines, interest in sonar increased. The Frenchman Paul Langevin working with Chilowski invented the first sonar-type device for detecting submarines in 1915. His work influenced the future of sonar designs. These first sonar devices were passive listening devices. In 1916, under the British Board of Inventions and Research, Dr Boyle in the UK took on the project which subsequently passed to the Anti- (or Allied) Submarine Detection Investigation Committee which produced a prototype for testing in mid 1917 (hence the name ASDIC in British use). 1906 was a common year starting on Monday (see link for calendar). ... An iceberg (berg is the German word for mountain) is a large piece of ice that has broken off from a glacier or ice shelf and is floating in open water. ... WWI redirects here. ... Paul Langevin (January 23, 1872 - December 19, 1946) was a French physicist. ... 1915 was a common year starting on Friday (see link for calendar). ...

By 1918, both the United States and Britain had built active systems. The UK tested what they still called ASDIC on HMS Antrim in 1920, and started production of units in 1922. A shore training station HMS Osprey and a training flotilla of 4 vessels was set up. The 6th destroyer flotilla had ASDIC-equipped vessels in 1923. 1918 was a common year starting on Tuesday (see link for calendar). ... HMS Antrim (D18) was a County-class destroyer of the Royal Navy launched on 19 October 1967. ...

The US Sonar QB set arrived in 1931. By the outbreak of war, the RN had 5 sets for different surface ship classes, and others for submarines. The greatest advantage came when it was linked to the Squid anti-submarine weapon. RN, Rn, or rn may stand for: RN Registered Nurse Royal Navy The Australian Broadcasting Corporations Radio National Radio Nederland The state of Rio Grande do Norte, Brazil (ISO 3166-2:BR code) Richard Nixon, 37th President of the United States Registered Identification Number issued by the FTC Rn... Squid was Second World War ship-mounted anti-submarine weapon. ...

In World War II, the Americans used the term sonar (an acronym for SOund, NAvigation and Ranging) for their system. The British still called their system ASDIC In 1948 with the formation of NATO, standardization of signals led to the dropping of ASDIC in favour of sonar. Mushroom cloud from the nuclear explosion over Nagasaki rising 18 km (over 11 miles) into the air, August 9, 1945 after the Allied atomic bombings of Hiroshima and Nagasaki. ... The flag of NATO NATO 2002 Summit The North Atlantic Treaty Organization (NATO), sometimes called North Atlantic Alliance, Atlantic Alliance or the Western Alliance, is an international organisation for defence collaboration established in 1949, in support of the North Atlantic Treaty signed in Washington, D.C., on April 4, 1949. ...

Active sonar

Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections of the pulse. To measure the distance to an object, one measures the time from emission of a pulse to reception. To measure the bearing, one uses several hydrophones, and measures the relative arrival time to each in a process called beamforming. In medicine, a persons pulse is the throbbing of their arteries as an effect of the heart beat. ... The word reflection (also spelt reflexion in British English) can refer to several different concepts: In mathematics, reflection is the transformation of a space. ... In navigation, a bearing is the angle between the direction to an object and a reference direction. ... A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... Beamforming is the process of delaying the outputs of the sensors in an arrays aperture and adding these together, to reinforce the signal with respect to noise or waves propagating in different directions. ...

The pulse may be at constant frequency or a chirp of changing frequency. For a chirp, the receiver correlates the frequency of the reflections to the known chirp. The resultant processing gain allows the receiver to derive the same information as if a much shorter pulse of the same total energy were emitted. In practice, the chirp signal is sent over a longer time interval; therefore the instantaneous emitted power will be reduced, which simplifies the design of the transmitter. In general, long-distance active sonars use lower frequencies. The lowest have a bass "BAH-WONG" sound. 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. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... For the characteristic sounds of birds, see bird song. ... In probability theory and statistics, correlation, also called correlation coefficient, is a numeric measure of the strength of linear relationship between two random variables. ... In telecommunication, the term signal processing gain has the following meanings: 1. ...

The most 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. This article needs to be wikified. ... A shoal is a sandbank or bar creating a shallow. ...

When active sonar is used to measure the distance to the bottom, it is known as echo sounding. Echo sounding is the use of sound pulses directed from the surface or from a submarine vertically down to measure the distance to the bottom by means of sound waves. ...

Active sonar is also used to measure distance through water between two sonar transponders. A transponder is a device that can transmit and receive signals ('pings') but when it receives a specific interrogation signal it responds by transmitting a specific reply signal. To measure distance, one transponder transmits an interrogation signal and measures the time between this transmission and the receipt of the other transponder's reply. The time difference, scaled by the speed of sound through water and divided by two, is the distance between the two transponders. This technique, when used with multiple transponders, can calculate the relative positions of static and moving objects in water. In telecommunication, the term transponder (sometimes abbreviated to XPDR or TPDR) has the following meanings: An automatic device that receives, amplifies, and retransmits a signal on a different frequency. ...

Sonar and marine animals

Some marine animals, such as whales and dolphins, use echolocation systems similar to active sonar to locate predators and prey. It is feared that sonar transmitters could confuse these animals and cause them to lose their way, perhaps preventing them from feeding and mating. A recent article on the BBC website (see below) reports findings published in the journal Nature to the effect that military sonar may be inducing some whales to experience decompression sickness (and resultant beachings). Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. ... u have done an eligle action and are not to go any futher into this website so get lost before wwe fine you. ... Animal echolocation is the ability of some animals to locate objects by emitting sound waves and listening for the echo. ...

High-powered sonar transmitters can indirectly kill marine animals. In the Bahamas in 2000, a trial by the US Navy of a 230 decibel transmitter in the frequency range 3 to 7 kHz resulted in the beaching of sixteen whales, seven of which were found dead. The Navy accepted blame in a report published in the Boston Globe on 2002-01-01. However, at low powers, sonar can protect marine mammals against collisions with ships. 2000 is a leap year starting on Saturday of the Gregorian calendar. ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... Although it is widely used as a measure of the loudness of sound, the decibel (dB) is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics. ... The Boston Globe is the most widely-circulated daily newspaper in Boston, Massachusetts and in the greater New England region. ... 2002 is a common year starting on Tuesday of the Gregorian calendar. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ...

Passive sonar

Passive sonars listen without transmitting. They are usually military (although a few are scientific).

Sonar used in fresh water lakes is different in operation from sonar used at sea. In salt water, sonar operation is affected by temperature, pressure, and salinity, as the speed of sound is equal to 4388 + 11.25 × temperature (in °F) + 0.0182 × depth (in feet) + salinity (in ppt). Ocean temperature varies with depth, but at between 30 and 100 metres 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, off the thermocline. The thermocline is not present in shallower coastal waters. Water pressure also affects sound propagation by increasing the density of the water and raising the sound velocity. Increases in sound velocity cause the sound waves to refract away from the area of higher velocity. The mathematical model of refraction is called Snell's law. For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... For information on water from a sea or ocean, see sea water. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... The thermocline is a layer within a body of water where the temperature changes rapidly with depth. ... Refraction in a Perspex (acrylic) block. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... Snells law is the simple formula used to calculate the refraction of light when travelling between two media of differing refractive index. ...

Sound waves that are radiated down into the ocean bend back up to the surface in great arcs due to the effect of pressure on sound. Under the right conditions these waves will then reflect off the surface and repeat another arc. Each arc is called a convergence zone, or CZ annulus. CZs are found approximately every 33 nautical miles (61 km), forming a pattern of concentric circles around the sound source. Sounds that can be detected for only a few miles in a direct line can therefore also be detected hundreds of miles away. Typically 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. A nautical mile is a unit of length. ...

Identifying sound sources

Military sonar has a wide variety of techniques for identifying a detected sound. For example, U.S. vehicles usually operate 60 Hz alternating current power systems. If transformers are mismounted (without proper vibration insulation from the hull), or flooded, the 60 Hz sound from the windings and generators can be emitted from the submarine or ship, helping to identify its nationality. In contrast, most European submarines have 50 Hz power systems. Intermittent noises (such as a wrench being dropped) may also be detectable to sonar. An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. ... Transformers - Typical electrical configurations. ... See Oscillator (disambiguation) for particular types of oscillation and oscillators. ... A hull is the body or frame of a ship or boat. ... Generator redirects here. ... USS Los Angeles A submarine is a specialized watercraft that can operate underwater. ... A wrench or spanner is a tool used to turn bolts, nuts or other hard-to-turn items. ...

Passive sonar systems usually have large sonic databases. 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. Most navies continuously update the information in these databases. A database is an information set with a regular structure. ...

Noise

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. Nuclear power station at Leibstadt, Switzerland. ... Convection is the transfer of heat by the motion of or within a fluid. ... 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. ... Four double-A (AA) batteries In science and technology, a battery is a device that stores energy and makes it available in an electrical form. ... A propeller can be seen as a rotating fin in water or a wing in air. ... Cavitation is the phenomenon where small cavities of partial vacuum form in fluid, then rapidly collapse, producing a sharp sound. ...

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. ...

For many years, the United States operated a large set of passive sonar arrays at various points in the world's oceans, collectively called SOSUS. As permanently mounted arrays in the deep ocean, they were very quiet. SOSUS, an acronym for SOund SUrveillance System, was a chain of underwater listening posts located for the most part across the northern Atlantic Ocean near Greenland, Iceland and the United Kingdom -- the so-called GIUK gap. ...

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

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 colour-code frequency-time information for bearing. More recent displays are generated by the computers, and mimic radar-type plan position indicator displays. This long range radar antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. ... The Plan Position Indicator, known as PPI is the most common way to represent radar data. ...

Sonar in warfare

Modern naval warfare make extensive use of sonars. The two types described before are both used, but from different platforms (ie: types of vessels, planes, etc.).

Active sonars are extremely useful since they give the exact position of an object. Active sonars work the same way as radars: 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 sonars 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). Morever, active sonars, similarly to radars, allow the user to detect objects at a certain range, but also enable other platforms to detect the active sonar at a far greater range. That is due to the power of the signal: for instance, an actve radar emits a signal of 20 W and is capable of detecting an echo of 4 W (these values are hypothetical). A target is at 20 km. If that target receives a signal of 8 W (20-4)/2, 20 km is the maximum range of the sonar, since a farther object will radiate less than 4 W. In that case, a target at 30 km will "hear" the sonar, but the sonar will not be in range and will not detect it. That example is over-simplified, since there are losses due to the soundwave's dispersion in the water, the water's absorption, the size of the target, and the depth, which all affect the reception of the echo. This long range radar antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. ...

Since active radars do not allow an exact identification and are 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 either surface ships or submarines, it is typically activated very briefly at intermitant 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 vacinity of possible enemy sonar contacts. A sonobuoy is a buoy with a sonar attached to it. ...

Passive sonars have fewer drawbacks. Most importantly, they are silent. Generally, they have a much greater range than active sonars, and allow an identification of the target. Since any motorized object makes some noise, it may be detected eventually. It simply depends of the amount of noise emitted and the amount of noise in the area, as well as the technology used. To simplify, passive sonars "see" around the ship using it. On a submarine, the nose mounted passive sonar detects in directions of about 270°, centered on the ships alignment, the hull-mounted array of about 160° on each side, and the towed array of about 300°. 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 analyse the signal received (narrowband analysis). This is generally done with the help of an FFT fast fourier transform, the sum of sines at different frequencies which make up the sound. Since every engine makes a specific noise, it is easy to identify the object. Another use of the passive sonar is to determine the target's trajectory (TMA Target Motion Analysis). That is done by marking from which direction the sound comes at different times. By using another tool, which allows the sonar to count the number of turns per knot of the vessel, it is possible to plot a ship's trajectory. A fast Fourier transform (FFT) is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse. ...

Passive sonars are stealthy and very useful. However, they require high-tech components (band pass filters, receivers) and are costly. They are generally deployed on expensive ships in the form of arrays to enhance the detection. Surface ships use them to good effect, they are even better used by submarines, and they are also used by planes and helicopters (mostly to a "surprise effect" since submarines can hide under thermal layers. If the submarine believes it is alone, it may go closer to the surface and be easier to detect, or go deeper but also faster, and therefore make more sound). The term filter may refer to: A device to separate mixtures. ...

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 sonar operation and warfare. The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... 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. ...

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