Contenido

El rendimiento de la detección, clasificación y localización de un sonar depende del entorno y del equipo receptor, además del equipo emisor en un sonar activo o del ruido radiado por el objetivo en un sonar pasivo.

sound propagation

Sonar performance is affected by variations in the speed of sound, especially in the vertical plane. Sound travels more slowly in fresh water than in salt water, varying as a function of the modulus of elasticity and the density of mass. The modulus of elasticity is sensitive to temperature, the concentration of dissolved impurities (usually salinity) and pressure, with the effect of density being minor. According to Mackenzie,[5]​ the speed of sound c (in m/s) in sea water is approximately equal to:.

Where T is the temperature (in degrees Celsius, for values ​​between 2 and 30 °C), S the salinity (in parts per thousand, for values ​​between 25 and 40) and D the depth in m (for values ​​between 0 and 8000 m). This empirical equation is reasonably accurate for the indicated ranges. Ocean temperature changes with depth, but between 30 and 100 m there is an often noticeable change, called a thermocline, which divides the warmer surface water from the colder deep water that makes up the bulk of the ocean. This can make sonar difficult, as a sound originating on one side of the thermocline tends to bend or refract as it crosses it. The thermocline may be present in shallower coastal waters, where however wave action often mixes the water column, removing it. The pressure of water also affects the propagation of sound in a vacuum, increasing its viscosity at higher pressures, which causes the sound waves to retract away from the area of ​​greatest viscosity. The mathematical model of refraction is called Snell's Law.

Sound waves that radiate toward the ocean floor curve back to the surface in large sine arcs due to increasing pressure (and therefore greater speed of sound) with depth. The ocean must be at least 1850 m deep so that sound waves echo back off the bottom rather than refracting back to the surface, reducing bottom loss throughput. Under the right conditions these sound waves will concentrate near the surface and be reflected back to the bottom repeating another atx arc. Each focus on the surface is called a convergence zone, forming a ring on sonar. The distance and width of the convergence zone depends on the temperature and salinity of the water. For example, in the North Atlantic convergence zones are located approximately every 33 nautical miles (61 km), depending on the time of year. Sounds that can be heard from just a few miles in a direct line can also be detected hundreds of miles further away. With powerful sonars the first, second and third convergence zones are quite useful; Beyond them the signal is too weak and the thermal conditions too unstable, reducing the reliability of the signals. The signal naturally attenuates with distance, but modern sonar systems are very sensitive, being able to detect targets despite low signal-to-noise ratios.

If the sound source is deep and the conditions are right, propagation can occur in the "deep sound channel." This provides extremely low propagation loss for a receiver in the channel, which is because the sound trapped in the channel is lossless at the boundaries. Similar spreads can occur in the "surface ribbon" under good conditions. However, in this case there are losses due to reflection on the surface.

In shallow waters the propagation is generally by repeated sounds on the surface and bottom, and considerable losses can occur.

Sound propagation is also affected by the absorption "Absorption (sound)") of water as well as the surface and bottom. This absorption changes with frequency, due to different mechanisms in seawater. For this reason, sonar that needs to operate at long distances tends to use low frequencies, so that the effects of absorption are minimized.

The sea contains many sources of noise that interfere with the desired signal. The main sources of noise are due to waves and navigation. The movement of the receiver through the water can also produce low propagation noise, depending on its decibels.

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 active interference that does not occur in passive sonar. This dispersion effect is different from that which occurs in room reverberation, which is a reflective phenomenon. An analogy is the scattering of a car's headlights in fog: a beam of light from a powerful flashlight can penetrate the fog, but headlights are less directional and produce a "blur" in which the returned reverberation dominates. Similarly, to overcome reverberation in water, an active sonar needs to emit a narrow wave.

White characteristics

A sonar target, such as a submarine, has two main characteristics that influence the performance of the equipment. For active sonar it is its reflective characteristics, known as target "strength". For passive sonar, the nature of the noise radiated by the target. In general, the radiated spectrum will consist of continuous noise with spectral lines used to classify it.

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

Countermeasures

Attacked submarines can launch active countermeasures to increase the noise level and create a large false target. Passive countermeasures include isolating noisy devices and coating the hull of submarines.

El sonar activo usa un emisor de sonido y un receptor. Cuando los dos están en el mismo lugar se habla de funcionamiento monoestático. Cuando el emisor y el receptor están separados, de funcionamiento biestático. Cuando se usan más emisores o receptores espacialmente separados, de funcionamiento multiestático. La mayoría de los equipos de sonar son monoestático, usándose la misma matriz para emisión y recepción, aunque cuando la plataforma está en movimiento puede ser necesario considerar que esta disposición funciona biestáticamente. Los campos de sonoboyas activas pueden funcionar multiestáticamente.

El sonar activo crea un pulso de sonido, llamado a menudo un «ping», y entonces oye la reflexión "Reflexión (sonido)") (eco) del mismo. Este pulso de sonido suele crearse electrónicamente usando un proyecto sonar") formado por un generador de señal, un amplificador de potencia y un transductor o matriz electroacústica, posiblemente un conformador de haces"). Sin embargo, puede crearse por otros medios, como por ejemplo químicamente, usando explosivos, o térmicamente") mediante fuentes de calor. También puede crearse mediante el infrasonido.

Para calcular la distancia a un objeto se mide el tiempo desde la emisión del pulso a la recepción de su eco y se convierte a una longitud conociendo la velocidad del sonido. Para medir el rumbo se usan varios hidrófonos, midiendo el conjunto el tiempo de llegada relativo a cada uno, o bien una matriz de hidrófonos, midiendo la amplitud relativa de los haces formados mediante un proceso llamado conformación de haz"). El uso de una matriz reduce la respuesta espacial de forma que para lograr una amplia cobertura se emplean sistemas multihaces. La señal del blanco (si existe) junto con el ruido se somete entonces a un procesado de señal, que para los equipos simples puede ser sólo una medida de la potencia. Se presenta entonces el resultado a algún tipo de dispositivo de decisión que califica la salida como señal o ruido. Este dispositivo puede ser un operador con auriculares o una pantalla, en los equipos más sofisticado un software específico. Pueden realizarse operaciones adicionales para clasificar el blanco y localizarlo, así como para medir su velocidad.

El pulso puede ser de amplitud "Amplitud (física)") constante o un pulso de frecuencia modulada (chirp) para permitir la compresión de pulso") en la recepción. Los equipos simples suelen usar el primero con un filtro lo suficientemente ancho como para cubrir posibles cambios Doppler debidos al movimiento del blanco, mientras los más complejos suelen usar la segunda técnica. Actualmente la compresión de pulso suele lograrse usando técnicas de correlación digital. Los equipos militares suelen tener múltiples haces para lograr una cobertura completa mientras los más simples sólo cubren un arco estrecho. Originalmente se usaba un único haz realizando el escaneo perimetral mecánicamente, pero esto era un proceso lento.

Especialmente cuando se usan transmisiones de una sola frecuencia, el efecto Doppler puede usarse para medir la velocidad radial del blanco. La diferencia de frecuencia entre la señal emitida y la recibida se mide y se traduce a una velocidad. Dado que los desplazamientos Doppler pueden deberse al movimiento del receptor o del blanco, debe tenerse la primera en cuenta para lograr un valor preciso.

El sonar activo se usa también para medir la distancia en el agua entre dos transductores (radioemisores) de sonar o una combinación de hidrófono y proyector. Cuando un equipo recibe una señal de interrogación, emite a su vez una señal de respuesta. Para medir la distancia, un equipo emite una señal de interrogación y mide el tiempo entre esta transmisión y la recepción de la respuesta. La diferencia de tiempo permite calcular la distancia entre dos equipos. Esta técnica, usada con múltiples equipos, puede calcular las posiciones relativas de objetos estáticos o en movimiento.

En época de guerra, la emisión de un pulso activo era tan comprometida para el camuflaje de un submarino que se consideraba una brecha severa de las operaciones.

Adverse effects on marine fauna

High-powered sonar emitters can affect marine wildlife, although it is not known exactly how. Some marine animals such as whales and dolphins use echolocation systems similar to active sonar to detect predators and prey. It is feared that sonar emitters could confuse these animals.

It has been suggested that military sonar panics whales, causing them to surface so quickly that they suffer some form of decompression sickness. This hypothesis was first raised in an essay published in the journal Nature in 2003, which reported acute injuries caused by gas bubbles (indicative of decompression syndrome) in stranded whales shortly after the start of military maneuvers off the Canary Islands in September 2002.[6]​.

In 2000 in the Bahamas, a US Navy test of sonar transmissions caused the stranding of seventeen whales, seven of which were found dead. The Navy took responsibility in a report that found that the dead whales had suffered acoustically induced hemorrhages in their ears.[7] The resulting disorientation likely led to stranding.

A type of medium-frequency sonar has been linked to mass deaths of cetaceans around the world, and blamed by environmentalists for these deaths.[8] On October 20, 2005, a lawsuit was filed in Santa Monica, California, against the United States Navy for violating sonar practices of several environmental laws, including the National Environmental Policy Act, the Marine Mammal Protection Act, and the Endangered Species Act. Act*.[9]​.

El sonar pasivo detecta sin emitir. Se usa a menudo en instalaciones militares, así mismo tiene aplicaciones científicas, como detectar la ausencia o presencia de peces en diversos entornos acuáticos.

Identification of sound sources

Passive sonar has a wide variety of techniques to identify the source of a detected sound. For example, American ships typically have 60 Hz AC motors. If the transformers or generator are mounted without proper vibration isolation from the hull or are flooded, the 60 Hz sound from the motor can be emitted by the ship, which can help identify its nationality, as most European submarines have 50 Hz systems. Intermittent sound sources (such as a dropped wrench) can also be detected with monitoring equipment. sound passive. Recently, the identification of a signal was carried out by an operator according to his experience and training, but currently computers are used for this task.

Passive sonar systems can have a large sonic database, although final classification is usually performed manually by the sonar operator. A computer system often uses this database to identify classes of ships, actions (for example, the speed of a ship, or the type of weapon fired), and even particular ships. The US Office of Naval Intelligence publishes and constantly updates sound classifications.

Noise limitations

Passive sonar usually has severe limitations due to the noise generated by the engines and propeller. For this reason, many submarines are powered by nuclear reactors that can be cooled without pumps, using silent convection systems, or by fuel cells or batteries, which are also silent. Submarine thrusters are also designed and built to emit as little noise as possible. High-speed propulsion usually creates tiny air bubbles, a phenomenon known as cavitation and has a characteristic sound.

Sonar hydrophones can be towed behind the ship or submarine to reduce the effect of noise generated by the water itself. Towed units also combat the thermocline, since their height can be adjusted to avoid being in this zone.

Most passive sonars used a two-dimensional representation. The horizontal direction of it was the bearing and the vertical direction was the frequency, or sometimes the time. Another representation technique was to color code the frequency-time information of the marking. The most recent screens are generated by computers and imitate typical radar position indicator screens.

La guerra naval hace un uso extensivo del sonar. Se usan los dos tipos descritos anteriormente, desde varias plataformas: buques de superficie, aeronaves e instalaciones fijas. La utilidad de los sonares activos y pasivos depende de las características del ruido radiado por el blanco, generalmente un submarino. Aunque en la Segunda Guerra Mundial se usó principalmente el sonar activo, excepto por parte de los submarinos, con la llegada de los ruidosos submarinos nucleares se prefirió el sonar pasivo para la detección inicial. A medida que los submarinos se hacían más silenciosos se fue usando más el sonar activo.

El sonar activo es extremadamente útil dado que proporciona la posición exacta de un objeto. Su uso es sin embargo algo peligroso, dado que no permite identificar el blanco y cualquier buque cercano a la señal emitida la detectará. Eso permite identificar fácilmente el tipo de sonar (normalmente por su frecuencia) y su posición (por la potencia de la onda sonora). Más aún, el sonar activo permite al usuario detectar objetos dentro en un determinado alcance, pero también permite que otras plataformas detecten el sonar activo desde una distancia mucho mayor.

Debido a que el sonar activo no permite una identificación exacta y es muy ruidoso, este tipo de detección se usa desde plataformas rápidas (aviones y helicópteros) o ruidosas (la mayoría de buques de superficies), pero rara vez desde submarinos. Cuando un sonar activo se usa en superficie, suele activarse muy brevemente en periodos intermitentes, para reducir el riesgo de detección por el sonar pasivo de un enemigo. Así, el sonar activo suele considerarse un apoyo del pasivo. En las aeronaves el sonar activo se usa en sonoboyas desechables que se lanzan sobre la zona a patrullar o cerca de los contactos de un posible enemigo.

El sonar pasivo escucha los ruidos por lo que tiene ventajas evidentes sobre el activo. Generalmente tiene un alcance mucho mayor que el activo y permite la identificación del blanco. Dado que cualquier vehículo de motor hace algo de ruido, terminará siendo detectado, dependiendo sólo de la cantidad de ruido emitido y del presente en la zona, así como la tecnología usada. En un submarino, el sonar pasivo montado a proa detecta en unos 270º respecto al centro del buque, la matriz montada en el casco, unos 160º a cada lado, y la matriz de la torreta en los 360º. Las zonas ciegas se deben a la propia interferencia del buque. Cuando se detecta una señal en cierta dirección (lo que significa que algo hace ruido en dicha dirección, a lo que se llama detección de banda ancha) es posible enfocar y analizar la señal recibir (análisis de banda estrecha). Esto se suele hacer usando una transformada de Fourier para mostrar las diferentes frecuencias que forman el sonido. Dado que cada motor hace un ruido específico, es fácil identificar el objeto.

Otro uso del sonar pasivo es determinar la trayectoria del blanco. Este proceso se llama Análisis del Movimiento del Blanco (TMA, Target Motion Analysis), y permite calcular el alcance, curso y velocidad del blanco. El TMA se realiza marcando desde qué dirección procede el sonido en momentos diferentes, y comparando el movimiento con el del buque del propio operador. Los cambios en el movimiento relativo se analizan usando técnicas geométricas estándar junto con algunas asunciones respecto a los casos límite.

El sonar pasivo es furtivo y muy útil, pero requiere componentes muy sofisticados y caros (filtros de paso de banda, receptores, ordenadores, software de análisis, etcétera). Suele equiparse en barcos caros para mejorar la detección. Los buques de superficie lo usan eficazmente, pero es incluso mejor usado en submarinos y también se emplea en aviones y helicópteros.

Anti-submarine sonar

Until recently, sonars on surface ships were typically mounted on the hull, sides, or bow. It was soon determined after its first uses that a means of reducing navigation noise was needed. First canvas mounted on a frame was used, and then steel protections. Currently domes are usually made of reinforced plastic or pressurized rubber. These sonars are mainly active, such as the SQS-56").

Some features of the most modern surface ship sonars are as follows:.

• - Low frequency transmission and reception. This achieves greater range since sound propagation losses increase with frequency.

• - Simultaneous passive and active detection. This allows the detection of submarines and torpedoes at the same time.

• - OMNI, rotary-directive transmissions or combination of both; allowing detection of near and far targets simultaneously by combining the small dead zone of the OMNI transmission with the high level of power emitted by the directive transmission.

• - Stabilization and control of the transmission/reception beams which improves the detection threshold and works both in deep waters and on coasts.

• - FM transmissions mixed with CW for contact detection with low and high doppler simultaneously.

An example is the most modern sonar of the Spanish Navy, the LWHP53SN") developed by Indra Sistemas and Lockheed Martin installed on the frigate Cristóbal Colón (F-105) "Cristóbal Colón (F-105)"), which incorporates all these characteristics.

Due to ship noise problems, towed sonars are also used. These also have the advantage of being able to be located at greater depths. However, there are limitations to its use in shallow waters. One problem is that the winches needed to launch and retrieve these sonars are large and expensive. An example of this type of sonar is Sonar 2087") manufactured by Thales Underwater Systems").

torpedo sonar

Modern torpedoes typically include active/passive sonar, which can be used to directly locate the target, but also to follow wakes. A pioneering example of this type of torpedo is the Mark 37").

mine sonar

Mines can incorporate sonar to detect, locate and recognize their target. An example is the CAPTOR mine.

Anti-mine sonar

Mine Countermeasure (MCM) sonar is a specialized type of sonar used to detect small objects. Most of them are mounted on the hull, an example being the Type 2093").

underwater sonar

Submarines rely on sonar much more than surface ships, which cannot use it at great depths. These kits can be hull-mounted or towed. In addition, they are very useful in oceanographic issues.

aerial sonar

Helicopters can be used for anti-submarine warfare by deploying active/passive sonobuoy fields or employing submersible sonar, such as the AQS-13. Conventional aircraft can also launch sonobuoys, having more autonomy and capacity to do so. The processing of the data collected by these equipment can be carried out on the aircraft or on a ship. Helicopters have also been used in mine countermeasures missions, using towed sonars such as the AQS-20A.

They can be towed or independent. A pioneering example was the German Sieglinde.

Underwater communications

Ships and submarines are equipped with special sonars for underwater communication. A NATO standard allows the different types to interact. An example of this equipment is Sonar 2008"). This is one of the most important.

marine surveillance

For many years the United States operated a large array of passive sonar arrays at various locations in the world's oceans, collectively called SOSUS (Sound Surveillance System) and later IUSS (Integrated Undersea Surveillance System). A similar system is believed to have been operated by the Soviet Union. Since arrays permanently mounted on the ocean floor were used, they were placed in very quiet places to achieve long ranges. Signal processing was done using large computers on the ground. With the end of the Cold War a SOSUS array has been destined for scientific use.

underwater safety

Sonar can be used to detect frogmen and other divers. This may be necessary around ships or at port entrances. Active sonar can also be used as a deterrent mechanism. An example of these teams is the Cerberus.

Interception sonar

This sonar is designed to detect and locate hostile sonar transmissions. An example is the Type 2082") equipped on the Vanguard class submarines.

Fishing applications

Fishing is a major industry subject to growing demand, but global catch volumes are falling as a result of increasing resource scarcity. The industry faces a future of continued global consolidation until a point of sustainability can be reached. However, the consolidation of fishing fleets has led to a growing demand for sophisticated electronic fishing location equipment such as sensors, transmitters and sonars. Historically, anglers have used many different techniques to locate schools of fish. However, acoustic technology has been one of the most important forces behind the development of modern commercial fishing vessels.

Sound waves travel differently through fish than through clean water because their air-filled swim bladder has a different density than seawater. This difference in density allows the detection of schools of fish using reflected sound. Currently, commercial fishing vessels rely almost entirely on acoustic equipment to detect fish.

Companies such as Marport Canada, Wesmar, Furuno, Krupp and Simrad make sonar and acoustic instruments for the fishing industry. For example, network sensors take various measurements underwater and transmit the information to an onboard receiver. Each sensor is equipped with one or more acoustic transducers depending on its specific function. Data is transmitted using acoustic telemetry and received on a helmet-mounted hydrophone. The signals are processed and displayed on a high resolution monitor.

Depth calculation

By emitting sound waves directly to the bottom and recording the return echo it is possible to calculate the depth, since the speed of sound in water is more or less stable over a small depth range.

Network location

Acoustic equipment mounted on the nets is used, which transmits the recorded information by cable or acoustic telemetry to the fishing vessel. This way you know exactly the distance of the net from the bottom and the surface, the amount of fish inside it, and other relevant data.

Vessel speed calculation

Sonars have been developed to measure the speed of the ship relative to the water and the seabed.

ROV/UUV Sonars

Small sonars have been equipped on ROVs and UUVs to allow their operation in low visibility conditions. These sonars are used to scan ahead of the vehicle.

Aircraft location

Aircraft are equipped with sonars that function as buoys to allow them to be located in the event of an accident at sea.

Biomass estimation

Sonar can be used to estimate the biomass "Biomass (ecology)") present in an aquatic region, based on the sound reflection returned by it. The main difference with fishery location equipment is that quantitative hydroacoustic analysis requires that measurements be made with equipment that is sensitive and well calibrated enough to obtain reliable measurements.

Hydroacoustic equipment provides a repeatable and non-invasive method of collecting continuous, high-resolution (sub-meter) data in three-dimensional sections, allowing the abundance and distribution of fishery resources to be measured.

Acoustic labels

To track the movements of fish, whales, etc., an acoustic device can be attached to an animal that emits pulses at certain intervals, possibly encoding, for example, depth.

Wave measurement

A vertical acoustic transducer mounted on the seafloor or on a platform can be used to make measurements of wave pitch and molecules. From this statistics of the surface conditions at a given location can be derived.

Measurement of water speed

Special short-range sonars have been developed to allow measurement of water velocity, in a vacuum.

Determination of the type of fund

Sonars have been developed that can be used to characterize the seabed: mud, sand, gravel, silt, etc. This is usually achieved by comparing the direct and reflected returns of the fund.

Calculation of bottom topography

Side scan sonar can be used to compile data on the topography of an area. Low frequency sonars such as GLORIA") have been used in the exploration of the continental shelf while higher frequency sonars are used for detailed explorations of smaller areas.

Characterization of the marine subsoil

Powerful low-frequency sonars have been developed to enable characterization of the surface layers of the seabed.

Synthetic aperture sonar

Various synthetic aperture sonars have been built in the laboratory and some have been used in graphite mine search and disposal systems.

underwater archeology

Detection of wrecks and underwater deposits and their location on the seabed.

• - Hackmann, Willem D. Seek & Strike: Sonar, Anti-submarine Warfare, and the Royal Navy, 1914-54. (London: HMSO, 1984).

• - Hackmann, Willem D. «Sonar Research and Naval Warfare 1914-1954: A Case Study of a Twentieth-Century Science.» Historical Studies in the Physical and Biological Sciences 16#1 (1986) 83-110.

Contenido

El rendimiento de la detección, clasificación y localización de un sonar depende del entorno y del equipo receptor, además del equipo emisor en un sonar activo o del ruido radiado por el objetivo en un sonar pasivo.

sound propagation

Sonar performance is affected by variations in the speed of sound, especially in the vertical plane. Sound travels more slowly in fresh water than in salt water, varying as a function of the modulus of elasticity and the density of mass. The modulus of elasticity is sensitive to temperature, the concentration of dissolved impurities (usually salinity) and pressure, with the effect of density being minor. According to Mackenzie,[5]​ the speed of sound c (in m/s) in sea water is approximately equal to:.

Where T is the temperature (in degrees Celsius, for values ​​between 2 and 30 °C), S the salinity (in parts per thousand, for values ​​between 25 and 40) and D the depth in m (for values ​​between 0 and 8000 m). This empirical equation is reasonably accurate for the indicated ranges. Ocean temperature changes with depth, but between 30 and 100 m there is an often noticeable change, called a thermocline, which divides the warmer surface water from the colder deep water that makes up the bulk of the ocean. This can make sonar difficult, as a sound originating on one side of the thermocline tends to bend or refract as it crosses it. The thermocline may be present in shallower coastal waters, where however wave action often mixes the water column, removing it. The pressure of water also affects the propagation of sound in a vacuum, increasing its viscosity at higher pressures, which causes the sound waves to retract away from the area of ​​greatest viscosity. The mathematical model of refraction is called Snell's Law.

Sound waves that radiate toward the ocean floor curve back to the surface in large sine arcs due to increasing pressure (and therefore greater speed of sound) with depth. The ocean must be at least 1850 m deep so that sound waves echo back off the bottom rather than refracting back to the surface, reducing bottom loss throughput. Under the right conditions these sound waves will concentrate near the surface and be reflected back to the bottom repeating another atx arc. Each focus on the surface is called a convergence zone, forming a ring on sonar. The distance and width of the convergence zone depends on the temperature and salinity of the water. For example, in the North Atlantic convergence zones are located approximately every 33 nautical miles (61 km), depending on the time of year. Sounds that can be heard from just a few miles in a direct line can also be detected hundreds of miles further away. With powerful sonars the first, second and third convergence zones are quite useful; Beyond them the signal is too weak and the thermal conditions too unstable, reducing the reliability of the signals. The signal naturally attenuates with distance, but modern sonar systems are very sensitive, being able to detect targets despite low signal-to-noise ratios.

If the sound source is deep and the conditions are right, propagation can occur in the "deep sound channel." This provides extremely low propagation loss for a receiver in the channel, which is because the sound trapped in the channel is lossless at the boundaries. Similar spreads can occur in the "surface ribbon" under good conditions. However, in this case there are losses due to reflection on the surface.

In shallow waters the propagation is generally by repeated sounds on the surface and bottom, and considerable losses can occur.

Sound propagation is also affected by the absorption "Absorption (sound)") of water as well as the surface and bottom. This absorption changes with frequency, due to different mechanisms in seawater. For this reason, sonar that needs to operate at long distances tends to use low frequencies, so that the effects of absorption are minimized.

The sea contains many sources of noise that interfere with the desired signal. The main sources of noise are due to waves and navigation. The movement of the receiver through the water can also produce low propagation noise, depending on its decibels.

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 active interference that does not occur in passive sonar. This dispersion effect is different from that which occurs in room reverberation, which is a reflective phenomenon. An analogy is the scattering of a car's headlights in fog: a beam of light from a powerful flashlight can penetrate the fog, but headlights are less directional and produce a "blur" in which the returned reverberation dominates. Similarly, to overcome reverberation in water, an active sonar needs to emit a narrow wave.

White characteristics

A sonar target, such as a submarine, has two main characteristics that influence the performance of the equipment. For active sonar it is its reflective characteristics, known as target "strength". For passive sonar, the nature of the noise radiated by the target. In general, the radiated spectrum will consist of continuous noise with spectral lines used to classify it.

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

Countermeasures

Attacked submarines can launch active countermeasures to increase the noise level and create a large false target. Passive countermeasures include isolating noisy devices and coating the hull of submarines.

El sonar activo usa un emisor de sonido y un receptor. Cuando los dos están en el mismo lugar se habla de funcionamiento monoestático. Cuando el emisor y el receptor están separados, de funcionamiento biestático. Cuando se usan más emisores o receptores espacialmente separados, de funcionamiento multiestático. La mayoría de los equipos de sonar son monoestático, usándose la misma matriz para emisión y recepción, aunque cuando la plataforma está en movimiento puede ser necesario considerar que esta disposición funciona biestáticamente. Los campos de sonoboyas activas pueden funcionar multiestáticamente.

El sonar activo crea un pulso de sonido, llamado a menudo un «ping», y entonces oye la reflexión "Reflexión (sonido)") (eco) del mismo. Este pulso de sonido suele crearse electrónicamente usando un proyecto sonar") formado por un generador de señal, un amplificador de potencia y un transductor o matriz electroacústica, posiblemente un conformador de haces"). Sin embargo, puede crearse por otros medios, como por ejemplo químicamente, usando explosivos, o térmicamente") mediante fuentes de calor. También puede crearse mediante el infrasonido.

Para calcular la distancia a un objeto se mide el tiempo desde la emisión del pulso a la recepción de su eco y se convierte a una longitud conociendo la velocidad del sonido. Para medir el rumbo se usan varios hidrófonos, midiendo el conjunto el tiempo de llegada relativo a cada uno, o bien una matriz de hidrófonos, midiendo la amplitud relativa de los haces formados mediante un proceso llamado conformación de haz"). El uso de una matriz reduce la respuesta espacial de forma que para lograr una amplia cobertura se emplean sistemas multihaces. La señal del blanco (si existe) junto con el ruido se somete entonces a un procesado de señal, que para los equipos simples puede ser sólo una medida de la potencia. Se presenta entonces el resultado a algún tipo de dispositivo de decisión que califica la salida como señal o ruido. Este dispositivo puede ser un operador con auriculares o una pantalla, en los equipos más sofisticado un software específico. Pueden realizarse operaciones adicionales para clasificar el blanco y localizarlo, así como para medir su velocidad.

El pulso puede ser de amplitud "Amplitud (física)") constante o un pulso de frecuencia modulada (chirp) para permitir la compresión de pulso") en la recepción. Los equipos simples suelen usar el primero con un filtro lo suficientemente ancho como para cubrir posibles cambios Doppler debidos al movimiento del blanco, mientras los más complejos suelen usar la segunda técnica. Actualmente la compresión de pulso suele lograrse usando técnicas de correlación digital. Los equipos militares suelen tener múltiples haces para lograr una cobertura completa mientras los más simples sólo cubren un arco estrecho. Originalmente se usaba un único haz realizando el escaneo perimetral mecánicamente, pero esto era un proceso lento.

Especialmente cuando se usan transmisiones de una sola frecuencia, el efecto Doppler puede usarse para medir la velocidad radial del blanco. La diferencia de frecuencia entre la señal emitida y la recibida se mide y se traduce a una velocidad. Dado que los desplazamientos Doppler pueden deberse al movimiento del receptor o del blanco, debe tenerse la primera en cuenta para lograr un valor preciso.

El sonar activo se usa también para medir la distancia en el agua entre dos transductores (radioemisores) de sonar o una combinación de hidrófono y proyector. Cuando un equipo recibe una señal de interrogación, emite a su vez una señal de respuesta. Para medir la distancia, un equipo emite una señal de interrogación y mide el tiempo entre esta transmisión y la recepción de la respuesta. La diferencia de tiempo permite calcular la distancia entre dos equipos. Esta técnica, usada con múltiples equipos, puede calcular las posiciones relativas de objetos estáticos o en movimiento.

En época de guerra, la emisión de un pulso activo era tan comprometida para el camuflaje de un submarino que se consideraba una brecha severa de las operaciones.

Adverse effects on marine fauna

High-powered sonar emitters can affect marine wildlife, although it is not known exactly how. Some marine animals such as whales and dolphins use echolocation systems similar to active sonar to detect predators and prey. It is feared that sonar emitters could confuse these animals.

It has been suggested that military sonar panics whales, causing them to surface so quickly that they suffer some form of decompression sickness. This hypothesis was first raised in an essay published in the journal Nature in 2003, which reported acute injuries caused by gas bubbles (indicative of decompression syndrome) in stranded whales shortly after the start of military maneuvers off the Canary Islands in September 2002.[6]​.

In 2000 in the Bahamas, a US Navy test of sonar transmissions caused the stranding of seventeen whales, seven of which were found dead. The Navy took responsibility in a report that found that the dead whales had suffered acoustically induced hemorrhages in their ears.[7] The resulting disorientation likely led to stranding.

A type of medium-frequency sonar has been linked to mass deaths of cetaceans around the world, and blamed by environmentalists for these deaths.[8] On October 20, 2005, a lawsuit was filed in Santa Monica, California, against the United States Navy for violating sonar practices of several environmental laws, including the National Environmental Policy Act, the Marine Mammal Protection Act, and the Endangered Species Act. Act*.[9]​.

El sonar pasivo detecta sin emitir. Se usa a menudo en instalaciones militares, así mismo tiene aplicaciones científicas, como detectar la ausencia o presencia de peces en diversos entornos acuáticos.

Identification of sound sources

Passive sonar has a wide variety of techniques to identify the source of a detected sound. For example, American ships typically have 60 Hz AC motors. If the transformers or generator are mounted without proper vibration isolation from the hull or are flooded, the 60 Hz sound from the motor can be emitted by the ship, which can help identify its nationality, as most European submarines have 50 Hz systems. Intermittent sound sources (such as a dropped wrench) can also be detected with monitoring equipment. sound passive. Recently, the identification of a signal was carried out by an operator according to his experience and training, but currently computers are used for this task.

Passive sonar systems can have a large sonic database, although final classification is usually performed manually by the sonar operator. A computer system often uses this database to identify classes of ships, actions (for example, the speed of a ship, or the type of weapon fired), and even particular ships. The US Office of Naval Intelligence publishes and constantly updates sound classifications.

Noise limitations

Passive sonar usually has severe limitations due to the noise generated by the engines and propeller. For this reason, many submarines are powered by nuclear reactors that can be cooled without pumps, using silent convection systems, or by fuel cells or batteries, which are also silent. Submarine thrusters are also designed and built to emit as little noise as possible. High-speed propulsion usually creates tiny air bubbles, a phenomenon known as cavitation and has a characteristic sound.

Sonar hydrophones can be towed behind the ship or submarine to reduce the effect of noise generated by the water itself. Towed units also combat the thermocline, since their height can be adjusted to avoid being in this zone.

Most passive sonars used a two-dimensional representation. The horizontal direction of it was the bearing and the vertical direction was the frequency, or sometimes the time. Another representation technique was to color code the frequency-time information of the marking. The most recent screens are generated by computers and imitate typical radar position indicator screens.

La guerra naval hace un uso extensivo del sonar. Se usan los dos tipos descritos anteriormente, desde varias plataformas: buques de superficie, aeronaves e instalaciones fijas. La utilidad de los sonares activos y pasivos depende de las características del ruido radiado por el blanco, generalmente un submarino. Aunque en la Segunda Guerra Mundial se usó principalmente el sonar activo, excepto por parte de los submarinos, con la llegada de los ruidosos submarinos nucleares se prefirió el sonar pasivo para la detección inicial. A medida que los submarinos se hacían más silenciosos se fue usando más el sonar activo.

El sonar activo es extremadamente útil dado que proporciona la posición exacta de un objeto. Su uso es sin embargo algo peligroso, dado que no permite identificar el blanco y cualquier buque cercano a la señal emitida la detectará. Eso permite identificar fácilmente el tipo de sonar (normalmente por su frecuencia) y su posición (por la potencia de la onda sonora). Más aún, el sonar activo permite al usuario detectar objetos dentro en un determinado alcance, pero también permite que otras plataformas detecten el sonar activo desde una distancia mucho mayor.

Debido a que el sonar activo no permite una identificación exacta y es muy ruidoso, este tipo de detección se usa desde plataformas rápidas (aviones y helicópteros) o ruidosas (la mayoría de buques de superficies), pero rara vez desde submarinos. Cuando un sonar activo se usa en superficie, suele activarse muy brevemente en periodos intermitentes, para reducir el riesgo de detección por el sonar pasivo de un enemigo. Así, el sonar activo suele considerarse un apoyo del pasivo. En las aeronaves el sonar activo se usa en sonoboyas desechables que se lanzan sobre la zona a patrullar o cerca de los contactos de un posible enemigo.

El sonar pasivo escucha los ruidos por lo que tiene ventajas evidentes sobre el activo. Generalmente tiene un alcance mucho mayor que el activo y permite la identificación del blanco. Dado que cualquier vehículo de motor hace algo de ruido, terminará siendo detectado, dependiendo sólo de la cantidad de ruido emitido y del presente en la zona, así como la tecnología usada. En un submarino, el sonar pasivo montado a proa detecta en unos 270º respecto al centro del buque, la matriz montada en el casco, unos 160º a cada lado, y la matriz de la torreta en los 360º. Las zonas ciegas se deben a la propia interferencia del buque. Cuando se detecta una señal en cierta dirección (lo que significa que algo hace ruido en dicha dirección, a lo que se llama detección de banda ancha) es posible enfocar y analizar la señal recibir (análisis de banda estrecha). Esto se suele hacer usando una transformada de Fourier para mostrar las diferentes frecuencias que forman el sonido. Dado que cada motor hace un ruido específico, es fácil identificar el objeto.

Otro uso del sonar pasivo es determinar la trayectoria del blanco. Este proceso se llama Análisis del Movimiento del Blanco (TMA, Target Motion Analysis), y permite calcular el alcance, curso y velocidad del blanco. El TMA se realiza marcando desde qué dirección procede el sonido en momentos diferentes, y comparando el movimiento con el del buque del propio operador. Los cambios en el movimiento relativo se analizan usando técnicas geométricas estándar junto con algunas asunciones respecto a los casos límite.

El sonar pasivo es furtivo y muy útil, pero requiere componentes muy sofisticados y caros (filtros de paso de banda, receptores, ordenadores, software de análisis, etcétera). Suele equiparse en barcos caros para mejorar la detección. Los buques de superficie lo usan eficazmente, pero es incluso mejor usado en submarinos y también se emplea en aviones y helicópteros.

Anti-submarine sonar

Until recently, sonars on surface ships were typically mounted on the hull, sides, or bow. It was soon determined after its first uses that a means of reducing navigation noise was needed. First canvas mounted on a frame was used, and then steel protections. Currently domes are usually made of reinforced plastic or pressurized rubber. These sonars are mainly active, such as the SQS-56").

Some features of the most modern surface ship sonars are as follows:.

• - Low frequency transmission and reception. This achieves greater range since sound propagation losses increase with frequency.

• - Simultaneous passive and active detection. This allows the detection of submarines and torpedoes at the same time.

• - OMNI, rotary-directive transmissions or combination of both; allowing detection of near and far targets simultaneously by combining the small dead zone of the OMNI transmission with the high level of power emitted by the directive transmission.

• - Stabilization and control of the transmission/reception beams which improves the detection threshold and works both in deep waters and on coasts.

• - FM transmissions mixed with CW for contact detection with low and high doppler simultaneously.

An example is the most modern sonar of the Spanish Navy, the LWHP53SN") developed by Indra Sistemas and Lockheed Martin installed on the frigate Cristóbal Colón (F-105) "Cristóbal Colón (F-105)"), which incorporates all these characteristics.

Due to ship noise problems, towed sonars are also used. These also have the advantage of being able to be located at greater depths. However, there are limitations to its use in shallow waters. One problem is that the winches needed to launch and retrieve these sonars are large and expensive. An example of this type of sonar is Sonar 2087") manufactured by Thales Underwater Systems").

torpedo sonar

Modern torpedoes typically include active/passive sonar, which can be used to directly locate the target, but also to follow wakes. A pioneering example of this type of torpedo is the Mark 37").

mine sonar

Mines can incorporate sonar to detect, locate and recognize their target. An example is the CAPTOR mine.

Anti-mine sonar

Mine Countermeasure (MCM) sonar is a specialized type of sonar used to detect small objects. Most of them are mounted on the hull, an example being the Type 2093").

underwater sonar

Submarines rely on sonar much more than surface ships, which cannot use it at great depths. These kits can be hull-mounted or towed. In addition, they are very useful in oceanographic issues.

aerial sonar

Helicopters can be used for anti-submarine warfare by deploying active/passive sonobuoy fields or employing submersible sonar, such as the AQS-13. Conventional aircraft can also launch sonobuoys, having more autonomy and capacity to do so. The processing of the data collected by these equipment can be carried out on the aircraft or on a ship. Helicopters have also been used in mine countermeasures missions, using towed sonars such as the AQS-20A.

They can be towed or independent. A pioneering example was the German Sieglinde.

Underwater communications

Ships and submarines are equipped with special sonars for underwater communication. A NATO standard allows the different types to interact. An example of this equipment is Sonar 2008"). This is one of the most important.

marine surveillance

For many years the United States operated a large array of passive sonar arrays at various locations in the world's oceans, collectively called SOSUS (Sound Surveillance System) and later IUSS (Integrated Undersea Surveillance System). A similar system is believed to have been operated by the Soviet Union. Since arrays permanently mounted on the ocean floor were used, they were placed in very quiet places to achieve long ranges. Signal processing was done using large computers on the ground. With the end of the Cold War a SOSUS array has been destined for scientific use.

underwater safety

Sonar can be used to detect frogmen and other divers. This may be necessary around ships or at port entrances. Active sonar can also be used as a deterrent mechanism. An example of these teams is the Cerberus.

Interception sonar

This sonar is designed to detect and locate hostile sonar transmissions. An example is the Type 2082") equipped on the Vanguard class submarines.

Fishing applications

Fishing is a major industry subject to growing demand, but global catch volumes are falling as a result of increasing resource scarcity. The industry faces a future of continued global consolidation until a point of sustainability can be reached. However, the consolidation of fishing fleets has led to a growing demand for sophisticated electronic fishing location equipment such as sensors, transmitters and sonars. Historically, anglers have used many different techniques to locate schools of fish. However, acoustic technology has been one of the most important forces behind the development of modern commercial fishing vessels.

Sound waves travel differently through fish than through clean water because their air-filled swim bladder has a different density than seawater. This difference in density allows the detection of schools of fish using reflected sound. Currently, commercial fishing vessels rely almost entirely on acoustic equipment to detect fish.

Companies such as Marport Canada, Wesmar, Furuno, Krupp and Simrad make sonar and acoustic instruments for the fishing industry. For example, network sensors take various measurements underwater and transmit the information to an onboard receiver. Each sensor is equipped with one or more acoustic transducers depending on its specific function. Data is transmitted using acoustic telemetry and received on a helmet-mounted hydrophone. The signals are processed and displayed on a high resolution monitor.

Depth calculation

By emitting sound waves directly to the bottom and recording the return echo it is possible to calculate the depth, since the speed of sound in water is more or less stable over a small depth range.

Network location

Acoustic equipment mounted on the nets is used, which transmits the recorded information by cable or acoustic telemetry to the fishing vessel. This way you know exactly the distance of the net from the bottom and the surface, the amount of fish inside it, and other relevant data.

Vessel speed calculation

Sonars have been developed to measure the speed of the ship relative to the water and the seabed.

ROV/UUV Sonars

Small sonars have been equipped on ROVs and UUVs to allow their operation in low visibility conditions. These sonars are used to scan ahead of the vehicle.

Aircraft location

Aircraft are equipped with sonars that function as buoys to allow them to be located in the event of an accident at sea.

Biomass estimation

Sonar can be used to estimate the biomass "Biomass (ecology)") present in an aquatic region, based on the sound reflection returned by it. The main difference with fishery location equipment is that quantitative hydroacoustic analysis requires that measurements be made with equipment that is sensitive and well calibrated enough to obtain reliable measurements.

Hydroacoustic equipment provides a repeatable and non-invasive method of collecting continuous, high-resolution (sub-meter) data in three-dimensional sections, allowing the abundance and distribution of fishery resources to be measured.

Acoustic labels

To track the movements of fish, whales, etc., an acoustic device can be attached to an animal that emits pulses at certain intervals, possibly encoding, for example, depth.

Wave measurement

A vertical acoustic transducer mounted on the seafloor or on a platform can be used to make measurements of wave pitch and molecules. From this statistics of the surface conditions at a given location can be derived.

Measurement of water speed

Special short-range sonars have been developed to allow measurement of water velocity, in a vacuum.

Determination of the type of fund

Sonars have been developed that can be used to characterize the seabed: mud, sand, gravel, silt, etc. This is usually achieved by comparing the direct and reflected returns of the fund.

Calculation of bottom topography

Side scan sonar can be used to compile data on the topography of an area. Low frequency sonars such as GLORIA") have been used in the exploration of the continental shelf while higher frequency sonars are used for detailed explorations of smaller areas.

Characterization of the marine subsoil

Powerful low-frequency sonars have been developed to enable characterization of the surface layers of the seabed.

Synthetic aperture sonar

Various synthetic aperture sonars have been built in the laboratory and some have been used in graphite mine search and disposal systems.

underwater archeology

Detection of wrecks and underwater deposits and their location on the seabed.

• - Hackmann, Willem D. Seek & Strike: Sonar, Anti-submarine Warfare, and the Royal Navy, 1914-54. (London: HMSO, 1984).

• - Hackmann, Willem D. «Sonar Research and Naval Warfare 1914-1954: A Case Study of a Twentieth-Century Science.» Historical Studies in the Physical and Biological Sciences 16#1 (1986) 83-110.