Dream
Sonar (from English SONAR, an acronym for Sound Navigation And Ranging, 'sound navigation') is a technique that uses underwater sound propagation primarily to navigate, communicate or detect submerged objects.
Sonar can be used as a means of acoustic location, working in a similar way to radar, with the difference that instead of emitting electromagnetic waves it uses sound impulses. In fact, acoustic localization was used in the air before GPS, and SODAR (Sonar Vertical Scanning Aerial) is still applicable for atmospheric research. The acoustic signal can be generated by piezoelectricity or by magnetostriction.
The term "sonar" is also used to refer to the equipment used to generate and receive infrasound sound. The frequencies used in sonar systems range from intrasonic to extrasonic (between 20 Hz and 20,000 Hz), the capacity of the human ear. However, in this case it would be necessary to refer to a hydrophone and not to a sonar. The sonar has both capabilities: it can be used as a hydrophone or as a sonar.
There are other sonars that do not cover the spectrum of the human ear, (mine hunters); they can span several high-frequency ranges, (80 kHz or 350 kHz), for example. They gain in accuracy when determining the object, but lose in range.
Although some animals (such as dolphins and bats) have probably used sound for object detection for millions of years, its use by humans was first recorded by Leonardo da Vinci in 1490. It was said to be used a tube inserted in the water to detect ships, putting an ear at its end. In the 19th century, underwater bells were used as a complement to lighthouses to warn sailors of danger.
The use of sound for underwater 'echolocation' appears to have been spurred by the Titanic disaster in 1912. The world's first patent on such a device was granted by the British Office of Patents to English meteorologist Lewis Richardson a month after the Titanic sank and German physicist Alexander Behm obtained another for a resonator in 1913. Canadian engineer Reginald Fessenden invented modern sonar in 1914 that could detect an iceberg two miles away, though he was unable to tell in which direction it was.
During World War I, and due to the need to detect submarines, more research was done on the use of sound. The British were soon using underwater microphones, while French physicist Paul Langevin, together with Russian émigré electrical engineer Constantin Chilowski, worked on the development of active sound devices for detecting submarines in 1915. Although piezoelectric and magnetostrictive transducers later superseded electrostatics they used, this work influenced the future of detector designs. Although modern transducers typically use a composite material as the active part between the light head and heavy tail, many other designs have been developed. For example, sound-sensitive light plastic films and fiber optics have been used in hydrophones (acoustic-electric transducers for aquatic use), while Terfenol-D and PMN have been developed for projectors. Piezoelectric composite materials are manufactured by several companies, including Morgan Electro Ceramics.
In 1916, under the auspices of the British Invention and Research Council, Canadian physicist Robert Boyle took charge of the active sonar project, building a prototype for testing in mid-1917. This work, for the Anti-Submarine Division, was carried out in absolute secrecy, and used piezoelectric quartz crystals to produce the world's first feasible sound-active underwater detection apparatus. Meanwhile, in the same laboratory, Albert Beaumont Wood was in charge of the development of passive listening systems.
By 1918 both France and Britain had built active systems. The British tested their ASDIC (as active detection equipment was known) on HMS Antrim in 1920 and began production of units in 1922. The 6th Destroyer Flotilla had ASDIC-equipped ships in 1923. An anti-submarine training ship, HMS Osprey, and a training flotilla of four ships were established on the Isle of Portland in 1924. The American Sonar QB did not arrive until 1931.
By the start of World War II, the British Royal Navy had five kits for different classes of surface ships and one for submarines, incorporated into a complete anti-submarine attack system. The effectiveness of early ASDICs was limited by the use of depth charges as an anti-submarine weapon. This required the attacking ship to pass over the submerged contact before dropping the charges, thus losing sonar contact in the moments before the attack. The attack thus required blind firing, during which time the submarine commander could successfully take evasive action. This situation was remedied by the use of several ships cooperating together and the adoption of "forward-launched weapons", such as the Hedgehog and later the Squid, which dropped loads at a target located in front of the attacker and therefore still in ASDIC contact. Developments during the war led to ASDIC equipment using different waveforms, allowing blind spots to be continuously covered. Later acoustic torpedoes were used.
At the start of World War II British sonar technology was transferred to the United States. Research on sonar and underwater sound has expanded enormously, particularly in this country. Many new types of military sonar were developed, including sonobuoys, submersible sonar, and mine detection sonar. This work formed the basis for postwar developments aimed at countering nuclear submarines. Sonar continued to be developed in many countries for both military and civilian uses. In recent years, most military developments have been focused on low-frequency active systems.
In World War II the United States used the term SONAR for its systems, an acronym coined as the equivalent of RADAR. In 1948, with the formation of NATO, signal standardization led to the abandonment of the term ASDIC in favor of SONAR.
Sonar performance factors
The detection, classification and localization performance of a sonar depends on the environment and the receiving equipment, as well as the emitting equipment in an active sonar or the noise radiated by the target in a passive sonar.
Sound propagation
Sonar performance is affected by variations in the speed of sound, especially in the vertical plane. Sound travels slower in fresh water than in salt water, varying as a function of modulus of elasticity and bulk density. The modulus of elasticity is sensitive to temperature, to the concentration of dissolved impurities (usually salinity) and to pressure, the effect of density being less. According to Mackenzie, the speed of sound c (in m/s) in seawater is approximately equal to:
c=1448.96+4.591T− − 5.304⋅ ⋅ 10− − 2T2+2.374⋅ ⋅ 10− − 4.2T3+1.340(S− − 35)+1.630⋅ ⋅ 10− − 2D+1.675⋅ ⋅ 10− − 7D2− − 1.025⋅ ⋅ 10− − 2T(S− − 35)− − 7.139⋅ ⋅ 10− − 13TD3{displaystyle c=1448.96+4.591T-5.304cdot 10^{-2T^{2}+2.374cdot 10^{-4.2}T^{3}+1.340(S-35)+1.630cdot 10^{-2}D+1.675cdot 10^{-7}{3}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{2}{c2}{c2}{cdot =1⁄2}{c2}{c2}{c2}{c2}{c2}{c2}{c2}{c2}{c2}
Where T is the temperature (in degrees Celsius for values between 2 and 30 °C), S is the salinity (in parts per thousand, for values from 25 to 40) and D the depth in m (for values between 0 and 8000 m). This empirical equation is reasonably accurate for the ranges indicated. The ocean's temperature changes with depth, but between 30 and 100 m there is an often noticeable shift, called a thermocline, which divides the warmer surface water from the cooler depths that make up the bulk of the ocean. This can make sonar action difficult, as a sound originating on one side of the thermocline tends to bend or refract as it crosses. The thermocline may be present in shallower coastal waters, where however wave action often mixes the water column, washing it away. Water pressure also affects the propagation of sound in a vacuum, increasing its viscosity at higher pressures, causing sound waves to retract away from the area of higher viscosity. The mathematical model of refraction is called Snell's Law.
Sound waves radiating towards the ocean floor are bent back to the surface in large sinusoidal arcs due to increasing pressure (and thus greater speed of sound) with depth. The ocean must be at least 1850m deep for sound waves to echo back off the bottom instead of refracting back to the surface, reducing bottom loss performance. Under the right conditions these sound waves will concentrate near the surface and will 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 found 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 an in-channel receiver, which is because sound trapped in the channel is lossless at the edges. Similar propagations can occur on 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, which can cause considerable losses.
Sound propagation is also affected by absorption from water as well as from the surface and bottom. This absorption changes with frequency, due to different mechanisms in seawater. This is why sonar that needs to operate over long distances tends to use low frequencies, so as to minimize the effects of absorption.
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 using active sonar, 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 with passive sonar. This scattering effect is different from what happens in a room's reverberation, which is a reflective phenomenon. An analogy is the scattering of car headlights in fog: a beam from a powerful flashlight can penetrate the fog, but the headlights are less directional and produce a "blur" in which the returned reflection dominates. Similarly, to overcome reverberation in water, active sonar needs to emit a narrow waveform.
Characteristics of white
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 the "strength" of the target. 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 the isolation of noisy devices and the coating of the hull of submarines.
Sonar Active
Active sonar uses a sound emitter and a receiver. When both are in the same place, it is called monostatic operation. When the emitter and receiver are separated, bistatic operation. When more spatially separated transmitters or receivers are used, multistatic operation. Most sonar equipment is monostatic, using the same matrix for transmission and reception, although when the platform is in motion it may be necessary to consider that this arrangement works bistatically. Active sonobuoy fields can work multistatically.
Active sonar creates a pulse of sound, often called a "ping," and then hears the reflection (echo) of it. This sound pulse is usually created electronically using a sonar project consisting of a signal generator, a power amplifier, and an electroacoustic transducer or array, possibly a beamformer. However, it can be created by other means, such as chemically, using explosives, or thermally using heat sources. It can also be created using infrasound.
To calculate the distance to an object, the time from the emission of the pulse to the reception of its echo is measured and converted to a length knowing the speed of sound. To measure heading, several hydrophones are used, measuring the arrival time relative to each one as a whole, or an array of hydrophones, measuring the relative amplitude of the beams formed by a process called beamforming. The use of a matrix reduces the spatial response so that multibeam systems are used to achieve wide coverage. The target signal (if any) along with the noise is then subjected to signal processing, which for simple equipment may only be a measure of power. The result is then presented to some kind of decision device that qualifies the output as signal or noise. This device can be an operator with headphones or a screen, in the most sophisticated equipment a specific software. Additional operations can be performed to classify the target and locate it, as well as to measure its speed.
The pulse can be either a constant amplitude or a frequency modulated pulse (chirp) to allow pulse compression on reception. Simple teams usually use the first with a filter wide enough to cover possible Doppler shifts due to the movement of the target, while more complex ones usually use the second technique. Pulse compression is now often achieved using digital correlation techniques. Military equipment often has multiple beams to achieve complete coverage while simpler ones only cover a narrow arc. Originally a single beam was used to perform the perimeter scan mechanically, but this was a slow process.
Especially when using single frequency transmissions, the Doppler effect can be used to measure the radial velocity of the target. The frequency difference between the emitted and the received signal is measured and translated into a speed. Since Doppler shifts can be due to receiver or target motion, the former must be taken into account to achieve an accurate value.
Active sonar is also used to measure the distance in the water between two sonar transducers (radio transmitters) or a combination hydrophone and projector. When a device receives an interrogation signal, it in turn emits a response signal. To measure the distance, a device emits an interrogation signal and measures the time between this transmission and the receipt of the response. The time difference allows calculating the distance between two teams. This technique, used with multiple pieces of equipment, can calculate the relative positions of static or moving objects.
During wartime, the emission of an active pulse was so compromised for submarine camouflage that it was considered a severe breach of operations.
Adverse effects on marine fauna
High-powered sonar emitters can affect marine life, although exactly how is not known. Some marine animals such as whales and dolphins use active sonar-like echolocation systems 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 syndrome. This hypothesis was first raised in a paper published in the journal Nature in 2003, which reported acute gas bubble injuries (indicative of decompression syndrome) in stranded whales shortly after the start of maneuvers. military next to the Canary Islands in September 2002.
In 2000 in the Bahamas a US Navy test of sonar transmissions led to the stranding of seventeen whales, seven of which were found dead. The Navy claimed responsibility in a report that found the dead whales had suffered acoustically induced hemorrhages in the ears. The resulting disorientation likely led to the stranding.
A type of medium-frequency sonar has been linked to mass cetacean deaths around the world, and blamed by environmentalists for these deaths. On October 20, 2005, a lawsuit was filed in Santa Monica, California against the United States Navy for sonar violations of various environmental laws, including the National Environmental Policy Act, the Marine Mammal Protection Act and the Endangered Species Act .
Sound passive
Passive sonar detects without emitting. Often used in military installations, it also has scientific applications such as detecting the absence or presence of fish in various aquatic environments.
Identification of sound sources
Passive sonar uses a wide variety of techniques to identify the source of a detected sound. For example, US ships are often equipped with 60 Hz alternating current motors. If the transformers or generator are mounted without proper vibration isolation from the hull or are flooded, the 60 Hz sound of the motor may be emitted by the vessel, 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 passive sonar equipment. Recently, the identification of a signal was carried out by an operator based on his experience and training, but currently computers are used for this purpose.
Passive sonar systems can have a large sonic database, although final classification is often done manually by the sonar operator. A computer system often uses this database to identify ship classes, actions (for example, a ship's speed, or the type of weapon fired), and even individual ships. The US Office of Naval Intelligence publishes and constantly updates sound classifications.
Noise limitations
Passive sonar is often severely limited by 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 make as little noise as possible. High speed propulsion often 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, as 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 the frequency, or sometimes the time. Another representation technique was to color-code the frequency-time information of the marking. The most recent displays are computer generated and mimic typical radar position indicator displays.
Military applications
Naval warfare makes extensive use of sonar. Both types described above are used from various platforms: surface ships, aircraft and fixed installations. The usefulness of active and passive sonars depends on the characteristics of the noise radiated by the target, usually a submarine. Although active sonar was mainly used in World War II, except by submarines, with the advent of noisy nuclear submarines, passive sonar was preferred for initial detection. As submarines became quieter, active sonar became more widely used.
Active sonar is extremely useful as it provides the exact position of an object. Its use is however somewhat dangerous, since it does not allow the identification of the target and any ship close to the emitted signal will detect it. This makes it possible to easily identify the type of sonar (usually by its frequency) and its position (by the power of the sound wave). Furthermore, active sonar allows the user to detect objects within a certain range, but it also allows other platforms to detect active sonar from a much greater distance.
Because active sonar does not allow exact identification and is very noisy, this type of detection is used from fast (planes and helicopters) or noisy (most surface ships) platforms, but rarely from submarines. When active sonar is used on the surface, it is often activated very briefly in intermittent periods, to reduce the risk of passive sonar detection of an enemy. Thus, active sonar is often considered a support of the passive. In aircraft, active sonar is used in disposable sonobuoys that are dropped over the area to be patrolled or near the contacts of a possible enemy.
Passive sonar listens for noise, so it has obvious advantages over active sonar. It generally has a much greater range than the active one and allows the identification of the target. Since any motor vehicle makes some noise, it will end up being detected, depending only on the amount of noise emitted and present in the area, as well as the technology used. On a submarine, the bow-mounted passive sonar detects at about 270º amidships, the hull-mounted array about 160º to each side, and the turret array at 360º. Blind zones are due to the ship's own interference. When a signal is detected in a certain direction (meaning something is making noise in that direction, called broadband detection) it is possible to focus and analyze the received signal (narrowband analysis). This is usually done by using a Fourier transform to show the different frequencies that make up the sound. Since each motor makes a specific noise, it is easy to identify the object.
Another use of passive sonar is to determine the trajectory of a target. This process is called Target Motion Analysis (TMA, Target Motion Analysis), and allows you to calculate the range, course and speed of the target. The TMA is done by marking from which direction the sound comes at different times, and comparing the movement with that of the operator's own ship. Changes in relative motion are analyzed using standard geometric techniques together with some assumptions regarding limiting cases.
Passive sonar is stealthy and very useful, but it requires very sophisticated and expensive components (band-pass filters, receivers, computers, analysis software, etc.). It is often equipped on expensive ships to improve detection. Surface ships use it effectively, but it is even better used in submarines and is also used in airplanes and helicopters.
Anti-submarine sonar
Until recently, sonars on surface ships were usually mounted on the hull, on the sides, or on the bow. It was soon determined after its first few 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 characteristics of the most modern surface ship sonars are the following:
- Low frequency transmission and reception. This achieves greater scope as the noise spread losses increase frequently.
- Simultaneous passive and active detection. This allows the detection of submarines and torpedoes at the same time.
- OMNI transmissions, directive-rotative or combination of both; allowing detection of nearby targets and another distant simultaneously by combining the small dead zone of the OMNI transmission with the high level of power issued by the directive transmission.
- Stabilization and control of transmission/reception beams, thereby improving the detection threshold and working in both deep and coastal waters.
- FM transmissions mixed with CW for detection of contacts 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 Cristóbal Colón frigate (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 depth. However, there are limitations to its use in shallow water. One problem is that the winches required to launch and retrieve these sonars are large and expensive. An example of this type of sonar is the Sonar 2087 manufactured by Thales Underwater Systems.
Torpedo sonar
Modern torpedoes often include active/passive sonar, which can be used to directly locate the target, but also to follow trails. 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.
Sonar antimines
Mine Countermeasure (MCM) sonar is a specialized type of sonar used to detect small objects. Most of these are hull-mounted, the Type 2093 being an example.
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 matters.
Aerial sonar
Helicopters can be used for anti-submarine warfare by deploying fields of active/passive sonobuoys or using a submersible sonar, such as the AQS-13. Conventional aircraft can also launch sonobuoys, having more autonomy and capacity for it. The processing of the data collected by this equipment can be carried out in the aircraft or on a ship. Helicopters have also been used in mine countermeasure missions, using towed sonars such as the AQS-20A.
Countermeasures
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 these teams 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 points in the world's oceans, collectively called the Sound Surveillance System (SOSUS) and later IUSS (Integrated Undersea Surveillance System, 'integrated underwater surveillance system'). A similar system is believed to have been operated by the Soviet Union. As permanently mounted arrays were used on the ocean floor, they were located 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 matrix 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 harbor entrances. Active sonar can also be used as a deterrent mechanism. An example of such equipment is the Cerberus.
Sonar Interception
This sonar is designed to detect and locate hostile sonar transmissions. An example is the Type 2082 fitted on the Vanguard class submarines.
Civil applications
Fishing applications
Fishing is an important industry subject to increasing demand, but the volume of global catches is 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 brought with it a growing demand for sophisticated electronic fishing locating equipment such as sensors, transmitters and sonars. Historically, fishermen 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 bladders have a different density than seawater. This difference in density allows detection of schools of fish using reflected sound. Currently, commercial trawlers rely almost entirely on acoustic equipment to detect fish.
Companies like Marport Canada, Wesmar, Furuno, Krupp, and Simrad make sonars and acoustic instruments for the fishing industry. For example, sensor nets 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 range of depths.
Network discovery
Acoustic equipment mounted on the nets is used, which transmits the recorded information by cable or acoustic telemetry to the fishing vessel. Thus, the distance of the net to the bottom and the surface, the amount of fish within it, and other relevant data are known exactly.
Calculation of ship speed
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 fitted to 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 their location in the event of an accident at sea.
Scientific applications
Biomass estimation
Sonars can be used to estimate the biomass present in an aquatic region, based on the sound reflection returned by it. The main difference with fish locating equipment is that quantitative hydroacoustic analysis requires measurements to be made with sufficiently sensitive and well calibrated equipment to obtain reliable measurements.
Hydroacoustic equipment provides a repeatable, non-invasive method of collecting continuous, high-resolution (sub-meter) data in three-dimensional sections, allowing measurement of the abundance and distribution of fishery resources.
Acoustic tags
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 tone and molecules. From this statistics of the conditions on the surface of a given location can be derived.
Measuring the speed of water
Special short-range sonars have been developed to allow the measurement of the speed of water, in a vacuum.
Determining 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 sonars can be used to make topographical data for an area. Low frequency sonars such as GLORIA have been used for exploration of the continental shelf while higher frequency ones are used for detailed exploration of smaller areas.
Characterization of the marine subsoil
Powerful low-frequency sonars have been developed to allow characterization of the surface layers of the seafloor.
Synthetic aperture sonar
Various synthetic aperture sonars have been built in the laboratory and some have been used in search and removal systems for graphite mines.
Underwater Archaeology
Detection of wrecks and underwater deposits and their location on the seabed.
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