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95-415: Echo sounding or depth sounding is the use of sonar for ranging , normally to determine the depth of water ( bathymetry ). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight , along with knowledge of the speed of sound in water, allows determining the distance between sonar and target. This information

190-633: A piezoelectric transmitter ). His work was developed and implemented by other scientists and technnicians such as Chilowski, Florisson and Pierre Marti. Though a fully operational échosondeur (sonar) was not ready for use in wartime, there were successful trials both off Toulon and in the English Channel as early as 1920, and French patents taken for civilian uses. Oceanographic ships and French high-sea fishing assistance vessels were equipped with Langevin-Florisson and Langevin Marti recording sonars as early as

285-550: A strip chart recorder where an advancing roll of paper was marked by a stylus to make a permanent copy of the depth, usually with some means of also recording time (each mark or time 'tic' is proportional to distance traveled) so that the strip charts could be readily compared to navigation charts and maneuvering logs (speed changes). Much of the world's ocean depths have been mapped using such recording strips. Fathometers of this type usually offered multiple (chart advance) speed settings, and sometimes, multiple frequencies as well. In

380-411: A hydrophone/transducer receives a specific interrogation signal it responds by transmitting a specific reply signal. To measure distance, one transducer/projector transmits an interrogation signal and measures the time between this transmission and the receipt of the other transducer/hydrophone reply. The time difference, scaled by the speed of sound through water and divided by two, is the distance between

475-495: A narrow arc, although the beam may be rotated, relatively slowly, by mechanical scanning. Particularly when single frequency transmissions are used, the Doppler effect can be used to measure the radial speed of a target. The difference in frequency between the transmitted and received signal is measured and converted into a velocity. Since Doppler shifts can be introduced by either receiver or target motion, allowance has to be made for

570-465: A number of different marine robotic vehicles. It operates by using a transducer to emit a pulse through the water and listen for echos to return. Using that data, it's able to determine the distance from the strongest echo, which can be the seafloor, a concrete structure, or other larger obstacle. A fishfinder is an echo sounding device used by both recreational and commercial fishers. As well as an aid to navigation (most larger vessels will have at least

665-487: A pulse to reception is measured and converted into a range using the known speed of sound. To measure the bearing , several hydrophones are used, and the set measures the relative arrival time to each, or with an array of hydrophones, by measuring the relative amplitude in beams formed through a process called beamforming . Use of an array reduces the spatial response so that to provide wide cover multibeam systems are used. The target signal (if present) together with noise

760-428: A simple depth sounder), echo sounding is commonly used for fishing . Variations in elevation often represent places where fish congregate. Schools of fish will also register. In areas where detailed bathymetry is required, a precise echo sounder may be used for the work of hydrography. There are many considerations when evaluating such a system, not limited to the vertical accuracy, resolution, acoustic beamwidth of

855-520: A steel tube, vacuum-filled with castor oil , and sealed. The tubes then were mounted in parallel arrays. The standard US Navy scanning sonar at the end of World War II operated at 18 kHz, using an array of ADP crystals. Desired longer range, however, required use of lower frequencies. The required dimensions were too big for ADP crystals, so in the early 1950s magnetostrictive and barium titanate piezoelectric systems were developed, but these had problems achieving uniform impedance characteristics, and

950-512: A system later tested in Boston Harbor, and finally in 1914 from the U.S. Revenue Cutter Miami on the Grand Banks off Newfoundland . In that test, Fessenden demonstrated depth sounding, underwater communications ( Morse code ) and echo ranging (detecting an iceberg at a 2-mile (3.2 km) range). The " Fessenden oscillator ", operated at about 500 Hz frequency, was unable to determine

1045-565: A target ahead of the attacker and still in ASDIC contact. These allowed a single escort to make better aimed attacks on submarines. Developments during the war resulted in British ASDIC sets that used several different shapes of beam, continuously covering blind spots. Later, acoustic torpedoes were used. Early in World War II (September 1940), British ASDIC technology was transferred for free to

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1140-413: Is bistatic operation . When more transmitters (or more receivers) are used, again spatially separated, it is multistatic operation . Most sonars are used monostatically with the same array often being used for transmission and reception. Active sonobuoy fields may be operated multistatically. Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections ( echo ) of

1235-640: Is an extension of a dual frequency vertical beam echosounder in that, as well as measuring two soundings directly below the sonar at two different frequencies; it measures multiple soundings at multiple frequencies, at multiple different grazing angles, and multiple different locations on the seabed. These systems are detailed further in the section called multibeam echosounder . Echo sounders are used in laboratory applications to monitor sediment transport, scour and erosion processes in scale models (hydraulic models, flumes etc.). These can also be used to create plots of 3D contours. The required precision and accuracy of

1330-436: Is approximately 1.5 kilometres per second. The speed of sound will vary slightly depending on temperature, pressure and salinity; and for precise applications of echosounding, such as hydrography , the speed of sound must also be measured, typically by deploying a sound velocity probe in the water. Echo sounding is a special purpose application of sonar used to locate the bottom. Since a historical pre- SI unit of water depth

1425-404: Is because the distance between the fish and the transducer changes as the boat passes over the fish (or the fish swims under the boat). When the fish enters the leading edge of the sonar beam, a display pixel is turned on. As the fish swims toward the centre of the beam, the distance to the fish decreases, turning on pixels at shallower depths. When the fish swims directly under the transducer, it

1520-426: Is closer to the boat so the stronger signal shows a thicker line. As the fish swims away from the transducer, the distance increases, which shows as progressively deeper pixels. The image to the right shows a school of white bass aggressively feeding on a school of threadfin shad . Note the school of baitfish near the bottom. When threatened, baitfish form a tightly packed school, as the individuals seek safety in

1615-455: Is easy to get more detail on screen when the fishfinder's frequency is high. Deep-sea trawlers and commercial fishermen normally use low frequency (50–200 kHz); modern fishfinders have multiple frequencies to view split-screen results. The image above, at right, clearly shows the bottom structure—plants, sediments and hard bottom are discernible on sonar plots of sufficiently high power and appropriate frequency. Slightly more than halfway up from

1710-453: Is its zero aging characteristics; the crystal keeps its parameters even over prolonged storage. Another application was for acoustic homing torpedoes. Two pairs of directional hydrophones were mounted on the torpedo nose, in the horizontal and vertical plane; the difference signals from the pairs were used to steer the torpedo left-right and up-down. A countermeasure was developed: the targeted submarine discharged an effervescent chemical, and

1805-415: Is the source level , PL is the propagation loss (sometimes referred to as transmission loss ), TS is the target strength , NL is the noise level , AG is the array gain of the receiving array (sometimes approximated by its directivity index) and DT is the detection threshold . In reverberation-limited conditions at initial detection (neglecting array gain): where RL is the reverberation level , and

1900-427: Is then passed through various forms of signal processing , which for simple sonars may be just energy measurement. It is then presented to some form of decision device that calls the output either the required signal or noise. This decision device may be an operator with headphones or a display, or in more sophisticated sonars this function may be carried out by software. Further processes may be carried out to classify

1995-431: Is then typically used for navigation purposes or in order to obtain depths for charting purposes. Echo sounding can also be used for ranging to other targets, such as fish schools . Hydroacoustic assessments have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish. The word sounding

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2090-444: Is used for all types of depth measurements, including those that don't use sound , and is unrelated in origin to the word sound in the sense of noise or tones. Echo sounding is a more rapid method of measuring depth than the previous technique of lowering a sounding line until it touched bottom. German inventor Alexander Behm was granted German patent No. 282009 for the invention of echo sounding (device for measuring depths of

2185-402: Is very low, several orders of magnitude less than the original signal. Even if the reflected signal was of the same power, the following example (using hypothetical values) shows the problem: Suppose a sonar system is capable of emitting a 10,000 W/m signal at 1 m, and detecting a 0.001 W/m  signal. At 100 m the signal will be 1 W/m (due to the inverse-square law ). If

2280-713: The Titanic disaster of 1912. The world's first patent for an underwater echo-ranging device was filed at the British Patent Office by English meteorologist Lewis Fry Richardson a month after the sinking of Titanic , and a German physicist Alexander Behm obtained a patent for an echo sounder in 1913. The Canadian engineer Reginald Fessenden , while working for the Submarine Signal Company in Boston , Massachusetts, built an experimental system beginning in 1912,

2375-452: The Royal Navy had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine system. The effectiveness of early ASDIC was hampered by the use of the depth charge as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in

2470-551: The hull or become flooded, the 60 Hz sound from the windings can be emitted from the submarine or ship. This can help to identify its nationality, as all European submarines and nearly every other nation's submarine have 50 Hz power systems. Intermittent sound sources (such as a wrench being dropped), called "transients," may also be detectable to passive sonar. Until fairly recently, an experienced, trained operator identified signals, but now computers may do this. Passive sonar systems may have large sonic databases , but

2565-488: The 1930s American engineers developed their own underwater sound-detection technology, and important discoveries were made, such as the existence of thermoclines and their effects on sound waves. Americans began to use the term SONAR for their systems, coined by Frederick Hunt to be the equivalent of RADAR . In 1917, the US Navy acquired J. Warren Horton 's services for the first time. On leave from Bell Labs , he served

2660-492: The 1970s, compounds of rare earths and iron were discovered with superior magnetomechanic properties, namely the Terfenol-D alloy. This made possible new designs, e.g. a hybrid magnetostrictive-piezoelectric transducer. The most recent of these improved magnetostrictive materials is Galfenol . Other types of transducers include variable-reluctance (or moving-armature, or electromagnetic) transducers, where magnetic force acts on

2755-458: The Admiralty archives. By 1918, Britain and France had built prototype active systems. The British tested their ASDIC on HMS  Antrim in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school HMS Osprey and a training flotilla of four vessels were established on Portland in 1924. By the outbreak of World War II ,

2850-674: The British Board of Invention and Research , Canadian physicist Robert William Boyle took on the active sound detection project with A. B. Wood , producing a prototype for testing in mid-1917. This work for the Anti-Submarine Division of the British Naval Staff was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy, no mention of sound experimentation or quartz

2945-651: The French physicist Paul Langevin , working with a Russian immigrant electrical engineer Constantin Chilowsky, worked on the development of active sound devices for detecting submarines in 1915. Although piezoelectric and magnetostrictive transducers later superseded the electrostatic transducers they used, this work influenced future designs. Lightweight sound-sensitive plastic film and fibre optics have been used for hydrophones, while Terfenol-D and lead magnesium niobate (PMN) have been developed for projectors. In 1916, under

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3040-609: The United States. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed. These included sonobuoys , first developed by the British in 1944 under the codename High Tea , dipping/dunking sonar and mine -detection sonar. This work formed the basis for post-war developments related to countering the nuclear submarine . During

3135-471: The ability to identify a vegetation layer or a layer of soft mud on top of a layer of rock. Most hydrographic operations use a 200 kHz transducer, which is suitable for inshore work up to 100 metres in depth. Deeper water requires a lower frequency transducer as the acoustic signal of lower frequencies is less susceptible to attenuation in the water column. Commonly used frequencies for deep water sounding are 33 kHz and 24 kHz. The beamwidth of

3230-415: The area near the boat. When active sonar is used to measure the distance from the transducer to the bottom, it is known as echo sounding . Similar methods may be used looking upward for wave measurement. Active sonar is also used to measure distance through water between two sonar transducers or a combination of a hydrophone (underwater acoustic microphone) and projector (underwater acoustic speaker). When

3325-498: The attack had the advantage that the German acoustic torpedo was not effective against a warship travelling so slowly. A variation of the creeping attack was the "plaster" attack, in which three attacking ships working in a close line abreast were directed over the target by the directing ship. The new weapons to deal with the ASDIC blind spot were "ahead-throwing weapons", such as Hedgehogs and later Squids , which projected warheads at

3420-505: The beam pattern suffered. Barium titanate was then replaced with more stable lead zirconate titanate (PZT), and the frequency was lowered to 5 kHz. The US fleet used this material in the AN/SQS-23 sonar for several decades. The SQS-23 sonar first used magnetostrictive nickel transducers, but these weighed several tons, and nickel was expensive and considered a critical material; piezoelectric transducers were therefore substituted. The sonar

3515-469: The bearing of the iceberg due to the 3-metre wavelength and the small dimension of the transducer's radiating face (less than 1 ⁄ 3 wavelength in diameter). The ten Montreal -built British H-class submarines launched in 1915 were equipped with Fessenden oscillators. During World War I the need to detect submarines prompted more research into the use of sound. The British made early use of underwater listening devices called hydrophones , while

3610-458: The bottom of the ocean being displayed versus time (the fathometer function that eventually spawned the sporting use of fishfinding). The temperature and pressure sensitivity capability of fishfinder units allow one to identify the exact location of the fish in the water by the use of a temperature gauge. Many modern fishfinders also have track-back capabilities to check changes in movement in order to switch position and location whilst fishing. It

3705-404: The bottom to the left of the screen centre and about a third away from the left side, this image is also displaying a fish – a light spot just to the right of a 'glare' splash from the camera's flashbulb. The X-axis of the image represents time, oldest (and behind the soundhead) to the left, most recent bottom (and current location) on the right; thus the fish is now well behind the transducer, and

3800-547: The bottom. The first fishfinder, i.e. sonar device meant to find underwater fish or schools of fish, was invented in Japan in the 1940s by the Furuno brothers, who were radio repairmen. Building from the knowledge of fishermen who were able to determine the presence of fish, and their number, from bubbles, the Furuno brothers first planned to detect these bubbles with sonar, a new technology at

3895-404: The center of the school. This typically looks like an irregularly shaped ball or thumbprint on the fishfinder screen. When no predators are nearby, a school of baitfish frequently appears as a thin horizontal line across the screen, at the depth where the temperature and oxygen levels are optimal. The nearly-vertical lines near the right edge of the screen show the path of fishing lures falling to

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3990-444: The characteristics of the outgoing ping. For these reasons, active sonar is not frequently used by military submarines. A very directional, but low-efficiency, type of sonar (used by fisheries, military, and for port security) makes use of a complex nonlinear feature of water known as non-linear sonar, the virtual transducer being known as a parametric array . Project Artemis was an experimental research and development project in

4085-434: The depth charges had been released, the attacking ship left the immediate area at full speed. The directing ship then entered the target area and also released a pattern of depth charges. The low speed of the approach meant the submarine could not predict when depth charges were going to be released. Any evasive action was detected by the directing ship and steering orders to the attacking ship given accordingly. The low speed of

4180-404: The depth of water. The fathom is a unit of water depth, from which the instrument gets its name. The fathometer is an echo sounding system for measurement of water depth. A fathometer will display water depth and can make an automatic permanent record of measurements. Since both fathometers and fishfinders work the same way, and use similar frequencies and can detect both the bottom and fish,

4275-412: The echoes. Since the original signal is much more powerful, it can be detected many times further than twice the range of the sonar (as in the example). Active sonar have two performance limitations: due to noise and reverberation. In general, one or other of these will dominate, so that the two effects can be initially considered separately. In noise-limited conditions at initial detection: where SL

4370-456: The electro-acoustic transducers are of the Tonpilz type and their design may be optimised to achieve maximum efficiency over the widest bandwidth, in order to optimise performance of the overall system. Occasionally, the acoustic pulse may be created by other means, e.g. chemically using explosives, airguns or plasma sound sources. To measure the distance to an object, the time from transmission of

4465-399: The end of an arm was rotated around a circular scale at a fixed speed by a small electric motor. The circular scale was calibrated in terms of depth of water. The instrument was arranged to send out a pulse of ultrasonic waves as the lamp passed the zero point of the scale. The transducer was then arranged to detect any reflected ultrasound impulses; the lamp would flash when an echo returned to

4560-427: The entire signal is reflected from a 10 m target, it will be at 0.001 W/m when it reaches the emitter, i.e. just detectable. However, the original signal will remain above 0.001 W/m until 3000 m. Any 10 m target between 100 and 3000 m using a similar or better system would be able to detect the pulse, but would not be detected by the emitter. The detectors must be very sensitive to pick up

4655-500: The government as a technical expert, first at the experimental station at Nahant, Massachusetts , and later at US Naval Headquarters, in London , England. At Nahant he applied the newly developed vacuum tube , then associated with the formative stages of the field of applied science now known as electronics , to the detection of underwater signals. As a result, the carbon button microphone , which had been used in earlier detection equipment,

4750-458: The heave component (in single beam echosounding) to reduce soundings for the motion of the vessel experienced on the water's surface. Once all of the uncertainties of each sensor are established, the hydrographer will create an uncertainty budget to determine whether the survey system meets the requirements laid down by IHO. Different hydrographic organisations will have their own set of field procedures and manuals to guide their surveyors to meet

4845-576: The hydrographic echo sounder is defined by the requirements of the International Hydrographic Organization (IHO) for surveys that are to be undertaken to IHO standards. These values are contained within IHO publication S44. In order to meet these standards, the surveyor must consider not only the vertical and horizontal accuracy of the echo sounder and transducer, but the survey system as a whole. A motion sensor may be used, specifically

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4940-408: The instruments have merged. In operation, an electrical impulse from a transmitter is converted into a sound wave by an underwater transducer , called a hydrophone , and sent into the water. When the wave strikes something such as a fish, it is reflected back and displays size, composition, and shape of the object. The exact extent of what can be discerned depends on the frequency and power of

5035-476: The introduction of radar . Sonar may also be used for robot navigation, and sodar (an upward-looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low ( infrasonic ) to extremely high ( ultrasonic ). The study of underwater sound is known as underwater acoustics or hydroacoustics . The first recorded use of

5130-505: The largest individual sonar transducers ever. The advantage of metals is their high tensile strength and low input electrical impedance, but they have electrical losses and lower coupling coefficient than PZT, whose tensile strength can be increased by prestressing . Other materials were also tried; nonmetallic ferrites were promising for their low electrical conductivity resulting in low eddy current losses, Metglas offered high coupling coefficient, but they were inferior to PZT overall. In

5225-498: The late 1950s to mid 1960s to examine acoustic propagation and signal processing for a low-frequency active sonar system that might be used for ocean surveillance. A secondary objective was examination of engineering problems of fixed active bottom systems. The receiving array was located on the slope of Plantagnet Bank off Bermuda. The active source array was deployed from the converted World War II tanker USNS  Mission Capistrano . Elements of Artemis were used experimentally after

5320-701: The limitations, they were still usable for rough estimates of depth, such as for verifying that the boat had not drifted into an unsafe area. Eventually, CRTs were married with a fathometer for commercial fishing and the fishfinder was born. With the advent of large LCD arrays, the high power requirements of a CRT gave way to the LCD in the early 1990s and fishfinding fathometers reached the sporting markets. Nowadays, many fishfinders available for hobby fishers have color LCD screens, built-in GPS, charting capabilities, and come bundled with transducers. Today, sporting fishfinders lack only

5415-404: The magnetostrictive unit was much more reliable. High losses to US merchant supply shipping early in World War II led to large scale high priority US research in the field, pursuing both improvements in magnetostrictive transducer parameters and Rochelle salt reliability. Ammonium dihydrogen phosphate (ADP), a superior alternative, was found as a replacement for Rochelle salt; the first application

5510-417: The main experiment was terminated. This is an active sonar device that receives a specific stimulus and immediately (or with a delay) retransmits the received signal or a predetermined one. Transponders can be used to remotely activate or recover subsea equipment. A sonar target is small relative to the sphere , centred around the emitter, on which it is located. Therefore, the power of the reflected signal

5605-563: The mid/late 1920s. One of the first commercial echo sounding units was the Fessenden Fathometer, which used the Fessenden oscillator to generate sound waves. This was first installed by the Submarine Signal Company in 1924 on the M&;M liner SS Berkshire. Distance is measured by multiplying half the time from the signal's outgoing pulse to its return by the speed of sound in water, which

5700-403: The moments leading up to attack. The hunter was effectively firing blind, during which time a submarine commander could take evasive action. This situation was remedied with new tactics and new weapons. The tactical improvements developed by Frederic John Walker included the creeping attack. Two anti-submarine ships were needed for this (usually sloops or corvettes). The "directing ship" tracked

5795-490: The ocean or floats on a taut line mooring at a constant depth of perhaps 100 m. They may also be used by submarines , AUVs , and floats such as the Argo float. Passive sonar listens without transmitting. It is often employed in military settings, although it is also used in science applications, e.g. , detecting fish for presence/absence studies in various aquatic environments – see also passive acoustics and passive radar . In

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5890-403: The other factors are as before. An upward looking sonar (ULS) is a sonar device pointed upwards looking towards the surface of the sea. It is used for similar purposes as downward looking sonar, but has some unique applications such as measuring sea ice thickness, roughness and concentration, or measuring air entrainment from bubble plumes during rough seas. Often it is moored on the bottom of

5985-421: The permanent record of the big ship navigational fathometer, and that is available in high end units that can use the ubiquitous computer to store that record as well. Fishfinders may use higher frequencies to improve the image of underwater objects. Side-looking transducers provide additional visibility of underwater objects on either side of the boat's path. Commercial and naval fathometers of yesteryear used

6080-402: The projectors consisted of two rectangular identical independent units in a cast-iron rectangular body about 16 by 9 inches (410 mm × 230 mm). The exposed area was half the wavelength wide and three wavelengths high. The magnetostrictive cores were made from 4 mm stampings of nickel, and later of an iron-aluminium alloy with aluminium content between 12.7% and 12.9%. The power

6175-665: The pulse transmitted. Knowing the speed of the wave in the water, the distance to the object that reflected the wave can be determined. The speed of sound through the water column depends on the temperature, salinity and pressure (depth). This is approximately c = 1404.85 + 4.618 T - 0.0523 T + 1.25 S + 0.017 D (where c = sound speed (m/s), T = temperature (degrees Celsius), S = salinity (per mille) and D = depth). Typical values used by commercial fish finders are 4921 ft/s (1500 m/s) in seawater and 4800 ft/s (1463 m/s) in freshwater . The process can be repeated up to 40 times per second and eventually results in

6270-410: The pulse. This pulse of sound is generally created electronically using a sonar projector consisting of a signal generator, power amplifier and electro-acoustic transducer/array. A transducer is a device that can transmit and receive acoustic signals ("pings"). A beamformer is usually employed to concentrate the acoustic power into a beam, which may be swept to cover the required search angles. Generally,

6365-456: The radial speed of the searching platform. One useful small sonar is similar in appearance to a waterproof flashlight. The head is pointed into the water, a button is pressed, and the device displays the distance to the target. Another variant is a " fishfinder " that shows a small display with shoals of fish. Some civilian sonars (which are not designed for stealth) approach active military sonars in capability, with three-dimensional displays of

6460-597: The required standards. Two examples are the US Army Corps of Engineers publication EM110-2-1003, and the NOAA 'Field Procedures Manual'. [REDACTED] Media related to Echo sounding at Wikimedia Commons Sonar Sonar ( sound navigation and ranging or sonic navigation and ranging ) is a technique that uses sound propagation (usually underwater, as in submarine navigation ) to navigate , measure distances ( ranging ), communicate with or detect objects on or under

6555-461: The sea and distances and headings of ships or obstacles by means of reflected sound waves) on 22 July 1913. Meanwhile, in France, physicist Paul Langevin (connected with Marie Curie and better known for his research work in nuclear physics ) was recruited by French Navy laboratories at the beginning of World War 2 and conducted (then secret) research on active sonars for anti-submarine warfare (using

6650-433: The sonar operator usually finally classifies the signals manually. 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 the most effective countermeasures to employ), and even particular ships. Fishfinder Fishfinders were derived from fathometers , active sonar instruments used for navigation and safety to determine

6745-408: The surface of the water, such as other vessels. "Sonar" can refer to one of two types of technology: passive sonar means listening for the sound made by vessels; active sonar means emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before

6840-437: The surfaces of gaps, and moving coil (or electrodynamic) transducers, similar to conventional speakers; the latter are used in underwater sound calibration, due to their very low resonance frequencies and flat broadband characteristics above them. Active sonar uses a sound transmitter (or projector) and a receiver. When the two are in the same place it is monostatic operation . When the transmitter and receiver are separated it

6935-600: The target and localise it, as well as measuring its velocity. The pulse may be at constant frequency or a chirp of changing frequency (to allow pulse compression on reception). Simple sonars generally use the former with a filter wide enough to cover possible Doppler changes due to target movement, while more complex ones generally include the latter technique. Since digital processing became available pulse compression has usually been implemented using digital correlation techniques. Military sonars often have multiple beams to provide all-round cover while simple ones only cover

7030-405: The target submarine on ASDIC from a position about 1500 to 2000 yards behind the submarine. The second ship, with her ASDIC turned off and running at 5 knots, started an attack from a position between the directing ship and the target. This attack was controlled by radio telephone from the directing ship, based on their ASDIC and the range (by rangefinder) and bearing of the attacking ship. As soon as

7125-556: The technique was in 1490 by Leonardo da Vinci , who used a tube inserted into the water to detect vessels by ear. It was developed during World War I to counter the growing threat of submarine warfare , with an operational passive sonar system in use by 1918. Modern active sonar systems use an acoustic transducer to generate a sound wave which is reflected from target objects. Although some animals ( dolphins , bats , some shrews , and others) have used sound for communication and object detection for millions of years, use by humans in

7220-454: The temperature, pressure and salinity. These factors are used to estimate more accurately the actual sound speed in the local water column. This technique is often used by the US Office of Coast Survey for navigational surveys of US coastal waters. A single-beam echo sounder is one of the simplest and most fundamental types of underwater sonar. They are ubiquitous in the boating world and used on

7315-600: The time. They invented the first through-hull transducer and found they were able to detect the fish themselves. In 1948 they introduced their fishfinder for use in commercial fishing vessels; the Furuno Fish Finder is the world's first practical fishfinder. The first fishfinder marketed to consumers in America for recreational fishing was the Lowrance Fish Lo-K-Tor (also nicknamed "The Little Green Box"), which

7410-458: The torpedo went after the noisier fizzy decoy. The counter-countermeasure was a torpedo with active sonar – a transducer was added to the torpedo nose, and the microphones were listening for its reflected periodic tone bursts. The transducers comprised identical rectangular crystal plates arranged to diamond-shaped areas in staggered rows. Passive sonar arrays for submarines were developed from ADP crystals. Several crystal assemblies were arranged in

7505-427: The transducer is also a consideration for the hydrographer, as to obtain the best resolution of the data gathered a narrow beamwidth is preferable. The higher the operating frequency, the narrower the beamwidth. Therefore, it is especially important when sounding in deep water, as the resulting footprint of the acoustic pulse can be very large once it reaches a distant sea floor. A multispectral multibeam echosounder

7600-418: The transducer, and by its position on the scale would indicate the elapsed time and therefore the depth of the water. These also gave a small flickering flash for echos off of fish. Like today's low-end digital fathometers, they kept no record of the depth over time and provided no information about bottom structure. They had poor accuracy, especially in rough water, and were hard to read in bright light. Despite

7695-464: The transmit/receive beam and the acoustic frequency of the transducer . The majority of hydrographic echosounders are dual frequency, meaning that a low frequency pulse (typically around 24 kHz) can be transmitted at the same time as a high frequency pulse (typically around 200 kHz). As the two frequencies are discrete, the two return signals do not typically interfere with each other. Dual frequency echosounding has many advantages, including

7790-409: The two platforms. This technique, when used with multiple transducers/hydrophones/projectors, can calculate the relative positions of static and moving objects in water. In combat situations, an active pulse can be detected by an enemy and will reveal a submarine's position at twice the maximum distance that the submarine can itself detect a contact and give clues as to the submarine's identity based on

7885-481: The very broadest usage, this term can encompass virtually any analytical technique involving remotely generated sound, though it is usually restricted to techniques applied in an aquatic environment. Passive sonar has a wide variety of techniques for identifying the source of a detected sound. For example, U.S. vessels usually operate 60 Hertz (Hz) alternating current power systems. If transformers or generators are mounted without proper vibration insulation from

7980-473: The vessel is now passing over a dip in the ocean floor or has just left it behind. The resulting distortion depends on both the speed of the vessel and how often the image is updated by the echo sounder. With the Fish Symbol feature disabled, an angler can learn to distinguish between fish, vegetation, schools of baitfish or forage fish , debris , etc. Fish will usually appear on the screen as an arch. This

8075-436: The water was initially recorded by Leonardo da Vinci in 1490: a tube inserted into the water was said to be used to detect vessels by placing an ear to the tube. In the late 19th century, an underwater bell was used as an ancillary to lighthouses or lightships to provide warning of hazards. The use of sound to "echo-locate" underwater in the same way as bats use sound for aerial navigation seems to have been prompted by

8170-465: Was a large array of 432 individual transducers. At first, the transducers were unreliable, showing mechanical and electrical failures and deteriorating soon after installation; they were also produced by several vendors, had different designs, and their characteristics were different enough to impair the array's performance. The policy to allow repair of individual transducers was then sacrificed, and "expendable modular design", sealed non-repairable modules,

8265-559: Was a replacement of the 24 kHz Rochelle-salt transducers. Within nine months, Rochelle salt was obsolete. The ADP manufacturing facility grew from few dozen personnel in early 1940 to several thousands in 1942. One of the earliest application of ADP crystals were hydrophones for acoustic mines ; the crystals were specified for low-frequency cutoff at 5 Hz, withstanding mechanical shock for deployment from aircraft from 3,000 m (10,000 ft), and ability to survive neighbouring mine explosions. One of key features of ADP reliability

8360-531: Was being loaded on the cable-laying vessel, World War I ended and Horton returned home. During World War II, he continued to develop sonar systems that could detect submarines, mines, and torpedoes. He published Fundamentals of Sonar in 1957 as chief research consultant at the US Navy Underwater Sound Laboratory . He held this position until 1959 when he became technical director, a position he held until mandatory retirement in 1963. There

8455-669: Was chosen instead, eliminating the problem with seals and other extraneous mechanical parts. The Imperial Japanese Navy at the onset of World War II used projectors based on quartz . These were big and heavy, especially if designed for lower frequencies; the one for Type 91 set, operating at 9 kHz, had a diameter of 30 inches (760 mm) and was driven by an oscillator with 5 kW power and 7 kV of output amplitude. The Type 93 projectors consisted of solid sandwiches of quartz, assembled into spherical cast iron bodies. The Type 93 sonars were later replaced with Type 3, which followed German design and used magnetostrictive projectors;

8550-456: Was invented in 1957 and entered the market in 1959. It retailed for $ 150 at the time, equivalent to $ 1,610 in 2024. Originally the subject of controversy due to its perceived unfair advantage, it faced the potential of being banned by some states but its use was eventually accepted. By the early 1970s, a common pattern of depth finder used an ultrasonic transducer immersed in water, and an electromechanical readout device. A neon lamp mounted on

8645-426: Was little progress in US sonar from 1915 to 1940. In 1940, US sonars typically consisted of a magnetostrictive transducer and an array of nickel tubes connected to a 1-foot-diameter steel plate attached back-to-back to a Rochelle salt crystal in a spherical housing. This assembly penetrated the ship hull and was manually rotated to the desired angle. The piezoelectric Rochelle salt crystal had better parameters, but

8740-593: Was made – the word used to describe the early work ("supersonics") was changed to "ASD"ics, and the quartz material to "ASD"ivite: "ASD" for "Anti-Submarine Division", hence the British acronym ASDIC . In 1939, in response to a question from the Oxford English Dictionary , the Admiralty made up the story that it stood for "Allied Submarine Detection Investigation Committee", and this is still widely believed, though no committee bearing this name has been found in

8835-567: Was provided from a 2 kW at 3.8 kV, with polarization from a 20 V, 8 A DC source. The passive hydrophones of the Imperial Japanese Navy were based on moving-coil design, Rochelle salt piezo transducers, and carbon microphones . Magnetostrictive transducers were pursued after World War II as an alternative to piezoelectric ones. Nickel scroll-wound ring transducers were used for high-power low-frequency operations, with size up to 13 feet (4.0 m) in diameter, probably

8930-507: Was replaced by the precursor of the modern hydrophone . Also during this period, he experimented with methods for towing detection. This was due to the increased sensitivity of his device. The principles are still used in modern towed sonar systems. To meet the defense needs of Great Britain, he was sent to England to install in the Irish Sea bottom-mounted hydrophones connected to a shore listening post by submarine cable. While this equipment

9025-404: Was the fathom , an instrument used for determining water depth is sometimes called a fathometer . Most charted ocean depths are based on an average or standard sound speed. Where greater accuracy is required, average and even seasonal standards may be applied to ocean regions. For high accuracy depths, usually restricted to special purpose or scientific surveys, a sensor may be lowered to measure

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