How does sonar system work?

Sonar Technology is an acronym for Sound Navigation & Ranging (SONAR). Sonar is the technology of making use of sound waves to navigate, communicate and detect objects under the surface of the water. Sonar also used in air 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.

During the 1930s American engineers developed their own underwater sound-detection technology, and important discoveries were made, such as thermoclines, that would help future development.[9] After technical information was exchanged between the two countries[clarification needed] during the Second World War, Americans began to use the term SONAR for their systems, coined as the equivalent of RADAR.

There are two types of Sonar Technology -

• Active Sonar - It emits an acoustic signal or pulse into the water and if an object is in the way of the acoustic pulse then the sound bounces back and returns an echo to the sonar transducer. The sonar transducer, in turn, measures the strength of the signal. By determining the time between the emission of the acoustic signal and its reception, the transducer is able to determine the orientation and range of the object.

• Passive Sonar - These systems are used primarily to detect noise from marine objects (such as submarines or ships) and marine animals like whales. Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels that do not want to be found or for scientific missions that concentrate on quietly “listening” to the ocean. Rather, it only detects sound waves coming towards it. Passive sonar cannot measure the range of an object unless it is used in conjunction with other passive listening devices. Multiple passive sonar devices may allow for triangulation of a sound source.

How does Sonar work?

Sonar is simply making use of an echo. When an animal or machine makes a noise, it sends sound waves into the environment around it. Those waves bounce off nearby objects, and some of them reflect back to the object that made the noise. It's those reflected sound waves that you hear when your voice echoes back to you from a canyon. Whales and specialized machines can use reflected waves to locate distant objects and since their shape and movement. The range of low-frequency sonar is remarkable. Dolphins and whales can tell the difference between objects as small as a BB pellet from 50 feet (15 meters) away, and they use sonar much more than sight to find their food, families, and direction. The LFA sonar being tested by the military can travel thousands of miles and could cover 80% of the earth's oceans by broadcasting from only four points. The frequency that both whales and the military use fall between 100 and 500 Hz. Whales send signals out between 160 and 190 Db, the Navy has tested its sonar signals at levels up to 235 Db.

Applications of Sonar

Anti-submarine warfare

Such sonars are primarily active in operation. An example of a conventional hull-mounted sonar is the SQS-56. Towed arrays (linear) or variable depth sonars have limitations on their use in shallow water. A problem is that the winches required to deploy/recover these are large and expensive. VDS sets are primarily active in operation while towed arrays are passive. An example of a modern active/passive ship towed sonar is Sonar 2087 made by Thales Underwater Systems.

Torpedoes

Modern torpedoes are generally fitted with an active/passive sonar. This may be used to home directly on the target, but wake homing torpedoes are also used. An early example of an acoustic homer was the Mark 37 torpedo.  A widely used US device was the towed AN/SLQ-25 Nixie while Mobile submarine simulator (MOSS) was a free device. A modern alternative to the Nixie system is the UK Royal Navy S2170 Surface Ship Torpedo Defence system.

Mines

Mines may be fitted with a sonar to detect, localize and recognize the required target. Further information is given in acoustic mine and an example is the CAPTOR mine.

Submarine navigation

Submarines rely on sonar to a greater extent than surface ships as they cannot use radar at depth. The sonar arrays may be hull mounted or towed. Information fitted on typical fits is given in Oyashio class submarine and Swiftsure class submarine.

Aircraft

Helicopters can be used for anti-submarine warfare by deploying fields of active/passive sonobuoys or can operate dipping sonar, such as the AQS-13. Fixed wing aircraft can also deploy sonobuoys and have greater endurance and capacity to deploy them. Processing from the sonobuoys or Dipping Sonar can be on the aircraft or on the ship. Dipping sonar has the advantage of being deployable to depths appropriate to daily conditions Helicopters have also been used for mine countermeasure missions using towed sonars such as the AQS-20A.

Underwater communications

Dedicated sonars can be fitted to ships and submarines for underwater communication. See also the section on the underwater acoustics page.

Ocean surveillance

For many years, the United States operated a large set of passive sonar arrays at various points in the world's oceans, collectively called Sound Surveillance System (SOSUS) and later Integrated Undersea Surveillance System (IUSS). A similar system is believed to have been operated by the Soviet Union. Signal processing was carried out using powerful computers ashore. With the ending of the Cold War, a SOSUS array has been turned over to scientific use.

Underwater security

Sonar can be used to detect frogmen and other scuba divers. This can be applicable around ships or at entrances to ports. Active sonar can also be used as a deterrent and/or disablement mechanism. One such device is the Cerberus system.

Hand-held sonar

AN/PQS-2A handheld sonar, shown with detachable flotation collar and magnetic compass. Limpet Mine Imaging Sonar (LIMIS) is a hand-held or ROV-mounted imaging sonar designed for patrol divers (combat frogmen or clearance divers) to look for limpet mines in low visibility water. The LUIS is another imaging sonar for use by a diver. Integrated Navigation Sonar System (INSS) is a small flashlight-shaped handheld sonar for divers that displays range.

Intercept sonar

This is a sonar designed to detect and locate the transmissions from hostile active sonars. An example of this is the Type 2082 fitted on the British Vanguard class submarines.

Fisheries

Fishing is an important industry that is seeing growing demand, but world catch tonnage is falling as a result of serious resource problems. The industry faces a future of continuing worldwide consolidation until a point of sustainability can be reached. Historically, fishermen have used many different techniques to find and harvest fish. However, acoustic technology has been one of the most important driving forces behind the development of the modern commercial fisheries. Acoustic technology is especially well suited for underwater applications since sound travels farther and faster underwater than in air. Today, commercial fishing vessels rely almost completely on acoustic sonar and sounders to detect fish. Fishermen also use active sonar and echo sounder technology to determine water depth, bottom contour, and bottom composition. Companies such as eSonar, Raymarine UK, Marport Canada, Wesmar, Furuno, Krupp, and Simrad make a variety of sonar and acoustic instruments for the deep sea commercial fishing industry.

Net location

The net sounder is an echo sounder with a transducer mounted on the headline of the net rather than on the bottom of the vessel. Nevertheless, to accommodate the distance from the transducer to the display unit, which is much greater than in a normal echo-sounder, several refinements have to be made. Two main types are available. The first is the cable type in which the signals are sent along a cable. The second type is the cable less net-sounder – such as Marport Trawl Explorer - in which the signals are sent acoustically between the net and hull mounted receiver/hydrophone on the vessel.

ROV and UUV

Small sonars have been fitted to Remotely Operated Vehicles (ROV) and Unmanned Underwater Vehicles (UUV) to allow their operation in murky conditions. These sonars are used for looking ahead of the vehicle. The Long-Term Mine Reconnaissance System is a UUV for MCM purposes.

Vehicle location

Sonars which act as beacons are fitted to aircraft to allow their location in the event of a crash in the sea. Short and Long Baseline sonars may be used for caring out the location, such as LBL.

Prosthesis for the visually impaired

In 2013 an inventor in the United States unveiled a "spider-sense" bodysuit, equipped with ultrasonic sensors and haptic feedback systems, which alerts the wearer of incoming threats; allowing them to respond to attackers even when blindfolded.

Wave measurement

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

Water velocity measurement

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

Bathymetric mapping

Side-scan sonars can be used to derive maps of seafloor topography (bathymetry) by moving the sonar across it just above the bottom. Low-frequency sonars such as GLORIA have been used for continental shelf wide surveys while high-frequency sonars are used for more detailed surveys of smaller areas.

Sub-bottom profiling

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

Synthetic aperture sonar

Various synthetic aperture sonars have been built in the laboratory and some have entered use in mine-hunting and search systems. An explanation of their operation is given in synthetic aperture sonar.

Parametric sonar

Parametric sources use the non-linearity of water to generate the difference frequency between two high frequencies.

Sonar in extraterrestrial contexts

Use of sonar has been proposed for determining the depth of hydrocarbon seas on Titan.

Medical purpose

Sonar isn’t solely used for surveillance or by warfare submarines; it is also used by doctors to detect cysts and cancerous cells, a process which is known as ultrasonography. Doctors infiltrate their patients with sound waves that scatter and ricochet inside the body, enabling them to detect muscles and organs in much greater detail than X-rays would allow.