Sonar

asdicvariable depth sonaractive sonarpassive sonardipping sonarsoundsound gearASDIC (SONAR)ASDICSsonars
Sonar (originally an acronym for sound navigation ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.wikipedia
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Acronym

initialismacronymsinitials
Sonar (originally an acronym for sound navigation ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, "Rd" for "road" or "Dr" for "Doctor"), an acronym is a word formed from the first letter or first few letters of each word in a phrase (such as "sonar", created from "sound navigation and ranging").

Acoustic location

echolocationsound locatoracoustic source localization
Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water.
Both of these techniques, when used in water, are known as sonar; passive sonar and active sonar are both widely used.

Underwater acoustics

underwater soundunderwater acousticacoustic
The study of underwater sound is known as underwater acoustics or hydroacoustics.
The field of underwater acoustics is closely related to a number of other fields of acoustic study, including sonar, transduction, acoustic signal processing, acoustical oceanography, bioacoustics, and physical acoustics.

Submarine navigation

Sonar (originally an acronym for sound navigation ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
Operating in stealth mode, they cannot use their active sonar systems to ping ahead for underwater hazards such as undersea mountains, drilling rigs or other submarines.

Hydroacoustics

hydroacousticacoustic methodsacoustic survey
The study of underwater sound is known as underwater acoustics or hydroacoustics.
Hydroacoustics, using sonar technology, is most commonly used for monitoring of underwater physical and biological characteristics.

SODAR

SOnic Detection And Ranging
Sonar may also be used in air for robot navigation, and SODAR (an upward-looking in-air sonar) is used for atmospheric investigations.
Sodar systems are in fact nothing more than sonar systems used in the air rather than in water; more specifically, since they operate using the Doppler effect with a multi-beam configuration to determine wind speed, they are the exact in-air equivalent to a subclass of sonar systems known as acoustic Doppler current profilers.

Reginald Fessenden

FessendenReginald Aubrey FessendenFessenden, Reginald
The Canadian engineer Reginald Fessenden, while working for the Submarine Signal Company in Boston, built an experimental system beginning in 1912, a system later tested in Boston Harbor, and finally in 1914 from the U.S. Revenue (now Coast Guard) Cutter Miami on the Grand Banks off Newfoundland.
During his life he received hundreds of patents in various fields, most notably ones related to radio and sonar.

Robert William Boyle

Robert Boyle
In 1916, under 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.
Robert William Boyle (October 2, 1883 – April 18, 1955) was a physicist and one of the most important early pioneers in the development of sonar.

Fessenden oscillator

The "Fessenden oscillator", operated at about 500 Hz frequency, was unable to determine 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).
It was the first successful acoustical echo ranging device.

Sonobuoy

sonobuoyssonar buoysearch buoys
These included sonobuoys, first developed by the British in 1944 under the codename High Tea, dipping/dunking sonar and mine-detection sonar.
A sonobuoy (a portmanteau of sonar and buoy) is a relatively small buoy (typically 5 in, in diameter and 3 ft long) expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research.

Albert Beaumont Wood

A B WoodA. B. WoodAlbert B. Wood
In 1916, under 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.
Albert Beaumont Wood DSc (1890 – 19 July 1964), better known as A B Wood, was a British physicist, known for his pioneering work in the field of underwater acoustics and sonar.

Acoustic torpedo

acousticacoustic homing torpedopassive acoustic
Later, acoustic torpedoes were used.
An acoustic torpedo is a torpedo that aims itself by listening for characteristic sounds of its target or by searching for it using sonar (acoustic homing).

Ultrasound

ultrasonicultrasonicsultrasounds
The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic).
A common use of ultrasound is in underwater range finding; this use is also called Sonar.

Isle of Portland

PortlandPortland, EnglandHM Naval Base Portland
An anti-submarine school HMS Osprey and a training flotilla of four vessels were established on Portland in 1924.
It was a centre for Admiralty research into asdic submarine detection and underwater weapons from 1917 to 1998; the shore base HMS Serepta was renamed HMS Osprey in 1927.

Acoustic mine

acoustic
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 10000 ft, and ability to survive neighbouring mine explosions.
Depending on its design, it will either passively listen to its environment, depending only on the noise that is made by passing ships or actively send out audio pulses, not unlike a sonar, listening to the lapse in time in which the echo returns to it.

Piezoelectricity

piezoelectricpiezoelectric effectpiezo-electric
Although piezoelectric and magnetostrictive transducers later superseded the electrostatic transducers they used, this work influenced future designs.
The first practical application for piezoelectric devices was sonar, first developed during World War I.

Multibeam echosounder

multibeam sonarmultibeammultibeam sonar bathymetry
Use of an array reduces the spatial response so that to provide wide cover multibeam systems are used.
A multibeam echosounder is a type of sonar that is used to map the seabed.

Terfenol-D

Lightweight sound-sensitive plastic film and fibre optics have been used for hydrophones (acousto-electric transducers for in-water use), while Terfenol-D and PMN (lead magnesium niobate) have been developed for projectors.
Its initial application was in naval sonar systems.

Reflection (physics)

reflectionreflectedreflective
Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections (echo) of the pulse.
In acoustics, reflection causes echoes and is used in sonar.

Chirp

chirp functionChirp modulationchirp signal
The pulse may be at constant frequency or a chirp of changing frequency (to allow pulse compression on reception).
It is commonly used in sonar, radar, and laser, but has other applications, such as in spread-spectrum communications.

Fishfinder

fish findersfathometerfish finder
Another variant is a "fishfinder" that shows a small display with shoals of fish.
A fishfinder or sounder (Australia) is an instrument used to locate fish underwater by detecting reflected pulses of sound energy, as in sonar.

Echo sounding

echo sounderfathometerdepth sounder
When active sonar is used to measure the distance from the transducer to the bottom, it is known as echo sounding.
Echo sounding is a type of sonar used to determine the depth of water by transmitting sound waves into water.

Sonar signal processing

signal processing
The target signal (if present) together with noise is then passed through various forms of signal processing, which for simple sonars may be just energy measurement.
No matter whether active sonar or passive sonar, the information included in the reflected signal can not be used without technical signal processing.

Beamforming

beam formingbeamformerAntenna beamforming
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.
It has found numerous applications in radar, sonar, seismology, wireless communications, radio astronomy, acoustics and biomedicine.

Pulse compression

pulse compression radarchirp radarintra-pulse modulation
The pulse may be at constant frequency or a chirp of changing frequency (to allow pulse compression on reception).
Pulse compression is a signal processing technique commonly used by radar, sonar and echography to increase the range resolution as well as the signal to noise ratio.