Hydrophone

hydrophoneshydroacoustichydroacousticshydrophobichydrophone arrayhydrophonichydrophonic equipmentocean bottom hydrophonespicking up their echoesreceiver
A hydrophone (Ancient Greek ὕδωρ = water[1] and φωνή = sound[1]) is a microphone designed to be used underwater for recording or listening to underwater sound.wikipedia
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Piezoelectricity

piezoelectricpiezoelectric effectpiezo-electric
They developed a piezoelectric hydrophone by increasing the power of the signal with a vacuum tube amplifier; the high acoustic impedance of piezoelectric materials facilitated their use as underwater transducers.
The detector consisted of a transducer, made of thin quartz crystals carefully glued between two steel plates, and a hydrophone to detect the returned echo.

Sonar

asdicvariable depth sonaractive sonar
From late in World War I until the introduction of active sonar in the early 1920s, hydrophones were the sole method for submarines to detect targets while submerged; they remain useful today.
The British made early use of underwater listening devices called hydrophones, while 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.

William Henry Bragg

William BraggSir William BraggSir William Henry Bragg
Later in the war the British Admiralty belatedly convened a scientific panel to advise on how to combat U-boats; it included the Australian physicist William Henry Bragg and the New Zealand physicist Sir Ernest Rutherford.
The Navy had a hydrophone research establishment at Aberdour Scotland, staffed with navy men.

Beamforming

beam formingbeamformerAntenna beamforming
The array may be steered using a beamformer.
In passive sonar, and in reception in active sonar, the beamforming technique involves combining delayed signals from each hydrophone at slightly different times (the hydrophone closest to the target will be combined after the longest delay), so that every signal reaches the output at exactly the same time, making one loud signal, as if the signal came from a single, very sensitive hydrophone.

SOSUS

Sound Surveillance Systemdeep sea listening equipmentNavy facility
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.
They decided on a system to monitor low-frequency sound in the SOFAR channel using multiple listening sites equipped with hydrophones and a processing facility that could detect submarine positions by triangulation over hundreds of miles.

Anti-submarine warfare

ASWanti-submarineantisubmarine warfare
In 1918 airships of the Royal Naval Air Service engaged in anti-submarine warfare experimented by trailing dipped hydrophones.
Acoustics particularly in active and passive sonar, sonobuoys, and fixed hydrophones aid in the detection of radiated noise. Sonar can be mounted on the hull or in a towed array.

Transducer

transducerstransductiontransduce
A small single cylindrical ceramic transducer can achieve near perfect omnidirectional reception.
Hydrophones – converts changes in water pressure into an electrical signal

Communication with submarines

submarine communicationscommunicatedcommunicate with deeply submerged submarines
Communication with submarines
Sound travels far in water, and underwater loudspeakers and hydrophones can cover quite a gap.

Underwater acoustics

underwater soundunderwater acousticacoustic
Underwater acoustics
These compressions and rarefactions are detected by a receiver, such as the human ear or a hydrophone, as changes in pressure.

Reflection seismology

seismic reflectionseismic explorationseismic
Reflection seismology
In water, hydrophones are used, which convert pressure changes into electrical signals.

Infrasound

infrasonicsubsonicinfra-sound
These are capable of clearly recording extremely low frequency infrasound, including many unexplained ocean sounds.
The Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission uses infrasound as one of its monitoring technologies, along with seismic, hydroacoustic, and atmospheric radionuclide monitoring.

Geophone

Geophone arraygeophone flute
Geophone
Hydrophone

Carbon microphone

carbon transmittercarbon button microphonesbutton microphone
On one face was a 1 mm thick brass diaphragm which was coupled by a short brass rod to a carbon microphone.

Paul Langevin

LangevinPaul-LangevinLangevin, Paul
Early in the war the French President Poincare (himself a physicist) provided Paul Langevin with the facilities needed to work on a method to locate submarines by the echos from sound pulses.

Vacuum tube

vacuum tubestubethermionic valve
They developed a piezoelectric hydrophone by increasing the power of the signal with a vacuum tube amplifier; the high acoustic impedance of piezoelectric materials facilitated their use as underwater transducers.

Acoustic impedance

impedanceacoustical impedanceradiation impedance
They developed a piezoelectric hydrophone by increasing the power of the signal with a vacuum tube amplifier; the high acoustic impedance of piezoelectric materials facilitated their use as underwater transducers.

Ernest Rutherford

RutherfordLord RutherfordLord Rutherford of Nelson
Later in the war the British Admiralty belatedly convened a scientific panel to advise on how to combat U-boats; it included the Australian physicist William Henry Bragg and the New Zealand physicist Sir Ernest Rutherford.

Aberdour

Aberdour CastleEaster Aberdour
However, Bragg took the lead, in July 1916 he moved to the Admiralty hydrophone research establishment at Hawkcraig on the Firth of Forth.

Firth of Forth

ForthFirthFirth of Foth
However, Bragg took the lead, in July 1916 he moved to the Admiralty hydrophone research establishment at Hawkcraig on the Firth of Forth.

Microphone array

arraysacoustical arraysarray
Multiple hydrophones can be arranged in an array so that it will add the signals from the desired direction while subtracting signals from other directions.

United States Navy

U.S. NavyNavyUS Navy
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.

Soviet Union

SovietUSSRSoviets
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.

Cold War

the Cold Warcold-warCold War era
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.

Greenland

🇬🇱GreenlandicGL
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.

Iceland

🇮🇸IcelandicISL
SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U.S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland, Iceland and the United Kingdom known as the GIUK gap.