Enav Sonar - Copy

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CONTENTSA. Historical Background of SONAR

B. Principles of Sonar1.SONAR Basics

2.Glimpse of Sound Acoustics

3.Development of SONAR

4.Echo-sounding

C. Classifications/Kinds of SONAR

D. SONAR Systems

E. Practical SONAR Devices

F. Factors Affecting the Range and Effectiveness of SONAR

G. Uses of SONAR

H. Effects of SONAR to Marine Animal

I. SONAR Counter Measures



SONAR

Acronym for Sound Navigation and

Ranging , a detection system based on the

reflection of underwater sound waves, just as radar is based on the reflection of

radio waves in the air.

It is a technique based on echolocation

used for the detection of objects

underwater.



Historical Background of SONAR

1490 – Leonardo Da Vinci first recorded the useby humans of sounds for communication and

object detection.

19th century – an underwater bell was used as

an ancillary to lighthouses to provide warning of hazards.

1906 – the first sonar device was developed by

shipbuilder Lewis Nixon.

1912 – the use of sound ‘echo locate’ underwaterin the same way as bats use sound for aerial

navigation seems to have further prompted by the

Titanic Disaster.



1913 – world’s first patent for an underwater

echo ranging device was filed. Alexander Behmobtained a patent for an echo sounder.

1914 – Reginald Fessenden built an experimental

system which could detect an iceberg 2 mi. range.

1915 – British made early use of underwaterhydrophones.

1916 – Robert Boyle took on the active sonar

project, producing a prototype for testing in mid-

1917. 1918 – both the U.S. and Britain had built active

systems, though the British were well in advance

of the U.S.



1920 – they tested their ASDIC on HMS Antrim

and started production of units in1922

. 1923 – the 6th Destroyer Flotilla had ASDIC –

equipped vessels.

1924 – an anti-submarine school, HMS Osprey,

and a training flotilla of four vessels wereestablished on Portland

1931 – the U.S. Sonar QB set arrived.

1939 – the Admiralty made up the story that the

letters stood for ASDIC.

1948 – with the formation of NATO,

standardization of signals ld to the dropping of

ASDIC in favor of sonar.



Basics of SONAR

SONAR works as follows: A machine sends out sound waves (ultrasonic

sound )

The sound bounces off the seafloor; the reflected

sound waves are detected by the machine. The distance between the machine and the

reflecting surface can be calculated from the time

the sound takes to travel to the seafloor and back.

By making measurements in different places, thecontours of the seafloor can be plotted. As a

general rule, the closer you can get the instrument

to the seafloor, the greater the resolution of the

contour map.



Glimpse of Sound Acoustics

Sound move quite efficiently through water, far more easily

than they do through air. The ability of sound to travel over great distances allows

remote sensing in a water environment.

Sound travels in water in a moving series of pressure fronts

known as compressional wave .

The local speed of sound can change depending on theconditions of water such as salinity, pressure, and

temperature, but it is independent of the characteristics of

sound itself.

Sound waves are useful for remote sensing in a water

environment because some of them can travel for hundreds

of kilometers without significant attenuation.

The level of attenuation of a sound wave is dependent on its

frequency- HF sound is attenuated rapidly, while ELF sound

can travel virtually unimpeded throughout the ocean.



Development of SONAR

April 23, 1916 – first known sinking of a submarine (German

U-Boat, UC-3) detected by hydrophone in Atlantic.

1934 – first echo-ranging equipment installed in the American

destroyers of Desdiv 20, one of which was USS Rathburne (DD-

113).

1939 – West Coast Sound School opened in San Diego. Atlantic

Fleet Sound School opened at the sub base in New London,Connecticut. First sound class graduated March 1940. Later the

school as transferred to Key West, Florida .

September 1941 – USS Kearny torpedoed by U-Boats. Later the

USS Rueben James (DD-45) was sunk by torpedo fire, the first

destroyer to be lost in WWII. October 1941 – Bathythermograph introduced to the Fleet.

Officers specialists were first trained and assigned to take

observations aboard ships.

January 1942 – ASW unit established in Boston to collect and

evaluate ASW data for recommendations to the Navy.



Echo Sounding

a process of sonar device to remotely measurehe depth of the ocean floor. Also known as bathymetry measurement. Instruments that make thesemeasurements are called echo sounders .

Echo sounders measure the depth by generating a shortpulse of sound, or ping , and then listening for the echoof the pulse from the bottom. The time between thetransmission of a pulse and the return of its echo is thetime it takes the sound to travel to the bottom andback. Knowing this and the speed of sound in water

allows you to calculate the range to the bottom.

Note: speed of sound = 1500 m/s



Projector

a device used by echo sounders to producesound waves.

Boomers

one type of projector system whichdetonates explosive charges underwater.

Sparkers

use high energy electrical discharges tocreate plasma bubbles.

Air guns

use compressed air to create a collapsingbubble underwater.

used primarily for seismic surveys. they are limited in that the amplitude,

frequency and duration of the sound pulses they create cannot be maintained from one ping to thenext.





1) a transmitter,

2) a loudspeaker,3) a microphone,

4) a receiver, and

5)various indicating devices.





A transmitter is called a "driver," and consists of a highfrequency audio oscillator and a power amplifier .

The loudspeaker and microphone are combined in a

device called a "transducer" or "projector." The transducer is mounted outside of the ship's hull below the waterline,and combines the functions of a loudspeaker and amicrophone.

The sonar receiver is similar to a radio receiver. The

indicating devices tell the sonar operator, by means ofboth visual and audio indications, what is going onbeneath the surface of the ocean around his ship. Theseindicators include a bearing indicator, range indicator,plan position indicator and other devices.











Imaging SONAR is a high-frequency sonar thatproduces “video-like “imagery

using a narrow field of view.



It consists of smaller SONARsystems that can be mounted ontripods and lowered to the bottomof the waterway.



It produces 3-Dimensional imagery ofobjects using an array receiver.



Searchlight SONAR transmits a signal and uses

returning echoes for detection of targets andmeasurement of both range and bearing.



Placed inside of a shell and towedbehind a vessel. It produces strip-like images from both sides of thedevice





The SOFAR channel acts as a waveguide for

sound, and low frequency sound waves within thechannel may travel thousands of miles beforedissipating.







Speed of Sound

Absorption

Spreading

Scattering

Reflection

Refraction

Noise



Anti-submarine warfare Torpedoes Mines

Submarines Aircraft Underwater communications Ocean surveillance

Underwater security Fisheries Biomass estimation Bottom type assessment



Until recently, ship SONARs were usually withhull mounted arrays, either amidships or atthe bow. It was soon found after their initial

use that a means of reducing flow noisewas required. The first were made of canvason a framework, then steel ones were used.Now domes are usually made of reinforced

plastic or pressurized rubber. Such SONARsare primarily active in operation.

An example of a conventional hullmounted SONAR is the SQS-56.



Because of the problems of ship noise, towed SONARsare also used. These also have the advantage ofbeing able to be placed deeper in the water.

However, there are limitations on their use in shallowwater. These are called towed arrays (linear) or variable depth SONARs (VDS) with 2/3D arrays. Aproblem is that the winches required to

deploy/recover these are large and expensive. VDS

sets are primarily active in operation while towedarrays are passive.

An example of a modern active/passive ship towedSONAR is Sonar 2087 made by Thales Underwater Systems.



Modern torpedoes are generally fittedwith an active/passive SONAR. This may

be used to home directly on the target,but wake following torpedoes are alsoused.

An early example of an acoustic homer

was the Mark 37 torpedo.



Mines may be fitted with a SONAR todetect, localize and recognize the

required target. An example is the CAPTOR mine.



Submarines rely on SONAR to a greater extent than surface ships as they cannot

use RADAR at depth. The SONAR arraysmay be hull mounted or towed.Information fitted on typical fits is given inOyashio class submarine and Swiftsure

class submarine.



Helicopters can be used for anti-submarinewarfare by deploying fields ofactive/passive sonobuoys or can operate

dipping SONAR, such as AQS-13. Fixed wingaircraft can also deploy sonobuoys andhave greater endurance an capacity todeploy them. Processing from thesonobuoys or dipping SONAR can be on

the aircraft or on ship. Helicopters have also been used for mine

countermeasure missions using towedSONARs such as AQS-20A.



Dedicated SONARs can be fitted to shipsand submarines for underwater

communication.



For many years, the United States operated a largeset of passive SONAR arrays at various points in theworld’s oceans, collectively called Sound

Surveillance System (SOSUS) and later IntegratedUndersea Surveillance System (IUSS). A similar system isbelieved to have been operated by the Soviet Union.

As permanently mounted arrays in the deep oceanwere utilized, they were in very quiet conditions so

long ranges could be achieved. Signal processingwas carried out using powerful computers ashore.With the ending of the Cold War a SOSUS array hasbeen turned over to scientific use.



SONAR can be used to detect frogmenand other scuba divers. This can be

applicable around ships or at entrancesto ports. Active SONAR can also be usedas deterrent and/or disabledmechanism. One such device is the

Cerberus system.



Historically, fishermen have used manydifferent techniques to find and harvestfish. However, acoustic technology has

been on of the most important drivingforces behind the development of themodern commercial fisheries.

Fishermen also use active SONAR andecho sounder technology to determinewater depth, bottom contour, andbottom composition.



Biomass estimation uses SONAR todetect fish, etc. As the sound pulse

travels through water it encountersobjects that are of different density thanthe surrounding medium, such as fish,that reflect sound back toward the

sound source. These echoes provideinformation on fish size, location, andabundance.



SONARs have bee developed that can be

used to characterize the sea bottom into,

for example, mud, sand, and gravel.

Relatively simple SONARs such as echo

sounders can be promoted to seafloor

classification systems via add-on modules,

converting echo parameters in to sedimenttype. Different algorithms exist, but they are

all based on charges in the energy or

shape of the recorded sounder pings.



High-powered SONAR transmitters may

harm marine animals, although the precise

mechanisms for this are not well

understood. Some marine animals such aswhales and dolphins, use echolocation

systems similar to active SONAR to locate

predators and prey. It is feared that SONARtransmitters could confuse these animals

and cause them to lose their way, perhaps

preventing them from feeding and mating.



It has been suggested that military SONAR

may induce whales to panic and surface

too rapidly leading to a form of

decompression sickness. This was first raisedby a paper published in the journal Nature

in 2003. It reported acute gas-bubble

lesions (indicative of decompressionsickness) in whales that beached shortly

after the start of a military exercise off the

Canary Islands in September 2002.



In the Bahamas in 2000, a SONAR trial bythe United States Navy of transmitters in thefrequency range 3-8 kHz at a source level of223-235 decibels re 1 µPa (scaled to adistance of 1m) resulted in the beaching ofseventeen whales, seven of which werefound dead. The Navy accepted blame ina report, which found the dead whales to

have experienced acoustically-inducedhemorrhages around the ears. The resultingdisorientation may have led to thestranding.



A kind of sonar called mid-frequency sonar has beencorrelated with mass cetacean stranding throughoutthe world’s oceans, and has therefore been singled

out by environmentalists as causing the death ofmarine mammals. International press coverage of

these events can be found at this active sonar newsclipping Web site. A lawsuit was filed in Santa Monica,California on 19 October, 2005 contending that the

U.S. Navy has conducted sonar exercises in violationof several environmental laws, including the National

Environmental Policy Act, the Marine MammalProtection Act, and the Endangered Species Act.



Active (powered) countermeasures maybe launched by a submarine under attack to raise the noise level and/or provide a large false target. Passive (i.e.non-powered) countermeasures includemounting noise generating devices on

isolating devices and coating the hull ofsubmarines.

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Enav Sonar - Copy