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SONAR

Introduction to Remote Sensing

GISC 6325 / GEOS 5325

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What is SONAR?

So sound

Na navigation andR ranging

A sensor is used to detect objects through theuse of high or low frequency sound waves.

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Sound Properties

Sound travels (slower than EMR) at 4,800 fps or1460 meters per secondwe will use 1500 mps.

(in elastic mediums - air, water, or earthNOTina vacuum)

Sound waves are measured in hertz(Hz). Thehuman ear can detect frequencies ranging from20 Hz to 20,000 Hz.

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How does Sonar work

Sound wave sent outward: Animalsnoisesmade with their bodies, seismicexplosions orimpact plates, ultrasoundtransducer converts

sound to electricity and back, shipsping oremit a burst of acoustic energy.

Sound waves returned:Animalswaves sensed

through ears (bats) or teeth and bones (whales),seismicwaves sensed through geo-phones,shipswaves sensed by hydrophones or (next)

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How does Sonar work

Any listening system that consist of

(1) a hydrophone(2) an electronic receiver

(3) a bearing indicator

(4) a speaker or headphones.

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Sonar Noise

The sound-listening problem for the

operator consists primarily of learning to

distinguish between :

(1) sounds emitted by another ship's machinerythrough the hull and from the propeller

(2) the multitude of other sounds that exist in theocean.

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Sonar Noise

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Navigation and Ranging Issues

Depth is determined by dividing travel time of sound by 2 andthen multiplying by 1500 mps

12 seconds travel time

12/2 = 6X1500 = 9000 meters deep The Doppler principle applicable to all wave motion was

developed by the Austrian physicist, Christian Doppler (1803-1853).

Frequency of sound appears to increase when an observer movestoward a source and appears to decrease when he moves awayfrom it. Similarly, if the source is moving toward the observer,the frequency is higher; if the source is moving away from theobserver, it is lower.

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Sonar References

http://hnsa.org/doc/sonar/chap1.htm

The Historic Naval Ship Association

http://www.indepthconsulting.com/Sonar/Sidescan.htm

In Depth ConsultingSide Scan Imaging

http://www.nauticalcharts.noaa.govNOAA Office of Coast Survey

http://hnsa.org/doc/sonar/chap1.htmhttp://www.indepthconsulting.com/Sonar/Sidescan.htmhttp://www.indepthconsulting.com/Sonar/Sidescan.htmhttp://www.nauticalcharts.noaa.govtus.htm/http://www.nauticalcharts.noaa.govtus.htm/http://www.indepthconsulting.com/Sonar/Sidescan.htmhttp://www.indepthconsulting.com/Sonar/Sidescan.htmhttp://hnsa.org/doc/sonar/chap1.htm

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What do we use sonar for?

First developed in WWII to detect submarines

Used to detect icebergs

Water depth Locate sunken ships/or other historical objects

Military uses it still to detect subs and aim

weapons Locate fish or track animals that are being studied

Mapping underwater features (we will do this)

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How a map is madeA Sonar echo recorder is dragged behind a ship

and is called a towfish It sends out a ping sound travels to the

bottom and is reflected back to the hydrophone

An instrument on the ship collects and analyzesthe data

These points of data are combined to create a

picture of the seafloorA ship must travel over the area that is being

studied multiple times this is called mowing the

grass

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Sea floor off of L.A. A mosaic map

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Types of Imaging Sonar

Side-Scan Sonar Systems Used for mapping the sea

floor for nautical charts,

bathymetric maps, maritime

archeology, and surveys.

The intensity of the acoustic

reflections from the seafloor

of this fan-shaped beam isrecorded in a series of cross-track

slices. When stitched together along the direction of motion,these slices form an image of the sea bottom within the swath

(coverage width) of the beam.

http://en.wikipedia.org/wiki/Acousticshttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Light_beamhttp://en.wikipedia.org/wiki/Acoustics

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Side-Scan Sonar Systems

The sound frequencies used in side-scan sonar usually rangefrom 100 to 500 kHz; higher frequencies yield betterresolution but less range.

Notice that the volcano casts a shadow to the left, and the slopefacing to the right is very bright. Smaller bumps also cast smallshadows making the topography look lumpy. Each image is 3 km(1.8 miles) wide.

http://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Kilohertzhttp://en.wikipedia.org/wiki/Temporal_resolutionhttp://en.wikipedia.org/wiki/Temporal_resolutionhttp://en.wikipedia.org/wiki/Kilohertzhttp://en.wikipedia.org/wiki/Frequency

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Single-beam Sonar Systems

Single beam sonar data are collected along transect lines andtypically cannot provide continuous coverage of the seafloor.

The output resolution of the data are determined by thefootprint size, sampling interval, sampling speed, and distancebetween transects.

Used primarily for mapping channels and bathymetry for

hydrologic and engineering applications.

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Multi-beam Sonar Systems

Instead of just one transducer pointing down, multibeambathymetry systems have arrays of 12 kHz transducers,

sometimes up to 120 of them, arranged in a precise geometricpattern on ships hulls.

The swath of sound they send out covers a distance on eitherside of the ship that is equal to about two times the water depth.The sound bounces off the seafloor at different angles and isreceived by the ship at slightly different times.

the signals are then processed by computers

on board the ship, converted into water depths, andautomatically plotted as a bathymetric map

with an accuracy of about 5 meters to less than

a meter with differential GPS.

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Multi-beam Sonar Systems

http://celebrating200years.noaa.gov/transformations/hydrography/image11.html

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Tale of the Sea

USSMonitor A 987-ton armored turret

gunboat

Designed by John Ericsson, a

Swedish born engineer 172 feet long with a 41.5 foot

beam and a draft of 10.5 feet

59 officers and men

a pair of eleven-inchDahlgren smoothbore shellguns on a rotating turret.

CSS Virginia (Merrimac) One of the earliest ironclad

fighting ships.

Designed by Lt. J. M.

Brooke, CSN 275 feet long with a 38.5 foot

beam and a draft of 22 feet

320 officers and men

two 7-inch Brooke rifles, twosimilar 6-inch Brooke rifles,and six 9-inch Dahlgrensmooth-bore cannons

http://www.history.navy.mil/photos/images/h50000/h50954.jpg

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Tale of the Sea (March 9, 1862)

The two Ironclads clashed in lower Chesapeake Bay around10:00am.

They hammered at each other for four hours with no discernabledamage to either ship.

A blast from the 7-inBrooke rifle, throughthe turret slit,temporarily blindedthe Monitors

Captain. TheMonitor headed for

shallow water.

Thinking they won thebattle, The Confederate

Ship left the battle sceneand headed South toretire. Later on May 10,1862, unable to retreatdownriver, the Captainordered it blown up.

http://oceanexplorer.noaa.gov/explorations/monitor01/history/media/monitorbattle.html

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Tale of the Sea

(Dec. 31, 1862) While the design ofMonitorwas well-

suited for river combat, her lowfreeboard and heavy turret made herhighly unseaworthy in rough waters.

This feature probably led to the earlyloss of the originalMonitor, whichfoundered during a heavy storm.Swamped by high waves while under

tow byRhode Island, she sank onDecember 31, 1862 in theAtlanticOcean offCape Hatteras, NorthCarolina. 16 of 62 crewmen were lostin the storm.

http://en.wikipedia.org/wiki/USS_Rhode_Island_(1861)http://en.wikipedia.org/wiki/December_31http://en.wikipedia.org/wiki/1862http://en.wikipedia.org/wiki/Atlantic_Oceanhttp://en.wikipedia.org/wiki/Atlantic_Oceanhttp://en.wikipedia.org/wiki/Cape_Hatterashttp://en.wikipedia.org/wiki/North_Carolinahttp://en.wikipedia.org/wiki/North_Carolinahttp://en.wikipedia.org/wiki/North_Carolinahttp://en.wikipedia.org/wiki/North_Carolinahttp://en.wikipedia.org/wiki/Cape_Hatterashttp://en.wikipedia.org/wiki/Atlantic_Oceanhttp://en.wikipedia.org/wiki/Atlantic_Oceanhttp://en.wikipedia.org/wiki/1862http://en.wikipedia.org/wiki/December_31http://en.wikipedia.org/wiki/USS_Rhode_Island_(1861)

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Tale of the Sea

For more than a century, theresting place of the USSMonitorremained undiscovered. Therewere numerous searches andoccasional claims of discovery;however, no one could show proofof the Monitors location.

Then, in August 1973, scientists aboardDuke Universitys research vessel

Eastward, usingsonar, located 22wrecks in the area where Monitor hadreportedly gone down.

The footprint included the size andshape of the hull and armor belt, thelocation of and details about the turret,pilothouse and other deck features, aswell as the expected sonar signature. Allbut one site was eventually eliminated

from consideration.

USSMonitor

http://www.brooklynonline.com/images/sailors.jpg

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Tale of the Sea

USSMonitor

This object resembling theMonitorwas located

approximately 16 milessouth-southeast of CapeHatteras Lighthouse. The

wreck was described as "lyingin 220 feet of water on a hard

sand and shell-strewn floor."

Although the size and shapematched the known

dimensions of theMonitor,investigators were unable toquickly verify its identity.

http://www.history.navy.mil/photos/images/h50000/h50954.jpghttp://oceanexplorer.noaa.gov/explorations/monitor01/finding/media/mon_whiting.html

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Tale of the SeaUSSMonitor

During the first week of April 1974, a second cruise to theMonitorsite produced detailed photographic and television tape records ofthe site. The ship was upsidedown!!

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Tale of the Sea

USSMonitor

The wreck site wasdesignated as the United

States' first marine sanctuary. In 1998 the warship's

propeller was raised to thesurface.

On 16 July 2001, divers fromthe Monitor National MarineSanctuary brought to thesurface the 30-tonne steamengine.

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Tale of the Sea

USSMonitor

In 2003, after 41 days ofwork, the revolutionary

revolving gun turret wassalvaged by the U.S. NationalOceanic and Atmospheric

Administration (NOAA) anda team of U.S. Navy divers.

http://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administration