sonar(2)
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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
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