how night vision works.docx

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Digital Image Processing

HOW NIGHT VISION WORKS

ABSTRACT:

Night Vision scopes and binoculars are electro-optical devices that intensify (oramplify e!isting light instead of relying on light source of their own. Thedevices aresensitivetoabroadspectrumoflight"fromvisiblethrough infrared.#naccessory illuminator can increase the light available at the infrared end of thespectrumbycastingabeamoflightthatisnotvisibletothehumaneye.#ninfrared

night vision system senses heat radiated by things and produces a videopicture of the heat scene. The gadget thatsensestheheat is a photocathode" similar to the one in a video camera" e!cept it issensitive to infrared radiation instead ofvisiblelight. There are two methodsof operating night vision systems" being either in a $passive$ mode or an$active$ mode. Passive systems amplify the e!isting environmental ambientlighting" while active systems rely on an infrared light source to provideufficientillumination. #ctive systems are often usedtoday on many consumerdevices such ashomevideocameras



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.%ow Night Vision&or'

introductionto%owNightVision &or'The first thing you probably thin' ofwhenyouseethewordsnightvision isaspy or action movie you$ve seen" inwhich someone straps on a pair ofnight-vision goggles to find someoneelse in a dar' building on a moonlessnight.#ndyoumayhavewondered)othose things really wor'* +an you

actuallyseeinthedar'*

NightVision,mageallery

Theanswerismostdefinitelyyes.&iththepropernight-visioneuipment"youcansee a person standing over /00yards (123 m away on a moonless"cloudynight4 Night vision can wor' in two very different ways" depending on thetechnologyused.

Infrared Light:

,norder tounderstandnightvision" it is important to understandsomethingaboutlight. The amount of energy in a lightwave is related to itswavelength: Shorter

wavelengthshavehigherenergy. 5f visiblelight" violet has themostenergy"andredhas

the least. 6ust ne!t to the visible lightspectrumistheinfraredspectrum.



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,nfrared light is a small part of the lightspectrum.

Infrared light can be split into three categories:

Near-infrared(near-,7-+losesttovisible light"near-,7haswavelengthsthatrangefrom0.8to1.3microns"or800billionthsto1"300billionthsofameter.

9id-infrared (mid-,7 - 9id-,7

%as wavelengths ranging from 1.3

To 3 microns.both near ,7 and mid,7 are used by a variety of electon-)evices including remotecontrols.

Thermal-infrared (thermal-,7 - 5ccupying the largest part of the infraredspectrum"thermal-,7haswavelengthsrangingfrom3micronstoover30microns.

Basic Technologies:

Night vision work in two very different ways, depending on the

technology used

,mageenhancement -Thiswor'sbycollecting the tiny amounts of light"includingthelowerportionoftheinfraredlightspectrum"thatarepresentbut maybe imperceptible to our eyes"easilyobservetheimage.

Thermal imaging - This technology operates by capturing theupper portion of the infraredlight spectrum" which is emitted asheat byobects instead of simplyreflected as light. %otter obects"suchaswarmbodies"emitmoreof this light than cooler obects li'etreesorbuildings.

,N;7#-79,N#T57S

?asicallywhatan,7,doesisthrowouta beam of infra-red light that is nearinvisibletothena'edeyebutyourNV)can see it.This allows you to use yourscope even in total dar'ness. The ,7,wor'sli'eaflashlightandthedistanceyoucanseewith itwillbe limited.&edo use the most powerful eye-safeilluminator on the mar'et. This allowsour ,7, to e!tend out to 100 yards%owever" because of the power at ashort distance the ,7, may cover only

@0-A0Boftheviewingarea.



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1.;ront=ens/.Photocathode3. 9icro-channel@.%igh Voltage PowerSupplyC.PhosphorusScreenA.


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1.# conventional lens" called the obective lens" captures ambient light andsomenear-infraredlight.

/. The gathered light is sent to the image-intensifiertube.,n most NV)s" thepower supply for theimage-intensifiertubereceives

3. power from two N-+ell or two ## batteries. The tube outputs a highvoltage" about C"000 volts" to the image-tube components.

@.Theimage-intensifiertubehasaphotocathode"whichis used to convertthephotonsoflightenergyintoelectrons.

C.#sthe electrons pass throughthetube"similarelectronsarereleasedfromatoms in the tube" multiplying the original number of electrons by a factor ofthousands through the use of amicrochannelplate(9+Pin thetube.The9+P iscontained inavacuumand has metalelectrodeson eithersideof thedisc.&hentheelectronsfromthephotocathodehitthefirstelectrodeofthe9+P"theyareacceleratedintotheglass microchannels by the C"000-Vbursts

being sent betweentheelectrode pair. #n interesting fact isthatthemicrochannelsinthe9+Parecreated at a slight angle (about a C-degreeto2-degreebiastoencourageelectroncollisionsandreducebothionand direct-light feedbac'from the phosphors on the output side.#t the end of theimage-intensifier tube" theelectrons hit a screen coated withphosphors"

which provides a perfectimage. The energy of the electronscauses thephosphors to reach an phosphorous plate and this plate

e!citedstate and they release photons.These phosphorscreatethe greenimage.

The green phosphor iage is viewed through another lens,

called the ocular lens, which allows you to agnify and focus

the iage$

Theral Iaging %rocess



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Iage of a sall dog taken in id& infrared '(theral() light

'false color)

Thermalimaging"alsocalledasthermographic or thermal video" is a type ofinfraredimaging. Thermo graphic cameras detect radiation intheinfraredrangeof(roughlyG00H1@"000 nanometers or 0.GH1@ Im and produce

images of that radiation.Theamountof radiation emittedbyanobect increaseswithtemperature" thereforethermographallowsoneto see variations intemperature(hence the name. &hen viewed by thermographic camera" warmobects stand outwellagainstcoolerbac'groundsD humans and other warm-bloodedanimals become easilyvisible againsttheenvironment"dayornight.

,t has many other uses. ;or e!ample"firefightersuseittoseethroughsmo'e.Thermalimagingcamerasare also installed in some lu!ury cars to aid thedriver.Somephysiologicalactivities"particularly responses" in human beings andotherwarm-blooded animals can also be monitored with thermo graphicimaging.,nsteadof++)sensors"mostthermal imaging cameras use +95S

;ocalPlane#rray(;P#.

enerations:

NV)shavebeenaroundformorethan @0years.They arecategoriEedbygeneration.nitedStates

#rmyandusedin&orld&ar,, and the Jorean &ar" these NV)suseactiveinfrared.

eneration 1 - The ne!t generation of NV)s moved away from active infrared"using passive infrared instead.This also meansthattheydonotwor'verywellon cloudyormoonlessnights.eneration-1NV)s use the same image-intensifier tube technology as eneration 0" with both cathode andanode" so image distortion and shorttubelifearestillaproblem.

eneration / - 9aor improvements in image-intensifier tubes resulted ineneration-/NV)s.Theyofferimproved resolution and performanceover

eneration-1devices"and are considerably more reliable. The biggest gain ineneration/ istheability tosee in e!tremely low light conditions" suchas amoonless night. This increased sensitivity is due to the addition of themicrochannel plate to the image-intensifiertube.

eneration 3 - &hile there are no substantial changes in the underlyingtechnology from eneration /" theseNV)s have even better resolution andsensitivity. This is because the photocathodeismadeusinggalliumarsenide"

which is very efficient at convertingphotons to electrons. #dditionally" the



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9+P iscoatedwithan ionbarrier"which dramatically increases the life of thetube.

eneration @ - &hatisgenerally 'nownas eneration @orfilmless and gatedtechnology shows significant overallimprovement in both low-and high-level lightenvironments.The removal of the ion barrier from the 9+P that was added in eneration 3

technology reduces the bac'ground noise and thereby enhances the signal tonoise ratio.Night Vision


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+ommon applications for night visioninclude:

9ilitary eneration @ - &hat is generally 'nown as eneration@orfilmless and gatedtechnology shows significant overallimprovement in bothlow-and high-level light environments.The removal of the ion barrier from the 9+P that was added in eneration 3technology reduces the bac'ground noise and thereby enhances the signal tonoise ratio.

Night Vision


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+ommon applications for night vision include: Military =aw enforcement

#t the ,nternational 9otor Show (,## in ;ran'furt" Siemens has introduceda night vision system that wor's with infrared technology. 5ne uarter of

all serious traffic accidents ta'e place in the evening or at night. =awenforcement

#t the ,nternational 9otor Show (,##in ;ran'furt" Siemens has introduced anight vision system that wor's withinfrared technology. 5ne uarter of allserious traffic accidents ta'e place in the evening or at night. Night Visionma'esa vehicleKsdar'enedsurroundingsvisibleout toadistanceof 1C0 meters.Night Vision generates an electronically processed video iage that can bedisplayed in real timein thehead-updisplay.Thepedestrianmar'inginthevideoimage has been realiEed by Siemens V)5 as a prototypewith image

processingelectronics.ThisanalyEesall the imagedataaccording to temperaturedifferences and typical shapes and mar's pedestrians on the monitorwith a

warning. ,twill be some time before these special features will be ready formar'etlaunch.

+5N+=>S,5N:

,tKsacriticalstudy"whichplaysavitalroleinmodernworld as it is involvedwith advanced use of scienceand technology.The advancesin technology havecreated the tremendousopportunitiesforVisionSystemand,mageProcessing.Thetechnology has evolved greatly since their

introduction"leadingtoseveralgenerationsofnightvisioneuipmentwith performance increasing and pricedecreasing.;rom the above discussionwe can conclude that thisfieldhasrelatively more advantages thandisadvantagesand hence is veryusefulinvariedbranches.

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