Night Vision Technology Seminar Report Pdf Free Download

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Night vision-technology-seminar-report-pdf.1.Night Vision TechnologyIntroductionNight vision technology, by definition, literally allows one to see in the dark. Originallydeveloped for military use, it has provided the United States with a strategic militaryadvantage, the value of which can be measured in lives. Federal and state agencies nowroutinely utilize the technology for site security, surveillance as well as search andrescue. Night vision equipment has evolved from bulky optical instruments in lightweightgoggles through the advancement of image intensification technology.The first thing you probably think of when you see the words night vision is a spy oraction movie you've seen, in which someone straps on a pair of night-vision goggles tofind someone else in a dark building on a moonless night. And you may have wondered'Do those things really work? Can you actually see in the dark?'

The answer is most definitely yes. With the proper night-vision equipment, you can see aperson standing over 200 yards (183 m) away on a moonless, cloudy night! Night visioncan work in two very different ways, depending on the technology used. Image enhancement - This works by collecting the tiny amounts of light,including the lower portion of the infrared light spectrum, that are present butmay be imperceptible to our eyes, and amplifying it to the point that we caneasily observe the image. Thermal imaging - This technology operates by capturing the upper portionof the infrared light spectrum, which is emitted as heat by objects instead ofsimply reflected as light. Hotter objects, such as warm bodies, emit more of thislight than cooler objects like trees or buildings.In this article, you will learn about the two major night-vision technologies. We'll alsodiscuss the various types of night-vision equipment and applications. But first, let's talkabout infrared light.The BasicsIn order to understand night vision, it is important to understand something about light.The amount of energy in a light wave is related to its wavelength: Shorter wavelengthshave higher energy. Of visible light, violet has the most energy, and red has the least.

Justnext to the visible light spectrum is the infrared spectrum.Infrared light can be split into three categories: Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengthsthat range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of ameter. Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1.3 to 3microns. Both near-IR and mid-IR are used by a variety of electronic devices,including remote controls. Thermal-infrared (thermal-IR) - Occupying the largest part of the infraredspectrum, thermal-IR has wavelengths ranging from 3 microns to over 30microns.The key difference between thermal-IR and the other two is that thermal-IR is emitted byan object instead of reflected off it. Infrared light is emitted by an object because of whatis happening at the atomic level.AtomsAtoms are constantly in motion.

They continuously vibrate, move and rotate. Even theatoms that make up the chairs that we sit in are moving around. Solids are actually inmotion! Atoms can be in different states of excitation. In other words, they can havedifferent energies.

If we apply a lot of energy to an atom, it can leave what is called theground-state energy level and move to an excited level. The level of excitation dependson the amount of energy applied to the atom via heat, light or electricity.An atom consists of a nucleus (containing the protons and neutrons) and an electroncloud. Think of the electrons in this cloud as circling the nucleus in many differentorbits.

Although more modern views of the atom do not depict discrete orbits for the.electrons, it can be useful to think of these orbits as the different energy levels of theatom. In other words, if we apply some heat to an atom, we might expect that some of theelectrons in the lower energy orbitals would transition to higher energy orbitals, movingfarther from the nucleus.Once an electron moves to a higher-energy orbit, it eventually wants to return to theground state. When it does, it releases its energy as a photon - a particle of light. Yousee atoms releasing energy as photons all the time. For example, when the heatingelement in a toaster turns bright red, the red color is caused by atoms excited by heat,releasing red photons.

An excited electron has more energy than a relaxed electron, andjust as the electron absorbed some amount of energy to reach this excited level, it canrelease this energy to return to the ground state. This emitted energy is in the form ofphotons (light energy).

The photon emitted has a very specific wavelength (color) thatdepends on the state of the electron's energy when the photon is released.Anything that is alive uses energy, and so do many inanimate items such as engines androckets. Energy consumption generates heat. In turn, heat causes the atoms in an object tofire off photons in the thermal-infrared spectrum. The hotter the object, the shorter thewavelength of the infrared photon it releases. An object that is very hot will even begin toemit photons in the visible spectrum, glowing red and then moving up through orange,yellow, blue and eventually white. Be sure to read How Light Bulbs Work, How LasersWork and How Light Works for more detailed information on light and photon emission.In night vision, thermal imaging takes advantage of this infrared emission.

In the nextsection, we'll see just how it does this.Thermal Imaging and Image EnhancementHere's how thermal imaging works: A special lens focuses the infrared light emitted by all of the objects in view. The focused light is scanned by a phased array of infrared-detectorelements. The detector elements create a very detailed temperature patterncalled a thermogram. It only takes about one-thirtieth of a second for thedetector array to obtain the temperature information to make thethermogram. This information is obtained from several thousand points inthe field of view of the detector array. The thermogram created by the detector elements is translated into electricimpulses. The impulses are sent to a signal-processing unit, a circuit board with adedicated chip that translates the information from the elements into data forthe display. The signal-processing unit sends the information to the display, where itappears as various colors depending on the intensity of the infraredemission. The combination of all the impulses from all of the elementscreates the image.Image courtesy of Infrared, Inc.The basic components of a thermal-imaging systemTypes of Thermal Imaging DevicesMost thermal-imaging devices scan at a rate of 30 times per second. They can sensetemperatures ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000C), and can normally detect changes in temperature of about 0.4 F (0.2 C).Image courtesy of Infrared, Inc.It is quite easy to see everythingduring the day.Image courtesy of Infrared, Inc.but at night, you can seevery little.Image courtesy of Infrared, Inc.Thermal imaging lets you see again.There are two common types of thermal-imaging devices: Un-cooled - This is the most common type of thermal-imaging device.

Theinfrared-detector elements are contained in a unit that operates at room.temperature. This type of system is completely quiet, activates immediatelyand has the battery built right in. Cryogenically cooled - More expensive and more susceptible to damage fromrugged use, these systems have the elements sealed inside a container thatcools them to below 32 F (zero C). The advantage of such a system is theincredible resolution and sensitivity that result from cooling the elements.Cryogenically-cooled systems can 'see' a difference as small as 0.2 F (0.1 C)from more than 1,000 ft (300 m) away, which is enough to tell if a person isholding a gun at that distance!While thermal imaging is great for detecting people or working in near-absolutedarkness, most night-vision equipment uses image-enhancement technology.Image EnhancementImage-enhancement technology is what most people think of when you talk about nightvision.

In fact, image-enhancement systems are normally called night-vision devices(NVDs). NVDs rely on a special tube, called an image-intensifier tube, to collect andamplify infrared and visible light.The image-intensifier tube changes photons to electrons andback again.Here's how image enhancement works: A conventional lens, called the objective lens, captures ambient light andsome near-infrared light. The gathered light is sent to the image-intensifier tube. In most NVDs, thepower supply for the image-intensifier tube receives power from two N-Cellor two 'AA' batteries. The tube outputs a high voltage, about 5,000 volts, tothe image-tube components. The image-intensifier tube has a photocathode, which is used to convert thephotons of light energy into electrons. As the electrons pass through the tube, similar electrons are released fromatoms in the tube, multiplying the original number of electrons by a factor ofthousands through the use of a microchannel plate (MCP) in the tube.

AnMCP is a tiny glass disc that has millions of microscopic holes.(microchannels) in it, made using fiber-optic technology. The MCP iscontained in a vacuum and has metal electrodes on either side of the disc.Each channel is about 45 times longer than it is wide, and it works as anelectron multiplier.When the electrons from the photo cathode hit the first electrode of the MCP,they are accelerated into the glass microchannels by the 5,000-V bursts beingsent between the electrode pair. As electrons pass through the microchannels,they cause thousands of other electrons to be released in each channel using aprocess called cascaded secondary emission. Basically, the original electronscollide with the side of the channel, exciting atoms and causing other electronsto be released. These new electrons also collide with other atoms, creating achain reaction that results in thousands of electrons leaving the channel whereonly a few entered. An interesting fact is that the microchannels in the MCPare created at a slight angle (about a 5-degree to 8-degree bias) to encourageelectron collisions and reduce both ion and direct-light feedback from thephosphors on the output side. At the end of the image-intensifier tube, the electrons hit ascreen coated with phosphors.These electrons maintain theirposition in relation to the channelthey passed through, whichprovides a perfect image since theelectrons stay in the samealignment as the original photons.The energy of the electronscauses the phosphors to reach anPhoto courtesy of B.E. Meyers CompanyNight-vision images are knownfor their eerie green tint.excited state and release photons.These phosphors create the green image on the screen that has come tocharacterize night vision. The green phosphor image is viewed through another lens, called the ocularlens, which allows you to magnify and focus the image.

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The NVD may beconnected to an electronic display, such as a monitor, or the image may beviewed directly through the ocular lens.GenerationsGeneration 0 - The earliest (1950's) night vision products were based on imageconversion, rather than intensification. They required a source of invisible infrared (IR)light mounted on or near the device to illuminate the target area.Generation 1 - The 'starlight scopes' of the 1960's (Vietnam Era) have three imageintensifier tubes connected in a series.

These systems are larger and heavier than Gen 2and Gen 3. The Gen 1 image is clear at the center but may be distorted around the edges.(Low-cost Gen 1 imports are often mislabeled as a higher generation.Figure 1 illustrates first-generation night vision. Not a great topic sentence but it doeshas the advantage of calling attention to the figure. Incoming light is collimated by fiberoptic plates before impacting a photocathode t which releases electrons, which in turnimpact a phosphor screen. The excited screen emits green light into a second fiber opticplate, and the process is repeated.

The complete process is repeated three times providingan overall gain of 10,000.Generation 2 - The micro channel plate (MCP) electron multiplier prompted Gen 2development in the 1970s. The 'gain' provided by the MCP eliminated the need forback-to-back tubes - thereby improving size and image quality.

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The MCP enableddevelopment of hand held and helmet mounted goggles.Second-generation image intensification significantly increased gain and resolution byemploying a microchannel plate. Figure 2 depicts the basic configuration. These twosentences could have been combined: 'Figure2 depicts how second-generation image.plate.' The microchannel plate is composed of several million microscopic hollow glasschannels fused into a disk. Each channel, approximately 0.0125 mm in diameter, iscoated with a special semiconductor which easily liberates electrons.

A single electronentering a channel initiates an avalanche process of secondary emission, under influenceof an applied voltage, freeing hundreds of electrons. These electrons, effectivelycollimated by the channel, increase the resolution of the device. With additional electronoptics, details as fine as 0.025 mm can be realized (half the diameter of a human hair).Current image intensifiers incorporate their predecessor's resolution with additional lightamplification. The multialkali photocathode is replaced with a gallium arsenidephotocathode; this extends the wavelength sensitivity of the detector into the nearinfrared. The moon and stars provide light in these wavelengths, which boosts theeffectively available light by approximately 30%, bringing the total gain of the system toaround 30,000.No topic sentence.

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Indeed one might have moved this material to the front in a moredramatic way, perhaps by calling attention to the movie `Silence of the Lambs.' slightgreen tint similar to some sunglasses.

The apparent lighting of the landscape on a darknight is comparable to what the unaided eye would see on a clear winter night with freshsnow on the ground and a full moon.Generation 3 - Two major advancements characterized development of Gen 3 in thelate 1970s and early 1980s: the gallium arsenide (GaAs) photocathode and the ion-barrierfilm on the MCP. The GaAs photocathode enabled detection of objects at greaterdistances under much darker conditions. The ion-barrier film increased the operationallife of the tube from 2000 hours (Gen 2) to 10,000 (Gen 3), as demonstrated by actualtesting and not extrapolation.Generation 4 - for a good explanation of this commonly misunderstood advancementin night vision technology.When discussing night vision technology, you also may hear the term 'Omnibus' or'OMNI'. Army procures night vision devices through multi-year/multi-productcontracts referred to as 'Omnibus' - abbreviated as 'OMNI'. For each successive OMNIcontract, ITT has provided Gen 3 devices with increasingly higher performance. ( Seerange detection chart directly below) Therefore, Gen 3 devices may be further defined asOMNI 3, 4, 5, etc. Current Omnibus contract as of 2006 is OMNI 7.If you're using night vision to find a lost person in the woods, to locate boats or buoys onthe water, or to stargaze into the wilderness, you need Generation 3 because it creates thebest images when there is very little ambient light.

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