1. IntroductionThe word „Night vision‟ itself means the ability to see in low light conditions. Humans have poornight vision compared to many other animals.So we all might have a question in our mind that isthis really possible to see in the dark night? The answer is most definitely yes. With the propernight-vision equipment, you can see a person standing over 200 yards (183 m) away on amoonless, cloudy night!. Originallydeveloped for military use, it has provided the United Stateswith a strategic militaryadvantage, the value of which can be measured in lives. Federal and stateagencies nowroutinely utilize the technology for site security, surveillance as well as searchandrescue. Night vision equipment has evolved from bulky optical instruments inlightweightgoggles through the advancement of image intensification technology.The night has always had a mysterious and eerie aura to it, due to the darkness that itaccompanies. Through time, the dark has always been something that a lot of people fear. Asthey say, you never know what lurks in the dark. However, as technology developed, the nighthas become less of a scary monster and even became a sought after period of the day, all thanksto the invention of the night vision. If youre wondering how this innovation started in the firstplace, read on and learn the history of night vision.It has always been a point that man had todominate his enemies but at the same time making little damage as he can.In the beginning, men fought at daytime since night raids were considered to be very dangerous.They were and virtually impossible back then. With some time, men realized that surprising theirenemies with attacks were much effective and could be very devastating on their enemies side.This was the situation when torches became a hit, especially in the middle Ages. If a torch canlast longer, the better. However, brilliant may torches seem, it gave one big problem- it revealedthe position of the attacker.This problem was answered during the 1940s on the midst of WorldWar II, by the innovation of night vision. At first, it was only sniper riffles that had thistechnology, so that they would have the ability to foresee enemies even from a distance. The useof this gave a dramatic effect on the whole wars course. Ever since the Germans have found itsusefulness, they have begun developing innovative technology so that they can successfullydominate even the night.it was during the 1960s Vietnam Era, when military troops begandeveloping night vision technology. It was this time when the night vision goggles first came out
and promoted. There was a remarkable advantage seen on those military divisions that has nightvision goggles compared to those that did not have them. This became the reason why thegovernment along with the military pushed on with further research about the said technology. Interms of war, the technology was also used in the war against Iraq. It has proved to be anextremely excellent tool, especially for defensive purposes and guarding against the militia. Theadvantage is also present for thermal vision. Nonetheless, they can get the best of both worlds bycombining both thermal and night vision. Doing this gives overwhelming power over the night.Nowadays, night vision technology is widely available even to the public. Most likely,equipments with this feature are used by hunters since it is undeniably a reliable way for them todetect animals even during night time.Two technologies are used for night vision:-(1)Thermal ImagingThis work by collection the tiny amounts of light including the lower portion of infrared lightspectrum that are present but may be imperceptible to your eyes, and amplifying it to the pointthat we can easily observe the image.(2)Image EnhancementThis technology operates by capturing the upper portion of the infrared light spectrum, which isemitted as heat by the objects instead of simply reflected as light. Hotter object, such as warmbodies, emit more of this light than cooler objects likes trees or buildings.
2. Types of Night VisionThere are two type night vision such as2.1. Biological Night VisionIn biological night vision, molecules of rhodopsin in the rods of the eye undergo a change inshape as light is absorbed by them. The peak rhodopsin build-up time for optimal night vision inhumans is 30 minutes, but most of the adaptation occurs within the first five or ten minutes in thedark. Rhodopsin in the human rods is insensitive to the longer red wavelengths of light, so manypeople use red light to preserve night vision as it will not deplete the eyes rhodopsin stores in therods and instead is viewed by the cones..Some animals, such as cats, dogs, and deer, have a structure called tapetumlucidum in the backof the eye that reflects light back towards the retina, increasing the amount of light it captures. Inhumans, only 10% of the light that enters the eye falls on photosensitive parts of the retina. Theirability to see in low light levels may be similar to what humans see when using first or perhapssecond generation image intensifiers2.2. Technical Night VisionA night vision device (NVD) is an optical instrument that allows images to be produced in levelsof light approaching total darkness. They are most often used by military and law enforceagencies but are available to civilian users. In this technology various types of instruments areused.Details descriptions of this technology is described in next page.
3. Working of Technical Night VisionNight vision can works in two very different ways depending on the technology used. Beforediscussing about the types of night vision technology first known basic things of light.3.1. Light BasicsIn order to understand thermal imaging, it is important to understand something about light. Theamount of energy in a light wave is related to its wavelength: Shorter wavelengths have higherenergy. Of visible light, violet has the most energy, and red has the least. Just next to the visiblelight spectrum is the infrared spectrum. Fig1:-Spectrum of lightInfrared light can be split into three categories:-3.1.1. Near-infrared (near-IR)Closest to visible light, near-IR has wavelengths that range from 0.7 to 1.3 microns, or 700billionths to 1,300 billionths of a meter.3.1.2. Mid-infrared (mid-IR)Mid-IR has wavelengths ranging from 1.3 to 3 microns. Both near-IR and mid-IR are used by avariety of electronic devices, including remote controls.
3.1.3. Thermal-infrared (thermal-IR)Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3microns to over 30 microns.The key difference between thermal-IR and the other two is thatthermal-IR is emitted by an object instead of reflected off it. Infrared light is emitted by an objectbecause of what is happening at the atomic level.Night vision can work in two very different ways, depending on the technology used.3.2. Thermal ImagingA special lens focuses the infrared light emitted by all of the objects in view. The focused light isscanned by a phased array of infrared-detector elements. The detector elements create a verydetailed temperature pattern called a thermogram.. Fig2:-The basic of thermal imaging systemIt only takes about one-thirtieth of a second for the detector array to obtain the temperatureinformation to make the thermogram. This information is obtained from several thousand pointsin the field of view of the detector array. The thermogram created by the detector elements istranslated into electric impulses. The impulses are sent to a signal-processing unit, a circuit boardwith a dedicated chip that translates the information from the elements into data for the display.
The signal-processing unit sends the information to the display, where it appears as variouscolors depending on the intensity of the infrared emission. The combination of all the impulsesfrom all of the elements creates the image.It is quite easy to see at day time But at night you can see very little Thermal imaging lets you see again Fig3:-Different viewThere are two type of thermal imaging detector3.2.1. Uncooled DetectorThis the most common type of thermal imaging detector. The infrared elements are contained ina unit that operates a room temperature. This type of system is completely quit and activateimmediately and the battery built right in.3.2.2. Cooled Infrared DetectorMore expensive and susceptible to damage from rugged used, these system has cooled inside acontainer that cool them below zero c. These the of system can see more than 1000 ft(300m).
3.3. Image IntensifierThis method of night vision amplifies the available light to achieve better vision.Digram is givenbelow. A conventional lens capture the ambient light. This lens focuses available light (photons)on the photocathode of an image intensifier tube. Fig4:-Image intensifier processThe light energy causes electrons to be released from the cathode which are accelerated by anelectric field to increase their speed (energy level). These electrons enter holes in a microchannel plate and bounce off the internal specially-coated walls which generate more electronsas the electrons bounce through. This creates a denser “cloud” of electrons representing anintensified version of the original image.Achannel using a process called cascaded secondaryemissions electrons pass through the micro- channels, they cause thousands of other electronsto be released in each. Basically, the original electrons collide with the side of the channel,exciting atoms and causing other electrons to be released. These new electrons also collide withother atoms, creating a chain reaction that results in thousands of electrons. The final stage of theimage intensifier involves electrons hitting a phosphor screen. The energy of the electrons makesthe phosphor glow. The visual light shows the desired view to the user or to an attachedphotographic camera or video device. A green phosphor is used in these applications.
4. Night Vision DeviceNight-vision equipment can be split into three broad categories4.1. ScopesNormally handheld or mounted on a weapon, scopes are monocular (one eye-piece). Sincescopes are handheld, not worn like goggles, they are good for when you want to get a better lookat a specific object and then return to normal viewing conditions. Fig5:- scope (monocular)Depending on the model you can obtain higher power lens sets to economically increase theobservation range of your scope while others can be upgraded with camera adapters to permitcapture of night vision photographs and video. Some scopes can be converted to hands-freemono-goggles or adapted to weapon mounts to serve as night vision rifle scopes, while others arebest suited to marine applications thanks to their waterproof construction.
4.2. GogglesWhile goggles can be handheld, they are most often worn on the head. Goggles are binocular(two eye-pieces) and may have a single lens or stereo lens, depending on the model. Gogglesare excellent for constant viewing, such as moving around in a dark building. Fig6:-goggles worn on the headMany can be converted to long-range scopes and binoculars and some are even weaponmountable. While all include integrated short-range infrared illuminators that permit map readingand room-to-room searches in complete darkness, long-range illumination requires the additionof one of our infrared sports lights.4.3. CamerasCameras with night-vision technology can send the image to a monitor for display or to a VCRfor recording. When night-vision capability is desired in a permanent location, such as on abuilding or as part of the equipment in a helicopter, cameras are used. Many of the newercamcorders have night vision built right in.
5. GenerationsThese are the generations of night vision technology5.1. Generations 0The earliest (1950) night vision products were based on image conversion, rather thanintensification. They required a source of invisible infrared light mounted on or near the deviceto illuminate the target area.5.2. Generations 1In generation 1 three image intensifier tubes connected in series. These system are larger andhavier than gen2 and gen3. The gen1 clear at the center but may be distorted around the edges.Figure illustrate that first generation night vision. Incoming light is collimated by fiber opticsplates before impacting the a photocathode which release electron, which is turn impact aphosphor screen. The excited screen emits green light in to a second fiber plate, and the processis repeated. The complete process is repeated three times providing an overall gain of 10,000. Fig7:-Generations1
5.3. Generations 2The 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 improvingsize and image quality. The MCP enableddevelopment of hand held and helmet mountedgoggles.Second-generation image intensification significantly increased gain and resolutionbyemploying a microchannel plate.Figure depicts the basic configuration. These two sentences could have been combined:"Figure2 depicts how second-generation image ... plate." The microchannel plate is composed ofseveral million microscopic hollow glass channels fused into a disk. Each channel,approximately 0.0125 mm in diameter, is coated with a special semiconductor which easilyliberates electrons. A single electron entering a channel initiates an avalanche process ofsecondary emission, under influence of an applied voltage, freeing hundreds of electrons. Theseelectrons, effectively collimated by the channel, increase the resolution of the device.Withadditional electron optics, details as fine as 0.025 mm can be realized.Current image intensifiersincorporate their predecessors resolution with additional light amplification. The multialkaliphotocathode is replaced with a gallium arsenide photocathode; this extends the wavelengthsensitivity of the detector into the nearinfrared. The moon and stars provide light in thesewavelengths, which boosts theeffectively available light by approximately 30%, bringing thetotal gain of the systemto around 30,000. Fig8:-Generations2
5.4. Generation 3Two major advancements characterized development of Gen 3 in thelate 1970s and early 1980s:the gallium arsenide photocathode and the ionbarrier film on the MCP. The GaAs photocathodeenabled detection of objects at greater distances under much darker conditions. The ion-barrierfilm increased the operational life of the tube from 2000 hours (Gen 2) to 10,000 (Gen 3),asdemonstrated by actual testing and not extrapolation.5.5.Generation 4Generation 4 is used to describe the most advanced night vision technology. Referred to asFilmless & Gated image intensifiers by the US Military, Generation 4 image tubes provide anotable improvement over Gen 3 night vision. They not only offer increased detection range inpitch-black conditions, but with a dramatically reduced halo they also responsed better to brightsources. Whether you are looking for a night vision scope, a hands-free Generation 4 night visongoggles system, or a night vision weapons sight, we can offer a good selection to choose from.We also have Generation 4 night vision binoculars. Percentage of improving from generation to generation
6. ApplicationsThese are the common applications of night vision technology1. Military2. Hunting3. Security4. Navigation5. Wildlife observations6. Hidden object detectionThe original purpose of night vision was to locate enemy target at night. It is extensively by themilitary for that purpose, as well as for navigation and targeting. Police and security often useboth thermal imaging and image enhancement technology, particularly for surveillance. Hunterare use this to detect the animals and any other birds. Detectives and private investigator usenight vision to watch assigned to track.Many business have permanently-mounted cameras equipped with night vision to monitorsurroundings. A real amazing ability of thermal imaging, is that it reveals whether an has beendistributed , it can show that the ground has been dug up to bury something, even if there is noobvious sing to the naked eye. Law enforcement has used this to discover items that has beenhidden by the criminal, including money, drugs and bodies. Also recent changes to area such aswalls can be seen using thermal imaging, which have provided important clues in several cases.Many people are beginning to discover the unique world that can be found after darkness falls.
7. ConclusionsThrough night vision device we can see the object in dark environment.We have seen fourgeneration of this devices and seen different ranges.Initially this device was used by military butnow it also available for civilians.Today in the 21st century we have come a long way in thedevelopment of night vision technology, from the early 1940‟s. Night vision devices arebasically designed for utmost defensive purposesbut the application within the scientific or thecivilian range is often prohibited by law.In present scenario the applications of night visiontechnology is very essential to combat terrorism which is a major problem being faced bymankind.Finally we have seen that use of night vision devices. we find that night vision device is used inthe presence of ambient light or in case of cloudy whether. There are many types of night visiondevices available in the market but in all these devices one things is common: they producedgreen light. so in overcast and cloudy whether the performance of night vision devices decreasedmeans the detection range is decreased compared to ambient light such as moonlight or starlight.