Night vision device

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Image:24-Hour Operations, Baghdad, 18 October 2007.jpg
A U.S. Army soldier uses a helmet mounted vision device during operations in Baghdad, Iraq.

A night vision device (NVD) is an optical instrument that allows images to be produced in levels of light approaching total darkness. They are most often used by the military and law enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system. Many NVDs also include sacrificial lenses, IR illuminators, and telescopic lenses.

NVDs are mounted appropriately for their specific purpose, with more general-purpose devices having more mounting options. For instance, the AN/PVS-14 is a monocular night vision device in use with the US military as well as by civilians. It may be mounted on the user's head for handsfree use with a harness or helmet attachment, either as a monocular device, or in aligned pairs for binocular "night vision goggles" which provide a degree of depth perception as do optical binoculars. The AN/PVS-14 may also be attached to a rifle using a Picatinny rail, in front of an existing telescopic or red dot sight, or attached to a single-lens reflex camera.[1] Other systems, such as the AN/PVS-22 or Universal Night Sight, are designed for a specific purpose, integrating an image intensifier into, for example, a telescopic sight, resulting in a smaller and lighter but less versatile system.[2]

Night vision devices were first used in World War II, and came into wide use during the Vietnam War.[3][4] The technology has evolved greatly since their introduction, leading to several "generations" of night vision equipment with performance increasing and price decreasing.

Contents

[edit] Function

Image:Photomultiplier.JPG
How night vision works.

Night vision devices (NVD) work in the near-infrared band at a wavelength of about 1 micrometer. For comparison, human visual range is about 0.4 to 0.7 micrometers. Unlike thermal imaging systems, which may operate on complete darkness using heat radiation signatures, well beyond the visible light spectrum, NVD's rely on ambient light, often from the moon and stars. The intensifier tubes use the photoelectric effect. As a photon collides with a detector plate, the metal ejects several electrons that are then amplified into a cascade of electrons that light up a phosphor screen. Often a dim star in the sky is enough to illuminate an entire field.

The night vision image does not have color information, and hence monochromatic displays are sufficient. A green phosphor (P22) display is generally used as the human eye is most sensitive to the color green in this wave length, which falls in the middle of the visible light spectrum.[5]

[edit] Passive and Active

There are two methods of operating night vision systems, being either in a 'passive' mode or an 'active' mode. Passive systems amplify the existing environmental ambient lighting, while active systems rely on an infrared light source to provide sufficient illumination. Early NVDs were designed to be used as active systems, as they did not have the sensitivity to operate on ambient light. Active systems are often used today on many consumer devices such as home video cameras.

Military applications generally require passive operation, as an active system's infrared illumination device is easily spotted and tracked by others equipped with night vision devices, placing the user at a tactical disadvantage.[6] However, most modern NVG devices include an inbuilt active IR illuminator which can be toggled for use when ambient light is not available.

[edit] Night Vision Technology

Image:Night vision NTC picture.jpg
A U.S. Army soldier uses a weapon mounted night vision device during a training exercise.

Night vision technology, which refers to the quality of the image intensifier tube housed by the NVD, is often classified into "Generations" following the pattern originated by the US Military. Referring to night vision in terms of its Generation is purely for indicative and reference purposes only, even though this has spread to become common consumer terminology. The United States Army class their current in-service devices with the Generation Family Type followed by the device's version or awarded contract.[7] The latest night vision device in service with the United States Army, as of October 2007, is the Gen III Omni VII, manufactured by ITT Corporation. [8] However, due to the fact that it is an autogated tube, the consumer market generally refers to this as being a 'Gen IV' device.

Within the European Union, Australia, and New Zealand, night vision devices are not referred to in terms of 'Generations', as the most recent image intensifiers in service is the XR5 autogated filmless tube from Photonis-DEP, and hence this product would be considered a ‘Gen IV’ type device by the consumer market.

[edit] Generation 0

The first night vision devices, the M1 and M3 infrared night sighting devices, also known as the "sniperscope" or "snooperscope", were introduced by the US Army in World War II, and also used in the Korean War, to assist snipers.[9] They were active devices, using a large infrared light source to illuminate targets. Their image intensifier tubes function using an anode and an S-1 photocathode, made primarily of silver, caesium, and oxygen to accelerate the electrons.[10] Parallel development of night vision systems by AEG occurred in Nazi Germany, and by the end of World War II, it had equipped approximately 50 Panzerkampfwagen V Panther tanks, which saw combat on both the Eastern and Western Fronts, and produced the "Vampir" man-portable system for infantry soldiers equipped with Sturmgewehr 44 assault rifles.[11]

[edit] Generation 1 (GEN I)

First generation passive devices, introduced during the Vietnam War were an adaptation of earlier "active" Gen 0 technology, and rely on ambient light instead of an infrared light source. Using an S-20 photocathode, their image intensifiers produce a light amplification of around 1000x[12], but are quite bulky and require moonlight to function properly.

Examples:

  • AN/PVS-2

[edit] Generation 2 (GEN II)

Second generation devices featured an improved image-intensifier tube utilizing microchannel plate (MCP)[13] with an S-25 photocathode[14], resulting in a much brighter image, especially around edges of the lens. This leads to increased illumination in low ambient light environments, such as moonless nights. Light amplification was around 20000x[15] Also improved were image resolution and reliability.

Examples:

[edit] Generation 3 (GEN III)

Third generation night vision systems maintain the MCP from Gen II, but now use a photocathode made with gallium arsenide, which further improves image resolution. In addition, the MCP is coated with an ion barrier film for increased tube life. The light amplification is also improved, to around 30000-50000x [19]

Examples:

[edit] Omnibus-VII

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) (http://www.nvl.army.mil/) is part of the governing body that dictates the name of the generation of night vision technologies. Although the recent increased performance associated with the GEN-III OMNI-VII components is impressive, the U.S. Army has not yet authorized the use of the name GEN-IV for these components.

GEN-III OMNI-VII devices can differ from Standard Generation 3 in two important ways. First, an automatic gated power supply system regulates the photocathode voltage, allowing the NVD to instantaneously adapt to changing light conditions.[23] The second, is a removed or greatly thinned ion barrier, which decreases the amount of electrons that are usually rejected by the Standard GEN III MCP, hence resulting in less image noise and the ability to operate with a luminous sensitivity at 2850K of only 700, compared to operating with a luminous sensitivity of at least 1800 for GEN III type image intensifiers.[24] The disadvantage to a thin or removed ion barrier is the overall decrease in tube life from a theoretical 20,000 hrs mean time to failure (MTTF) for Gen III type, to 15,000 hrs MTTF for GEN IV type. However, this is largely negated by the low numbers of image intensifier tubes that reach 15,000 hrs of operation before replacement.

It is important to note that while the consumer market classifies this type of system as "Generation 4", the United States military describes these systems as Generation 3 Autogated tubes (GEN-III OMNI-VII). Moreover, as autogating power supplies can be now be added to any previous generation of nightvision, 'autogating' capability does not automatically class the devices as a GEN-III OMNI-VII, as seen with the XD-4. Another point to note is that any postnominals appearing after a Generation type (ie: Gen II +, Gen III +) does not change the generation type of the device, but instead indicates a supposed advancement(s) over the original spec's requirements. [25]

Examples:

[edit] Other Technologies

Image:Night vision goggles experimental.jpg
Panoramic Night Vision Goggles in testing

The US Air Force is experimenting with Panoramic Night Vision Goggles (PNVGs) which double the user's field of view to around 95 degrees by using four 16mm image intensifiers tubes, rather than the more standard two 18mm tubes. They are in limited service with MC-130 Combat Talon and AC-130U Spooky aircrews.[28]

IN 2007 Xenonics Holdings, using newly patented technology, offered the first digital night seeing system, a hand held monocule device with 2-8X zoom capability branded Supervision. [29][30]

The PSQ-20, manufactured by ITT seeks to combine Thermal Imaging with image intensification, as does the Northrop Grumman Fused Multispectral Weapon Sight.[31][32]

[edit] Legality

Certain countries (e.g. Hungary and other European Union members) regulate possession of night-vision devices[citation needed]. Civilians are allowed to have Generation 1 and Gen1+ devices[citation needed], but citizen's access to Gen2 and up is outlawed by adopting international trafficking in arms regulations into national legislation[citation needed]. Generation 2 and higher devices are classified as military / law enforcement purpose and espionage tools. Use of any generation thermal or night vision equipment in hunting is also against regulations, due to their "un-hunterly" (unfair) nature to the game.[dubious – discuss]

Visiting foreign hunters should be aware of these restrictions, as night vision equipment found against the regulations may be confiscated.[citation needed][dubious – discuss]

[edit] US Patents

[edit] World Manufacturers of Night Vision Devices

[edit] See also

[edit] References

  1. ^ http://www.infrared1.com/PVS_14.html
  2. ^ http://www.nightvis.com/nv_sights/ANPVS22_Universal_Night_Sight.html
  3. ^ http://electronics.howstuffworks.com/nightvision2.htm
  4. ^ http://www.nvl.army.mil/about/index.php
  5. ^ http://www.hownightvisionworks.com/
  6. ^ http://www.nivitech.com/nightvision-eil.htm
  7. ^ http://www.morovision.com/hownightvisionworks.htm
  8. ^ http://www.morovision.com/hownightvisionworks.htm
  9. ^ http://electronics.howstuffworks.com/nightvision2.htm
  10. ^ http://www.globalsecurity.org/space/systems/images/night_vision.gif
  11. ^ http://www.achtungpanzer.com/articles/ir.htm
  12. ^ http://www.globalsecurity.org/military/systems/ground/nvg.htm
  13. ^ http://www.atncorp.com/ATNFAQ
  14. ^ http://www.globalsecurity.org/space/systems/images/night_vision.gif
  15. ^ http://www.globalsecurity.org/military/systems/ground/nvg.htm
  16. ^ http://www.globalsecurity.org/military/systems/ground/an-pvs-4.htm
  17. ^ http://www.globalsecurity.org/military/systems/ground/an-pvs-5.htm
  18. ^ http://www.photonis-nightvision.com/night-vision/supergen
  19. ^ http://www.globalsecurity.org/military/systems/ground/nvg.htm
  20. ^ http://www.globalsecurity.org/military/systems/ground/an-pvs-14.htm
  21. ^ http://www.photonis-nightvision.com/night-vision/xd-4
  22. ^ http://www.photonis-nightvision.com/night-vision/xd-4
  23. ^ http://www.nvisionoptics.com/files/docs/articles/articleletmay2007.pdf
  24. ^ http://www.nivitech.com/nightvision-gns.htm
  25. ^ http://www.atncorp.com/HowNightVisionWorks#gen11
  26. ^ http://www.nightvis.com/nv_sights/ANPVS22_Universal_Night_Sight.html
  27. ^ http://www.photonis-nightvision.com/night-vision/xr5
  28. ^ http://www.military.com/soldiertech/0,14632,Soldiertech_PNVG,,00.html
  29. ^ http://xenonics.sc48.biz/press/articles/article.php?article_id=72
  30. ^ http://xenonics.sc48.biz/press/articles/article.php?article_id=67
  31. ^ http://www.defensetech.org/archives/003732.html
  32. ^ http://www.irconnect.com/noc/press/pages/news_releases.html?d=65353
  33. ^ http://www.aiptek.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=FT95&Category_Code=NV&Store_Code=AS
  34. ^ http://www.urscorp.com/EGG_Division/navsea/index.php
  35. ^ https://www.eggcrane.com/metadot/index.pl?iid=1921
  36. ^ http://www.sensorsinc.com/facilitysecurity.html
  37. ^ http://www.es.northropgrumman.com/nightvision/
  38. ^ http://www.irconnect.com/noc/press/pages/news_releases.html?d=65353

[edit] External links

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