Night vision device



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.

Night vision devices were first used in World War II, and came into wide use during the Vietnam War. The technology has evolved greatly since their introduction, leading to several "generations" of night vision equipment with performance increasing and price decreasing. Another term is "night optical device" or NOD.

Generations
The classification below was initially introduced by the US manufacturers through the US government. European manufacturers do not abide by it.

Generation 0
The first practical commercial night vision device offered on the market was developed by Dr. Vladimir K. Zworykin working for the Radio Corporation of America and was intended for civilian use. At that time infra-red was commonly called black light, a term later restricted to Ultraviolet. It was not a success due to its size and cost.

The first military night vision devices were introduced by the German army as early as 1939. The first devices were being developed by AEG starting in 1935. In mid-1943, first tests with infrared night-vision (Nacht Jager) devices and telescopic rangefinders mounted on Panther started. Two different arrangements / solutions were created and used on Panther tanks. Solution A - Sperber FG 1250 (Sparrow Hawk), with range up to 600m, was made up of one 30 cm infrared searchlight and image converter operated by the commander. From late 1944 to March 1945, some Panzerkampfwagen V Panther Ausf G (and other variants) mounted with FG 1250, were successfully tested. By the end of World War II, the German army had equipped approximately 50 (or 63) Panther tanks, which saw combat on both the Eastern and Western Fronts. The "Vampir" man-portable system for infantrymen was being used with Sturmgewehr 44 assault rifles. Parallel development of night vision systems occurred in the USA. 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. 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 and an electrostatic inversion with electron acceleration were used to achieve gain.

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 1,000×, but are quite bulky and require moonlight to function properly.

Examples:
 * AN/PVS-2 Starlight scope
 * PNV-57E Tanker goggles

Generation 2 (GEN II)
Second generation devices feature an improved image-intensifier tube utilizing micro-channel plate (MCP) with an S-25 photocathode, resulting in a much brighter image, especially around the edges of the lens. This leads to increased illumination in low ambient light environments, such as moonless nights. Light amplification is around 20,000×. Also improved were image resolution and reliability.

Examples:
 * AN/PVS-4
 * AN/PVS-5
 * SUPERGEN

Later advancements in GEN II technology brought the tactical characteristics of "GEN II+" devices (equipped with better optics, SUPERGEN tubes, improved resolution and better signal-to-noise ratios) into the range of GEN III devices, which has complicated comparisons.

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. However, the ion barrier causes fewer electrons to pass through, diminishing the improvement expected from the Gallium arsenide photocathode. Because of the ion barrier, the "halo" effect around bright spots or light sources is larger too. The light amplification is also improved to around 30,000–50,000×. Power consumption is higher than GEN II tubes.

Examples:
 * AN/PVS-7
 * AN/NVS-7
 * AN/PVS-10
 * AN/PVS-14
 * AN/PNVS-14
 * CNVS-4949
 * PN-21K

Omnibus-VI - VII (GEN III+)
U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) 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-VI - 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-V - VII devices can differ from standard Generation 3 in one or both of two important ways. First, an automatic gated power supply system regulates the photocathode voltage, allowing the NVD to instantaneously adapt to changing light conditions. The second is a removed or greatly thinned ion barrier, which decreases the number 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 2,850 K of only 700, compared to operating with a luminous sensitivity of at least 1,800 for GEN III image intensifiers. 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 number 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 now be added to any previous generation of night vision, "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 (i.e., Gen II +, Gen III +) do not change the generation type of the device, but instead indicates an advancement(s) over the original specification's requirements.

Examples:
 * AN/PVS-22
 * NVS-22

AUTO-GATING
ATG function was designed to improve the BSP feature to be faster and to keep the best resolution and contrast at all times. It is particularly suitable for Aviator’s Night Vision goggles, operations in urban areas or for special operations. ATG is a unique feature that operates constantly, electronically reducing the “duty cycle” of the photocathode voltage by very rapidly switching the voltage on and off. This maintains the optimum performance of the I² tube, continuously revealing mission critical details, safeguarding the I² tube from additional damage and protecting the user from temporary blindness.

The benefits of ATG can easily be seen not only during day-night-day transitions, but also under dynamic lighting conditions when rapidly changing from low light to high light conditions (above 1 lx), such as sudden illumination of dark room. PHOTONIS ATG allows the tube to maintain as much as 90% of the nominal MTF and resolution of the high light level, whereas standard tubes without Auto-Gating would drop to 10-20 lp/mm, which is less than 25% of the nominal MTF and resolution of the high light level. A typical advantage of ATG is best felt when using a weapon sight which experiences a flame burst during shooting (see figures below showing pictures taken at the impact zone of a dropped bomb). ATG would reduce the temporary blindness that a standard BSP tube would introduce, allowing them to continuously maintain “eyes on target”.

ATG provides added safety for pilots when flying at low altitudes, and especially during takeoffs and landings. Pilots operating with night vision goggles are constantly subjected to dynamic light conditions when artificial light sources, such as from cities, interfere with their navigation by producing large halos that obstruct their field of view.

Comparison between leading American and European technology
In the late 1990s, innovations in photocathode technology through proprietary doped techniques developed solely by PHOTONIS, enabled a big advancement. These innovations significantly reduced the tube’s noise and increased the signal-to-noise ratio, which is the undisputed characteristic to describe the low light level performance of an image intensifier - and to allow comparison of tubes of various origins and technologies. These newly developed tubes started surpassing the performance of Gen 3 tubes.

By 2001, the United States federal government concluded that an I2 tube’s “Generation” was not a determinant factor of a tube’s global performance, making the term “Generation” completely irrelevant in determining the performance of an Image Intensifier Tube, and therefore eliminated the term as a basis of export regulations.

Figure of merit
Though image intensification technology employed by different manufacturers varies, from the tactical point of view night vision system is an optical device that enables vision at low light. The US government itself has recognized the fact that technology itself makes little difference as long as an operator can see clearly at night. Consequently the United States bases export regulations not on the generations, but on a calculated factor called figure of merit (FOM). The method of FOM calculation and its implications for export are briefly described in a National Defense University document called “The NATO Response Force” authored by Jeffrey P. Bialos, the Executive Director of the Transatlantic Security and Industry Program at the Johns Hopkins University and Stuart L. Koehl, a Fellow at the Center for Transatlantic Relations of the same university.

"… beginning in 2001, the U.S. implemented a new figure of merit (FOM) system for determining the release of night vision technology. FOM is an abstract measure of image tube performance, derived from the number of line pairs per millimeter multiplied by the tube's signal-to-noise ratio."

US-made tubes with a FOM greater than 1,400 are not exportable outside the US, however the Defense Technology Security Administration (DTSA) can waive that policy on a case-by-case basis.

Other technologies


The United States Air Force experimented with panoramic night vision goggles (PNVGs) which double the user's field of view to around 95 degrees by using four 16 mm image intensifier tubes, rather than the more standard two 18 mm tubes. They are in service with A-10 Thunderbolt II, MC-130 Combat Talon and AC-130U Spooky aircrew. The U.S. Naval Special Warfare Development Group was equipped with Panoramic Night Vision Goggles attached to their helmets during Operation Neptune Spear, the operation that killed Osama Bin Laden.

The AN/PSQ-20, manufactured by ITT (also known as the Enhanced Night Vision Goggle, ENVG), seeks to combine thermal imaging with image intensification, as does the Northrop Grumman Fused Multispectral Weapon Sight.

A new technology is being introduced to the consumer market currently. It was first shown at the 2012 Shot Show in Las Vegas, NV by Armasight. This new technology called Ceramic Optical Ruggedized Engine (CORE) produces much higher performance Gen 1 tubes. The main difference between CORE tubes and standard Gen 1 tubes is introduction of a ceramic plate instead of a glass one. This plate is produced of specially formulated ceramic and metal alloys. Thanks to the new technology edge distortion is minimized, photo sensitivity is greatly increased and the resolution can get as high as 60 lp/mm. Even so, CORE is still considered Gen 1 as it does not utilize a micro channel plate.

Legality
Certain countries (e.g. Hungary and other European Union members) regulate possession and or use of night-vision devices. German law forbids such devices if their purpose is to be mounted on firearms.

In the Netherlands, although being a full member of the European Union, the possession of night vision devices is not regulated, nor is it forbidden to use them mounted on (fire)arms. The usage of night vision equipment for night time hunting (weapon mounted) is only allowed with a special permit in certain areas (the Veluwe) for hunting wild Boar.

In Iceland, the use of night-vision devices for hunting is prohibited, while there are no restrictions on the devices themselves.

New Zealand rescue helicopter services use several sets of 3rd-generation night vision goggles imported from the USA, and the country is required to restrict access to the equipment to comply with the strict regulations regarding their export. There are no prohibitions on the ownership or use of night vision equipment for shooting non-indigenous game animals, such as rabbits, hares, deer, pigs, tahr, chamois, goats, wallabies, etc.

Most U.S. states have no such bans. In California, it is a misdemeanor to possess a device "designed for or adaptable to use on a firearm which, through the use of a projected infrared light source and electronic telescope, enables the operator thereof to visually determine and locate the presence of objects during the nighttime". This essentially covers scopes using Gen0 technology, but not the subsequent generations. There was an effort in 1995 to further expand restrictions to forbid night vision devices that did not incorporate a light source, but it did not become law.