NIGHT VISION GOGGLES (NVG)

During the history of warfare, operations at night have always been degraded significantly, if not totally avoided. Typically, soldiers fighting at night have had to resort to artificial illumination, e.g., at first fire and later with light sources such as searchlights. The use of light sources on the battlefield had the detrimental result of giving away tactical positions and information about maneuvers. The advent of new technologies initially in the 1950’s and continuing into the present time has changed this situation. The engineers and scientists at the US Army’s Communications-Electronics Command (CECOM) Night Vision & Electronic Sensors Directorate (NVESD) have discovered ways to capture available electro-magnetic radiation outside that portion of the spectrum visible to the human eye and have developed equipment to enable the American soldier to fight as well at night as during the day and to “Own the Night”.

Night vision devices (NVDs) provide night fighters with the ability to see, maneuver and shoot at night or during periods of reduced visibility. The Army used two different types of NVDs – image intensifiers and thermals. Image-Intensifying Devices are based upon light amplification and must have some light available. These devices can amplify the available light from 2,000 to 5,000 times. Thermal Forward-Looking Infrared (FLIR) detectors – sometimes called “sensors” – work by sensing the temperature difference between an object and its environment. FLIR systems are installed on certain combat vehicles and helicopters.

NVGs are electro-optical devices that intensify (or amplify) existing light instead of relying on a light source of their own. Image intensifiers capture ambient light and amplify it thousands of times by electronic means to display the battlefield to a soldier via a phosphor display such as night vision goggles. This ambient light comes from the stars, moon or sky glow from distant manmade sources, such as cities. The devices are sensitive to a broad spectrum of light, from visible to infrared (invisible). Users do not look through NVGs, you look at the the amplified electronic image on a phosphor screen.

Light enters the NVG through an objective lens and strikes a photo cathode powered by a high energy charge from the power supply. The energy charge accelerates across a vacuum inside the intensifier and strikes a phosphor screen (like a TV screen) where the image is focused. The eyepiece magnifies the image.

An NVG phosphor screen is purposefully colored green because the human eye can differentiate more shades of green than other phosphor colors. Like cameras, NVGs have various image magnifications. The distance at which a human-sized figure can be clearly recognized under normal conditions (moon and star light, with no haze or fog) depends on both the magnifying power of the objective lens and the strength of the image intensifier. The maximum viewing range is 100 feet to 400 feet.

A soldier can conduct his combat missions without any active illumination sources using only image intensifiers. The main advantages of image intensifiers as night vision devices are their small size, light weight, low power requirements and low cost. These attributes have enabled image intensifier goggles for head-worn, individual soldier applications and resulted in hundreds of thousands of night vision goggles to be procured by the US Army. Research and development continues today on image intensifiers in the areas of longer wavelength spectral response, higher sensitivity, larger fields of view and increased resolution.

The view through NVDs can be a lot like looking down a tunnel. Your normal field of view is almost 190 degrees – but that is cut down to 40 degrees with NVDs. That side -- or “peripheral” -- vision you’re accustomed to, and from which you often see dangers, is just not there. To adjust for that you must constantly turn your head to scan for the dangers on either side of you that you can’t see in your narrow field of view. (See the article in this issue titled, Proper Scanning Critical to NVG Operations).

At their best, NVGs cannot provide the same level of sharpness to what you see as what you’re accustomed to in the daytime. While normal vision is 20/20, NVGs can, at best, provide only 20/25 to 20/40, and even this is possible only during optimal illumination and when you have a high-contrast target or scene. As either illumination or contrast decreases, the NVG’s visual acuity drops, giving you an even more “fuzzy” image.

Normally you use both eyes (binocular vision) to pick up cues to help estimate the distance and depth of an abject. However, with NVDs you are essentially using one eye (monocular) vision, which can pose real problems. For example, when you are wearing NVDs and you view two objects of different sizes that are side-by-side, the larger object appears to be nearer. When you view overlapping objects through an NVD, the one that is in front “appears” to be nearer – maybe much more so than is true. In addition, some objects viewed through NVGs may appear to be farther away than they actually are. The reason for that is that we tend to associate the loss of detail sharpness with distance. On the other hand, a light source that is not part of a terrain feature – for example, a light atop a tower – may look closer than it actually is. It’s important to be aware of these potential problems and that NVG users tend to overestimate distance and underestimate depth (how tall an object is).

Your eye needs time to adjust from day to night vision. That’s why you can barely see when you first enter a dark movie theater during the daytime – your eyes need time to adjust to the darkness. So it is with NVGs. You are basically getting a dim-day view, so when you remove your NVGs, your eyes need time to adapt to the darkness. The amount of time you need depends on how long you have been wearing the NVGs. Most people achieve about a 75 percent dark-adaptation within 30 seconds of removing the goggles. This is especially important to keep in mind if you are using your NVGs as binoculars – basically lifting them to your eyes and then lowering them.

Military tacticians throughout history have seen the advantages of being able to maneuver effectively under cover of darkness. Historically, maneuvering large armies at night carried such risks that it was rarely attempted. During WW II, the United States, Britain, and Germany worked to develop rudimentary night vision technology. For example, a useful infrared sniper scope that used near-infrared cathodes coupled to visible phosphors to provide a near-infrared image converter was fielded. However this device had several disadvantages. The infrared sniper scope required an active IR searchlight that was so large it had to be mounted on a flatbed truck. This active IR searchlight could be detected by any enemy soldiers equipped with similar equipment. The rifle-mounted scope also required cumbersome batteries and provided limited range.

The infrared sniper scope showed that night vision technology was on the horizon. Military leaders immediately saw many uses for this technology beyond sniping at the enemy under cover of darkness. An army equipped with night vision goggles, helmets, and weapons sights would be able to operate 24 hours a day. The Army Corps of Engineers, for example, would be able to build bridges and repair roads at night providing a measure of safety from airborne attack. The next challenge in night vision technology would be the development of passive systems that did not require IR searchlights that might give away a soldier's position to the enemy.

Through the 1950's, Night Vision focused on improving upon the cascade image tube, a development of the Germans during WW II. Scientists at the Radio Corporation of America (RCA) were contracted to research and develop a near-infrared, two-stage cascade image tube. Using a new multi-alkali photocathode (developed at RCA), the new cascade image tube performed beyond everyone's expectations. This new system, known as Image Intensification (I2), gathered ambient light from the moon and the stars in the night sky and intensified this light.

Night Vision quickly adjusted their plans to improve upon this system. There were certain challenges attendant with this new technology: the gain was limited and the output image was upside down. A third electrostatic stage added to the tube resulted in more gain and re-inverted the image, but the tube grew to 17 inches long and 3.5 inches in diameter to maintain adequate edge resolution. This made the system too large for military applications. However, these developments were a major step forward in the development of passive, man-portable night vision systems.

By the mid-1960's, scientists and engineers at Night Vision fielded the first generation of passive night vision devices for U.S. troops, including a Small Starlight Scope that served as a rifle-mounted sight or as a handheld viewer. Realizing these systems were far from perfected, Night Vision research personnel came to refer to the development of this early equipment as the First Generation Image Intensifier Program. Scientists and engineers would go on to improve upon this technology to deliver a second and third generation of night vision equipment.

The first generation Small Starlight Scope was soon put to practical use in the field. With the United States' growing involvement in Vietnam, U.S. soldiers quickly recognized that they faced an enemy that relied on the cover of darkness to conduct its maneuvers and offensive operations. In 1964, the U.S. Army issued night vision equipment to the troops in Vietnam. The Vietnam War proved to be an important stage in the development of night vision systems.

Thermal imaging, based on the far infrared spectrum, forms an image of objects by sensing the differences between the heat radiated by a particular object or target and its surrounding environment. Up until the 1970's, early prototypes using this technology were very expensive.

While Night Vision focused much of its R&D efforts on developing practical night vision equipment based on near-infrared technology, Night Vision scientists were also striving for a technological advance that would lead the way to feasible Far Infrared night vision equipment. The technological advances that would lead Night Vision into developing thermal imaging systems in the 1970's was the advent of linear scanning imagers, consisting of multiple-element detector arrays. The multiple element arrays provided a high-performance, real-time framing imager that could be practically applied to military uses. This technology would lead to targeting and navigation systems known as Forward Looking Infrared (FLIR) systems. FLIR systems provide the advantage of 'seeing' not only at night but also through many smokes, fogs, and other obscuring conditions.

FLIR imaging systems capability became much in demand for all weapon systems platforms, spawning a proliferation of designs and prototypes for the various weapons platforms. As a result, a group of experts from NVL developed a design for a Universal Viewer for Far Infrared in 1973 that led to the family of Common Modules that were fielded by the thousands across many different platforms. The Common Modules based FLIR systems realized significant cost savings over previous designs.

The major test of these technological efforts came in late 1990/early 1991 when Iraqi armed forces invaded Kuwait. The United States of America and its allies immediately mobilized to force Saddam Hussein's forces out of Kuwait in Operation Desert Storm. Night vision systems would prove vital to operating in the desert environment. Night vision systems using I2 and FLIR technologies were used by ground troops and major weapon systems such as tanks, helicopters, missile systems and infantry fighting vehicles. Targeting systems using FLIR technology were particularly important to the major weapon systems due to their ability to 'see' through dense smoke, dust, fog, and haze at great distances. As in Vietnam, Operation Desert Storm showed Night Vision scientists and engineers that improvements could be made, for example sensor fusion that integrated I2 and FLIR capabilities.

The night vision industry has evolved through three stages, or "Generations," of development. Generation I technology is obsolete in the US market. We offer products based on Generation II, II+, III, and III+. Each generation offers more sensitivity and can operate effectively on less light.

Operating life expectancy of Generation I image intensifier tubes was about 2000 hours. Generation II tubes have a life expectancy from 2,500 hours to 4000 hours. Continuing improvements have increased the operating life expectancy of Generation III tubes to10,000 hours. This makes tube replenishment for the system virtually unnecessary. This is an important consideration when the intensifier tube normally represents 50% of the overall cost of the night vision system.

Most natural backgrounds reflect infrared light more readily than visible light. When reflectance differences between discernable objects are maximized, viewing contrast increases, making potential terrain hazards and targets far more distinguishable. Gen III's high infrared response complements this phenomenon, creating a sharper, more informative image.

Generation I

Amplification: 1,000x

The early 1960's was witness to the beginning of passive night vision. Technological improvements included vacuum tight fused fiber optics for good center resolution and improved gain, multi-alkali photocathodes and fiber optic input & output windows. GEN I devices lacked the sensitivity and light amplification necessary to see below full moonlight, and were often staged or cascaded to improve gain. As a result, GEN I systems were large and cumbersome, less reliable, and relatively poor low light imagers. They were also characterized by streaking and distortion.

Generation II

Amplification: 20,000x

The development of the Microchannel Plate (MCP) led to the birth of Generation II devices in the late 1960's and early 1970's. Higher electron gains were now possible through smaller packaging, and performance improvements made observation possible down to 1/4 moonlight. The first proximity focused microchannel plate (MCP) image intensifier tube was an 18mm used in the original AN/PVS-5 NVG. Generation II+ provides improved performance over standard Gen II by providing increased gain at high and low levels. Generation II+ equipment will provide the best image under full moonlight conditions and is recommended for urban environments.

Generation III

Amplification: 30,000 - 50,000x

The current state-of-the-art, the Generation III intensifier multiplies the light gathering power of the eye or video receptor up to 30,000 times. Requiring over 460 manufacturing steps, the GEN III intensifier is typically characterized by a Gallium Arsenide (GaAs) photocathode, which is grown using a metal organic vapor-phase epitaxy (MOVPE) process. The photon sensitivity of the GaAs phtocathode extends into the near-infrared region, where night sky illuminance and contrast ratios are highest. Sealed to an input window which minimizes veiling glare, the photocathode generates an electron current which is proximity focused onto a phosphor screen, where the electron energy is converted into green light which can then be relayed to the eye or sensor through an output window.

The GEN III Gallium Arsenide (GaAs) photocathode is uniquely sensitive beyond 800 nanometers, considered to be the critical near-infrared region where night sky illuminance levels are greatest. This spectral response shift to the red region results in improved Signal-to-Noise Ratios over GEN III's predecessors, delivering a three-fold improvement in visual acuity and detection distances.

Source: Global Security