Seeing In The Dark
DURING THE PERSIAN GULF WAR, IN 1991, TELEVISION VIEWERS AROUND the world witnessed the new effectiveness of night military operations. Laser-guided missiles methodically destroyed Iraqi targets with near-pinpoint precision as tanks stormed the Kuwaiti desert, overwhelming Saddam Hussein’s Republican Army forces. Although the combat took place in the dead of night, we saw the footage as if it were noon, for the coalition forces and television crews covering the war were equipped with an assortment of devices for seeing in the dark. Gen. Barry McCaffrey—now President Clinton’s drug czar, then commander of the 24th Infantry Division—said, “Our night vision capability provided the single greatest mismatch of the war.”
America’s high-tech military has a host of night-vision tools at its disposal. Foot soldiers wear helmet-mounted goggles as they stalk in jungles; snipers peer through rifle scopes that light up their targets; drivers raise periscopes to guide their jeeps and tanks; aviators fly at tree-top level using helmet-mounted binoculars; gunners on tanks, helicopters, and jets acquire, track, and illuminate targets on CRT screens. And military as well as civilian photographers attach devices to their camera lenses for turning night to day.
Military tacticians long ago recognized the advantages of fighting at night, and armies have attempted it sporadically throughout history. In the Battle of Trenton, in 1776, for example, Continental troops led by George Washington crossed the Delaware River in darkness, though a snowstorm delayed their attack until morning. In the War of 1812 and the Civil War, troops would sometimes surround the enemy at night and then attack the next day. But with no means of effectively seeing at night, such strategy often ended in disaster. Knowing this, commanders traditionally elected to take their chances on being annihilated by day rather than risk nocturnal miscalculations.
The problem with fighting at night, obviously, is that there isn’t enough light. There are two ways around this: Either provide more light or amplify what’s there. The earliest efforts at technology-assisted night fighting relied on the first option, as in the Union navy’s use of calcium lights to bombard Charleston Harbor in 1864 (see “The Limelight,” Invention & Technology , Fall 1997). But casting a powerful light on a target has the unwanted effect of revealing the at- tacker’s location. The first true night-vision systems would have to wait for the development of devices that could detect invisible wavelengths of light and amplify weak signals.
Late in World War II, German, American, and British forces introduced crude infrared rifle scopes that allowed snipers to operate at night. These “active” systems—meaning that they provided light rather than just rely on existing light —had a near-infrared (NIR) light source mounted on the scope. (NIR is next up in wavelength from visible light on the electromagnetic radiation spectrum.) The NIR light would shine on the object to be seen and reflect back to the scope, which converted the reflection into a visual image and made it brighter with a device called an image tube.
Originated in the 1920s to increase the sensitivity of television cameras, image tubes work by converting light into electricity. Certain substances, such as selenium, had been known since the 1870s to be photoemissive—that is, to emit electrons when a light shone on them. With proper use of lenses, a pattern of light—visible or invisible—upon a photoemissive surface can be converted into electrical impulses. In an image tube, a voltage is applied across the photoemissive surface, which is called a photocathode. This voltage accelerates the emitted electrons and causes them to multiply.
To create a visible image, the emitted electrons are directed against a phosphor surface. This type of surface is the opposite of photoemissive; it emits light when electrons strike it. The phosphor is in the form of a coating on an optic lens, which focuses the resulting visible image. The phosphor screen looks much like a black-and-white television with a greenish tint (green is used because the eye is most sensitive to that color). In essence, then, the earliest nightvision devices (NVDs) converted NIR light to electricity, amplified it, and then converted it to visible light.
Interest in night-vision equipment declined after its experimental use in World War II, and development proceeded slowly for the remainder of the 1940s. But in 1950 the overwhelming success of the Chinese Communist attack in Korea, much of it effectively pressed after dark, dramatically demonstrated that the ability to fight at night was essential in modern warfare. Our experiences in the Korean War fueled a movement to expand the Army’s night fighting capabilities.
The Army Corps of Engineers took the lead, precipitating a decade-long territorial dispute. The Corps had gotten into the night-vision business in World War II by building 60-inch carbon-arc searchlights for tracking planes. It also had researched the use of infrared light to follow planes when they went behind clouds, but the Signal Corps had developed radar, which proved superior. Having lost out to radar, the Corps of Engineers wondered what to do with its infrared expertise.
The Engineers had long wanted to carry out construction projects, such as building bridges, at night. They learned of the NIR sniper scopes built by the Germans and, using what they knew of them (from captured equipment and similar American technology), they built a pair of binoculars for use in driving construction vehicles after dark. This happened with little fanfare, but when they made the binoculars into a weapon sight, the Signal Corps tried to take over the project on the grounds that it was electronic. As Robert Wiseman, who headed the Engineers’ night-vision lab for 27 years, recalls: “The Corps of Engineers didn’t have very many exotic things—mostly things like barbed wire and earth-moving equipment—and here’s a sexy little thing, and they didn’t want to give it up to the Signal Corps. And then the Ordnance Corps wakes up and says, ‘That’s a weapon sight. We’re in charge of fire control; that ought to be ours.’” The infighting continued through the 1950s.
The Corps of Engineers’ development effort involved a several-decades-long collaboration between Army personnel and teams of experts in physics, optics, and electronics. The driving force came from the Army Night Vision Eaboratory, at Fort Belvoir along the Potomac River in Virginia, just south of Washington, D.C. Civilian engineers and scientists worked with soldiers and manufacturers in private industry. Acting as a systems integrator, the lab built prototypes in its fabrication and machine shops, using components and materials supplied by more than 50 contractors around the country. This approach was necessary because devising night-vision equipment required the assimilation of many different technologies, and no single private company had the capability or interest to build the total system.
Wiseman proved a visionary leader in guiding the effort through many ups and downs. He had served in the Army Air Corps during World War II as a communications and electronics officer and gone on to study electrical engineering at the University of Illinois. He became interested in night vision and the human eye when one of his professors, John Kraenbuehl, started a curriculum in illuminating engineering.
In 1953 Kraenbuehl took Wiseman to an Illuminating Engineering Society meeting in Chicago. There Wiseman met Oscar Cleaver, an electrical engineer from Fort Belvoir who wanted to start a program in night vision and was looking for someone to direct it. Kraenbuehl recommended Wiseman for the job, and he became chief of Fort Belvoir’s newly created Research and Photometric Section in 1954. (It eventually combined with other groups to become the Night Vision Lab.) The section began with a meager $200,000 budget.
As its first project, in 1954, the section set out to upgrade components of the rudimentary NIR sniper scopes the Army had developed. In using these, each sniper had to wear a heavy batterybackpack with a wire reaching over the shoulder. Because it was so cumbersome, the scope was built for use mostly on jeeps, tanks, and other large vehicles with plenty of room and power capacity. This type of active NIR technology became known as Generation 0. Its photocathode, designated S-1, had a silver cesium oxide photoemissive surface, which became the industry standard. The single-stage image tube had a gain of 60 (indicating the factor by which it amplified, or brightened, the image) and required a hefty 16,000 volts to drive it.
Wiseman decided to reduce the apparatus’s power usage at both ends by developing a more efficient NIR source and a more sensitive image tube. This would make practical a smaller and lighter battery pack. Wiseman’s group started a program with RCA to couple two image tubes end to end to create a cascading effect, greatly multiplying the gain. The image tube now took on the name of image intensifier. For prototypes, RCA proposed using a photocathode it had developed that used multialkali (a mixture of potassium, sodium, and antimony) for the photoemissive surface. This was easier to produce than silver cesium oxide 50 and offered increased sensitivity to visible light.
They first tested the new system, including the new photocathode, using visible light, and the visible-light version turned out to work so well that the team decided to forget about switching back to NIR. Ambient light from the night sky, such as moonlight, starlight, upper-atmosphere air glow, and any stray light from the battlefield, was enough by itself to yield recognizable images. This unexpected turn of events eliminated the need for an NIR source, which had two advantages: Its cumbersome power supply would no longer hamper a soldier, and perhaps more important, it prevented the enemy from locating its user with the simple NIR detector. That was already making active NIR a liability. The shift from NIR to visible light led to the advent of “passive” systems, which require only ambient light to operate. Passive visible-light scopes became the Army’s principal night-vision devices.
As well as RCA’s two-stage image intensifier tube worked, it had its problems. Gain was still insufficient, and the second stage inverted the image, making it appear upside down to the user. Adding a third stage solved these problems by increasing the gain and reinverting the image. The three-stage setup yielded Generation 1 technology in the late 1950s. Generation 1 detected both visible and NIR light using a photocathode called S-20, with a photoemissive surface of antimony, potassium, sodium, and cesium. This new photocathode, combined with the addition of the third stage, increased the gain to 25,000, allowing a rifle scope to see 400 yards.
Still, the intensifier tube was a bulky 18 inches long and 3 inches in diameter. The photocathodes and phosphor displays required curved surfaces to get an optically correct image, and because the curvature of the phosphor display of one tube was counter to that of the adjacent photocathode surface, stacking multiple sets of curved surfaces took up a lot of space. In addition, bright lights could overwhelm the early scopes, rendering them temporarily unusable; their tubes burned out quickly; and they had poor resolution. Still, they were better than no night vision at all.
Then in 1958 John Johnson, Robert Wiseman’s main idea man, heard a presentation on fiber optics and decided that it could solve the threestage tube-length problem. He envisioned growing the photocathode or applying the phosphor screen directly onto the surface of a fiber bundle. The image could be inverted by simply twisting the bundle. Johnson discussed the possibilities with the American Optical Company, which expressed little interest. American Optical referred him to Will Hicks, who had left the company to form Mosaic Fabrications. Hicks had just started the small business in his garage, pulling optical fibers by winding them around a drum attached to the axle of a jacked-up car.
After proving that he could make his fiber-optic assemblies vacuum-tight…a necessity in building image tubes…Hicks found a way to simplify the process by arranging millions of short fibers in the form of disks called fiber-optic plates…in effect, slices of solid bundles of fibers. One side of each plate was flat, allowing it to mate with other plates, so they could be stacked. The other side could be concave to match the focal plane of the adjoining phosphor display or photocathode surface.
Johnson’s highly creative work epitomized the innovative management style that Wiseman brought to the lab, a style that proved pivotal in the development of modern night vision. “When I got there, I was given a section made up of people nobody else could handle,” Wiseman recalls. Johnson was one of them. He was fresh out of George Washington University and very knowledgeable technically. He often spent entire weekends studying in the library and came to work on Monday full of new ideas. But he shunned administrative details and didn’t always follow through on ideas he introduced, instead constantly dropping one for another. This rubbed many people in the military and governmental bureaucracy the wrong way, and sometimes Johnson and his co-workers wouldn’t speak to one another. Wiseman held sessions in which his charges openly talked out their differences and helped one another with their problems. Each worker had a well-defined role, and Wiseman melded them together in a team, taking account of their differing needs and abilities.
The lab’s advances in fiber optics enabled it to win authority over the Army’s night-vision development from the Ordnance Corps. During the 1950s, to keep its finger in the pie, the Ordnance Corps had devised a night-vision television system for tanks, using an image intensifier. Wiseman’s group had mounted an image intensifier on a regular tripod for the same purpose. Army brass compared the two in a showdown at Philadelphia’s Frankford Arsenal in 1960. The Ordnance Corps system required flipping several switches and adjusting knobs. The Corps of Engineers’ periscope required only looking through an eyepiece and throwing a single switch. Its obvious superiority killed the Ordnance Corps project and solidified the Corps of Engineers’ hold on night-vision technology.
Having finally won the long intraservice rivalry, the lab saw its prosperity skyrocket in the early 1960s, after President John F. Kennedy told the Army to study what resources would be needed to fight a limited war. A committee headed by the physicist Luis Alvarez determined that night vision would play a critical role. Wiseman and Johnson briefed Alvarez on what they had achieved thus far and what they could do if they got the needed funds. Alvarez declared that their work was exactly what the Army needed.
In 1962 Wiseman was called in to brief Army brass and lay out plans for the future of nightvision development. The generals and colonels were impressed and told Wiseman to calculate the budget he would need to carry out his vision. If he wanted to take alternative paths to solving a problem, they said, he should pursue them all concurrently. Wiseman developed a three-phase plan with multiple approaches and came up with a proposed $7 million annual budget over seven years. To the amazement of military insiders, he was given $5 million of this, along with additional staff and another building to house them.
Flush with funding and manpower, the lab developed six new models of night-vision equipment. Then, after the technical requirements were finalized, the Army started figuring out how to use them. Nobody, it turned out, had a clear concept of what would be the most efficient strategy—issuing one per squad, one per soldier, or one per battalion. In 1964 the Army decided to build four battalions’ worth of equipment and test it at Fort Ord in California for a year.
Then in early 1965 America plunged headlong into the Vietnam War, and with priorities shifting, the Army diverted the NVDs bound for Fort Ord to Vietnam. During the war Night Vision Lab personnel interviewed Vietnam veterans to see what they needed, and some went overseas to evaluate their equipment in action. They established a program to accelerate development of new designs, which now included devices for airborne, combat-vehicle, and ground use.
The ability to see at night became a major defensive weapon in the Vietnam War. The Vietcong had previously inflicted great damage on their enemies by scouring the jungle and sneaking up on enemy soldiers in the dark. By patrolling with night scopes, U.S. ground troops could see them coming. Wiseman recalls that when he spoke with troops who had fought in Vietnam, “They would say, ‘You don’t know how many lives you’ve saved.’” Night vision and the helicopter were the two Vietnam innovations that would have a major effect on how future wars were fought.
Late in the 1960s came a technological breakthrough that many experts consider the most significant in the history of night-vision development: the microchannel plate (MCP). This wafer-thin device, about the size of a quarter, replaced the multiple stages in the image intensifier tube and so dramatically reduced the space required for the tube that now NVDs could be configured in the form of goggles that aviators and infantry troops could use hands-free. An MCP is a form of glass plate with millions of microscopic holes, or channels, running through it (this replaces the bundle of optical fibers). When a voltage is applied to accelerate electrons through it, the electrons repeatedly bounce off the channel walls, which are coated with the residue from etching the holes. As they do so, they dislodge additional electrons. The gain is proportional to the voltage applied. Each channel in the MCP corresponds to a pixel in the final image.
Development of the microchannel plate led to Generation 2 technology, which retained RCA’s multi-alkali photocathode and required 8,000 volts to convert the images. In Generation 2 the photocathode, microchannel plate, and phosphor screen —detector, amplifier, and display—are sealed together in a module less than an inch thick.
The concept of the microchannel plate had been around for decades, but no one could make it useful because they couldn’t get the holes small enough for good resolution or apply a secondary emission surface to the channel walls. People tried drilling the holes and making the plate from corrugated metal, with no success. Then John Johnson thought of etching the holes in a thin fiberoptic disk. Will Hicks at Mosaic made it work.
With NIR apparatus shrunk to a convenient size, researchers in the 1970s started working on a new way to acquire targets, with a technology called thermal imaging. As the name suggests, thermal imaging yields a picture of an object’s heat output, which resembles an ordinary visual image. All objects emit radiation whose wavelength varies with their temperature. Very hot objects emit visible light; cooler ones emit lower-energy infrared radiation. Thermal imaging operates in the far-infrared (FIR) band, next up the wavelength scale from the NIR band. Thermal imaging with FIR lacks the resolution of NIR image intensification, but it can see through clouds, haze, smoke, fog, and camouflage. It also has greater range because the longer infrared wavelengths penetrate farther. For this reason many aircraft are fitted with FIR equipment for navigation, weapons delivery, and surveillance.
The first FIR night-vision systems were developed by Texas Instruments in the late 1950s. They used a design with FIR detectors remaining stationary while oscillating mirrors continuously scanned a scene and beamed the image to the detectors. A big break came in 1964, when Texas Instruments developed a forward-looking infrared system that yielded a much clearer image. This capability spurred demand for FIR in the early 1970s. Forward-looking IRs saw use in aircraft-mounted launching systems for TOW and Dragon missiles. Their main drawback was that the infrared detectors had to be cooled to -196° centigrade to minimize electrical noise. Efforts during the 1970s and 1980s focused on satisfying this requirement in convenient ways and reducing the size of the units so that they could be hand-held.
As FIR thermal imaging was being improved, so were image-intensification devices. This parallel path led to a host of new technologies after Vietnam and gave the Night Vision Lab more ways to shine when the Persian Gulf War broke out in 1991. Night vision offered the coalition forces a capability Iraq didn’t have, as ground troops and helicopter pilots used image-intensification devices, such as binoculars, while fighterjet crews used thermal imaging in aiming their weapons. The combination of the two technologies resulted in an unprecedented offensive capability. The guided munitions we saw on television (footage that was itself taken with nightvision equipment) were actually only a small fraction of the ordnance used, but they had an enormous impact.
Adapting night-vision technology to the desert was a major undertaking. In Saudi Arabia and Kuwait, the lack of stable terrain features and the uniform color and temperature hindered the use of night-vision equipment. Sand dunes rose and ebbed unpredictably. Winds swirled sand during the day, and though they stopped at night, silt still hung in the air like a fog.
Nowhere was the challenge greater than in flying. Pilots of aircraft like the AH-1F Cobra and Apache attack helicopters like to fly low in battle to avoid detection. This socalled nap-of-the-earth flight often involves altitudes of less than 200 feet. With the relatively poor resolution of nightvision goggles, pilots suffer from reduced depth perception; they also lose peripheral vision because their field of view is narrowed to only 40 degrees (some compare it to looking through toilet-paper tubes). During the conflict four pilots crashed into sand dunes because they misjudged distances.
Fortunately, Operation Desert Shield, the precursor to Desert Storm, provided a training ground to .test NVDs and make adjustments before the war started. About half of the Night Vision Lab’s” personnel became involved, some going into the field. As a quick fix for helicopters, they fabricated brackets and mounted pulsed-laser diode aiming lights on the landing skids to give early warning of approaching sand dunes. These safety devices emitted NIR, but this was not a danger since the primitive Iraqi army did not have NIR detection devices.
Another problem was that the distances over which attacks took place were greater than military leaders had planned for. The far-flung scale of operations made distinguishing friend and foe difficult, a task exacerbated by the diversity of equipment the coalition used. Night-vision technicians installed NIR beacons on tanks to aid in identification. They also assembled large infrared telescopes that could see up to 20 miles. With these, troops confirmed the presence of Iraqi Scud mobile missile launchers in Kuwait. Lab personnel cannibalized thermal weapon sights from M60 tanks, which the Army is retiring, and, after making modifications, placed them on scout vehicles for surveillance.
Today Generation 3 image intensifies are the latest technology in night vision. The photocathode consists of gallium arsenide, a-siliconlike semiconductor that gives off more electrons per photon than the previous cesium-based photocathodes. It also lasts much longer. Image intensifiers can amplify image brightness up to 100,000 times, though the gain for the device as a whole is reduced to between 2,000 and 3,000 for better contrast and resolution.
Although several companies have manufactured image-tube night-vision devices over the years, only two do so now: ITT Night Vision and Litton Electron Devices. They use fabrication techniques borrowed from the semiconductor industry, working in clean rooms held to stricter requirements than hospital surgery units because particles as small as an atom can cause defects. Much of the work is conducted in a vacuum. The complex process of producing a pair of night-vision goggles involves more than 400 steps and 200 chemicals. Over the years yield rates for producing acceptable units have gone from single digits to 85 percent. The cost of producing night-vision systems has dropped steadily in a pattern paralleling that of color television, calculators, and computers. Quantities have grown, allowing economies of scale, and manufacturers have recouped development costs and accumulated valuable know-how.
The loss of military business has spurred increased marketing for commercial applications. Law-enforcement agencies, including the FBI, police departments, and border patrols, have become major users of image-tube devices in recent years. Image intensifiers can also improve vision for victims of retinitis pigmentosa and other forms of night blindness. Marine users, including fishermen, tugboat operators, sailors, and the Coast Guard, have also joined the trend. The new products come in the form of binoculars, monoculars, pocket scopes, and units that are mounted on cameras.
Intensifier-equipped video cameras are used in security and surveillance. Science and medical research have also created markets. Scientists use image tubes for microscopy. When they inject dyes into a specimen and beam it with a laser, fluorescence is given off, and it can be viewed through an image intensifier. This aids in early cancer detection, as doctors can spot differences in fluorescence between good and bad cells.
Thermal imaging has been used for years to detect hot spots in forest fires, electrical losses in power lines, and heat losses in housing. Texas Instruments and Hughes Industrial Electronics have teamed to develop an FIR video camera for use by law-enforcement agencies. Auto manufacturers are also researching the use of FIR on cars. Driving with it at night, they say, could have at least as much safety value as air bags and antilock brakes.
There may come a time, perhaps a technology generation or two in the future, when night-vision devices are as common as household flashlights. When that happens, everyone will own the night, not just the military.