Sensors Empower Future Soldiers

By Robert K. Ackerman
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U.S. Army scientists aim to prove that less is more.

The future infantry soldier, who already is looking at new personal armor and communications systems, also may be equipped with a multisensor system that can provide him with a range of spectral views that can be changed with the flip of a switch. Helmet-mounted sensors would comprise both infrared and image intensifiers, and rifle sights would provide multispectral capability. Information gleaned from these sensors would fuel network-centric operations.

These advances would not be limited to the muddy boots professional, however. U.S. Army aviators would enjoy better vision and force identification to enable them to shoot first with little fear of fratricide. Nonhuman participants such as unmanned aerial vehicles (UAVs) and robotic ground platforms also would see benefits from improved sensors that open up new capabilities. Ultimately, the future battlespace would be dominated by sensors out front on small robotic platforms. Non-line-of-sight weapons would affect a considerable amount of combat.

Much of the Army’s research into these new tactical sensor technologies is being performed by its Night Vision and Electronic Sensors Directorate (NVESD) of the Communications-Electronics Research and Development Center at Fort Belvoir, Virginia. Its director, Dr. A. Fenner Milton, explains that signal processing power, photolithography and materials technology all are emerging as key to successful sensor development.

The progress made by NVESD researchers tends to be driven by what the laboratory can do with components, he offers. If the NVESD can build a new component, it can build a new system, he declares. Despite the incorporation of advances from the commercial sector, the actual transducer that is at the heart of Army sensor systems must come from military-specific research.

The shift toward lighter, less heavily armored systems as defined by the Army’s Future Combat Systems (FCS) program (SIGNAL, November 2002, page 39), has increased the emphasis on information superiority. Sensors are the originators of that information, Milton states, so the laboratory has received greater support for improving sensor performance. And, with sensors proliferating across the spectrum of tactical operations, researchers must factor low cost into their design specifications.

Research and development at the NVESD concentrates on three technologies: image intensifiers, infrared thermal imagers, and laser rangefinders and designators. Image intensifier technology, which was the original night-vision enabler, has progressed several generations beyond its image tube origins. These technologies now are equipping goggles and rifle sights with improved low-light-level performance and resolution.

Milton points out that these technologies are still maturing. Right now, the laboratory is making much smaller cameras with reduced weight and power consumption. In addition to lightening physical demands on the individual soldier, future digital image intensifiers may be able to provide indirect-view imagery. This will allow significantly more image-processing capability than existing direct-view tubes provide. It also will allow the imagery to be displayed on a separate viewing device such as an eyescreen or a monitor, instead of viewed directly from the imaging tube.

“Our drive in image intensifier technology is toward smaller and indirect viewing,” Milton summarizes.

Infrared thermal imagers, which equip forward-looking infrared (FLIR) systems, currently are used on major platforms. In the past few years, second-generation thermal imaging technology has emerged to provide improved capabilities. These new systems are significantly better than those used in the 1991 Gulf War, although they did not see widespread use in this year’s Iraq War. Milton explains that they provide improved resolution and better performance in poor weather.

Now, infrared imaging research is focusing on development of a new capability that would be multispectral. “Our third-generation technology work is focused on developing focal-plane arrays that will simultaneously detect mid[wave] and longwave infrared,” Milton says. This would enable taking advantage of midwave infrared and longwave infrared detection together, as opposed to existing systems that specialize in only one or the other. Longwave FLIRs work better at search functions, while midwave is better suited to long-range identification. Researchers aim to put the advantages of both wavelength bands on a single camera, he offers.

This will enable rapid search and long-range combat identification. It will help ensure that U.S. forces “get the first shot,” Milton observes, as well as avoid fratricide and maintain strict rules of engagement without being placed at a disadvantage.

However, significant material challenges to reaching this goal loom. Using mercury-cadmium telluride materials to achieve this capability poses a problem. The laboratory has “substantial producibility programs” tasked with solving the difficulties of producing these materials at a reasonable cost, Milton says.

One focus is to try to grow mercury-cadmium telluride on a silicon substrate. However, the lattice constants of the mercury-cadmium compound and the silicon do not match exactly. Accordingly, defects can occur in putting these two materials together. Milton describes the laboratory’s effort as “a program that we have a lot of hope for, but clearly we cannot guarantee [success] at this point. There is still some risk left, but we have some very interesting avenues.” If this hurdle can be surmounted, it will lower the cost of sophisticated focal planes significantly, he observes.

The laboratory is moving from fabrication using liquid phase epitaxy to molecular beam epitaxy, he continues. This technology, combined with the successful goal of using a silicon substrate, would produce the needed capabilities at a reasonable cost.

For less expensive systems, the laboratory is working on uncooled focal plane array technologies, focusing on microstructures and vanadium oxide materials. This technology has advanced rapidly over the past few years, Milton notes, and scientists now can build thermal imagers that do not need cryocoolers. By eliminating these complex, weighty and expensive devices, infrared focal plane arrays can be built to be much smaller and lighter, use less power and cost much less. “It will lead to a revolution in land warfare, as it will open up all kinds of new markets for thermal imaging,” Milton predicts. New commercial applications also will emerge, and the U.S. Defense Department may be able to take advantage of the economies of scale across the board to reduce its own costs through high-volume sales.

The individual soldier may finally have “infrared on the head,” Milton says. These new infrared sensors will have a greatly improved target-clutter contrast over the detection capabilities of image intensifiers. This in turn will provide a significant improvement in night viewing for dismounted infantrymen. Users will be able to find targets more quickly and avoid ambush, as well as operate in a close environment where there is no ambient light for image intensifiers. Smaller UAVs also will be able to reap this technology benefit, and missiles could be equipped with uncooled seekers.

Thanks to recent advances in photolithography, these arrays already are available, and they could be introduced into the field within the next few years. The only hurdle remaining is to gear up for mass production, Milton offers. “We have 480- by 640-[pixel] arrays now with a measure of sensitivity of 30 milliKelvin—plenty good enough for the large majority of military applications,” he observes.

Laser rangefinders and designators, which are the third major NVESD technology, are used extensively to locate targets accurately and to direct laser-guided weapons. Much of the laboratory work involves producing lasers that are smaller and lighter so they can be used by individual soldiers and small UAVs.

Considerable laser imaging work has focused on eyesafe wavelengths. Applications would be narrow-field-of-view, long-range identification systems. Milton says that this work has come along well with substantial advances. The result is hitherto unavailable image tubes that work at the eyesafe wavelength of 1.5 microns. The laboratory now is looking at combinations of passive search and active identification, he states.

Success in this arena could provide soldiers with effective long-range, passive identification capabilities. The shorter wavelengths would provide high-resolution images at long range without threatening friendly forces with eye damage.

NVESD scientists have been pursuing some new avenues of research in laser development. One approach led to a simplified laser system pumped by an unusual commercial off-the-shelf technology. Instead of focusing their efforts on improving complicated laser constructs, the researchers developed a simple monoblock laser that incorporated 12 pieces into three elements. Mirrors were placed on the laser crystals, and all of the laser’s parts were anchored onto a common substrate. This removed the need for alignment as well as improved thermal properties.

Having fewer parts also improved shock resistance. Researchers attached the laser to an M-4 for more than 4,000 firings, and they installed it on an M-119 105-millimeter howitzer for several firings. None of these tests revealed any problems with this simplified laser.

But it was the development of this small laser’s flashlamp that broke the mold of conventional laser construction. A laboratory worker asked his daughter, who worked at a photographic supply store, to bring in some light sources. She brought a trash bag full of dozens of disposable cameras to the laboratory, where scientists disassembled them for their flash units. These commercial disposable camera flashlamps have proved both effective and reliable, as NVESD officials report that one of them has fired its laser more than 10,000 times. Similar flashlamps are being used in the Cobra and Storm laser rangefinders that have been employed in Afghanistan.

A program built around this technology developed a multifunction laser sensor that can serve as a rangefinder, near-infrared aim light, visible aim light, near-infrared illuminator and digital compass. Incorporated into the Cobra, the system is mounted on the M-4 and the M-119. This unit, based on the prototype, weighs 1.6 pounds, and a new version will weigh only 1 pound.

Advances in these three sensor categories may change the way the Objective Force Warrior views the battlespace. Because the imaging systems operate in vastly different wavelengths, they will require separate sensors. However, especially with the new image intensifiers allowing indirect viewing, these separate sensors could be linked into a single display system. So, a future soldier might wear on his helmet a small cluster of sensors each dedicated to a different tasking. The infantryman would change the view in his personal eyescreen merely by flipping a switch.

“Our goal is to make each camera so small and [operating at] such low power that it would not be a significant burden to have several of them on the individual,” Milton declares.

This same capability could be extended to unmanned vehicles, and Milton reports that researchers are looking to use robotic platforms to move these sensor systems in the forefront of the battle. Low-echelon units would control these robotic platforms to get that vital look over the hill. The result would be an increased first-shot capability with reduced fratricide, he notes.

Milton allows that the Army has increased its emphasis on sensors for robotic platforms. This would help avoid crew vulnerabilities in dangerous missions. For sensor researchers, this translates to lightweight packaging so that more sensors can fit on a small platform such as a smaller UAV. Several NVESD programs focus on that capability, he relates.

The network-centric warfare capability that is driving the ongoing force transformation may be able to receive information from these soldiers’ sensors. Milton emphasizes, however, that no plans exist to move each sensor’s data directly into the network. Current efforts involve moving information—as opposed to raw data—from multiple sensors into the network. Target detection, for example, probably would be automatically transmitted to all friendly forces in an area as part of the situational awareness picture. Moving a full image directly into the network probably would be constrained by bandwidth limitations, he offers.

Power remains an important issue in sensor development. Improved sensor capability could be offset by greater power demands, which would increase the weight a soldier would have to carry in batteries. This same issue would apply to small UAVs, which will require compact sensors with low power demands.

This low-power requirement also extends to helmet-mounted displays, where the military has its own research thrust beyond that of the commercial sector. The special military requirement for low power currently cannot be met by commercial personal display systems.

Milton admits to some challenges in building sensors in small-enough packages. “We’re really being pushed there in the case of small UAVs,” he reports. Getting a laser designator into a very small UAV is a challenge that the laboratory still faces.

One area where advances have been a key enabler of these sensor innovations is signal processing. Commercial breakthroughs in signal processing have proved extremely useful, as Army engineers are able to incorporate smaller computing devices into their systems. Milton relates that, in many cases, the Army is adapting technology that has been developed elsewhere. “For once, the Defense Department hasn’t had to pay the full freight,” he adds.