Army seeks to upgrade night-vision goggles.
The essence of these new goggles is "sensor-fusion," which combines conventional night-vision technology (called image intensification or I2) and thermal sensors (forward-looking infrared).
The I2 wavelength offers a clearer image and can see through glass windows. However, image intensification requires that there be sufficient light to intensify, which makes it ineffective in an Afghan cave. For example, "there was an immediate interest in IR [infrared] on the head when we went to Afghanistan, because of the caves," said A. Fenner Milton, director of the Army's Night Vision and Electronic Sensors Directorate.
On the other hand, IR relies on thermal contrast--heat emitted by the target versus the heat emitted by its background--which provides images with better contrast than 12, and can see through obscurants such as dust and smoke. "It requires very little temperature difference between the target and its background for the sensor to detect the target," said Milton.
The Army is combining the best of both technologies by creating fusion goggles that combine IR and I2 into a single image. These will replace some of the I2-only goggles, such as the PVS-7 and PVS-14.
Fusion goggles have been made possible by the development of uncooled IR sensors that has significantly reduced the weight of once-bulky IR devices. "They utilize both IR and 12 technologies and fuses them into a single picture," Milton said.
Milton predicts that within a couple of years, many American soldiers will have "IR on the head," via lightweight fusion goggles. "I think all the combat troops will have some form of IR," he added.
Current fusion goggles weigh 2 pounds (battery pack included) and allow field of vision 40 degrees horizontal and 30 degrees vertical. The sensors have selectable channels, from 100 percent near infrared to 100 percent long-wave Infrared. The batteries provide four hours of continuous operation.
Other technologies intruded to help enhance night-vision capabilities include range-gated lasers and 3rd generation forward-looking infrared systems.
Laser range-gating is a matter of timing. Lasers are vulnerable to obscurants such as fog, which reflects backscattered light that confuses the detectors in a laser device. The detector on a range-gated laser is timed to open only at the exact moment that the pulse is received. For example, if there's fog between the laser and the target, the laser pulse will bounce off the fog first and the target later, and thus the fog reflection will arrive at the detector first. The sensor is timed to open only for the reflection from the target. However, the range to the target must be determined beforehand for the sensor to open at the correct time. Two laser pulses are fired, the first to determine the range and the second to illuminate the target for the range-gated camera.
"You use these lasers for ID of targets at long range," Milton said. "You illuminate the target with a short pulse, and then you have a sensitive tube that turns on only for short periods, so you get a range-gated image right where the target is."
While I2 technology will gradually improve, the Army is exploring other wavelengths. The human eye sees wavelengths in the 0.4 (violet) to 0.7 (red) micron bands. I2 sees in the near-infrared band of 0.4 to 1 micron. Some mid-wave thermal sights and IR cameras operate at 3 to 5 microns, while others operate on the long-wave IR band of 8 to 12 microns. Longer wavelengths offer better contrast at the expense of resolution.
"We spent a lot of time making I2 better, more sensitive, higher resolution, halo-free and lighter," said Milton. "We made a lot of progress. I think the most interest now is in adding other wavelengths. We decided to go to infrared."
Milton doesn't believe that IR will replace I2. Each functions best under various lighting conditions. However, he predicts that IR will predominate "for platforms that require acquisition at very long ranges, such as in a weapons sight."
Another emerging technology is third-generation FLIR, which combines mid-wave and long-wave IR. The FLIR has two infrared detectors on one chip, with one set for mid-wave IR and the second for long-wave IR.
Third-generation FLIR exploits the fact that for most objects, the contrast between themselves and their backgrounds differs between the mid-wave and long-wave IR bands. The sensors use the difference between mid-wave and long-wave IR contrasts to show the target standing out from its background, which especially helps when searching for camouflaged or partially hidden objects. The FLIR also benefits from long-wave IR advantages in rapid search and mid-wave IR capabilities for long-range target identification.
Milton foresees scouts carrying tripod-mounted systems with multiple capabilities, including a high-performance FLIR, range-gated laser, laser illuminated rangefinder and a laser designator. "The tradeoff in deciding what technology is best is really dependent on the need and the operational environment. Both technologies [IR and I2] have advantages under certain conditions."
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|Date:||Apr 1, 2004|
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