This article appeared in the January 1998 issue of Code One Magazine.
Night vision goggles fall under a broad category of devices called image intensifiers. These devices consist of a photocathode, a microchannel plate, a phosphor screen, and an output window. The photocathode first converts light into electrons. Next, the microchannel plate then intensifies the electrons and projects them onto a phosphor screen, which reconverts the electrons into a visible image. The image is then viewed by the eye on the output window. The resulting image can be 20,000 to 50,000 times brighter than what can be seen with an unaided eye.
Night vision devices have evolved through four generations. The first, called Generation 0, refers to devices that relied on an external covert light source. The light for these early systems, which were first developed in the 1940s, was provided from large searchlights fitted with infrared filters. Generation 1 night vision systems came with advances in fiber optics in the early 1960s and required no external light source. Because they relied on a succession of intensification tubes placed end to end, Generation 1 devices were large and unwieldy. Generation 2 systems were smaller and lighter, benefiting from advances in microchannel plate technology made in the early 1970s. Improvements in how the intensifier reacted to changes in light levels resulted in a subcategory, called improved Generation 2 goggles, in the early 1980s. The use of gallium arsenide as the photocathode material distinguishes Generation 3 devices from earlier image intensifiers. This latest generation of night vision goggles can produce images three times brighter than previous goggles at low light levels.
AN/AVS-9 is the formal military designation of the NVG system used in the F-16, though it is more commonly referred to as ANVIS. The setup consists of a pair of light intensifier tubes and optics that attach to a curved metal bracket fixed to the outside of the helmet. The tube assembly can swing up and out of the field of view or be removed. The goggles are powered by a small lithium battery. Power can be switched on the helmet to a backup battery. The brackets must be custom fit to each helmet and pilots must perform a focusing routine with the goggles before each flight. The entire package adds about one and one-half pounds to the front of the helmet. The ANG at Fort Wayne, Indiana, has modified the strapping system on the back of the helmet to compensate for the added weight.
While the goggles do not turn night into day, they do open up the night considerably. Pilots can essentially fly daytime tactics at night. The biggest benefit expressed by pilots interviewed is a huge increase in situational awareness at night. More specifically, NVGs allow pilots to see a horizon line at night that would be invisibly black to the naked eye.
Looking through the goggles for the first time is impressive. Images appear as shades of green on black. NVGs reveal fine detail in what is little more than shadows when peering beneath the intensification tubes. Aircraft in the night sky normally appear as a series of moving strobe flashes. With the goggles, the same aircraft can be viewed distinctly between flashes. Lights incompatible with NVGs blossom with bright halos and lower the overall sensitivity of the goggles. This effect emphasizes the importance of NVG-compatible lighting inside and outside the aircraft. Long-time Code One readers may recall Joe Bill Dryden's first article on flying with night vision goggles published about ten years ago (October 1988 issue). In that article, Dryden stressed the importance of cockpit lighting for night operations with and without NVGs.
The NVIS modification is a comprehensive approach to NVG compatibility for the F-16. The modification is divided into two basic parts cockpit lighting and external lighting. The entire modification is relatively simple. The parts needed fit into two boxes totaling about two cubic feet as shipped. Aviano aircraft are being modified by a Lockheed Martin team in Italy. Fort Wayne's NVIS mod is being installed by government personnel at the F-16 depot at Hill AFB in Utah.
The cockpit portion of the modification replaces white cockpit lighting with an "NVIS green" lighting and replaces a couple of switches on the lighting control panels. Faceplates, and MFD bezels, are replaced with similar units that contain NVIS-compatible backlights. Some instruments are lighted with small post lamps containing green filtered bulbs. Green filters are placed over the threat azimuth display and existing cockpit flood lights. NVIS cap replacements are used on caution, warning, and advisory/status lights.
The external lighting modification involves replacing existing position and formation lights on the wingtips, intake sides, underside, tail, and upper fuselage with lights compatible with NVGs. The tail floodlight is changed as well. The standard strobe light is replaced with a dual-mode programmable strobe. (The ANG NVIS modification does not have the programmable strobe, but it may be added later.)
The external lighting system operates in two basic modes: normal and covert. The mode is switch-selectable in the cockpit on the exterior lighting panel. Most of the external light units have two or more small windows that contain diodes that emit infrared light for the covert mode. The infrared light is completely invisible to the non-NVG-aided eye.
USAF has taken a relatively conservative approach to incorporating NVGs into fighter aircraft, though it has used NVGs for special operations for some years. The US Army has used night vision systems with its ground and helicopter forces since the late 1960s. The US Navy and Marines began using NVGs in some of their A-6, F-18, and AV-8Bs in the late 1980s.
The Air National Guard has been a leader in incorporating night vision systems into the F-16. While night vision goggles have been used by ANG air defense F-16s for aircraft identification and drug interdiction missions since the early 1990s, the cockpit and external lighting were never modified to accommodate NVGs. (F-16 air defense pilots use lightsticks mounted in the cockpit.) The ANG is making a concentrated effort to install NVIS in its entire F-16 fleet as one of four corners in its "combat quadrangle." The quadrangle includes other capability upgrades and modifications for improving night operations, combat identification, high-threat survivability, and precision attack. The 163rd FS at Fort Wayne and the AATC in Tucson, Arizona, are leading the ANG in its night vision efforts.
USAF night vision efforts are concentrated on its A-10 and Block 40 F-16s. All A-10s and Aviano F-16s will be NVIS-equipped by early 1998. (Northrop Grumman is modifying the A-10s.) F-16 Block 40s at Eielson AFB, Alaska (PACAF), and at Cannon AFB, New Mexico (ACC), are expected to follow soon.
European F-16 operators will see night vision compatible cockpit lighting with the Mid-Life Update, or MLU. This capability is one of many in a long list of improvements that accompany MLU. No European F-16 unit is currently flying with NVGs. MLU aircraft have a slightly different implementation of cockpit lighting than that described and have no exterior lighting modifications.
NVGs have not been neglected in new aircraft design. The F-22 is the first aircraft to include NVG-compatible cockpit and exterior lighting in its baseline design. The Joint Strike Fighter will be similarly equipped.
Eric Hehs