Today’s fixed-wing and helicopter pilots can stay in the air when the sun goes down, often using night vision goggles (NVGs) and forward-looking infrared (FLIR) to help them to see in the dark, and the technology available right now is better than ever. Before we look at what the next-generation of systems might bring, it’s instructive to look back at how to how far we’ve come.

Evolution

The origins of NVGs can be traced back to early inventions such as the ‘black-light telescope’ created by Dr Vladimir Zworykin of the Radio Corporation of America, which used a silver-coated plate to convert invisible infrared rays into electrons that were projected onto a fluorescent viewing screen, as explained in Popular Science magazine back in 1936.

It was a time when scientists and engineers were working intently to harness electromagnetic waves to create radio and electro-optical devices. The technology was sufficiently developed by the Second World War to give a tactical advantage on the battlefield. Due to a limited sensitivity, the monocular scopes of that era (considered night vision ‘Generation 0’ or ‘GEN 0’) were used in tandem with infrared lights to illuminate the scene and were power-hungry – little hindrance for mounting on a tank perhaps, but it meant a bulky outfit for the rifleman, who would need to carry a large battery pack on his back. In the following decades, although they still needed the accompanying lights, the scopes improved, and the batteries became small enough be worn on a belt.

The creation of passive ‘GEN I’ tubes in the 1960s was a major step forward, as the upgraded image intensification technology amplified ambient light by around 1,000 times, allowing for use without an infrared illumination, although they still needed moonlight and clear skies.

The creation of passive ‘GEN I’ tubes in the 1960s was a major step forward

The ‘GEN II’ tubes of the 1970s introduced micro-channel plates and twisted fibre-optics, resulting in units that were both more powerful (light amplification of around 20,000 times) and more compact, with features including automatic brightness control. NVGs with a ‘full face’ mask began to be adopted by military pilots, but limitations such as weight (around 2 lb/1 kg) and the need to read cockpit instruments through the tubes meant they were uncomfortable and tiring to use. ‘Cut-away’ masks came in the 1980s, affording the ability to look under the tubes to read instruments, but the design of NVGs for aviation can be said to have fully matured in the 1990s, when ‘GEN III’ NVGs emerged with the best-ever performance (light amplification of around 30,000 to 50,000 times) and lightest weight, allowing for prolonged use. NVGs had reached a point where they could be widely adopted by civilian aircrews.

Although the predecessors of today’s NVGs used infrared light, modern forward-looking infrared (FLIR) devices have a different ancestry. Raytheon describes how in 1963, Texas Instruments’ Defense Systems and Electronics Division experimented with replacing the infrared film in aerial reconnaissance cameras with photoconductive detectors that could drive TV-style displays. These first-generation systems were used in the Vietnam War to pick up enemy movements at night. Early units were of considerable size and consumed a lot of power, as they had to be cooled far below freezing point, only later becoming smaller and able to operate at higher temperatures – current second-generation sensors are uncooled and of low power consumption.

Recent refinements

The NVG tubes produced today are still deemed GEN III units, although advances have been made in some designs with ‘autogated’ automatic brightness control and light sensitivity. Darrell Hackler, Senior Director of Global Business Development at NVG tube-maker Harris Corporation, said that they’re getting more out of today’s GEN III image intensifiers than expected, with resolution and intensification improving over the past five years. One factor, he said, is the use of cleaner manufacturing environments, which result in reduced contamination in the tubes.

Perhaps the biggest change in recent years has been the adoption of white phosphor goggles for civilian operators, allowing crews to see in something close to black-and-white (traditional NVGs used green-and-white as it was thought to be better for the eyes, Hackler explained).

the biggest change in recent years has been the adoption of white phosphor goggles for civilian operators

Jim Winkel is President of ASU, Inc., which announced its white phosphor NVGs at the Airborne Law Enforcement Agency Annual Convention in 2014. White-phosphor NVGs have better low-light performance and are more reliable, as well as exhibiting reduced halos, increased contrast and clearer images, said ASU. Winkel told AirMed&Rescue: “White phosphor provides crewmembers with better image clarity and decreased eye fatigue, resulting in a more natural and comfortable flight experience. The air medical community has been the early adopter of white phosphor – even ahead of the US Department of Defense, which is quickly catching up.”

Hackler commented that white is fast becoming the industry standard, with many users sending their NVGs to have green tubes replaced with white phosphor units.Other than the performance of the tubes, work has been done to make the goggle sets more comfortable to wear, an example being a lighter battery pack and mount (paired with a lighter helmet), as revealed by ASU, Inc. at HeliEXPO in 2017. ASU senior business development manager Kim Harris said at the time: “This combination of the new helmet and mount vastly improves the user experience. As a pilot that has flown with night vision goggles for decades, I have experienced first-hand how much the lighter helmet, battery pack and goggle mount can decrease strain on a pilot or crew members wearing the equipment. When flying several missions, every ounce matters.”

Advancements continue

Regarding airborne thermal-imaging surveillance systems, Adam DeAngelis, Director of Marketing, Surveillance Group, at FLIR Systems, Inc., commented that the technology has drastically improved: “Almost 20 years ago, the thermal imaging detectors in stabilised airborne systems were scanning arrays. What that meant was that there was typically a small group of detector ‘pixels’ and a mirror-like device would scan these rapidly to produce a full resolution image – typically 320x240. As technology increased, the detector became a staring array with a full group of detector ‘pixels’ in full resolutions of 320x240 and eventually 640x480 or 640x512 (PAL). This allowed much greater sensitivity and resolution. With the higher resolutions, it wasn’t just picking out the thermally different object on screen, it was actually seeing detail in the scene and of the object. FLIR’s current Star SAFIRE 380-HD and Star SAFIRE 380-HDc have full high-definition arrays of 1280x720 pixel ‘detectors’.” He continued: “For search and rescue, this means identifying someone in the water from much further away as well, since the level of detail has increased. In addition to this, multi-spectral options such as SWIR (short wave IR) and I^2 (image intensifying) sensors add to the ‘toolkit’ available for the airborne operator.”

As another example, a representative of Safran Electronics & Defense told AirMed&Rescue how the company’s latest, fourth-generation Euroflir 410 device improves on previous iterations. Changes include a move to high-definition resolution and a new, large-aperture lens system. It also now boasts an optional target laser for illumination of the scene to facilitate, for example, boat name identification.

Stay tuned for more

The history of NVG development features design improvements to reduce their size, weight and power consumption (a common goal in military equipment acquisition, known by the acronym SWaP). It’s likely that future evolutions will continue to improve in these areas, not least as producers such as mobile phone and electric car manufacturers seek to develop better battery technology. Said Winkel: “Stay tuned as more enhancements are on the horizon. Measures to reduce overall helmet weight on the crew member are underway, which will increase crew comfort and reduce neck strain."

Measures to reduce overall helmet weight on the crew member are underway, which will increase crew comfort and reduce neck strain

Specifically, Hackler indicated that there could be weight savings from using lighter optics – the use of polymer lenses is being explored, as these are less dense than the glass currently used. Harris is also looking at reducing forward projection, to bring the centre of gravity closer to the head, he added.

However, the next breakthrough in NVG tech may take the devices in a different direction. When you consider how modern life is dominated by digital solutions, it’s almost surprising that aviation NVGs remain so resolutely analogue. In fact, digital night vision is already in use in some military devices – and is even on sale to consumers. Retail website Night Vision, which markets digital scopes to hunters, says of the tech: “Digital night vision technology truly has turned our industry on its head. From toy store novelty only a few years ago, to today’s line of category killers, these products represent the future.”

Digital scopes work similarly to digital cameras: a sensor detects light and a screen displays the image. A gain of going digital would be the possibility to relay or record the signals, as is already the case with aircraft-mounted FLIR cameras. Furthermore, Armasite (a division of FLIR Systems, Inc.) highlights the fact that unlike traditional NVGs, they are not damaged by exposure to daylight. For flight, a major advantage of digital NVGs would be the flexibility of where you site the lens and sensor, with only the display screen being worn by the pilot – this would significantly reduce the weight of gear on the helmet.

It’s unlikely, though, that a single lens and sensor would be enough, as even if mounted in a moving turret and slaved to follow the movements of the pilot’s helmet, there would be significant, disorientating (possibly even nauseating) lag. You could, however, adopt a system similar to that used on the F-35 fighter jet, where imagery is processed from six external infrared cameras and projected onto the helmet visor. While the exact set-up may be costly to replicate (the F-35 helmet alone comes with a budget-busting price tag of some US$400,000), in 2016 Elbit Systems demoed its BriteNite system, which uses the same concept of piping digital imagery to the user. In this case, the feeds from an array of fixed external infrared and visible light sensors are processed and the appropriate section is fed to helmet-mounted goggles to match where the user is looking. In both systems, the imagery can be overlaid with instrument data and 3D mission symbology.

It’s worth noting that by using the visor for the heads-up display on the F-35, the user is afforded a wider field of view than the relative ‘tunnel vision’ of NVGs, which is often cited as a limitation on the current gear. Harris has looked at changing the field of view, said Hackler, but it seems that military aviators he’s spoken to suggested it isn’t a significant issue, as they have their heads ‘on a swivel’ in any case. Also, the trade off to increasing the field of view would be larger, heavier tubes, he noted.

On another tack, if you appreciated the move from green to white phosphor aviation NVGs, the next step could be full-colour goggles. There are a couple of ways that makers could implement this. For example, SCI Corp uses highly-sensitive digital sensors in its scopes aimed at ground users. ColorTac, on the other hand, is exploring a different methodology: a pair of matched coloured filters rotate in sync, one in front and one behind the NVG tube, providing two channels of light that the eye perceives as full colour. There are also the Sentinel-CNV goggles from Adams Industries, again for ground users, which ‘utilise proprietary modifications to deliver meaningful and repeatable colour contrast at low light levels associated with night-time operations’.

As for infrared cameras, Raytheon says it is now introducing third-generation devices, which promise even better imagery.

As with most fields in technology, it’s likely that we’ll mostly see gradual improvements in the devices offered, with occasional leaps forward, some of which may be surprising. For now, though, it seems safe to predict that we’ll move from analogue to fully digital systems. Hackler confirmed that moving away from direct-view imaging is a goal, and work is now being done to test digital night vision solutions for aviation. Perhaps today’s green-screen NVG tubes will be tomorrow’s museum pieces, fashionably retro with the hipster pilot?