Night vision (NV) technologies have come a long way since the first devices appeared in WWII, and where the dark was once a total asset, continued evolution of NV capabilities has meant tactics have also had to adapt now that the cover of darkness has slipped from night-time’s shoulders.
Since the first NV devices (NVDs) were deployed during WWII, through to their more widespread use of them during the Vietnam War, NV technology has, to a large extent, overcome the natural limits of human visual sensory perception, with advances and inventions driven rapidly by such conflicts and urgent need. More recent conflicts in Europe and the Middle East have involved troops from many European nations who have found themselves deployed facing a wide variety of threats and enduring extremes of environment, geography and weather; deployed with them have been some of the latest advances in NV tech, from weapon sights, target acquisition devices to night driving aids, and more. NV is a field that is continually evolving in generational increments. But where western nations previously held an advantage with the best NV tech, this position has largely been eroded over the years, though advances are being made to regain a technological lead.
This article looks at the importance of NV with some historical and operational background, the technology behind NVDs, together with some new technological solutions.
Darkness – No Longer a Great Place to Hide
In the mid-1980s, the US Army’s Center of Military History in Washington, DC published ‘Night Combat’, applicable across NATO, which looked back to the night operations of WWII with sentiments that, once tactically prudent in their entirety, have now been surpassed in many ways by NV technologies. A handful of extracts from that publication highlight how important darkness was in the past: “Darkness is helpful in achieving surprise, and the attacker will derive additional advantages from the defender’s inability to aim his fire effectively.” Furthermore, the booklet read: “During two world wars, night and other periods of poor visibility such as fog and snowstorms or rainstorms, gradually came to be considered the ideal time for action. Interference from the air reduced fighting and paralysed movements in daylight hours, with the result that the space between the front and the most remote corner of the rear areas was often empty and deserted. During the hours of darkness combat and movements resumed with new intensity.” Then the text went on to say that “The purpose of movements in darkness or obscurity is to conceal preparations and thereby achieve maximum surprise and effect.
Another important consideration is that night combat keeps the casualty rate at a minimum. Both elements apply to any operation from the time of assembly until its conclusion, whether it is a small unit action or a strategic envelopment. Movement and combat at night are inexpedient when a certain minimum amount of orientation is impossible because terrain conditions and the enemy situation are too uncertain, or when the moon or enemy action create conditions resembling daylight. Bright nights make it easier to conduct night operations, but they give the enemy more opportunity to observe and interfere.”
Well, no matter how good NVDs have become, operating at night remains essential in both defensive and offensive ops, and whether darkness or low visibility due to smoke or weather pose a challenge, infantry and other arms must be able use their weapon sights, head/helmet-mounted NVGs and handheld or tripod-mounted devices, such as monocular scopes for prolonged surveillance to observe, acquire targets and engage an enemy with accurate fire. So, while the above extracts caution ‘bright nights’, moonlight and man-made illumination, and underline the fact that operations have always had to take into tactical account being lit up at night, the only difference between then and now is knowing you are being lit up, or not. Today, the player with the best NV will have the advantage, though just because we now have NV devices to rely on, it does not mean soldiers can forget the basics of night operations’ training. Protecting natural night vision is a key aspect that the NVD-user must be aware of.
For example, adapting one’s eyesight to the dark is crucial if eyes are to perform the best they can at night. Adapting to the dark, the eyes increase their sensitivity to low levels of ambient light, and their ability to see in the dark increases up to a maximum of some 10,000 times after about 30 minutes in darkness. However, as every soldier will know, that sensitivity can be wrecked in an instant by a bright light. Using NVDs/NVGs will also hinder the eyes’ ability in the dark, although, if the eyes are allowed to reach their optimum night vision adaptation before NVGs are worn, then regaining full night vision after removing them will take little more than two minutes.
NVDs, NV goggles (NVGs) and/or night observation devices (NODs) are optoelectronic devices, capable of producing images in very low levels of light approaching total darkness. Some NVDs may work in tandem with an IR illuminator, making them active rather than passive devices, and typical/traditional images – conversions of both visible light and near-infrared (NIR) – have typically been monochrome, some latest systems offer a variety of colour palettes, which enhance target identification possibilities.
From ambient light image intensifiers to advanced, IR thermo-sensors and new white phosphor, 3rd-generation thermal imagers, not only has the choice of NVDs expanded, but so, too, have the operational applications for them grown beyond simply employing such devices for night-time ops; their capabilities now extend into other scenarios, such as ‘low-visibility’ daytime ops, where dust, smoke and poor weather conditions that once reduced the ability of war fighters to see can now be ‘penetrated’ by new NV equipment.
For its part, an image intensifier magnifies the amount of received photons from various natural sources of ambient light, such as starlight or moonlight and is a vacuum-tube based device that can generate an image from a very small number of photons so that a dimly lit scene can be viewed in real-time by the naked eye. When light strikes a charged photocathode plate, electrons are emitted through a vacuum tube that strike the microchannel plate that cause the image screen to illuminate with a picture in the same pattern as the light that strikes the photocathode, with the output visible light brighter than the incoming light.
In active illumination, image intensification is combined with an active source of illumination in the NIR or shortwave infrared (SWIR) band.
Such technologies include low light cameras where active IR NV combines IR illumination in the spectral range between 700–1,000nm, which is just below the visible spectrum of the human eye, with cameras sensitive to this light. The resulting scene is dark to a human observer, but appears as a monochrome image on a normal display device. With active IR NVDs incorporating illuminators that produce high levels of IR light, resulting images are typically higher resolution than are produced by other early generation NV tech. The drawback in today’s military ops is that active IR light can be detected by NVGs and latest NV technologies.
Another type of active illumination is that of laser range gated imaging, which uses a high-powered pulsed light source to illuminate a target, a technique which controls the laser pulses in conjunction with the shutter speed of the NVD camera’s detectors. Single pulse or multiple pulse imaging can provide not only target detection possibilities, but also recognition.
Finally, thermal imaging is where even very small temperature differences/thermal radiation between background and foreground objects can be detected by the NVD; they do not require a source of illumination to produce images in darkness and in moderate weather conditions, such as light fog, rain, and, to an extent, smoke. Thermal imagers use an on-board thermal sensor to detect different amounts of heat energy to generate an image, with vivid colours or contrasting grayscale details representing a very specific, very large data set.
Understanding what these colours and shades represent and learning how to best leverage them in the field allows the user to understand more precisely details about an identified target. Like any digital image, thermal images are made up of pixels, with the number of pixels in a thermal image determined by the optic’s resolution. Higher-resolution sensors generate images with a higher pixel-count and generally produce clearer results. In thermal imaging, each individual pixel represents a specific temperature data point, each of which is assigned a unique colour or shade based on their value, so that as the thermal sensor detects changes in heat energy, it will express this change by adjusting the colour or shade of a pixel. These pre-set gradients, or thermal palettes, determine pixel appearance and help identify different heat sources throughout a scene.
Most user applications focus on qualitative thermal imaging, which looks at the relative presence or absence of heat in a scene, rather than focusing on numeric temperature values. Reliable, qualitative thermal imaging hinges on recognising contrast between targets, objects of interest, and their environment. Detecting body heat or vehicle-engine heat, for example, will be priorities in certain scenarios, and establishing thermal palette preferences allows users to pinpoint heat sources reliably.
That said, training troops in the use of such optics so they understand the equipment’s imaging capability and what different kinds of targets look like in the field will be crucial to ensure their rapid understanding of what they are seeing under fire. Practice will ensure they can interpret and identify accurately what they see and act with the right response, and because users typically interpret thermal images differently, practice and personal experience will help soldiers under the stress of battle to resolve specific situations and images correctly. And current thermal imaging devices can offer to display the scene in a variety of different thermal palettes, whichever is chosen for a particular op, environment or personal preference. The most commonly used palette is ‘White Hot’ and displays warmer objects in white and cooler objects in black. Such greyscale palettes offer simplicity for scenes with a wide temperature span and generate images with realistic details. The versatility of White Hot makes it appealing for use in shifting landscapes and urban areas. A Sepia palette applies a warm, golden hue to the White Hot palette for reduced eye and mental fatigue and is ideal for instances of prolonged thermal surveillance where Sepia’s narrow visual spectrum keeps users comfortable during long viewing periods. Other palettes range from Rainbow High Contrast suited to identifying targets with only slight temperature differences to the ambient, to Outdoor Alert, which is optimised for night-time, body-heat detection, as well as general-purpose palettes for quick ID of thermal anomalies.
How NV systems have advanced is highlighted by some recent innovations by leading optronic players. Elbit Systems, for example, launched its SmartNVG last autumn, which is a C2 add-on to most existing NVGs and provides superimposed augmented reality navigation and operational symbology on any vision imaging system. This significantly improves the effectiveness of night operations and is compatible with common operating systems. Elbit is said to be the largest non-US military EO developer and is at the leading edge of NV technologies and applications including image intensification, uncooled and cooled thermal imaging for all bands. Elbit is the parent company of Instro, (part of Elbit’s ISTAR Division), which has participated in various UK MoD vehicle programmes offering low-light, situational awareness camera vision systems.
In a similar timeframe to the arrival of Elbit’s SmartNVG, and adding to its original, small clip-on thermal imager, ClipIR, which provides a fusion upgrade by injecting a thermal image into conventional NVDs, Thermoteknix brought to market its ClipIR XD. This has a 40-degree field of view, but with extended range performance and can take power from integrated helmet systems, reducing overall weight and improving helmet balance by not needing an internal battery. ClipIR XD also has an option for video input, allowing users to view video overlays, such as augmented reality symbology, directly through the NVD. The company has also brought out its CoVid Video Injection Unit, which enables the use of a head-up display (HUD) and to view HUD data covertly for combat operations in complete darkness. CoVid is powered by its host system and weighs less than 50 g when attached to a parent NVD.
With specific targeting for use by special forces, Thales recently introduced its BONIE High Performance (HP) NVG, for which the company collaborated with the French Special Operations Command in its development and together they consider it suited for dismounted, vehicle, marine and airborne freefall operations. The 640 g system provides end users with a wide aperture night vision binocular for effective use under extremely low light conditions. It has a 40° field-of-view with 1× magnification and includes second and third generation image intensifier tubes. It also incorporates an integrated IR illuminator for use in zero light conditions. The device also features an automatic cut-off capability when stowed on a combat helmet, which prevents inadvertent IR attracting the attention of enemy NV systems.
Qioptiq’s recent advancements in NV have been in the areas of image intensification, uncooled thermal and fused surveillance, target acquisition and engagement equipment and include, among several systems, its Kite In-Line (KiL) is a compact Image Intensified Weapon Sight that is mounted on a weapon in front of a magnified day sight. The KiL has particular advantages compared to other similar equipment, in that it offers an excellent range performance-to-weight ratio. The company’s SAKER fused weapon sight for assault rifles and sharpshooter weapon platforms is another innovation, which combines image intensifiere and thermal imaging technologies to deliver enhanced 24 hr capability to the user. Another clip-on solution is Qioptiq’s DRAGON-S (Sniper) thermal weapon sight offering a 24-hour surveillance and target engagement capability for use with a range of optical day-scopes.
Another player at the forefront of NV developments is Photonis, which, actually, makes the intensifier tubes for the new Thales system, mentioned earlier. The company states that simply being equipped with optimised NV gear is not a guarantee for success in the wide variety of terrains that will be encountered by the modern combatant, and troops must be prepared for ops in many different theatres. In terms of NV systems, an important measure of performance is said to be the Figure of Merit (FOM) number for intensified NV equipment and the company has, in recent years, developed what it says to be a fourth-generation NV standard for such multi-mission deployments, one that not only offers the highest FOM, but also an extended spectral range, fastest and highest auto gating resolution and smallest halo. The halo effect is when a bright light source comes into the NVD’s view, the entire night vision scene, or parts of it, becomes much brighter, and this can ‘white out’ other objects within the field of view. It’s also important that latest NV tech takes the spectral range into account. The colour spectrum of the night can widely vary; sometimes, during a moonless night, for example, it can be predominantly IR when there is night glow. The sky is otherwise predominantly blue. A wide spectral range that includes blue and UV sensitivity is therefore important, not just for better contrast of camouflage, but also to see in the many nights where blue dominates the night spectrum. The latest Photonis fourth-generation image intensifiers are said to be optimised for these modern-day multi-mission deployments.
The companies and recent product developments across the NV and optics sector are too many to mention here and the above few have been selected for no specific reason. Image intensifier systems have been regarded as the standard NV tech for hand-held and helmet-mounted devices for years now, with thermal imaging devices becoming more readily available for both hand-held and weapon-mount applications more recently, particularly as size, weight and power reductions have improved. And real-time fused systems that combine more than one imaging technology – image intensification, thermal imaging, and day scopes – are now increasingly entering the picture and practical experience is highlighting the 24-hour tactical benefits provided by such systems.
Tim Guest is a freelance journalist, UK Correspondent for ESD and former officer in the UK Royal Artillery.