Image Intensifiers — The Key to Night Vision

Image intensification is the basis of night vision, and devices for increasing visibility in the dark are the key to night fighting capability

Issue: 3 / 2019By Lt General Naresh Chand (Retd)Photo(s): By US Army
A US soldier with night vision goggle called the Enhanced Night Vision Goggle-Binocular or ENVG-B

It has always ben the dream of all armies to be able to carry out operations by day and night in all weather conditions. It was during World War II and the Korean War that the development of image-intensification technology began to help the snipers to engage their targets at night or in bad weather conditions.

Image intensification is the basis of night vision, and devices for increasing visibility in the dark are the key to night fighting capability.

Image Intensifier

How it works? Image intensifier is a device for increasing the intensity of existing light in the environment for an optical system to enable to operate in low-light conditions. These conditions could be night; light from fluorescence of materials in X-rays or gamma rays; for conversion of non-visible light sources such as near-infrared or short wave infrared to a visible image. Simply explained-the image intensifier is a vacuum tube in which image intensification is achieved by a complex conversion of energy particles. The system works by collecting photons through an objective lens which are then converted into electrons through a photocathode. Their electrical energy is then increased by a device called micro-channel plate (MCP) which is then converted back into light through a phosphor screen (that is why the image appears greenish in colour) and the final image can be viewed through an eyepiece lens. Photon is a particle representing a quantum of light or other electromagnetic radiation. The system is provided power with a sophisticated miniaturised power supply system. MCP is a key component where the electron amplification takes place. It is a thin disc that contains millions of densely spaced channels. When the electrons pass through these channels, they are multiplied manifold and strike the phosphor with greater energy which is thousands time brighter than the original image picked up in less/no light conditions.

Development in Image Intensifier Technology. Early snipers used image converters (sniperscopes) that required an infrared light source to illuminate their target and is now called Generation (Gen) 0. Further development took place when the starlight scope was developed during the early 1960s which used three improved image-intensifier tubes which produced a clear centre image with a distortion at the periphery. This was called Gen One. Gen Two was developed in the late 1960s with a major breakthrough with the development of the MCP. The photocathode process was further refined with the S-25 cathode resulting in much higher photo response. The size and weight was also reduced which enabled them to be used with head- and helmet-mounted goggles. In the mid-1970s, advance photocathode technology was developed in Gen 3 which increased the tube’s sensitivity dramatically; particularly in the near-IR region. This resulted in longer ranges for the system. However the process of development is work in progress. Some key developments are miniature highvoltage power supply system and increasing the reliability in excess of 15,000 hours without much degradation.

PHOTONIS has developed INTENS image intensifier tube which enables night vision capabilities in dark military mission conditions such as deep mountain valleys and jungle terrain. The tube offers bandwidth sensitivity from 400-1,000 nano metre and provides a 40 per cent increase in detection, recognition, and identification (DRI) over previous tubes. INTENS is equipped with an Auto-Gating power supply for operations in dynamic light conditions, a high-contrast green P22 phosphor and a signal to noise ratio of 30. The INTENS tube has an operational lifetime of over 10,000 hours.

ITT has developed a new high-performance image intensifier called Pinnacle for use in existing aviation and ground night vision systems. Pinnacle provides substantial performance increases in low light detection, high light resolution and intra-scene dynamic range (the ability to see detail in dark areas of a scene where bright cultural lighting is present. The new Pinnacle intensifier can be used in all aviation and ground systems that currently accept 18mm image intensifiers. The improved performance is possible due to a new high-performance MCP, a newly designed gating power supply and improved manufacturing process.

Thermal Imaging Technologies

Thermal Imaging (TI) is not related to image intensification but enables night vision. It does not rely on existing light through which the human eye can see a image but detects objects based on heat emitted by them. The warmer the object, the more infrared longwave light it radiates and the more detectable it is. However it does not have high resolution of the image as compared to image intensifier of the similar field of view. A special lens focuses the infrared light emitted by all of the objects in view which is scanned by infrared-detector elements which in turn form a detailed temperature pattern called a thermogram. The detector array works very fast and obtains the temperature information in about one-thirtieth of a second to make the thermogram. The thermogram is translated into electric impulses which are then converted into display data where it appears as various colors depending on the intensity of the infrared emission. There are two common types of thermal-imaging devices which are Un-cooled and Cryogenically cooled. Uncooled is the most common TI device which can operate at room temperature, is completely quiet and activates immediately. However there have been critical developments in uncooled thermal imagers with the use of vanadium oxide and amorphous silicon which have made them suitable for headmounted applications. Cryogenically cooled is more expensive but has an incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can discern a difference as small as 0.1 C from more than 300m away.

Combination of Image Intensifiers and Thermal Imagers

Night vision devices would become more effective if the image intensifier and the thermal imager is combined to bring out the best attributes of both. Earlier the thermal imagers had greater size, weight and power (SWaP) consumption thus it was not practical to use them in user mounted applications like night vision goggles (NVG). However advances in recent years with uncooled thermal imagers have greatly improved these features making them more suitable for head-mounted applications. This has resulted in Sensor Fusion.

Sensor Fusion. Sensor fusion combines the respective strengths of image intensifier and thermal imaging technologies into one device. Such a combination enables a user to view a much greater part of the light spectrum which can span from visible to nearinfrared to long-wave infrared. Thus the user can view the information from both the visible and thermal spectrums through a single device which gives him a greater advantage while carrying out military, security and law enforcement duties. This type of sensor fusion has led to the development of new night-vision technologies and devices like the enhanced night-vision goggle (ENVG) that combines a thermal imager with an image intensifier. The image intensifier works like a standard NVG in this system but image from the thermal sensor is through a video display. Both the inputs are then optically overlaid to provide a fused image. Developments are on to combine the video output of a thermal imager directly with the video output of an electronic output image intensifier. These new devices would then display a complete digitally fused image through HMD (head-mounted/helmet display) in a device known as the digitally enhanced night-vision goggle (ENVG-D).

Harris’ AN/PVS-14 Monocular Night Vision Device. AN/PVS-14 is designed for use by the individual soldier in a variety of ground-based night operations. It features the superior performance of the Gen 3 F9815 image intensifier tube with a variable gain control to achieve an optimum balance in the images seen by both eyes. For weapon firing, the AN/PVS-14 can be mounted on a MIL-STD-1913 weapon rail behind a standard collimated dot sight.

The Knight Vision PVS-22 Clip-On Night Vision Weapon Sight. PVS-22 uses the latest high performance Gen 3 intensifier tube in a proven design, where the catadioptric lens (refraction and reflection are combined in an optical system) provides high performance light collection with an effective f/1.2 in a light weight optic. The PVS-22 Weapon Sight is appropriate for front line rifles such as the M4 Carbine, M16A2/A4, M249, M14, and day sights with magnification up to 10x.

Night Vision Devices’ MINI BNVD AA 18mm. MINI BNVD AA 18mm is Dual Tube Night Vision Goggle with Single Gain Control. With a system weight of about 440 gm, the MINI BNVD is the lightest fully functional dual tube goggle in the world, which utilises 18mm Gen 2/3 Image Intensifiers and includes important features such as a fully focusing eyepiece and a focusable IR Illuminator.

Enhanced Night Vision Goggle-Binocular (ENVG-B) Programme

To operate more effectively at night, US Army has given $391.8 million three-year contract to L-3 Insight during May 2018 for the ENVG-B. The ENVG family represents helmet-mounted night-vision goggles that blend image intensification and long wave infrared sensors for combat at night, in bad weather, and in smoke and dust. ENVG III weapon sights also has a improved resolution and a wider field of view which enables rapid target acquisition.

Combination of ENVG III and Family of Weapons Sights-Individual (FWS-I) technology

The FWS-I, when mounted on a soldier’s weapon, will transmit its sight picture through radio to the ENVG III, which is mounted on a soldier’s helmet. The FWS-I can mount these rifles in front of day sights that have already been bore-sighted. The ENVG will combine thermal imaging with image intensification technology. A variety of modes will allow soldiers to see in their goggles only the image from the ENVG III itself, only the image from the FWS-I, or a combination of the two. Using a ‘picture-in-picture’ mode, the image from the FWS-I is displayed at the bottom right of the image that is coming from the goggle. This combines the rapid target acquisition technology and can be effectively be used for surveillance, aiming weapons during daylight, darkness, adverse weather and dirty battlefield conditions. This system should be with the US Army by the first quarter of 2019.