A Night Vision Device (NVD) is an optical instrument that allows images to be produced in levels of light approaching total darkness. They are most often used by the military and law enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system.
Many NVDs also include sacrificial lenses, IR illuminators, and telescopic lenses. Night vision devices were first used in World War II, and came into wide use during the Vietnam War. The technology has evolved greatly since their introduction, leading to several "generations" of night vision equipment with performance increasing and price decreasing. The US Army Night Vision and Electronic Sensors Directorate (NVESD) determines specific night vision device classifications from Gen 0 to Gen 3.
Night Vision Device Classifications
Generation 0 (GEN 0)
Generation 0 night vision devices use an active infrared light source to illuminate targets, and were first used during World War II by snipers and tanks of the German Army, with parallel developments by the United States. Their image intensifier tubes function using an anode and an S-1 photocathode, made primarily of silver, cesium, and oxygen to accelerate the electrons.
Generation 1 (GEN I)
First generation passive night vision devices were an adaptation of GEN 0 technology enhanced to rely on ambient light instead of an active infrared light source (which could be detected), and were first introduced during the Vietnam War.
Using an S-20 photocathode, their image intensifiers produce a light amplification of around 1000x, but are considered bulky and require moonlight (approximately 0.1 lux) to function properly.
Generation 2 (GEN II)
Second generation night vision devices feature an improved image-intensifier tube utilizing micro-channel plate (MCP) with an S-25 photocathode, resulting in a much brighter image than in earlier models, especially around the edges of the lens. This leads to increased illumination in low ambient light environments, such as moonless nights. Light amplification is around 20,000x. Also improved were image resolution and reliability.
Later advancements in GEN II technology brought the tactical characteristics of "GEN II+" devices (equipped with better optics, SUPERGEN tubes, improved resolution and better signal-to-noise ratios) into the range of GEN III devices, which has complicated comparisons.
Generation 3 (GEN III)
Third generation night vision devices utilize the micro-channel plate from Generation 2, but now use a photocathode made with gallium arsenide, which further improves image resolution. In addition, the MCP is coated with an ion barrier film for increased tube life (in the 20,000-active-hours range). The light amplification is also improved to around 30,000-50,000x.
The US Army Night Vision and Electronic Sensors Directorate (NVESD) is part of the governing body that dictates the name of the generation of night vision technologies. Although the recent increased performance associated with the GEN-III OMNI-VII components is impressive, the US Army has not yet authorized the use of the name GEN-IV for these components.
GEN-III OMNI-VII devices can differ from standard Generation 3 in two important ways. First, an automatic gated power supply system regulates the photocathode voltage, allowing the NVD to instantaneously adapt to changing light conditions. The second is a removed or greatly thinned ion barrier, which decreases the amount of electrons that are usually rejected by the Standard GEN III MCP, hence resulting in less image noise and the ability to operate with a luminous sensitivity at 2850K of only 700, compared to operating with a luminous sensitivity of at least 1800 for GEN III image intensifiers. The disadvantage to a thin or removed ion barrier is the overall decrease in tube life from a theoretical 20,000 hrs mean time to failure (MTTF) for Gen III type, to 15,000 hrs MTTF for GEN IV type. However, this is largely negated by the low numbers of image intensifier tubes that reach 15,000 hrs of operation before replacement.
It is important to note that while the consumer market classifies this type of system as "Generation 4", the United States military describes these systems as Generation 3 Autogated tubes (GEN-III OMNI-VII). Moreover, as autogating power supplies can now be added to any previous generation of night vision, "autogating" capability does not automatically class the devices as a GEN-III OMNI-VII, as seen with the XD-4. Another point to note is that any postnominals appearing after a Generation type (i.e.: Gen II +, Gen III +) do not change the generation type of the device, but instead indicates an advancement(s) over the original specification's requirements.
What is a Thermal Imaging Device?
A thermal imaging device gives the ability to see targets in darkness or smoke. During an interview at the International Robots & Vision Show, Dr. Austin Richards (Indigo Systems) stated that thermal imaging is a technology that creates a photographic image or video sequence of light emitted by an object at terrestrial temperatures. Infrared thermography is not the same as night vision. Night vision operates on the principle of light amplification, so in a totally dark environment light amplification would yield no image whereas a thermal imager would.
Where Did Thermal Imaging Devices Originate From?
Thermal imaging devices were first developed for military purposes. According to Bullard Thermal Imaging, "In the late 1950s and 1960s, Texas Instruments, Hughes Aircraft, and Honeywell developed single element detectors that scanned scenes and produced line images. These basic detectors led to the development of modern thermal imaging."
Uses for Night Vision and Thermal Vision:
Night Optics vision devices and thermal vision devices are primarily utilized for officer and war fighter safety, special forces operations, patrolling, critical infrastructure protection, land/air/sea surveillance, building entry, port and border security, airport security, search and rescue, aviation, criminal investigation, wildlife observation, wildlife management, camping and boating. They are primarily sold to the U.S. military, as well as local and federal law enforcement agencies, government agencies, international U.S. allies, homeland security forces, and commercial end-users.