Night Vision Gyaan

What is it?

A high-precision optical instrument which makes use of light amplification technique to in order to operate in little or no light environments.

Who dunnit?

Night vision devices or NVDs were first developed by AEG, a German Electric company in 1935 for the German military during World War II. USA Government pitched in around the same time to develop its own version to aid its military. This is believed to be the “GEN 0” (Generation 0) period in night vision technology which utilised the infrared light source to develop active devices.

“GEN I” era during the mid 1960’s saw the use of ambient light to develop rather passive units with image intensifiers producing a light amplification of 1000x.

Later in the 1970’s the “GEN II” devices improved the passive devices to work in much low ambient light like moonless nights with a 20 times improved magnification capability.

“GEN III” devices developed in the 1990’s brought in much better resolution and sensitivity and magnification factor increased by a factor of 50 than the original “GEN I” devices.

The present “GEN III+” and “GEN IV” technology brings in much better performance in low as well as high-level light environment. Additionally it provides an improved signal to noise ratio along with seamless adjustment to fluctuating light conditions.

Technology

Night vision technology works in three different ways:

1) Thermal Imaging: Generally we are able to see the visible portion of what the spectrum of light offers but “Thermal imaging” or “Thermography”, is the means by which we can see the infrared portion of the spectrum. This technology in particular exploits the upper portion (3 microns – 30 microns in wavelength) of the infrared light or the “Thermal-IR” band. As we know that light is emitted (in the form of photons) when the electrons in an object are excited to high-energy states created by heating. Thermal-IR band however, accounts for the invisible light (to human eye) emitted by objects owing to their natural heat.

The main tool for this task is a thermographic camera which can pick up electromagnetic waves between 0.9 – 14 microns. The infrared light emitted by objects in view is captured by special lens, scanned using detector elements to create a detailed temperature pattern called “thermogram” and converted to electrical impulses which are finally processed for display in various colours depending upon radiation intensity.

Thermal-imaging devices can again be of two types:-

• Un-cooled: The most common type in which the detector elements can operate in room temperature. It is completely quiet, activates quickly and has a built-in battery.
• Cryogenically cooled: They are typically housed in a vacuum-sealed case and cryogenically coo below zero degrees. They have incredible resolution and sensitivity that result from cooling the elements and hence can sense a temperature difference of the order of 0.1 C from more than 300 m away.

2) Image intensifiers: This method of night vision amplifies the available ambient light to achieve better vision. The device consists of a conventional lens which sends the captured infrared light to an image-intensifier tube. The tube consists of a photocathode which converts the photons into electrons. These electrons further release thousands of other electrons when made to accelerate across micro-channels in a tiny glass disc known as “Microchannel Plate” (MCP) using high voltage. Finally these electrons hit a screen coated with phosphors while maintaining their position in relation to the channel it passed through and hence being in alignment with the original photons. Further the phosphors release photons and create a green image on the screen. This green image is viewed using an ocular lens which allows us to magnify and focus the image.

All image intensifiers operate in the above fashion. Technological differences over the past 40 years have resulted in substantial improvement to the performance of these devices which have categorized them into generations as mentioned above.

3) Active illumination: Active illumination technologies work on the principle of coupling imaging intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band. Examples of such technologies include inexpensive low light cameras.

Applications

Modern Night vision devices work surprisingly very effectively even in complete darkness. From being “GEN 0” devices that only aided the military on the battlefield, they have travelled a long distance of evolution to be used in various arenas like surveillance, wildlife observation, security, navigation, law-enforcement and entertainment. It is still used extensively by the military for that purpose, as well as for navigation, surveillance and targeting. Police and security often use both thermal-imaging and image-enhancement technology, particularly for surveillance. Wildlife photographers and nature enthusiasts use NVDs to maneuver through the woods at night. Detectives and private investigators depend heavily on night vision to track people.. Many businesses have permanently-mounted cameras equipped with night vision to monitor the surroundings.

NVDs are typically used in the form of Scopes (or monoculars), Goggles (or binoculars) and cameras. Infact now days many of the new camcorders have a built-in night vision feature like the Sony DCR-TRV17.

It is interesting to note that an animal's ability to see in low light levels may be similar to what humans see when using first- or perhaps second-generation image intensifiers !!