How Night Vision Works
HOW NIGHT VISION WORKS
Author - C. J. Boedeker - The Night Vision Store & The
Opticstore
http://www.nightvisionstore.com
http://www.opticstore.com
During the history of warfare, operations at night have always
been degraded significantly, if not totally avoided. Typically,
soldiers fighting at night have had to resort to artificial
illumination, e.g., at first fire and later with light sources
such as searchlights. The use of light sources on the
battlefield had the detrimental result of giving away tactical
positions and information about maneuvers. The advent of new
technologies initially in the 1950's and continuing into the
present time has changed this situation. The engineers and
scientists at the Night Vision & Electronic Sensors Directorate
(NVESD) have discovered ways to capture available
electro-magnetic radiation outside that portion of the spectrum
visible to the human eye and have developed equipment to enable
the American soldier to fight as well at night as during the day
in order to "Own the Night".
Image Intensification: Image intensifiers capture ambient light
and amplify it thousands of times by electronic means to display
the battlefield to a soldier via a phosphor display such as
night vision goggles. This ambient light comes from the stars,
moon or sky glow from distant manmade sources, such as cities.
A soldier can conduct his combat missions without any active
illumination sources using only image intensifiers. The main
advantages of image intensifiers as night vision devices are
their small size, light weight, low power requirements and low
cost. These attributes have enabled image intensifier goggles
for head-worn, individual soldier applications and resulted in
hundreds of thousands of night vision goggles to be procured by
the US Army. Research and development continues today on image
intensifiers in the areas of longer wavelength spectral
response, higher sensitivity, larger fields of view, increased
resolution, advanced displays and image fusion.
Night Vision technology consists of two major types: image
intensification (light amplification) and thermal imaging
(infrared). Most consumer night vision products are light
amplifying devices.
Light amplification technology takes the small amount of light,
such as moonlight or starlight, that is in the surrounding area,
and converts the light energy (scientists call it photons), into
electrical energy (electrons). These electrons pass through a
thin disk that's about the size of a quarter and contains over
10 million channels. As the electrons travel through and strike
the walls of the channels, thousands more electrons are
released. These multiplied electrons then bounce off of a
phosphor screen which converts the electrons back into photons
and let you see an impressive nighttime view even when it's
really dark. All image intensified night vision products on the
market today have one thing in common: they produce a green
output image. In the night vision world there are generations
that reflect the level of technology used. The higher the
generation, the more sophisticated the night vision technology.
Generation 0 - The earliest (1950's) night vision products were
based on image conversion, rather than intensification. They
required a source of invisible infrared (IR) light mounted on or
near the device to illuminate the target area.
Generation 1 - The "starlight scopes" of the 1960's (Vietnam
Era) have three image intensifier tubes connected in a series.
These systems are larger and heavier than Gen 2 and Gen 3. The
Gen 1 image is clear at the center but may be distorted around
the edges. (Low-cost Gen 1 imports are often mislabeled as a
higher generation.
Generation 2 - The microchannel plate (MCP) electron multiplier
prompted Gen 2 development in the 1970s. The "gain" provided by
the MCP eliminated the need for back-to-back tubes - thereby
improving size and image quality. The MCP enabled development of
hand held and helmet mounted goggles.
Generation 3 - Two major advancements characterized development
of Gen 3 in the late 1970s and early 1980s: the gallium arsenide
(GaAs) photocathode and the ion-barrier film on the MCP. The
GaAs photocathode enabled detection of objects at greater
distances under much darker conditions. The ion-barrier film
increased the operational life of the tube from 2000 hours (Gen
2) to 10,000 (Gen 3), as demonstrated by actual testing and not
extrapolation.
Thermal Imaging:
Most objects in natural scenes, as well as human beings and
manmade objects emit electro-magnetic radiation in the form of
heat. Thermal imagers or infrared viewers (also known as FLIRs)
gather the infrared radiation and form an electronic image for
the soldier. Since they do not rely on reflected ambient light,
thermal imagers are totally light-level independent. They also
have significant penetration capabilities through obscurants
such as fogs, hazes, and conventional battlefield smokes. There
are two varieties of thermal imaging systems: cooled and
uncooled. Cooled thermal imaging requires cryogenic cooling.
Lower performing uncooled thermal imaging systems require no
detector cooling but have sufficient performance to provide the
low to medium performance required by individual soldier sights,
infantry vehicles, navigation, robotics and missile seekers.
Present research and development in cooled thermal imaging are
pursuing multi-spectral imaging, improved sensitivity and
resolution, and embedded signal processing to aid the soldier in
target acquisition missions. Current uncooled research is
directed at smaller size packages and power consumption with
lower cost and increased sensitivity, resolution and field of
view. Small, palm-sized uncooled thermal imagers are now
available.
About the author:
C. J. Boedeker provides Night Vision equipment and Consulting
for both Professional and Hobbyist applications. He can be
reached at http://www.nightvisionstore.com or
http://www.opticstore.com
posted by nightvisionguy @ 1:26 PM
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