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Definition
Night vision is a spy or action movie you've seen, in which someone straps
on a pair of night-vision goggles to find someone else in a dark building on a
moonless night. With the proper night-vision equipment, you can see a person standing
over 200 yards (183 m) away on a moonless, cloudy night. Night vision can work
in two very different ways, depending on the technology used. "
Image enhancement - This works by collecting the tiny amounts of light, including
the lower portion of the infrared light spectrum, that are present but may be
imperceptible to our eyes, and amplifying it to the point that we can easily observe
the image.
" Thermal imaging - This technology operates by capturing
the upper portion of the infrared light spectrum, which is emitted as heat by
objects instead of simply reflected as light. Hotter objects, such as warm bodies,
emit more of this light than cooler objects like trees or buildings.
To
study about night vision technology we should first know about ligt.
The
amount of energy in a light wave is related to its wavelength: Shorter wavelengths
have higher energy. Of visible light, violet has the most energy, and red has
the least. Just next to the visible light spectrum is the infrared spectrum.
Night vision technology consists of two major types: light amplification (or intensification)
and thermal (infrared).
Most consumer night vision products are light amplifying
devices. All ITT Night Vision products use light-amplifying technology. This
technology takes the small amount of light that's in the surrounding area (such
as moonlight or starlight), 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 more than 10 million
channels. As the electrons go through the channels, they strike the channel walls
and thousands more electrons are released. These multiplied electrons then bounce
off of a phosphor screen which converts the electrons back into photons and lets
you see an impressive nighttime view even when it's really dark.
In
night vision, thermal imaging takes advantage of this infrared emission. Thermal
imaging works as
1. A special lens focuses the infrared light emitted by all
of the objects in view.
2. The focused light is scanned by a phased array
of infrared-detector elements. The detector elements create a very detailed temperature
pattern called a thermogram. It only takes about one-thirtieth of a second for
the detector array to obtain the temperature information to make the thermogram.
This information is obtained from several thousand points in the field of view
of the detector array.
3. The thermogram created by the detector elements
is translated into electric impulses.
4. The impulses are sent to a signal-processing
unit, a circuit board with a dedicated chip that translates the information from
the elements into data for the display.
5. The signal-processing unit sends
the information to the display, where it appears as various colors depending on
the intensity of the infrared emission. The combination of all the impulses from
all of the elements creates the image. Types
Of Thermal Imaging Devices
Most thermal-imaging
devices scan at a rate of 30 times per second. They can sense temperatures ranging
from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C), and can
normally detect changes in temperature of about 0.4 F (0.2 C).
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