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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. The first thing you probably think of when you
see the words 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. And you may have wondered "Do those things really
work? Can you actually see in the dark?" The answer is most definitely yes.
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.
Here's how thermal imaging works: A special lens focuses the infrared light emitted by all
of the objects in view. 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.
The thermogram created by the
detector elements is translated into electric impulses. 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.
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.
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