Digital Night Vision
Digital night vision is a newer consumer technology
that gives results similar to Starlight technology with some
additions and advantages. The positive side is that this technology
can give results that are comparable to earlier Generation 1
devices at less cost and without the distortions inherent in
Generation 1 “Starlight technology” night vision.
The negative side is that this is about the extent of its capabilities.
It does not compare to Generation 2 or later Starlight technology
devices. Digital night vision also has a significantly reduced
range. Even some of today’s Generation 1 night vision
devices will often outperform these devices when viewing beyond
reasonably close distances.
The technology for this type of night vision is quite
different from standard night vision and generally works like
this. The light comes into the device through an objective lens
and is then processed through a highly sensitive charged coupling
device (CCD) and then sent to a Liquid Crystal Display (LCD)
where you can view the image. This can vary a bit and there
might be an eyepiece to look into to view the output rather
than a LCD screen. If you are trying to remain undetected by
whom or what you are viewing, the eyepiece devices are preferable,
as they will not illuminate your face as an LCD will. As with
standard night vision devices, you are not looking directly
at an amplified image but rather a processed and recreated image.
Some digital video cameras have a "0 Lux" mode that
works essentially the same way.
One great advantage of Digital Night Vision is that
you can also look through these devices in the daylight without
the concerns of damaging it. They are similar to Generation
1 night vision devices in that they only amplify available light
and require an IR illuminator to see in dark areas. Most digital
night vision devices are equipped with IR diodes (a bank of
small IR lights). They also often come with multiple filters
so that the image can be viewed in shades of green, red or gray.
The green filters give you the greatest image contrast and detail
and appear similar to standard night vision devices. Red filters
are used to preserve your own night vision (like using a red
light to view star charts so your eyes don’t take such
a long time to readjust to the darkness). The gray or neutral
filter minimizes the amount of light to your eyes and appears
somewhat like a black and white display.
Thermal-Imaging
“Thermal-Imaging Night Vision” is much
different than what we have looked at with light amplification
devices. We will only briefly define these types of devices
since many people confuse standard night vision devices with
thermal-imaging abilities. At this point, the technology starts
at about $10,000 which is generally cost-prohibitive for most
consumers. Recent advances in technologies might bring new thermal-imaging
devices into the $1000 range very soon.
Thermal-imaging devices look at heat, not visible
light. Unlike image-intensifiers, they are unaffected by smoke
or fog and they can be used in absolute darkness since they
are not dependant on visible light. They have infrared-detectors
that are sensitive to the invisible infrared portion of the
electromagnetic wave (heat). All objects emit heat or infrared
radiation. Thermal-imaging devices have infrared-detector elements
that see this portion of the spectrum only. The image is usually
seen as a gray-scale view contrasting with image-enhancement
technology that is viewed in green scale (that eerie green view).
Some of the more expensive models even display the resulting
views in color on small screens. Color representations or images
are called thermograms. By convention the cooler colors are
represented by blacks, blues and greens. Whites, reds, and yellows
represent the warmer colors.
Detail in thermal-image viewing is also very different
since you are looking at heat differences and not at light reflecting
off surfaces that give you the shadows and details we are accustomed
to seeing with visible light. Other details that are not seen
in visible light are apparent when looking through a thermal-imaging
device. Since we are looking at heat, after leaning against
a wall with your hand, looking through a thermal-imaging device
you would see a hand print on the wall. Even the wall itself
might show the internal studs as a slightly different color
since the part of the wall where the studs are attached is slightly
denser and subsequently heats and cools at a different rate.
Freshly painted areas would be a slightly different color or
freshly dug holes in the ground show up visually, whereas in
daylight these details are invisible to your eyes. These types
of details make thermal-imaging devices very applicable to law
enforcement type of uses.
Thermal-Imaging designs
Thermal-Imaging devices come in two basic designs:
cooled and uncooled. The cooled versions are much more expensive
and more susceptible to damage. The elements in cryogenically-cooled
systems are also much more sensitive. By cooling the elements
these systems can have incredible resolution and sensitivity.
They can “see” as little as 0.2ºF differences
in temperature at more than a 1000 feet away. The elements in
the cooled system are sealed and kept at a constant temperature
below 32ºF.
Uncooled devices are much more common and durable…
although these are all electronic devices that must be handled
with a reasonable level of care. In uncooled thermal-Imaging
devices the infrared-detector elements are contained in a unit
that operates at room temperature. The devices are completely
quiet, have built in batteries, and activate immediately.
How Thermal-Imaging Works
The basic operation of a thermal imaging device
is a five-step process:
- A special lens focuses the incoming infrared radiation (heat
given off from all objects) of the objects in the view.
- The focused radiation is scanned by a “phased array”
of infrared detectors. Thousands of points and heat readings
for the field of view are collected in only one thirtieth of
a second. The detector elements create a very detailed “temperature
map” called a thermogram.
- The thermogram created by the infrared detector elements
is translated into electric impulses.
- The electric impulses are sent to a circuit board, called
a signal-processing unit, which has a dedicated chip for translating
the electric impulses into data for the display.
- The signal-processing unit sends the data to the display,
where it appears as various colors or shades depending on the
temperature of the infrared emission. The image is created from
the combination of all the impulses from all of the elements.
Conclusions
- Digital night vision devices, like standard
night vision devices, require available light to amplify.
They have a shorter range than standard night vision devices
but lack the distortions that are found in Generation 1 night
vision.
- You can use digital night vision devices in
the daytime without concerns of damaging the elements like
with standard night vision devices.
- Thermal-imaging devices look at the invisible
heat being radiated from all objects and require no light
at all to operate.
- Since thermal-imaging devices do not "look"
at visible light they can be used in any condition of lighting.
The view is different than with light-amplification devices
and things like shadows, reflections, and shades that we are
accustomed to seeing in the light do not show up with thermal-imaging.
- New technologies may bring thermal-imaging
devices onto the market at much more reasonable and affordable
prices.
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