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Thermal-Imaging & Digital Night Vision


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:

  1. A special lens focuses the incoming infrared radiation (heat given off from all objects) of the objects in the view.
  2. 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.
  3. The thermogram created by the infrared detector elements is translated into electric impulses.
  4. 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.
  5. 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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