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Low-Light Cameras (Part Ⅱ)
Hayden Hsu 2008/7/30

In the second part of this article, we introduce another hot technology — thermal imaging, which also gets popular in the low-light cameras.

In the second part of this article, we introduce another hot technology — thermal imaging, which also gets popular in the low-light cameras.

Thermal Imaging Technology

Contrary to other technologies that need at least a small amount of light to produce images, thermal imaging needs no light at all. It produces clear images in total darkness, in all weather conditions. "The interest for thermal imaging cameras is growing and the market is growing every year," said Christiaan Maras, Marketing Manager Eurasia, FLIR Systems. "More and more security professionals are discovering the benefits of thermal imaging. It increases situational awareness and there are no maintenance costs involved."

Market leader FLIR Systems produces a range of thermal imaging camera systems, with low power consumption and cooled or uncooled detectors. Some systems can detect a man-sized target at a distance of about 100 meters away, while others are capable of detecting a man at a distance more than 15 kilometers away.

Thermal imaging cameras are being installed for a wide variety of applications. Installations can be seen at borders, ports, airports, nuclear plants, petrochemical installations and warehouses.

Cooled versus Uncooled

There is a difference between how far one can see with a cooled and with an uncooled thermal imaging camera. Cooled camera systems are more expensive, but generally have a longer range than uncooled ones under many conditions. "A typical cooled camera has a 15-micron pixel pitch (spacing between pixel centers). With a 500-millimeter lens and 0.75-meter critical dimension, a man will subtend 12 pixels at a range of 2.1 kilometers," explained Maras. "The conclusion to be drawn from this sample calculation is that identification of a man at multi-kilometer ranges requires a lens in the 500-millimeter focal length range."

Now take the case of an uncooled sensor, which has inherently less sensitivity than a cooled one with comparable optics and bigger pixels. A typical uncooled sensor has a 38-micron pitch. This increased pixel size shortens the 500-millimeter lens identification range to 0.8 kilometers, said Maras. "The lesson to take home is that extremely long range thermal imaging applications are best served by cooled camera systems. This is particularly true in humid atmospheric conditions."

Atmospheric Conditions

Although thermal imaging cameras can see through total darkness, light fog, light rain and snow, the distance they can see is affected by these atmospheric conditions. Even in clear skies, inherent atmospheric absorption places limits on how far a particular IR camera system can see. "In essence, the farther an IR signal must travel from the target to the camera, the more of that signal is lost along the way," said Maras.

Rain and fog can limit the range of thermal imaging systems due to light scattering caused by droplets of water. There are different types of fog, and some fogbanks are denser than others because water droplets have grown bigger through accretion. "A thermal imaging camera will have more difficulty seeing through dense fog, and its range will be reduced. The same goes for heavy rainfall and snow," said Maras. Additionally, rain can reduce contrast because it will cool the surfaces of targets. "Despite degraded performance in fog, rain and snow, thermal imaging cameras will allow operators to see targets farther than is possible with visible-light imaging systems."

Rise to the Challenge

Is pricing still an issue? One of the hardest things to do today is market education. Some potential users do not know about available technologies or the costs associated with them, said Maras. "Our experience has proved that they discover the power of thermal imaging and its price, they become very enthusiastic and install thermal imaging practically immediately."

What has helped tremendously in the past couple of years to increase the popularity of thermal imaging is price. "Unfortunately, not everyone is aware of this. While people are thinking that a thermal imaging camera is expensive, FLIR offers a thermal camera for less than $4,700," Maras said. Cameras incorporating the TriWave technology are expected to sell in the $5,000 to $8,000 price range.

Another application is driver vision enhancement. BMW installs thermal imaging cameras as an option in its 7-, 6- and 5-series models. Images are projected on an LCD on the dashboard; drivers can see up to fives times farther than with headlights, enabling them to spot other vehicles, curves, pedestrians and animals in harsh conditions.

More Information

Low-Light Cameras (Part I)

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