Long wave infrared (LWIR) thermal cameras can turn heat into pictures. Thermal emissions from people, animals, vehicles, or even landscapes appear as “heat signatures” that look like stylized photographs made of colorful blobs. The blobs indicate the relative warmth of the different areas of an object detected by the camera’s sensors.
The Problem of Thermal Noise
Everything, from stars in the sky to insects on the ground, emits heat. Instruments that detect heat can produce inaccurate results when background heat “noise” interferes with “seeing” the discrete heat emitted by the observed object or organism.
LWIR cameras cope with “noise” in two ways: by using detectors called microbolometers or using those detectors together with cooling equipment to eradicate thermal “noise.”
Microbolometers
Microbolometers have specially treated surfaces made of vanadium oxide (Vox) or amorphous silicon (a-Si). When heat strikes these surfaces, the electrons on them become excited. The camera measures the change in surface resistance in each pixel of the excited surface to create an image.
Uncooled Cameras
Most LWIR cameras used for surveillance or security are uncooled. Their microbolometers are sensitive enough to bypass excess thermal noise from the environment, which makes them suitable for outdoor use. The images they create differentiate the heat signatures of living things and inanimate objects, making it possible to trace the movements of people, animals, and vehicles during both daytime and nighttime.
Building engineers and inspectors use uncooled thermal cameras to detect water damage or electrical malfunctions. When electronics aren’t putting out the amount of heat expected during normal operation, building inspectors can pinpoint the problem areas with uncooled LWIR cameras.
Cooled LWIR Cameras
Certain scientific and medical applications require a level of detail that is unattainable with an uncooled LWIR camera. Cooled LWIR cameras contain a “cryocooler” that can lower the sensor temperature to extreme levels, as low as -321° Fahrenheit.
Extreme cold increases the camera’s sensitivity to heat by lowering the temperature far below the thermal “noise” to less than the noise from the area around the object the camera is observing. The sensor can receive minute thermal signals from the target area or object without disruption from the excess heat of surrounding areas or objects.
Cooled LWIR cameras are useful in astronomy to detect the most distant, red-shifted light from faraway galaxies. They perform “spectral filtering” to screen out the heat from flames or chemicals to observe, for example, the behavior of underlying combustibles substances or particles. They are also useful in medical applications, like detecting small abnormalities that wouldn’t be “visible” to an uncooled camera.
Whether you should use a cooled or uncooled LWIR camera depends on the application and the level of detail required for effective results.