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Infrared thermography (IRT), thermal imaging and thermal video are examples of infrared imaging science. Thermographic cameras usually detect radiation in the long infrared range of the electromagnetic spectrum (approximately 9,000-14,000 nanometers or 9-14 μm) and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects with a temperature above absolute zero according to the law of black body radiation, thermography allows to see the environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore, the thermography allows to see variations of temperature. When viewed through a thermal imaging camera, warm objects stand out well against colder backgrounds; humans and other warm-blooded animals are easily visible against the environment, day or night. As a result, thermography is particularly useful for military and other surveillance camera users.

Some physiological changes in humans and other warm-blooded animals can also be monitored with thermal imaging during clinical diagnosis. Thermography is used in the detection of allergies and veterinary medicine. It is also used for breast screening, though mainly by alternative professionals, as it is much less accurate and specific than competing techniques. Government and airport personnel used thermography to detect suspected cases of swine flu during the 2009 pandemic.

Thermography has a long history, although its use has increased dramatically with the commercial and industrial applications of the last fifty years. Firefighters use thermography to see through smoke, to find people, and to locate the base of a fire. Maintenance technicians use thermography to locate overheating joints and sections of power lines, which are a sign of impending failure. Building technicians can view thermal signatures that indicate heat leaks in faulty thermal insulation and can use the results to improve the efficiency of heating and air conditioning units.

The appearance and operation of a modern thermal imager is often similar to a camcorder. Often, the live thermogram reveals temperature variations so clearly that a photograph is not necessary for analysis. Therefore, a recording module is not always built-in.

Unspecialized CCD and CMOS sensors have most of their spectral sensitivity in the wavelength range of visible light. However, using the "drag" area of ​​its spectral sensitivity, ie the part of the infrared spectrum called near infrared (NIR), and using a closed-circuit camera, it is possible in certain circumstances to obtain true thermal images of objects with temperatures of approximately 280 ° C (536 ° F) and higher.

Specialized thermal imaging cameras use focal plane matrices (FPAs) that respond to longer wavelengths (medium and long wavelength infrared). The most common types are InSb, InGaAs, HgCdTe and QWIP FPA. New technologies use low-cost and non-cooled microbolometers as FPA sensors. Its resolution is considerably lower than that of optical cameras, mostly 160x120 or 320x240 pixels, up to 1024 × 768 [3] for the more expensive models. Thermal imaging cameras are much more expensive than their visible spectrum counterparts, and high-end models often have export restrictions due to military uses of this technology. Older bolometers or more sensitive models like the InSb require cryogenic cooling, usually by a miniature Stirling cycle cooler or liquid nitrogen.