How it works?
In the most basic of terms, thermal imaging allows you to see an object’s heat radiating off itself. Thermal cameras are equipped with “detectors” that record the level of radiation emitted from the surface of an object. The radiant energy passes through the optics of the camera and the detectors converts this energy into an electrical output from each detector pixel. The electronic output is displayed as a two dimensional image usually on an LCD viewing screen although some cameras also have a viewﬁnder.
Specialised thermal imaging cameras use focal plane arrays (FPAs) that respond to longer wavelengths (mid- and long-wavelength infrared). The most common types are InSb (Indium Antinomic), InGaAs (Indium Gallium Arsenide), HgCdTe (Mercury Cadmium Telluride) and QWIP (Quantum Well Infrared Photodetector) FPA. The newest technologies use low-cost, uncooled microbolometers as FPA sensors. Their resolution is considerably lower than that of optical cameras, mostly 160×120 or 320×240 pixels, up to 1280 x 1024 for the most expensive models. Thermal imaging cameras are much more expensive than their visible-spectrum counterparts, and higher-end models are often export-restricted due to the military uses for this technology. Older bolometers or more sensitive models such as InSb require cryogenic cooling, usually by a miniature Stirling cycle refrigerator or liquid nitrogen.
The thermal imaging camera would next employ a series of mathematical algorithms. Since the camera is only able to see the electromagnetic radiation that is impossible to detect with the human eye, it will build a picture in the viewer and record a visible picture, usually in a JPG format.
The presented image is called a “Thermogram” and it displays the energy levels as either Black & White (Grayscale) or series of false colours, as a two dimensional image. Most cameras offer a selection of different colour palettes that may best suit a particular application. Some thermal cameras use a grayscale instead. Police helicopters, for instance, use a greyscale to make suspects stand out.
The features and price of a thermal camera is greatly dependent on its speciﬁcations, in particular, the number of detectors built-in. Entry-level models typically offers 160 x 120 pixels, the higher end models – equipped with 1280 x 1024 pixels. The choice of using a thermal camera depends greatly on the area of the intended application and in all practicality – the budget for such an acquisition.