Thermography is a type of infrared imaging. Thermal technology detect radiation in the infrared range of the electromagnetic spectrum and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black body radiation law. The electromagnetic spectrum is the collection of frequencies It’s the distribution of electromagnetic radiation emitted or absorbed by that particular object.
The electromagnetic spectrum extends from below the low frequencies used for radio communication to gamma radiation at the short-wavelength high-frequency covering wavelengths from thousands of kilometers down to a fraction of the size of an atom.