14
Theory of thermal imaging
14.1
Introduction
The subjects of infrared radiation is still new to many who will use an infrared camera.
In this section the theory behind thermal imaging will be given.
14.2
The electromagnetic spectrum
The electromagnetic spectrum is divided arbitrarily into a number of wavelength re-
gions, called
bands
, distinguished by the methods used to produce and detect the
radiation. There is no fundamental difference between radiation in the different bands
of the electromagnetic spectrum. They are all governed by the same laws and the
only differences are those due to differences in wavelength.
10067803;a1
Figure 14.1 The electromagnetic spectrum. 1: X-ray; 2: UV; 3: Visible; 4: IR; 5: Microwaves; 6: Radiowaves.
Thermal imaging makes use of the infrared spectral band. At the short-wavelength
end the boundary lies at the limit of visual perception, in the deep red. At the long-
wavelength end it merges with the microwave radio wavelengths, in the millimeter
range.
The infrared band is often further subdivided into four smaller bands, the boundaries
of which are also arbitrarily chosen. They include: the
near infrared
(0.75–3 μm), the
56
Publ. No. 1 557 544 Rev. a121 – ENGLISH (EN) – October 6, 2005
