ABSTRACT
William Herschel (1738-1822) in 1800, the discoverer of the planet
Uranus, got to know the heating effect in sunlight that occurred
beyond the red end of the visible spectrum and understood its
importance (Herschel, 1800). He called the region the thermometric
spectrum, the term infrared (IR) being coined later (Krus et al.,
1962; Liu et al., 2007). The IR-radiation extends from the red
edge of the visible spectrum at ∼0.70 nm to 1 mm (beyond which microwave region commences). The IR is, in general, is divided into
five subregions (Byrnes, 2009), such as (i) near-IR (0.70-1.4 μm),
(ii) short-wavelength IR (SWIR; 1.4-3.0μm), (iii) mid-wavelength IR
(MWIR; 3.0-8.0 μm), (iv) long-wavelength IR (LWIR; 8.0-14.0 μm),
which provides a better penetration through smoke, smog, dust,
water vapor, etc., and (v) very long-wavelength IR (VLWIR; 20.0-
1000.0 μm).
