Transparency of the Earths Atmosphere

Our atmosphere is not transparent to all wavelengths of the electromagnetic spectrum. Absorption in the Earth s atmosphere occurs by different molecules. 

There are only two windows where the atmosphere becomes transparent to electromagnetic radiation. The so called optical window comprises the whole range of visible light (400-700 nm) and is in the range from 300 nm (this corresponds to the UVC band) to around 1100 nm. As it is shown below, there exist several small windows in the IR. 

The radio window ranges from about 1 cm to about 11m wavelengths. 

A schematic representation of absorption in the IR and Radio domain is given in Fig. 9.1. This figure illustrates the relatively small domain of visible radiation. 

Water and NH3 absorb at wavelengths 8 pm, gases like CO2 or CH4 absorb at longer wavelengths. Bands in the IR are listed in Table 9.1. 

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