Abstract

The description of atmosphere monitoring using methods of electromagnetic radiation absorption in the Terahertz (THz) region is the main topic of this chapter. The absorption in THz region is due mainly to intense rotational transitions of the water molecules. THz radiation is the electromagnetic spectrum with the frequency defined from 0.1 to 10 THz (1 THz=10¹² Hz). This spectral range corresponds to a wavelength between 30 ?m and 3 mm. Terahertz frequencies lay between the operation ranges of classical microwave and infrared spectroscopy and thus cannot be effectively covered by any of these techniques. Significant progress in the development of THz spectroscopy has been achieved only in the last 30 years, when suitable for use sources and detectors of THz radiation have been developed.