Infrared emission spectroscopy

A review is made of the instruments and of the observation modes that are used for the study of the Earth's atmosphere with emission spectroscopy. A short comparison is made between heterodyne and optical techniques and details are provided of the second technique with a few examples of real instruments. The role of Fourier transform spectroscopy is underlined and the rationale associated with the choice of the observation geometry and of the spectral resolution is discussed.