What is self and air broadening effects?

[nordmoon]

What is self and air broadening effects? I have read that they appear in atmospheric modelling. Is this pressure broadening?

 

[sylas]

What is self and air broadening effects? I have read that they appear in atmospheric modelling. Is this pressure broadening?

There is a "broadening" in spectral lines of emission of radiation from a gas. This is quite important for remote sensing by satellites with microwave sounders, and also for modeling how radiation interacts with the atmosphere. It is also relevant to study of emission lines in the spectrum from a dense plasma, such as the atmosphere of a star.

For problems relating to how thermal radiation interacts with an atmosphere, the relevant effect is called "pressure broadening" or "collisional broadening"; the collisions between atoms in a dense gas can alter the energy of radiation emission, which broadens the corresponding spectral line. It's a rather horribly complicated effect to model accurately; in fact I understand there is no exact theory to describe the broadening effects of pressure on spectral lines; although there are adequate heuristic descriptions.

Wikipedia gives a brief summary of the kinds of broadening of spectral lines that can occur; and this may help give pointer to where to find more detail from more technical sources of information. See Spectral line broadening and shift within the wikipedia article on "Spectral Line".

A good discussion is also available in http://www.sundogpublishing.com/AtmosRad/index.html, by Grant W. Petty (Published 2006, Sundog publishing). The link goes to a webpage for the book and you can browse the first edition for free. Pressure broadening and doppler broadening are discussed in chapter 9.

Cheers -- sylas