# Homework Help: Radiative Transfer + Emissivity

1. Mar 31, 2010

### nordmoon

1. The problem statement, all variables and given/known data

This isn't so much of a homework but rather I am trying to understand the physics. The solution to the radiative transfer for a isothermal homogeneous gas of layer consists of one part that describes the absorption and one part that describes the emission.

1. What happens to the light scattered? Does this count here?
2. What is emissivity - is this emission?
3. Is light absorbed while it passes throu the gas - does the first term account for this?
4. Can you use the eq. below to simulate the spectra in which both absorption and emission takes place? I am asking because the in the books I have seen they assume strong emitting gas and takes the first term = 0 and for strong absorbing gas and says that emissivity = source function = 0. You can account for both of them?
5. What happens if you have different temperatures in the gas? Do you get a mixture of spectra with different temperatures? Is this a troublesome for diagnostics in which temperatures to be determined? Or does the weaker T blend in the the spectra and you only see the spectra of the highest temperature?
6. What is self-absorption?

2. Relevant equations

I (l) = I(0)exp(-kv N l) + Sv(1-exp(-kv N l)

where Sv is the blackbody, kv absorption coefficient, l is optical length of gas column, N is number of atoms/molecules per volume and I(0) is the intensity before it enters the gas cloud.

3. The attempt at a solution

See above.