Experimental option!!!!
Calculate a spectrum with high spectral resolution using an importance sampling method.  

mc_spectral_is [wvl]

 
The spectral variation of Rayleigh scattering and molecular absorption is fully included as well the spectral variation of aerosol and cloud scattering and absorption coefficients. The spectral variation of the phase matrix is neglected, for all wavelengths the phase matrix of the calculation wavelength is assumed.

Use the optional argument wvl to specify calculation wavelength. If not set, the central wavelength of the selected spectral interval is used.

This method is very efficient for calculations with very high spectral resolution, e.g. simulations for trace gas retrievals, in particular when polarization is required. For more details refer to emde2011. See also mc_spectral_wvl.