Calculate a spectrum with high spectral resolution using an importance sampling method (Emde et al., 2011).
The spectral variation of Rayleigh scattering and molecular absorption is fully included as well as 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.
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.
Emde, C., Buras, R., & Mayer, B., (2011), "ALIS: An efficient method to compute high spectralresolution polarized solar radiances using the Monte Carlo approach." J. Quant. Spectrosc.Radiat. Transfer. Vol. 112, pp. 1622‒ 1631.