The variable SSA (Single Scattering Albedo) is a dimension-less variable that defines the spectrally-independent ratio between an aerosol scattering and extinction coefficients, thus controling the fraction of aerosol absorption and scattering. Its values range from 0 to 1, with typical aerosol values between 0.85 and 1 (Holben et al., 1998, Hess et al., 1998, Dubovik et al., 2002).
If SSA=-1 (default value), libRadtran will internally use the predefined spectral dependency of the SSA from the aerosol model selected in IHAZE.
Defining a spectrally-constant value of SSA is useful only for monochromatic calculations or in wavelength regions where the optical properties of aerosols can be considered constant, e.g. the ultraviolet range.
Holben, B., Eck, T., Slutsker, I., Tanré, D., Buis, J., Setzer, A., Vermote, E., Reagan, J., Kaufman, Y., Nakajima, T., et al., (1998), "AERONET—A Federated Instrument Network and Data Archive for Aerosol Characterization." Remote Sensing of Environment, Vol. 66, No. 1, pp. 1-16.
Hess, M., Koepke, P., & Schult, I. (1998), "Optical properties of aerosols and clous: the software package OPAC." Bulletin of the Americal Meteorologic Soctiety. Vol. 79, No. 5, pp. 831‒ 844.
Dubovik, O.; Holben, B., Eck, T., Smirnov, A., Kaufman, Y., King, M., Tanré, D., Slutsker, I., (2002), "Variability of absorption and optical properties of key aerosol types observed in worldwide locations." Journal of the Atmospheric Sciences, Vol. 59, pp. 590-608.