Information content of aerosol optical properties with respect to their size distribution.

The successful retrieval of the aerosol size distribution from solar and sky radiation measurements depends mainly on the information content in the optical parameters chosen for measurement. We systematically discuss how much information the scattering function and the extinction coefficient of the aerosol particles provide about their size distribution. We use a method which allows selection of an optimum set of optical data (i.e., scattering functions and extinction coefficients at certain wavelengths and scattering angles) and determination of the invertible particle radius range. Results applying a numerical inversion algorithm to two types of synthetic optical data are presented. A set of scattering functions at specific wavelengths and scattering angles allows good inversion results in the 0.1-40-microm radius range. A second set, combining scattering functions with extinction coefficients, is sensitive to inaccuracies in the refractive index assumed for the inversion, although they do have a slightly larger invertible particle radius range, from 0.08 to 40 microm. Useful inversion results can be obtained even with statistical errors up to 8% in the experimental data.