Particle-size-distribution retrieval from backscattered polarized radiation measurements: a proposed method

Equations are derived for estimating the size distribution of particles from measurements of components of the Stokes vector of radiation backscattered from an optically thick, plane-parallel aerosol. A two-step inversion procedure is needed. The inverse (Fredholm) size-distribution procedure utilizes the lowest-order angular moment of the element S44 of the normalized scattering matrix at different wavelengths obtained from an inverse radiative-transfer procedure. This procedure requires time-dependent, backscattered polarized radiance measurements at long and short times after radiation pulses at different wavelengths illuminate the aerosol; the procedure is based on the assumption of azimuthal symmetry in order to obtain an uncoupling of the components of the polarized radiance. If the radiation wavelengths are between 0.3 and 10.6 μm, the procedure will work best if the radii of spherical particles are between 0.04 μm and a few micrometers.