Since most solid particles in the Earth and planetary atmospheres have
irregular shapes, quantifying the effects of particle nonsphericity o
n the results of remote sensing of the atmosphere is an important prob
lem. In this paper, we perform a general theoretical survey of linear
polarization of light scattered by polydisperse, randomly oriented, ro
tationally symmetric particles of size comparable to the wavelength of
radiation. Our paper deals with polydispersions of nonspherical parti
cles because (1) averaging light-scattering characteristics over sizes
provides more realistic modeling of natural particle ensembles and (2
) comparisons of scattering properties of particles of a single size a
re usually meaningless because of the complicated interference structu
re and high-frequency ripple of monodisperse scattering patterns. In o
ur computations, we use the T-matrix approach, as extended recently to
randomly oriented particles by Mishchenko V. Opt. Soc. Amer. A 8, 871
(1991)]. Following Hansen and Travis [Space Sic. Rev. 16, 527 (1974)]
, we assume that the scattering properties of polydisperse particles d
epend primarily on only the effective size parameter and effective var
iance of the size distribution, the particular shape of the distributi
on being of minor importance. Therefore, to describe the dispersion of
particle sizes in the ensemble, we employ a convenient power law dist
ribution of particle equivalent-sphere size parameters. Size-averaged
light-scattering characteristics are calculated by numerically integra
ting monodisperse quantities using a Gaussian quadrature formula. The
results of extensive numerical calculations for particles of different
shape and refractive index are presented in the form of color contour
diagrams of linear polarization as a function of scattering angle and
effective equivalent-sphere size parameter. The influence of particle
size distribution, shape, and refractive index on the polarization pa
tterns is examined in detail and implications for polarimetric remote
sensing of nonspherical aerosols are discussed. The diagrams displayed
include calculations for over 150,000 different monodisperse particle
s in random orientation with equivalent-sphere size parameters up to 3
0 and may be used to interpret results of laboratory measurements and
remote observations of light scattering by small particles.