Light scattering properties of spheroidal particles

Abstract

Light scattering characteristics of spheroidal particles are studied for a wide range of particle parameters and orientations. The method of computation is based on the scattering theory for a homogeneous spheroid developed by us, and the calculation is extended to fairly large spheroidal particles of a size parameter up to 30. Effects of the particle size, shape, index of refraction, and orientation on the scattering efficiency factors and the scattering intensity functions are investigated and interpreted physically. The scattering properties of prolate and oblate spheroids with incidence parallel to the rotation axis constitute the extremes. The prolate spheroids at parallel incidence have steep and high resonance maxima in the scattering efficiency factors and broad and low forwardscattering peaks in the intensity functions; on the other hand, the oblate spheroids at parallel incidence have broad and low resonance maxima and sharp and high forwardscattering peaks. With an increase of the incidence angle, he scattering behavior of prolate spheroids approaches that of oblate spheroids at parallel incidence and vice versa. It is shown that, for oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder. Effects of absorption on the extinction efficiency factors and scattering intensity functions are examined. Some problems in numerical calculation of the spheroidal wave functions and the infinite series solutions are discussed.