Light scattering by Gaussian random particles: Ray optics approximation

We model the shapes of irregular small particles using multivariate lognormal statistics (Gaussian random shape), and compute absorption and scattering cross sections, asymmetry parameters, and scattering phase matrices in the ray optics approximation. The random shape is fully described by the autocovariance function, which can be conveniently modeled by two statistical parameters: the standard deviation of radius and the correlation length of angular variations. We present an efficient spherical harmonics method for generating sample Gaussian random particles, and outline a ray tracing algorithm that can be adapted to almost arbitrary, mathematically star-like particles. We study the scattering and absorption properties of Gaussian random particles much larger than the wavelength by systematically varying their statistical parameters and complex refractive indices. The results help us understand, in part, light scattering by solar system dust particles, and thereby constrain the physical properties of, for example, asteroid regoliths and cometary comae.