A Monte Carlo ray-tracing model for scattering and polarization by large particles with complex shapes

We present a new model based on Monte Carlo ray tracing which simulates sca ttering and linear polarization by particles with arbitrary shapes and size s much larger than the wavelength. The model, called S-Scat, provides a pow erful tool for exploring the relationship between actual physical propertie s of large particles and the single-particle parameters used in multiple-sc attering radiative transfer models, and will be particularly valuable for s tudies of icy outer solar system surfaces. We describe the model algorithm and apply the model to examine absorption and scattering behavior of single , irregular particles as functions of particle size, shape, and optical con stants. Single-scattering albedos are investigated first, with results used to test the validity of the widely used equivalent slab model. Single-scat tering phase functions are examined next, along with possibilities of param eterization via simple analytic expressions. Finally, the behaviors of line ar polarization functions are explored, along with internal path lengths an d the spatial distribution of scattered light in close proximity to the par ticle.