A Study of the Physical Geometric Optics Method In the Case of a Spheroid

The physical geometric optics method (PGOM) is used to calculate single-scattering properties (namely, the extinction efficiency, single-scattering albedo, and phase matrix) of moderate to large-sized faceted particles. We present the application of PGOM to spheroidal particles. It is important to understand the optical properties of spheroidal particles because they can be used to model more complicated shapes in light scattering computation, such as dust aerosols. This will contribute to our overall understanding of the effects aerosols have on the Earth’s radiation budget. The limitation of implementing PGOM to a spheroid is that a spheroid is not a faceted particle, so it is not currently possible to implement PGOM. There are other methods used to compute the light scattering properties of spheroid particles, but they only work for small-sized particles. There are currently no accurate or computationally efficient methods to compute the light scattering properties of moderate to large-sized spheroidal particles. In this project, we approximate the shape of the spheroid as a faceted particle. As the number of sides of the faceted particle increases, the particle will approach a spheroid. In this simulation, we implemented PGOM for moderate to large-sized facets with the following number of sides: 100, 150, 200, 250, 300, 350, 400, 450, and 500. In addition, we used an aspect ratio of 1.5 and size parameter of 150 when the particle is weakly and strongly absorbing. We compare the scattering phase matrix elements as well as the extinction efficiency, single-scattering albedo, and asymmetry factor with the numerically exact extended boundary condition method (EBCM). The goal of this study is to estimate the smallest number of facets required for the PGOM method to converge to the EBCM.