Simulation of backscattering phase function with the geometric optics method using a paired ray-tracing technique

Geometric optics methods with intensity mapping have been widely used to calculate the single-scattering properties of randomly oriented non-spherical particles with large size parameters, but the backscattering phase functions are often underestimated. The primary reason is that the coherent backscatter enhancement (CBE) is not addressed when the intensity mapping technique is used. In this paper, the phase difference between each pair of conjugate reversible rays is computed in the ray-tracing module of the improved geometric optics method (IGOM), and the effect of CBE is incorporated by considering the interference between conjugate rays. The phase functions of regular hexagons, roughened hexagons, and spheroids with different size parameters and refractive indices are simulated using both the original IGOM and the IGOM with CBE considered (IGOM-CBE), and the results are compared to rigorous numerical simulations that solve Maxwell's equations. The results show that the near-backscattering phase functions calculated with the IGOM-CBE are more consistent with rigorous numerical simulations for all cases, indicating that the paired ray-tracing process effectively improves the backscatter simulated by the geometric optics method.