Research On The Scattering Properties Of Non-spherical Atmospheric Particles Based On The Finite Difference Time Domain Method

The intensity and polarization information change due to the sunlight’s particle scattering in the atmosphere. The properties of particle scattering explain the formation mechanism of the sky polarization pattern and have been widely used in weather forecasting, optical media inversion etc. Although the Mie theory can solve the spherical particle scattering, it is difficult to obtain analytical solutions for non-spherical particle. As for the non-spherical particle scattering, we implement the algorithm of finite difference time domain, simulate the scattering by typical atmosphere non-spherical single particle and particle clusters, and finally analyze the intensity and polarization distribution of scattered light under different factors.This thesis includes the following contents:(1) We analyze the limitations of independent scattering and single scattering, summarize the coordinates and symbol definitions of the scattering problem, simulate the scattering properties by spherical droplets based on the Mie theory, review the research methods of non-spherical particle scattering.(2) We implement the single non-spherical particle scattering computation based on the finite difference time domain by calculating the elements of the scattering phase matrix P11 and-P12/P11 to represent the intensity and degree of polarization distribution of scatterd light respectively. The results show the effectiveness of the algorithm.(3) We simulate the scattering properties by single particle of aerosols and cirrus. The results show that energy mainly distributed in the forward scattering; the degree of polarization is zero in the directly forward (0°) and backward (180°), and oscillated between positive and negative values in other regions; the properties of aerosol scattering are more sensitive to the particle properties than those of cirrus.(4) For clusters, we establish the log-normal and bimodal gamma distributions to describe the particle size distribution of aerosol and cirrus respectively. We simulate the scattering properties by clusters under different distributions. The results show that the curve of intensity by cluster eliminate the oscillation of single particle; the polarization distribution is very sensitive to the size distribution for aerosol cluster, but the properties of cirrus cluster are nearly identical under different distributions.