2006 年 26 巻 4 号 p. 283-295
A numerical code of finite-difference time domain (FDTD) method to solve a light scattering by irregular particles has been developed. Using a standard 2nd order FDTD scheme and an absorbing boundary condition by a perfectly matched layer (PML), it is found that the light scattering features for size parameter x≤50 at wavelength 1.381μm for spherical ice particles have been successfully demonstrated by this FDTD code with spatial grid increment δ= 2./20. In the same numerical conditions, the light scattering calculations for hexagonal column aggregates are performed taking into account the particle's random orientation. The averaged phase function for the aggregate shows rather a flat angular dependence with no prominent peak features, which differs from the results of geometrical optics approximations for larger aggregate particles. Furthermore, a decrease of the side/back scattering efficiency and an increase of the asymmetry factor around the interference region of the particle's size are confirmed.