Radar Backscattering Computations for Fractal-Shaped Snowflakes
Radar Backscattering Computations for Fractal-Shaped Snowflakes
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DOI：
10.2151/jmsj.86.459
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发表时间：
2008-06
影响因子：
3.1
通讯作者：
H. Ishimoto
中科院分区：
文献类型：
--
作者：
H. Ishimoto
我们提出了一个基于颗粒形状分形特性的大雪花模型。通过蒙特卡罗模拟，制备了分形维数为1.8 ~ 2.4的颗粒。导出了模拟粒子投影图像的圆度参数，分形维数为2.1的粒子的平均圆度约为0.4；这个平均圆度与报道的大冰集体测量值相匹配。采用时域有限差分法计算了分形维数为2.1、粒径为~ 20 mm的冰粒子在95 GHz、35 GHz和9.8 GHz微波频率下的后向散射截面。并与等体积球体和随机取向等体积六角形柱的实验结果进行了比较。我们的雪花模型的雷达后向散射截面值在瑞利区域以外的尺寸范围内小于等体积球体。此外，雪花模型与等体积六角形柱的后向散射截面存在较大差异，特别是在35GHz频率下。
We propose a model for large snowflakes based on the fractal nature of their particle shapes. Monte Carlo simulations were conducted to make particles with a fractal dimension of 1.8 to 2.4. The roundness parameter for the projected images of the modeled particles was derived, and an average roundness of approximately 0.4 for particles with fractal dimension 2.1 was indicated; this average roundness matched reported values measured for large ice aggregates. The finite difference time domain method was used to calculate the backscattering cross-sections of ice particles with a fractal dimension of 2.1 and a particle diameter of up to ∼20 mm at microwave frequencies of 95 GHz, 35 GHz, and 9.8 GHz. The results were compared with those of equivalent-volume spheres and randomly oriented equivalent-volume hexagonal columns. Our snowflake model had smaller values of radar backscattering cross-sections than did the equivalent-volume spheres in the size range out of the Rayleigh regime. Furthermore, large differences in backscattering cross-sections between the snowflake model and the equivalent-volume hexagonal column were confirmed, in particular at a frequency of 35GHz.