沙尘大气电磁波多重散射及衰减

为了使干旱沙漠地区的电子系统能够全天候的工作, 必须开展沙尘大气的电磁波多重散射及衰减特性研究. 根据Mie理论、沙尘大气粒子尺寸分布和能见度的关系得到了电磁波沙尘大气传播衰减的计算方法, 计算了不同沙尘大气能见度的37 GHz电磁波的衰减, 与其他经验公式及文献中的实验结果进行比较, 文中方法得到的结果更接近于测量结果. 为了研究较低能见度沙尘暴中电磁波的传播特性, 需研究沙尘大气的多重散射效应. 应用Monte Carlo模拟方法, 在沙尘粒子为干燥和5%水含量时, 模拟了37 GHz和93 GHz电磁波在沙尘大气中传播时考虑多重散射效应的衰减, 并与基于Mie理论的计算结果进行比较, 结果显示, 在37 GHz时, 沙尘大气的多重散射对衰减的影响小, 在93 GHz时多重散射显著, 沙尘大气能见度越低, 多重散射的影响越显著. 粒子水含量增加使电磁波的衰减显著增大, 对多重散射的影响不明显. 因此, 在相同大气能见度下, 沙尘天气越干燥, 多重散射影响越大, 电磁波衰减减小越显著.

Multiple scattering and attenuation for electromagnetic wave propagation in sand and dust atmosphere

For an electronic system operation under the conditions of all-weather in arid and semiarid areas, the studies of the attenuation and multiple scattering are necessary for electromagnetic wave propagations in sand and dust atmosphere. Based on Mie theory, a method of calculating the attenuations for electromagnetic wave propagation through sand and dust atmosphere is presented in this paper, which relate to the particle size distributions and visibilities for sand and dust atmosphere. The attenuations at 37 GHz are given for various visibilities, and are compared with the results calculated from other formulas and the experimental data from the literature. The attenuations are closer to the experimental results. In order to investigate into electromagnetic wave propagations in lower visibility sand and dust atmosphere, the multiple scattering in sand and dust storms are necessarily analyzed. At 37 and 93 GHz, the extinction cross sections, albedos and asymmetry factors are calculated by Mie theory for various size sand and dust particles. By the Monte Carlo (MC) simulation method, the attenuations for including the multiple scattering effects are calculated under the conditions of dry and 5% water content in sand and dust particles, respectively, and are compared with the results from Mie theory. The results are shown that the difference between the attenuation obtained by Mie and that by MC is small at 37 GHz. The influence of the multiple scattering on attenuation is small and may be ignored at 37 GHz. At 93 GHz, the difference between the attenuation obtained by Mie and that by MC is clear, and the attenuation obtained by using Mc simulation is smaller than that based on Mie theory. The effect of the multiple scattering on attenuation is evident at 93 GHz. The lower the visibility, the more notable the effect on attenuation is. For different sand and dust storms, the particle refractive indexes and the particle size distributions are different. For the sand and dust storms in Tengger desert and the blowing sand and dust atmosphere in north China, the attenuations at 93 GHz are analysed. In Tengger desert, the attenuation and the multiple scattering are larger than in blowing sand and dust atmosphere. The results show that the more the large size particles in sand and dust storms, the stronger the effect multiple scattering on attenuation is. Hence, for stronger sand and dust storms, the attenuation and the effect of multiple scattering become important. With the increase of water content in particle, the imaginary part of refractive index increases, the attenuation greatly increases, and the effect of the multiple scattering on attenuation is weakly varied. The analyses show that the attenuations for electromagnetic wave propagation in arid sand and dust atmosphere are smaller than in moisture sand and dust atmosphere under the condition of the same visibility.