非球形冰晶的毫米波k-Z_e关系研究

Relationship between the extinction coefficient and radar reflectivity factor of non-spherical ice crystals

针对毫米波雷达处理数据的实际需要,应用离散偶极子近似法DDA,获得了非球形冰晶的后向散射及衰减截面并进行了参数化,并主要基于细化的冰云模型,假设冰晶粒子谱为Γ分布,通过模拟取样各1330次(代表1330种粒子分布),分别计算得到了W波段(94 GHz)与Ka波段(35 GHz)毫米波雷达探测的冰云衰减系数k及雷达反射率因子Z e,而且利用数值模拟的方法,建立了k-Z e关系的具体表达式。计算表明,非球形和非瑞利散射对W波段毫米波雷达衰减的影响较大,而且在同样滴谱分布条件下,W波段毫米波雷达的衰减比Ka波段毫米波雷达的大几倍,此外细化的冰云模型对k-Z e关系具有影响。本研究对中纬度非降水性冰云的毫米波雷达的衰减订正具有参考价值,并对中国的毫米波雷达应用具有借鉴作用。

Targeting at processing and analyzing the data of millimeter-wave radars, backscattering and extinction cross sections of non-spherical ice crystals are obtained and parameterized using Discrete Dipole Approximation （DDA） method. Sampling for 1330 times （representing 1330 Particles Size Distribution （PSD） of ice crystals）, attenuation coefficient （k） and radar reflectivity factor （Ze） are calculated based on a refined model for representing the ice hydrometeors by assuming gamma PSD. The accurate formulas of k-Ze relationships are derived using numerical simulation for W （94 GHz） and Ka （35 GHz） band radar. The results show that non-spherical and non-Rayleigh scattering effects of ice crystals on 94 GHz radar attenuation are larger than that on 35 GHz. The attenuation at 94 GHz is more than that at 35 GHz with the same PSD, and that the impacts of ice clouds models on k-Ze relations are remarkable. The results may be suitable for attenuation correction of non-precipitating ice clouds in midlatitude for millimeter-wave radars and provide a reference for millimeter-wave cloud radars in China.