为研究卷云的非球形粒子对毫米波雷达的散射特性,利用矩量法计算了卷云六种非球形冰晶粒子最大尺寸与散射截面之间的双指数函数关系.利用三种假设模型：Ⅰ. B-H混合模型、Ⅱ.等效椭球模型、Ⅲ.等效球模型分别验证NASA 在2007年7月31日一次卫星与飞机同步测云试验数据,对比后发现模型Ⅰ(B-H模型)模拟4个位置处实测的结果最好,模型Ⅱ的结果其次,模型Ⅲ的结果最差,但是B-H模型模拟1号,2号,3号位置处的雷达反射率因子与实测值相比偏低,分析原因认为粒子谱探测仪器忽略了滴晶粒子贡献.加入滴晶粒子后统一拟合1号,2号,3号以及4号的普适性粒子谱,拟合其满足B-H模型时冰水含量与雷达反射率因子之间的关系式,将CVI仪器实测的冰水含量值代入上面的关系式得到反演的雷达反射率因子,对比CRS毫米波雷达实测的雷达反射率因子可知：当云中冰水含量小于0.1342 g/m3,冰晶中的空气含量对雷达反射率因子的影响要远大于粒子的取向问题;当云中冰水含量介于0.134 2~0.199 4 g/m3,冰晶中的空气含量可以忽略不计而仅考虑粒子的取向问题;当云中冰水含量大于0.199 4 g/m3,B-H模型将不再适用.因此为了利用毫米波雷达反射率因子精确地反演云中冰晶粒子,应以冰水含量为前提考虑B-H模型中冰晶粒子的取向以及空气含量.

In order to study the scattering properties of non-spherical ice particles which are detected by millimeter-wave radar, the backscattering cross sections of six kinds of non-spherical ice crystals of cirrus were studied. The double-exponential function relationships between particles’ maximum sizes and backscattering cross sections is fitted. Three assumed models: I. B-H mixing model, II. Equivalent ellipsoid model, III. Equivalent sphere model, respectively, were used to simulate the data provided by the NASA’s synchronous satellite and airplanes experiment for cloud observation on July 31, 2007. The results showed that the data retrieved by B-H mixing model agree very well with the measured results at four positions compared with the results retrieved by other two models. However the retrieved results by B-H mixing model at 1#, 2#, 3# positions are lower than values detected by CRS millimeter wave radar. This is because cloud size distribution detector ignores the droxtals which are beyond the detection range. Considering these droxtals and fitting all size distributions at 1#, 2#, 3# and 4#, the common size distribution which meets B-H model can be acquired and the relationship between Ice Water Content (IWC) and Z can be fitted. Putting IWC measured by CVI instrument into above formula (IWC-Z), the retrieved radar reflectivity factors can be acquired, and then compared with the results detected by CRS millimeter wave radar. The results show that the influence of air content on radar reflectivity factor is larger than particle’s orientation when IWC is below 0.134 2 g/m3. The influence of air content can be ignored while the particle’s orientation should be considered when the value of IWC is between 0.134 2 g/m3 and 0.199 4 g/m3. B-H model is not applicable when IWC is larger than 0.199 4 g/m3. Based on above analysis, the orientation and air content must be considered under the premise of IWC in order to accurately retrieve ice particles using millimeter-wave radar.