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降水粒子空间取向对双线偏振雷达观测影响模拟研究
A Simulation Study on Raindrop Orientation Variation to Dual Linear Polarimetric Radar Observation with Different Transmitting and Receiving Model
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摘要: 该文从降水粒子散射和衰减理论出发, 采用数值模拟方法, 分析了雷达波束通过均匀雨区时, 双发双收偏振模式与单发单收偏振模式下, 水平、垂直偏振波之间的耦合关系, 比较了两种收发模式下, 由于雨滴倾斜引起的水平反射率因子ZH及其误差ΔZH, 差分反射率因子ZDR及其误差ΔZDR, 差传播相移ΥDP、差传播相移率KDP及其在不同偏振模式下的差异ΔKDP随距离的变化情况。结果表明:因实际大气中雨滴倾斜角较小, 雨滴倾斜引起的模式间ZH, ZDP的差别不大; 而受雨滴倾斜影响, 单发单收模式的KDP要大于双发双收模式。该文还提出了ZH, ZDR真值的两种定义方式, 分别为考虑与未考虑雨滴倾斜对散射效果的影响。未考虑雨滴倾斜的真值代表了雨滴实际的微物理结构, 剔除了传播效应的影响, 更能精确反映雨滴的实际大小, 在定量估测降水等雷达资料的应用中具有更好的代表性, 因此以未考虑雨滴倾斜作为ZH, ZDR真值较为合理。Abstract: On the basis of scattering and attenuation theory of raindrop, the coupling relation between vertical and horizontal polarimetric wave is analyzed with numerical simulation methods in the same transmission and receiving waves (STSR) and alternate transmission and receiving horizontal and vertical waves (ATAR) model. While radar beam passes through uniform rain area, the variety of horizontal reflectivity ZH and its error ΔZH, differential reflectivity ZDR and its error ΔZDR, the differential propagation phase shift ΦDP and specific differential propagation phase shift KDP and its difference ΔKDP brought by raindrop slant are compared respectively along with distance between the two polarimetric models. The results indicate that the ZH of STSR are bigger and ZDR are smaller than ATAR model while raindrop is slant, so the errors of ZH and ZDR in STSR model are bigger when attenuation are not considered. While attenuation is considered, the errors of ZH in STSR are small, the errors of ZDR of 3.2 cm are small too, and that of 5.7, 10.7 cm are big. However, the difference of ZH and ZDR between models is little because the raindrop slant is small in real air. Influenced by raindrop slant KDP is bigger in ATAR model than in STSR, it decreases less than in STSR model, so the difference of ΔKDP between models is more while the slant angle increases. The shorter the wave length, the bigger the KDP, and the larger the ΔKDP are impacted by slant. In addition, two real value definitions of ZH and ZDR are addressed, by which the scattering effect of raindrop slant is considered or not. The actual microphysical structure of raindrop can be better represented by the value of not considering slant, the influence of propagation effect is eliminated, and the full size is reflected accurately, which are better representatives on the application of radar data such as quantitative estimation precipitation. It is more reasonable that the none-slant-consideration ZH, ZDR values are regarded as the real definitions.
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图 2 波长3.2 cm (a)、5.7 cm (b) 不同雨滴倾斜角, 在ATAR, STSR模式下波束通过均匀雨区的ΦDP值
Fig. 2 The ΦDP value while beam pass through uniform rain area with ATAR and STSR models in different slant angles by 3.2 cm (a), 5.7 cm (b) wave length
表 1 不同波长, 不同雨滴倾斜角, 不同距离处, 两种收发模式的偏振参量及误差值
Table 1 Polarimetric value with ATAR and STSR model in different wave length and different slant angles at different distances
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