球形粒子毫米波k-Z关系研究

A study of the relationship between the attenuation coefficient and radar reflectivity factor for spherical particles in clouds at millimeter wavelengths.

中文关键词:  球形粒子，毫米波， k-Z关系

英文关键词:Spheric particle, Millimeter wave, k-Z relationship

中文摘要:

      由于毫米波更接近云粒子尺度，毫米波雷达越来越多地被用来探测云粒子及尺度较小的降水粒子。但是，在使用毫米波雷达探测时，要考虑云和降水粒子散射和吸收以及大气气体吸收所造成的衰减。结合毫米波测云雷达数据处理的实际需要，研究云中衰减系数-k-与雷达反射率因子Z的关系。假设粒子为小球形，云、雨滴谱分别服从K-M分布和Γ分布，通过模拟取样各1330次，应用米散射理论计算公式，分别计算得到W波段（3.2 mm）与K波段（8.6 mm）毫米波雷达探测球形云（包括水云、冰云）和降水粒子的衰减系数 k及雷达反射率因子Z，并建立 k-Z-关系的具体表达式。计算表明，在同样滴谱分布条件下，W波段（3.2 mm）毫米波雷达的衰减要比K波段（8.6 mm）毫米波雷达大5—10倍。本研究对毫米波雷达的衰减订正有参考价值，所给出的k-Z关系系数可用于3.2和8.6 mm波雷达定量测量云特征的衰减订正计算。

英文摘要:

      Because of millimeter wavelengths close to the scale of cloud particles, more and more millimeter radar systems are used to detect cloud and small precipitation particles. When using millimeter wavelength radars, the attenuation caused by cloud and precipitation particles’ scattering and absorption together with the water vapor and oxygen absorption at millimeter wavelength must be take into account. In order for the actual need of millimeter wavelengths cloud radar data processing, it is presumed that the cloud particles are sphere particles, and the cloud drop size spectra follow the K-M distribution and the rain drop size spectra follow the Gamma distribution by sampling them each for 1330 times, and by adopting the Mie scatter theory formula for computing scattering, absorbing and back scattering cross-sections, the attenuation coefficient k and radar reflectivity factor Z are calculated for 3.2 and 8.6 mm wavelengths and the k-Z relationship is obtained. The results show that the attenuation at the 3.2 mm is 5-10 times larger than that at 8.6 mm under the same conditions of drop size spectra. The k-Z relationship coefficients are available for attenuation correction of millimeter radars, and the formulas can be applied into correction for the 3.2 and 8.6 mm radar attenuation computations. 