基于云粒子衰减截面和气体吸收的回波强度订正技术

Attenuation correction of cloud radar reflectivity factor based on attenuation cross-section of cloud particles and atmospheric gases absorption

利用地基Ka波段(35GHz)云雷达在安徽寿县观测层状云数据,在基于云滴谱分布模型和忽略湍流对速度谱宽的影响下,利用雷达反射率因子和速度谱宽反演得到云滴谱参数,并计算出云体中值直径、粒子数浓度、液态水含量;利用离散偶极子近似(discrete dipole approximation,DDA)算法计算出云体中不同大小云粒子的衰减截面,得到云层衰减系数。对毫米波云雷达的探测数据进行衰减订正时,需要考虑大气吸收对电磁波所造成的衰减,大气衰减系数可以通过Liebe模式计算。结果表明:传播路径上的云层衰减系数主要受云层内的液态水含量影响,深厚且回波较强的水云对雷达电磁波的衰减较大;在Ka波段,气体衰减有限,但当水汽丰富时,不能忽视;经过衰减订正后的毫米波雷达数据质量有明显改善。

Using the stratiform cloud data observed from ground-based Ka-band (35 GHz) cloud radar in Shouxian county, Anhui province, based on cloud drop distribution model and ignoring the influence of turbulence on the velocity spectrum width, the drop spectrum parameters were obtained by utilizing the radar reflectivity factor and velocity spectrum width. The median diameter, particle number concentration and liquid water content were then obtained from the retrieved cloud drop-size spectrum. To solve the cloud layer attenuation coefficient, the discrete dipole approximation (DDA) algorithm was used to calculate the attenuation cross-sections of all cloud particles in different size. The attenuation of electromagnetic waves caused by atmospheric absorption is also taken into account to correct the millimeter-wavelength cloud radar data, such an attenuation coefficient can be calculated according to Liebe model. The results show that the cloud attenuation coefficient along the propagation path is more sensitive to the liquid water content;deep and strong echoes have severe attenuation on radar electromagnetic waves. Gas absorption is minor at Ka-band, but is considerable if the water vapor is rich in the atmosphere. And the quality of the millimeter-wave radar data after attenuation correction is significantly improved.