地物对新一代天气雷达双偏振量的影响研究

Study on the influence of ground on CINRAD dual polarization observations

中文关键词:  新一代天气雷达，双偏振升级，地物影响，主瓣和副瓣，质量控制，统计研究

英文关键词:CINRAD,Dual polarization upgrade ,Ground influence,Mainlobe and sidelobe,Quality control, Statistical study

中文摘要:

      双偏振量的数量级远小于回波强度（ZH），其观测的准确性是双偏振雷达资料应用的基础，地物引起的双偏振量异常此前大多被忽视。首次使用我国93部双偏振升级后的新一代天气雷达观测资料，通过长时间数据累积后的异常区确定地物影响的特征和范围，进而统计分析了该影响在我国业务雷达中的整体比例、影响的主要来源、影响与雷达型号和观测模式的关系、影响随时间的变化情况、影响的性质及双偏振量的分布特征等，所得结论如下：（1）地物使得双偏振量的累积值严重偏离降水区间，差分反射率因子（ZDR）累积值偏低1 dB以上，相关系数（ρHV）降至0.92以下，差分传播相移（ΦDP）的标准差大于10°，该特征成为识别地物影响的主要依据。（2）地物影响不限于低层，仰角抬升后副瓣接收的地物信号也能产生类似的效果，大部分雷达近地面区域的影响占比可达14%—32%、高仰角达4%—7%，远比地物对波束的遮挡现象严重。（3）地物影响主要由具备强散射能力的山脉和建筑物引起，当站点低于地形时，周围山脉是主要贡献；当站点与地形高度接近时，周围建筑物是主要贡献。（4）地物影响可用随机误差与系统误差的叠加来定量描述，使影响区内的双偏振量在单一时次的观测不确定性增大，且主瓣区域的影响比副瓣区域更严重。上述研究为新一代天气雷达双偏振量的精细化质量控制提供了依据。

英文摘要:

      The magnitude of the dual polarization observations is much smaller than the reflectivity factor (ZH), and the accuracy of the observation is the basis for the application of dual polarization radar data. Anomalies in dual polarization observations caused by ground have largely been overlooked in the past. For the first time to utilize the observation data from 93 CINRAD radars upgraded with dual polarization, the characteristics and scope of ground influence are determined by the anomalous areas after long–term data accumulation. Then statistically analysis the overall proportion of the influence in CINRAD radars, the main sources of the influence, the relationship between the influence and radar types and observation modes, the temporal variations of the influence, the nature of the influence and the distribution characteristics of dual polarization observations. Results are as follows: (1) The ground caused the accumulated values of dual polarization observations deviated significantly from the precipitation interval, the differential reflectivity factor (ZDR) was decreased by more than 1 dB, the correlation coefficient (ρHV) fell below 0.92, and the standard deviation of differential phase (ΦDP) was greater than 10°. This characteristic served as the main basis for identifying ground influence. (2) The ground influence is not limited to the near–ground region, as the elevation angle increased, the sidelobe reception of ground signals can also produce similar effects. The proportion of influence in the near–ground region can reach 14% to 32%, while at high elevation angles it reached 4% to 7%, far more severe than the beam blockage. (3) The ground influence is mainly caused by mountains and buildings with strong scattering capabilities, when the site is below the terrain height, surrounding mountains being the main contributors, and when the site is close to the terrain height, buildings within urban areas being the main contributors. (4) The ground influence can be quantitatively described by the superposition of random errors and systematic errors, leading to increased uncertainty in the dual polarization observations within the affected area at a specific time. Moreover, the influence is more severe in the mainlobe region than in the sidelobe region. The above study provides a basis for the refined quality control of dual polarization parameters in CINRAD.