山地雷达估算降水的反射率因子订正方法研究

Mountainous Radar Estimation of Precipitation Reflectivity Factor Correction Method Research

我国很多新一代多普勒天气雷达位于地形复杂的山区,低仰角地形遮挡问题突出,遮挡区雷达估算降水时需要采用更高仰角的观测数据,而由于降水粒子下落过程中的微物理变化和水平运动,同一地点高处的反射率因子常与近地表处有很大的差异,直接用于估算地表降水会增大估算误差。本文提出一种反射率因子垂直订正方法,首先建立无遮挡观测区不同降水类型的雷达反射率因子垂直廓线(VPR),然后依据廓线的垂直变化特征,确定待订正的高度阈值和近地表目标高度,并将待订正高度以上的观测值订正到目标高度处。对比检验结果表明:经过订正后的目标反射率因子数据与实际观测数据值差异减少,一致性提高;而且,考虑遮挡因素使VPR低处的数据更准确;由于不同降水类型VPR差别明显,区分降水类型能避免误订正。本订正方法不仅适用于波束遮挡区,也普遍适用于远距离处波束较高时观测数据的订正。

Many new-generation Doppler weather radars in China are located in mountainous areas with complex topography,and the problem of low elevation angle terrain occlusion is prominent.When estimating precipitation by radar in the occluded area,observations with higher elevation angles need to be used,and due to the micro-physical changes and horizontal motion of precipitation particles during their descent,the reflectivity factor at high locations of the same site is often very different from that near the surface,which will increase the estimation error when used directly for estimating surface precipitation.In this paper,we propose a method for the vertical revision of reflectivity factor.First,we establish the vertical reflectivity factor profiles(VPR)of different precipitation types in the unobstructed observation area,and then revise the observations above the height to be revised to the target height by determining the height threshold to be revised and the near-surface target height based on the vertical variation characteristics of the profiles.The comparison test results show that:the revised target reflectivity factor data are less different from the actual observed data values,and the consistency is improved;moreover,the data at low VPR are more accurate by considering the occlusion factor;since the VPR of different precipitation types are significantly different,the differentiation of precipitation types can avoid mis-correction.The proposed revision method is not only applicable to the beam blocking area,but also generally applicable to the revision of the observed data at high beam height at long distances.