Rainfall Estimation Using Palarimetric Radar

在美国气象研究计划的支持下，主要研究人员将开发一种利用极化雷达测量降雨量的新方法。最近从极化气象雷达获得的证据表明，当现有的极化方法不能充分估计降雨量时，一个重要的原因是雨滴大小分布（DSD）的变异性。因此，了解DSD对极化降水估计算法性能的影响将是本研究工作的主要推动力。首席研究员将利用这些知识开发一种新的降雨估计方法。我们的想法是使用极化雷达数据根据DSD对各种降雨进行分类，以便适当的极化关系可以连续匹配每种降雨类型。降雨状态的特征将由各种极化变量导出。相应的DSD将由最先进的二维视频测量仪测量。disdimeter将被放置在一排紧密间隔的雨量计内的一个坑中，以消除风的影响，并获得独立的降雨量估计。将收集俄克拉何马州风暴中发现的所有降雨类型的风差计数据，以开发降雨状态分类并了解各种状态之间的差异。核实“匹配的”极化雨量估计将通过与位于俄克拉荷马州中南部的微网络（42个测量仪，间隔5公里，由美国农业部农业研究服务局操作）、俄克拉荷马州Mesonet（俄克拉荷马州每个县有一个或两个测量仪）和NOAA合作网络的雨量计数据进行比较来完成。后两组资料将主要用于评估距离对雷达雨量估计质量的影响。在远距离上，不均匀的雷达波束填充和降水的垂直分层增加了降水估计的不确定性。俄克拉何马市西部的Cimarron极化雷达、俄克拉何马州中部及周边地区的三台WSR-88D雷达以及诺曼的一个雨量计比较设施，为支持调查提供了一个独特的现场实验室。此外，首席研究人员在雷达和雨量计的比较方面有着悠久的历史。雷达雨量估计的改进将对降水预报的质量产生积极影响。改进估算将有助于减轻洪水造成的自然灾害，并使政府和商业组织更好地管理水资源。

Under support from the U.S. Weather Research Program, the Principal Investigators will develop a new method to measure rainfall using polarimetric radar. Recent evidence obtained from polarimetric weather radars suggests that when existing polarimetric methods fail to adequately estimate rainfall, a significant cause is the variability in drop size distribution (DSD). Thus, understanding the impact of DSD on the performance of the polarimetric algorithms for rainfall estimation will be a major thrust of this research effort. The Principal Investigators will exploit this knowledge to develop a novel approach for rainfall estimation. The idea is to use polarimetric radar data to classify various rainfall regimes according to their DSD so that appropriate polarimetric relations can be continuously matched to each rain type. Characterization of a rainfall regime will be derived from various polarimetric variables. The corresponding DSD's will be measured by a state-of-the-art two-dimensional video-disdrometer. The disdrometer will be placed in a pit within an array of closely spaced rain gauges to eliminate wind effects and to acquire independent estimates of rainfall. Disdrometer data will be collected in all types of rainfall found in Oklahoma storms to develop the rain regime classification and to understand the differences among the various regimes.Verification of the "matched" polarimetric rainfall estimates will be done by comparison with rain gauge data from a micronetwork (42 gages at 5 km spacing, operated by the Agricultural Research Service, USDA) in south-central Oklahoma, the Oklahoma Mesonet (one or two gauges in each Oklahoma county), and the NOAA Cooperative Network. The latter two data sets will be employed primarily to assess range effects on the quality of radar rainfall estimation. At long distances non-uniform radar beam filling and vertical stratification of precipitation add to the uncertainty in rainfall estimates. The complement of network rain gauges, the Cimarron polarimetric radar just west of Oklahoma City, three operational WSR-88D radars in and around central Oklahoma, and a rain gauge comparison facility in Norman, provide a unique field laboratory to support the investigation. In addition, the Principal Investigators have a long history of radar - rain gauge comparisons.Improvement in radar rainfall estimation will have a positive impact on the quality of precipitation forecasts. Improved estimates will assist in mitigation of natural disasters due to flooding and lead to better management of water resources by government and commercial organizations.