Field Studies of Raindrop Axis Ratio and Orientation Distributions Using an Improved 2D-Video Disdrometer and Dual-Polarized Radar

使用改进的二维视频测距仪和双偏振雷达对雨滴轴比和方向分布进行现场研究

• 批准号: 0140350
• 负责人: Viswanathan Bringi
• 金额: $ 37.85万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-05-01 至 2006-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0140350&HistoricalAwards=false
• 关键词: Field; Studies; Raindrop; Axis; Ratio

Polarimetric radar measurements of precipitation contain information about the shape of the precipitation particles. For raindrops, the shape may oscillate with time, but the average shape is approximately spheroidal, and the larger the drop the greater the deviation from spherical. Hence polarimetric measurements of rain contain information about drop size - information in addition to what is provided by the radar reflectivity alone. This is the basis for improved estimates of rainfall rate using polarimetry. This project contributes to radar polarimetry by directly measuring the sizes, shapes, and canting angles of individual drops at the ground. It employs an upgraded version of a video disdrometer manufactured by an Austrian firm, Joanneum Research. This instrument records the front and side view of each individual drop as it falls through a square, horizontal sampling area about 10 cm on the side. It measures the particle size, shape, canting angle, and fall speed. The data enable the calculation of a parameter relevant to polarimetric measurements, called "effective beta," which depends on the relation between size, shape, and canting angle. A recent theory shows that this parameter can also be inferred indirectly from radar observations of three polarimetric quantities, the reflectivity at horizontal polarization, the ratio of the reflectivities at horizontal and vertical polarization, and the differential propagation phase between the two polarization components. Furthermore, knowing the effective beta enables more accurate estimation of the rainfall rate. The purpose of the experiments is to test the theory by comparing radar estimates of beta with the values of this parameter determined directly from the disdrometer-measured properties of the drops. Experiments will be conducted at two sites: in Colorado, using the CSU-CHILL radar, and in Darwin, Australia, in collaboration with the Bureau of Meteorology Research Center. Using these sites will enable the evaluation of the theory in two climatic regimes with possibly different rainfall characteristics. The work should improve the accuracy of rainfall estimation by radar.

降水的极化雷达测量值包含有关降水颗粒形状的信息。 对于雨滴，形状可能会随着时间的流逝而振荡，但平均形状大约是球体的，并且滴度越大，与球形的偏差越大。 因此，降雨的极化测量值包含有关滴大小的信息 - 仅雷达反射率提供的信息。 这是改善使用极化法估计降雨速率的基础。 该项目通过直接测量地面单个滴的大小，形状和倾斜角来导致雷达极化法。 它采用了由奥地利公司Joanneum Research生产的视频序列计的升级版本。 该仪器记录了每个单独滴的前视图，当时它穿过正方形的水平采样区域，侧面约10厘米。 它可以测量粒径，形状，倾斜角度和跌落速度。 数据允许计算与极化测量相关的参数，称为“有效β”，该参数取决于大小，形状和倾斜角度之间的关系。 最近的一个理论表明，也可以从三个极化量的雷达观察结果，水平极化时的反射率，水平和垂直极化的反射率以及两个极化分量之间的差分传播阶段进行间接推断。 此外，知道有效的β可以更准确地估计降雨速率。 实验的目的是通过比较β的雷达估计与直接从滴度滴定仪的特性确定的该参数的值进行测试。 实验将在两个地点进行：在科罗拉多州，使用CSU-CHILL RADAR，以及在澳大利亚达尔文，与气象研究中心合作。 使用这些地点将在两个可能不同的降雨特征的气候制度中评估该理论。 这项工作应提高雷达降雨估计的准确性。