【作者】 肖艳姣；

【导师】 刘黎平；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2007， 博士

【摘要】 为了充分发挥新一代天气雷达网的作用,本文在雷达资料质量控制的基础上研究了新一代天气雷达网三维拼图技术,得到高分辨率的三维反射率拼图格点(经度、纬度和高度坐标)数据,并对雷达三维反射率数据进行了初步应用研究。本论文工作的开展为新一代天气雷达网资料的深度和广度应用(如强天气监测与临近预警报、雷达网资料的同化、在水文和航空中的应用等)提供了强有力的平台。论文的主要研究内容和初步结果如下:1)采用高度约束的反射率垂直梯度和水平纹理检查相结合的方法对非气象杂波进行了抑制,通过用来自不同雷达和不同大气条件下的多个个例进行检验,结果表明该方法能合理地识别非气象杂波。2)利用高分辨DEM(digital elevation model)数据计算了雷达波束阻挡率,得到了混合扫描仰角。通过与实测的反射率PPI进行比较,发现计算出来的波束阻挡率和雷达实测的波束阻挡情况具有很好的定性一致性和很强的定量相关性。根据各雷达的混合扫描仰角,绘制了区域雷达网的等射束高度拼图,以便分析雷达网的覆盖能力。3)研究了多种把极坐标雷达资料插到笛卡尔坐标系下的插值方法,并用反射率场的空间连续性以及插值前后强降水的中心位置和分级总雨量差作为衡量标准,评估了各种方法插值结果的好坏,结果发现,用斜距和方位的最近邻居与垂直线性内插相结合的插值方法得到的反射率场不仅具有空间连续性而且保留了体扫资料中原有的反射率结构特征。把用dBZ值和Z值插值的结果与实际观测值进行了对比分析,发现用dBZ插值的结果总体上更加接近观测值。4)在尽量排除非气象杂波、波束阻挡、距离衰减和波束展宽等因素的影响下,对3个区域雷达网同步观测进行了对比分析,以便检查各雷达之间的系统观测差。结果发现宜昌雷达和其周围的雷达相比观测的回波强度偏强,而武汉雷达和其周围的雷达相比观测的回波强度偏弱;常德雷达(CINRAD-SB型)与其周围雷达(CINRAD-SA型)同步观测相比,回波垂直高度偏低;其它雷达对的观测差异较小。5)研究了多种拼图方法(最近邻居法、最大值法、距离指数权重平均法和Cressman权重平均法)处理多雷达重叠覆盖区的数据,结果发现距离指数权重平均法对多雷达资料合成拼图特别有用,它既保留了原始雷达资料中近距离处的高分辨特征,同时确保了雷达能影响到它所覆盖的整个区域。雷达网三维拼图减轻了由雷达波束几何学引起的各种问题,如一定程度上填补了单雷达观测引起的静锥区、最低仰角以下的资料空白区、因波束阻挡以及高仰角间隙等原因引起的资料空白区。6)基于三维反射率拼图数据开发了一些雷达网产品,并把它与单站雷达产品拼图进行比较,证明了在雷达网3D拼图反射率数据上生成的各种产品是合理的。研究了层状云和对流云回波的6个特征参数的分布特征,在此基础上提出用模糊逻辑法进行层状云和对流云的识别。经三个个例的试验,证明模糊逻辑法得到的识别结果是合理的。更多还原

【Abstract】 This paper describes a technique of gridding radar reflectivity observations under quality control from multiple radars and combining them into a unified 3D merged reflectivity grid with high resolution. Then, some preliminary studies on the application of 3D reflectivity grid are made. The 3D mosaic grid is a powerful tool of the deep and wide application of radar network data (e.g. severe weather warning and nowcasting, data assimilations for convective-scale numerical over large domains, the application in hydrology and aviation) . The main contents and conclusions are as follows:1 A reflectivity quality control (QC) algorithm has been developed for identifying and removing non-precipitation echoes from the radar base reflectivity fields. The algorithm assumed that precipitation and non-precipitation echoes had different horizontal and vertical reflectivity structures. Two main parameters, vertical gradient of reflectivity with height constraint and horizontal texture of reflectivity, and a set of physically based rules and criteria were developed for the QC algorithm. The reflectivity QC algorithm has been tested using some volume scans of base level data from different radar sites and from different atmosphere conditions. Results have shown that the reflectivity QC algorithm is very successful in identifying non-precipitation echoes.2 The beam occultation, which is the percent of the radar beam power lost due to beam blockage, was calculated using an algorithm that used high resolution DEM(digital elevation model) data, radar beam pattern (Gaussian beam approximation), and radar beam propagation path (assuming radar beams propagate under standard atmospheric refraction conditions). Hybrid elevation angles and hybrid scan reflectivity were generated using based on beam occultation. Comparison of model-calculated beam occultation with radar observations indicated very good qualitative agreement and strongly quantitative correlation. In order to know the coverage capability of weather radar network, the standard refractive index beam heights (4/3 earth) were calculated for hybrid elevation angles for every radar in radar network, which were combined to produce a mosaicked beam height map.3 Four interpolation approaches were investigated to remap raw radar reflectivity fields onto a 3D Cartesian grid with high resolution. Through comparison of vertical and horizontal reflectivity cross section and estimated one-hour precipitation obtained by use of the four interpolation schemes, it was found that the vertical interpolation scheme with nearest neighbor on the range-azimuth plane was the most reasonable analysis scheme that provided consecutive reflectivity fields and retains high-resolution structure comparable to the raw data. Comparing reflectivity observation with corresponding reflectivity analysis obtained respectively by interpolation using reflectivity factor in dBZ and in mm6/m3 , results have shown that on the whole, the analysis field obtained by interpolation using reflectivity factor in dBZ was more accordant with observation field.4 In order to check spatial coherence and calibration differences of three regional radar network when they detected synchronously atmosphere, horizontal and vertical structure of reflectivity fields on equidistant line from radar-pairs were analyzed. Results have shown Wuhan radar’s echo intensities were weaker than that of adjacent radar, whereas, Yichang radar’s were stronger. Echo’s vertical structures are quite large variation on equidistant line when Changde radar simultaneously observes with around 3 radars, its echo height is obviously lower. Nevertheless, the others’echoes are consistent well.5 Four approaches of combining multiple-radar reflectivity fields were investigated. Results have shown the distance- exponential-weighted mean scheme provided a spatially consistent reflectivity mosaics while retaining the magnitude of the observations from the close radar. Mosaics could mitigate various problems that caused by the geometry of radar beam such as data voids with the cone of silence above the radar and in regions below the lowest beam.6 Based on 3D merged reflectivity grid, some radar network products used for warning effectively severe weather were developed, which were proved to be reasonable through Comparing radar network products with single radar product mosaics. The distribution characteristics of the six preparative reflectivity-morphological parameters from convective and stratiform rain were presented. Based on three of them, a fuzzy logic method for the partitioning of radar reflectivity into convective and stratiform rain classifications has been developed and tested using volume scan radar reflectivity data. Results have shown that the fuzzy logic method could separate reasonably stratiform and convective rain.更多还原