新一代天气雷达海浪回波特征分析和识别方法研究

Statistical characteristics of sea clutter and its identification with the CINRAD

海浪回波是影响沿海雷达定量降水估测和其他产品的重要因素,根据福州、温州的SA多普勒雷达收集的海浪回波资料,按出现时间关系将其分为两类。第1类海浪回波强度一般较强,主要出现在非台风期间降水过程的前后;第2类海浪回波强度较弱且均匀,仅在台风期间的雷达位置的近海域出现。通过分析资料得到两类海浪回波不同于对应降水回波的各种特征,确定识别海浪回波的最佳隶属函数。针对第1类海浪回波,考虑到海浪回波很少与降水回波混合,采用了基于回波分块和模糊逻辑的海浪回波识别方法,首先利用算法预处理条件判断是否执行算法识别,然后采用风暴单体识别与跟踪(SCIT)算法将回波组合成块,计算每个独立回波块的属性值,对符合要求的回波块和离散回波点再进行基于模糊逻辑的逐点识别,借鉴了刘黎平等2007年提出的分步式回波识别方法并加以改进来实现回波点的动态阈值识别。针对第2类海浪回波,直接采用了基于模糊逻辑的分步式海浪回波识别方法。分析表明,两种识别方法能分别对应识别出大部分海浪回波,回波分块和分步式方法对海浪回波的识别效果有明显的改善,有效地降低了降水回波被误判为海浪回波的概率。

Radar echo from sea clutter is an unpredictable event which often contaminates the precipitation measurement and other radar products in coastal areas. According to the sea clutter observed by SA Doppler radars in Fuzhou, and Wenzhou, it is divided into two kinds by the time when it appears. The first kind of sea clutter with strong strength mainly appears before and after a precipitation process during the period without typhoon. The second kind of sea clutter whose strength is generally weak and uniform only appears close to sea areas near the radar position during a typhoon. The reflectivity, radial velocity, spectrum width of velocity, and their spatial variations for sea clutter which are different from the corresponding precipitation in terms of echo are examined to determine the membership functions based on the sea clutter detection algorithm （SCDA）. For the first kind of sea clutter, considering its rare overlap with precipitation echo, the algorithm is based on the fuzzy logic and the echo piece-divizing using SCIT. Firstly, the pre-processing criteria can be used to determine when sea clutter is likely to take place so that sea clutter detection algorithm can be applied. Secondly, echoes are combined into pieces using SCIT, and if the area of an echo piece is more than 100 km2 the echo piece would be given an attribute value. The echoes would be calculated with an algorithm based on the fuzzy logical if the attribute value of the echo piece meets suitable conditions and the area of the echo piece is less than 100 km2. Inspired by Liu＇s two-step ground clutter detection algorithm, the author improved Liu＇s approach to identify the dynamic threshold. For the second kind of sea clutter, the algorithm is based on the fuzzy logic and the improved two-step approach. The analyses results show that most of sea clutters are detected effectively by the two kinds of identification method. The method of echo piece-divizing using SCIT and the improved two-step approach have obviously reduced the possibility of misidentifying precipitation echoes as sea clutters.