多普勒雷达速度图像识别及散度提取方法研究

大尺度风场往往是冷暖平流与大尺度辐合辐散运动相结合的结果,因此将大尺度风场的多普勒雷达速度特征提炼成以下4种类型:(1)暖平流与辐合迭加;(2)冷平流与辐合迭加;(3)暖平流与辐散迭加;(4)冷平流与辐散迭加。不同类型的风场引起零速度线不同的弯曲特征,对判断大尺度风场的辐合辐散有着指示作用。根据零速度线的弯曲程度以及一定距离圈上零速度点与雷达中心连线的夹角等,首先推导出定量计算大气辐合辐散值的算法,然后提出利用逐个调整法识别零速度点的方法。根据该算法,结合零速度点的识别技术,提出了图像识别原理与方法步骤。据此,能够从多普勒雷达基数据中提取出大气平均散度,得到大尺度天气系统不同高度的散度值,并进一步提出了散度平面位置显示(divergence PPI)的概念。通过实例,根据散度PPI与速度PPI的对比,分析了图像识别的效果,并将图像识别法提取的散度值与EVAD技术提取的散度值进行了对比分析。

A Study on Doppler Radar Velocity Pattern Recognition Technique and Divergence Extraction Approach

Large-scale wind fields always are a result of large convergence or divergence hybridized with cold or warm advection,so four sorts of mixed wind fields are abstracted:(1) warm advection combined with large scale convergence;(2) cold,with convergence;(3)warm,with divergence;(4)cold,with divergence.Different fields lead to unlike zero velocity lines characteristics,which have indicated effect to estimate divergence of large-scale wind fields.By means of the curve degree and the inter-angle between zero points in a distance ring and radar center,a quantificational arithmetic to calculate air divergence is deduced by mathematics approach at firstly,and then a method of one by one adjustment is introduced to identity zero velocity points.United with zero identified,a principle of pattern recognition and its approach are documented,whereby,air average divergences can be extracted from Doppler radar base data,the divergences of different levels are quantificationally received,and furthermore,an idea of divergence plan position indicator(div PPI) is advanced.On basis of two cases,the effect of picture identification is analyzed by contrasting div PPI with velocity PPI,divergences extracted by identification are compared with EVAD.