半透明云风矢量高度算法中代表运动像元的使用  

Use of Representative Pixels of Motion for Wind Vector Height Assignment of Semi-transparent Clouds

作　　者：张晓虎[1] 张其松[1] 许健民[1] 

机构地区：[1]国家卫星气象中心,北京100081

出　　处：《应用气象学报》2017年第3期270-282,共13页Journal of Applied Meteorological Science

基　　金：国家自然科学基金项目(41275036);公益性行业(气象)科研专项(GYHY201306001)

摘　　要：半透明云风矢量高度指定是卫星风矢量算法的重要部分,需要使用来自半透明云体的辐射和云下背景辐射两个变量。为了更精确地获得来自半透明云体的辐射,采用像元对追踪相关系数的贡献和红外亮温两个变量进行统计分析,将追踪图像块中的像元分为3个部分:小贡献像元、暖区段大贡献像元和冷区段大贡献像元;对暖区段、冷区段内大贡献像元的特征进行考察表明,冷区段的大贡献像元更能代表追踪图像块运动,称为代表运动像元。选择代表运动像元参与计算来自半透明云体的辐射,对半透明云风矢量高度指定算法进行改进,在该算法中分别使用和不使用代表运动像元,计算FY-2气象卫星风矢量,将结果与欧洲中期天气预报中心(ECMWF)分析场进行对比表明,在半透明云高度指定算法中使用代表运动像元,FY-2气象卫星风矢量误差明显降低。Height assignment of semi-transparent clouds needs two variables： Radiation from semitransparent clouds themselves and radiation from the background underneath semitransparent clouds. Generally, the former radiation is calculated using algorithms based on all pixels in tracer boxes. A new algorithm, how- ever, is proposed considering only pixels with great contribution to correlation coefficients during wind vector tracing stage, and only allow these pixels to join the calculation. Scatter diagrams are made with in- frared brightness temperature against their contribution to the feature tracking correlation coefficients. Scatter diagrams show a ＂C＂ shape pattern and can be used to recognize representative pixels of motion. Pixels with relative less contribution to correlation coefficients are at the left side of the ＂C＂ shape with in- frared brightness temperature in the middle range. The other pixels with relative more contributions are naturally separated into two branches with warmer and colder infrared brightness temperature respective- ly. When tracer boxes are partly covered by clouds, the warm branch pixel brightness temperature is with typical ground feature at both the scope and the variability. And when tracer boxes are totally covered by clouds, warm branch pixels are in the slot of clouds with typical cloud features among cloud cells. Thus, no matter tracer boxes are partly covered or totally covered by clouds, cold branch pixels with greater con- tribution to correlation coefficients are better at representing the cloud motion and can be named as pixels with contribution to the motion. The algorithm using different pixel＇s contribution to the feature tracking improves height assignment quality by effectively removing rapid changing pixels in tracer boxes when esti- mating the cloud height. Using representative pixels of motion at the estimation of radiation from semi- transparent clouds themselves, FY-2 wind vector height assignment quality is improved.

关 键 词：风矢量 半透明云风矢量高度指定 代表运动像元 

分 类 号：P412.27[天文地球—大气科学及气象学]