物理-统计反演和云-晴空辐射特征差异检测结合的全天空高云判别能力改进算法与初步试验

在全天空红外-可见光云像观测反演方法基础上,针对已往阈值法判断高云的局限性,提出改进的算法。对可见光图像可利用以太阳-天顶为连线的主平面两边相元特性的对称性来判断云的存在,对红外成像仪可利用同一仰角扫描时所得不同方位角亮温分布的非均匀性来判断云的存在。以北京2011年1 3月观测资料为基础,选择原阈值法未能判别出来的案例进行再处理,全天空可见光成像观测仪高云判别能力最高可达73.9%,全天空扫描式红外成像仪可达70.1%。该工作为天空的高云识别提供新的复合算法。

Improving the method for high cloud discriminability of All-Sky-Imagers based on physical-statistical relationship and radiation characteristics between cloudy and clear sky and its preliminary experiments

The threshold method is commonly used to determine cloud in sky, which has great limit when it comes to thin cirrus. This paper is focused on improving the ability of distinguishing high or thin cloud from sky. Based on the developed cloud detection by all-sky infrared and visible imagers, a new modified method is presented. Measurements of sky visible image and thermal infrared brightness temperature were conducted at the top of the laboratory building, using an automatic visible all-sky imager (ASI) and an automatic scanning infrared thermometer (SIRIS) developed by the Key Laboratory of Middle Atmosphere and Ulobal Environment Obscrvation (LAGEO),the Institute of Atmospheric Physics (IAP),Chinese Academy of Sciences. hhe characteristics of pixels which arc symmetrically disposed by the solar principal plane arc used to estimate the existence of cloud in a visible image. As for SIRIS, the heteropic distribution of brightness temperature (TB) from the same elevation and the different azimuth can tell whether there is cloud. The cases at Beijing during the period January to March 2011,in which clouds do exist yet cannot be detected before are sorted to test the algorithm. The result shows that the ability of distinguishing high cirrus for ASI has reached to 73.9% and for SIRIS has reached to 70.1%.This work provides a new composite algorithm for the high cloud recognition.