基于红外实时阈值的全天空云量观测

An Experiment Study of All-sky Cloud Amount Observation Based on Infrared Real-time Threshold

红外测温传感器在旋转平台控制下定时对全天空进行扫描,拼接全天空红外辐射亮温图像。利用天空中的云点与非云点在红外波段中表现出的不同特性,考虑不同仰角方向天空中云点与非云点的温度差异,结合地面环境参数,实时拟合天顶到水平区间内晴空时刻的温度阈值函数,利用阈值分割方式得出全天空云分布及云量信息。该方法可以有效减少地面环境参数及太阳光照对云图的影响,能够全天实时运行。将利用该方法获取的数据分别与人工观测数据及典型天气条件下可见光测云结果进行对比,结果表明该系统在云量观测方面具有一定的先进性和准确性。

The cloud typically covers about 50% of the earth surface, affecting the energy balance, water circula- tion of the earth, and influencing global climate. Cloud cover and cloud base height are the primary ele- ments in the observation of clouds, wherein the cloud amount reflects the regional weather and climate characteristics. However, the operating artificial observation method for cloud amount in China lacks ob- jectivity and costs too much workforce. Therefore, the research and development of an automatic measur- ing cloud device is extremely necessary. An infrared cloud detector based on the different characteristics of visible and infrared cloud images is developed in order to measure cloud amount. The infrared sensors regularly scan the whole sky under the control of the rotating platform, and stitching all-sky images of infrared brightness temperature. Based on the different characteristics of cloud images shown in infrared, different temperature at different elevation for the cloud point and non-cloud point is considered, combining with real-time infrared brightness temper- ature and ground environmental parameters. The temperature threshold functions are real-time determined from the zenith to the horizontal, the all-sky cloud distribution and cloud amount are derived using the method of segmentation. This method is effective in reducing the ground environmental parameters and the sunlight on the cloud images, and it can run properly throughout the day. The cloud measuring system can provide real-time analysis of the sky condition, cloud distribution and cloud amount. The system is fully automated and adaptable for all weather conditions, with high temporal resolution and accurate observation time, and it can show the cloud trajectory of the whole period and cloudiness trends. Measurements of cloud system has been performed experimental observation in the synthesize experi- ment base of Meteorological Observation Center of CMA since May 2011. Through the comparative data a- nalysis with the results of artificial observations and the visible cloud images, this measurement of cloud systems are proved to be able to provide results with high accuracy.