中文摘要：

云量是影响天文台址质量最重要的因素之一,对夜间云量的检测和处理尤为重要.采用地面云量相机对全天云量进行监测,所拍摄的图像需要有效的方法进行处理以量化云量.夜间云量图像受月光的影响严重,因此将夜间的云量图像分为有月夜和无月夜两类进行处理.针对无月夜情况,给出了夜间云量的处理过程.对图像中的亮星进行定位和测光,确定星等差.以晴夜图像中亮星的星等差为参照,将星等差低于阈值条件的亮星概率作为晴夜的概率标准.选取了3类图像对该方法进行测试并确定云量,分析了阈值条件对结果的影响.最后,讨论了该方法的适用范围和不确定性.

英文摘要：

The site quality of astronomical observatory critically depends on cloud coverage, and the measurement of cloudiness is particularly important for selecting a telescope site.In recent site testing work,all-sky camera is widely employed to detect cloud.Due to the impact of moon light,the measurements of cloudiness of all-sky images are considered to be divided into two categories,no-moon nights and moonlit nights. The method is described in this paper to deal with all-sky images in no-moon nights. By identifying the positions of bright reference stars and making photometry for a set of all-sky images in clear nights,we can set up a reference image with median smoothing of the differential magnitude values.The standard image can be taken as the threshold for clear nights,and the detectivity of stars in other images can be utilize to reveal cloud coverage. Three types of all-sky images,icy lens,part of cloud,and full of cloud,are selected to check up the method,and the effect of threshold determination on cloud estimates is discussed. Finally,the limitation and uncertainty of the method are discussed.