Estimation of cloudiness conditions on eight-point scale using the histogram technique applied to optical range images from all-sky camera

Automatic method for determining the cloud amount using optical range images from all-sky camera installed at Sayan Solar Observatory. Using the camera SBIG AllSky-340 allowed us to simultaneously determine the cloud amount by visual method (jpg-format images) and histogram method (fits-format images). We obtained parameters of the histogram profile of night sky brightness which response to change in cloud amount. The empiric formula for calculating the eight-point scale cloud amount which is the function of parameters of the histogram profile of the sky brightness is presented. The cloud amount values determined by two methods are compared. The results agree well, and the diversity does not exceed ±2 points.