Urban Night Sky Conditions Determination Method Based on a Low Resolution All-Sky Images

This paper describes the method of determining the night sky conditions for urban areas. The main purpose of this method is to enable digital detection of night sky conditions based on low resolution all-sky camera for urban astronomical observatories. It is crucial to mention here that this method only detects the condition of the night sky and does not measure the cloud coverage. The method involves pixel analysis and it consists of two main stages; (1) the preprocessing which include red-green-blue colour channels splitting and masking and (2) the night sky determination. In this study, we have found that the night sky conditions can be discriminate between clear and cloudy based on the peak of the all-sky image's histogram. Nighttime all-sky images with a peak pixel value of 74.53 and lower will be considered as a clear sky while those with a higher value of peak pixel value is considered as a cloudy night sky condition.