A Method for Observing and Counting Day-time Cloud Amounts in an Astronomical Site Survey

The cloud amount is one of the most important factors in an astronomical site survey. A data processing method for counting cloud amounts in a site survey is presented. The processing can effectively lead to accurate cloud amounts in the all-sky images taken by a fish-eye camera, and could avoid the errors introduced through the observation with naked eyes by different observers. Certain practical results demonstrate that the processing is reasonable and reliable. The method has been further applied to the sky images observed at the Oma candidate site in Oma Tibet, and the processing results are compared to the cloud amounts observed with naked eyes. The uncertainties and improvement of the method are also discussed.