New cloud free line of sight statistics measured with digital whole sky imagers

Cloud Free Line of Sight (CFLOS) statistics can be important to a number of applications involving transmittance of light through the atmosphere, including laser propagation, light propagation, and detection of objects by humans and instruments. This paper will discuss Cloud Free Line of Sight (CFLOS) and cloud persistence statistics determined from cloud measurements taken with Whole Sky Imagers (WSI). The WSIs are ground-based digital imaging systems that image the full upper hemisphere down to the horizon in wavebands in the visible and NIR. Digital automated WSI systems were originally developed by the Marine Physical Lab in the 1980's to address the CFLOS application, and then further developed for 24-hour day and night capability. Approximately three million image sets have been acquired with the Day/Night WSI in conjunction with DOE's ARM program. Recent advances in the cloud decision algorithms at Marine Physical Lab have enabled the extraction of processed cloud images of sufficient quality to obtain reliable cloud statistics. A test sample of approximately 4500 image sets has been processed to yield CFLOS statistics down to the horizon, as well as statistics related to the persistence of clouds and cloud holes. This talk will provide a brief overview of the instruments and current algorithm developments. The CFLOS results and sample persistence results will be presented.