4Pfister G, McKenzie R L, Liley J B, et al. Cloud coverage based on all-sky imaging and its impact on surface solar irradiance [ J]. Journal of Applied Meteorology, 2003, (42) : 1421-1434.
5K McGuftle, A Henderson-Sellerst. Almost a Century of "Imaging" Clouds Over the Whole-Sky Dome [J]. Bulletin of the American Meteorological Society, 1989, 70 (10) : 1243 - 1253.