위성관측운량 보정을 위한 알고리즘의 개발

The satellite-viewed cloudiness, a ratio of cloudy pixels to total pixels (Csat, prev), inevitably differs from the “ground-viewed” cloudiness (Cgrd) due to different viewpoints. Here we develop an algorithm to retrieve the satellite-viewed, but adjusted cloudiness to Cgrd (Csat, adj). The key process of the algorithm is to convert the cloudiness projected on the plane surface into the cloudiness on the celestial hemisphere from the observer. For this conversion, the supplementary satellite retrievals such as cloud detection and cloud top pressure are used as they provide locations of cloudy pixels and cloud base height information, respectively. The algorithm is tested for Himawari-8 level 1B data. The Csat, adj and Csat, prev are retrieved and validated with Cgrd of SYNOP station over Korea (22 stations) and China (724 stations) during only daytime for the first seven days of every month from July 2016 to June 2017. As results, the mean error of Csat, adj (0.61) is less that than that of Csat, prev (1.01). The percent of detection for ‘Cloudy’ scenario of Csat, adj (73%) is higher than that of Csat, prev (60%) The percent of correction, the accuracy, of Csat, adj is 61%, while that of Csat, prev is 55% for all seasons. For the December-January-February period when cloudy pixels are readily overestimated, the proportion of correction of Csat, adj is 60%, while that of Csat, prev is 56%. Therefore, we conclude that the present algorithm can effectively get the satellite cloudiness near to the ground-viewed cloudiness.