Improvement of solar irradiance estimates based on COMS-MI satellite images over Korea

Although previous research has been conducted to estimate the solar irradiance over Korea using satellite imagery, most of this work has employed foreign satellite imagery. In the present study, we provide improved estimates of global horizontal irradiance over Korea using satellite images obtained from the Communication, Ocean and Meteorological Satellite - Meteorological Imager (COMS-MI), Korea's first geostationary satellite. The Kawai and Kawamura methodology, which is considered adequate for studies of East Asia, is applied to estimate solar irradiance under both clear and cloudy conditions. We modified this method in two ways, using training data to improve the estimates of solar irradiance. First, the biases of irradiance under clear conditions were offset by applying the correction coefficient derived from the relationship between the satellite-based estimations and the ground-based observations made by the Korea Meteorological Administration. Second, the coefficient of cloud attenuation, Look-Up Table (LUT) was newly derived from the relationship between the satellite-estimated clear sky and ground-observed cloudy sky irradiances. Using this method, the instantaneous global horizontal irradiance over Korea was estimated for every fifteen minutes from May 2011 to April 2012. We evaluated the hourly and daily means of these estimations by comparing them with the observations made at twenty-four stations. The estimations and observations showed a strong correlation and the application of the correction coefficient and the modification of the LUT improved the accuracy of the solar irradiance estimations. The root mean square errors of the hourly and daily mean irradiances decreased from 44.5% to 22.6% and from 41.2% to 16.5% respectively.