Estimation of all-sky downward shortwave radiation from MTSAT-1R images and MODIS data

Abstract

Downward shortwave radiation (DSR) receipt at the Earth’s surface is an important parameter in models of ecosystem dynamics and climate change. This paper presents a methodology to estimate DSR using hourly geostationary satellite (MTSAT-1R) and MODIS BRDF albedo parameter product (MCD43C1). The proposed algorithm retrieves atmospheric parameters directly from MTSAT-1R images by searching and interpolating look-up tables (LUT), which are created by the SBDART. The derived cloud optical thickness together with surface albedo and DEM are used to calculate the instantaneous downward shortwave radiation under cloudy sky. Hourly and daily DSR is calculated by the diurnal cycle integration of hourly instantaneous downward flux. The retrieved daily DSR is compared with ground-based measurements at 96 stations from China Meteorological Administration (CMA). The results show that the estimated DSR is in good agreement with ground measurements over China with a correlation coefficient of 0.93 and a mean bias of 5.8%. Root-mean square differences in the daily DSR are 20.7% for all sky conditions. The daily DSR is also compared with observations on Tibetan Plateau and the results shows a correlation coefficient of 0.91 and a mean bias of 1.53%. Root-mean square differences are 17.5%. The differences between the satellite derived estimates and ground observations may be attributed to calibration uncertainty of the satellite sensor and the ground instruments, undetected cloud shadows, steps of the LUT parameters, uncertainty in determining surface reflectance, and errors in ground observations.