Estimation of clear-sky downward longwave radiation from satellite data in heihe river basin of northwest China

The atmospheric downward longwave radiation (DLR) is a key variable of land surface energy budget. In this study, the clear-sky DLR at high spatial resolution in Heihe River Basin was estimated from MODIS data, and three algorithms containing empirical and hybrid methods were compared. Compared with field measurement, the Idso scheme and Tang´s scheme had relatively better performance than Wang´s scheme, with RMSE of 27.50, 26.96, 30.23 W/m², respectively. For Idso scheme, the major error was caused by the distance between the lowest level of MOD07 and the surface level. For Wang and Tang´s scheme, the major error came from the difference between the atmospheric profiles used to train the schemes and the actual atmospheric condition in the study area. Net longwave radiation (NLR) was also calculated, and the RMSE of all sites was 31.24 W/m².