A technique for mapping downward longwave radiation using satellite and ground-based data in the tropics

This paper presents a technique for mapping monthly average hourly downward longwave (LW↓) irradiance using ground- and satellite-based data. A model relating LW↓ irradiance to a satellite derived-brightness temperature of the earth-atmospheric system, relative humidity and ambient air temperature was formulated. This model was validated against LW↓ irradiance obtained from measurements at 4 sites in the tropics and discrepancy in terms of root mean square errors and mean bias errors was found to be 1.89% and −0.69%, respectively. After the validation, the model was used to calculate monthly average hourly LW↓ irradiance over Thailand and the results were displayed as LW↓ maps. These maps reveal the influence of various factors on LW↓ irradiance.