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 (<em>LW</em>_↓) irradiance using ground- and satellite-based data. A model relating <em>LW</em>_↓ 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 <em>LW</em>_↓ 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 <em>LW</em>_↓ irradiance over Thailand and the results were displayed as <em>LW</em>_↓ maps. These maps reveal the influence of various factors on <em>LW</em>_↓ irradiance.