A method for mapping monthly average hourly diffuse illuminance from satellite data in Thailand

• A method for mapping diffuse illuminance from satellite data is proposed.
• A global illuminance model is improved for calculating global illuminance.
• A diffuse fraction model is developed for extracting diffuse from global illuminance.
• Diffuse illuminance obtained from the method agrees well with the measurements.
• Diffuse illuminance maps of Thailand are generated using this method.

This paper presents a method for mapping monthly average hourly diffuse illuminance from satellite data. The calculation of monthly average hourly diffuse illuminance starts with the estimation of monthly average hourly global illuminance from MTSAT-1R satellite data using an improved satellite-based illuminance model. Next, a diffuse fraction model is developed from ground and satellite-based data which is then used to extract diffuse illuminance from the satellite-derived global illuminance. To assess the performance of the method, modeled diffuse illuminance obtained from this method is compared with that obtained from measurements at four stations in Thailand. There is good agreement between calculated and the measured values of monthly average hourly diffuse illuminance, with the root mean square difference and mean bias difference of 9.7% and −1.4% respectively. The model is used to map monthly average hourly diffuse illuminance for the country. The maps reveal the diurnal and seasonal variations in response to a range of factors including cloud cover, zenith angle and monsoonal effects.