1. Direct solar radiation available on clear days;Threkeld;Trans. ASHRAE,1958
2. Sunshine and solar radiation in Singapore;Sien;Meteorol. Mag.,1969
3. Space and time variability of solar radiation;Pack,1973
4. Reference insolation data base: A case history, with recommendations;Randall,1973
5. Correlation equation for hourly diffuse radiation on a horizontal surface;Orgill,1976