Modelling and Estimating Photosynthetically Active Radiation from Measured Global Solar Radiation at Calabar, Nigeria

In this research paper, measured monthly average daily radiometric data for global solar radiation on the horizontal surfaces and atmospheric parameters including relative humidity, sunshine hours, dew point temperature as well as the ambient temperatures (minimum and maximum) at Calabar, Nigeria obtained from the archives of the Nigeria Meteorological Agency, Oshodi Lagos, Nigeria for a 14-year period (2000-2013) were analysed and fifteen empirical models developed for predicting photo synthetically active radiation (PAR) for Calabar environment. The photo synthetically active radiation is estimated from measured global while the models are developed using extraterrestrial PAR, relative humidity, relative sunshine hours, dew point temperature as well as the relative ambient temperature (minimum and maximum) and clearness index. The performance of the models developed were tested for validation using mean bias error (MBE), root mean square error (RMSE), mean percentage error (MPE), Nash-Sutcliff equation (NSE), chi squares (χ2) and index of agreement (d). the linear, quadratic and polynomial regression models developed to estimate PAR judging from the model performance and validation test indicates that the proposed models could be used to estimate PAR in Calabar environ and other locations with similar climatological conditions across the globe.