Estimation of Shortwave Broadband Irradiance at the Bottom of the Atmosphere Over Ilorin in Central Nigeria Using Radiative Transfer Model

Abstract

Shortwave Broadband Irradiance (SBI) makes up about 96% of the Total Solar Irradiance (TSI) received on earth, and it is known to be the major driver of climate change. The SBI also contains ultraviolet radiation, which is harmful to inhabitants of Earth. The Direct Normal Irradiance (DNI) and Global Horizontal Irradiance (GHI) received at the surface in Ilorin (8.484°N, 4.675°E), Central Nigeria, have been computed using a radiative transfer model: the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS). The spectral range of the study was from 280 to 4000 nm under cloudless conditions, using aerosol retrieval data from Ilorin AERONET station for the year 2020. The results were compared to the satellite based dataset of the Copernicus Atmosphere Monitoring Service (CAMS) McClear Clear-Sky Irradiation service, and showed good correlation for both sources of irradiance for the period of study. The results show that the RMSEs were comparatively low for most of the year, except during the dry season when the RMSE for the Direct Normal Irradiance (DNI) reached 171.77 W/m2. This implies that the Copernicus Atmosphere Monitoring Service (CAMS) McClear Clear-Sky Irradiation service data is fairly accurate for estimating the irradiance values during the wet and dry seasons in Nigeria, but not for Direct Normal Irradiance (DNI) during the dry season