Estimation of photosynthetically active radiation using solar radiation in the UV-visible spectral band

In this paper, we discuss a method using the UV-visible band flux to estimate photosynthetically active radiation (PAR). We use radiative transfer models to calculate the ratio of PAR to the UV-visible flux and confirm that this ratio is close to constant regardless of atmospheric conditions. The best ratio identified in this study is 0.8644. We further introduce a UV-visible band model and use it to calculate the PAR flux using observational datasets, mainly taken from the US SURFRAD network. The results are compared with the observations. It is seen that the PAR values determined using this method are in good agreement with observations. The relative mean biases (rMB) for both clear- and all-sky conditions evaluated for seven SURFRAD stations are −1.04% and −4.85%, respectively. The corresponding relative root mean square errors (rRMS) are 6.22% and 17.97%, respectively.