Efficient modeling of sun/shade canopy radiation dynamics explicitly accounting for scattering

摘要

The separation of global radiation (R_g) into its direct (R_b) anddiffuse constituents (R_g) is important when modeling plantphotosynthesis because a high R_d:R_g ratio has been shown to enhanceGross Primary Production (GPP). To include this effect in vegetation models,the plant canopy must be separated into sunlit and shaded leaves. However,because such models are often too intractable and computationally expensivefor theoretical or large scale studies, simpler sun-shade approaches areoften preferred. A widely used and computationally efficient sun-shade modelwas developed by Goudriaan (1977) (GOU). However, compared to more complexmodels, this model's realism is limited by its lack of explicit treatment ofradiation scattering.Here we present a new model based on the GOU model, but which in contrastexplicitly simulates radiation scattering by sunlit leaves and theabsorption of this radiation by the canopy layers above and below (2-streamapproach). Compared to the GOU model our model predicts significantlydifferent profiles of scattered radiation that are in better agreement withmeasured profiles of downwelling diffuse radiation. With respect to thesedata our model's performance is equal to a more complex and much sloweriterative radiation model while maintaining the simplicity and computationalefficiency of the GOU model.