Comparison of Absorbed and Intercepted Fractions of PAR for Individual Trees Based on Radiative Transfer Model Simulations

The fraction of absorbed photosynthetically active radiation (fAPAR) is a key parameter for estimating the gross primary production (GPP) trees. For continuous, dense forest canopies, fAPAR, often equated with intercepted fraction, fIPAR. This assumption not valid individual trees in urban environments or parkland settings where canopy sparse and there are well-defined tree crown boundaries. Here, distinction between fAPAR fIPAR can be strongly influenced by background large illumination variations due to multi-scattering shadows buildings. study investigates radiative budget PAR bands using coupled leaf-canopy transfer model (PROSPECT-DART), considering suite tropical species over wide range assumed leaf chlorophyll contents. analyses simulate hyperspectral images (5 nm bandwidth) crowns selected (concrete vs. grass) conditions. We then use an artificial neural network-based method partition sunlit shaded leaves within each crown, as latter have lower values. Our results show decreases ratio diffuse direct scene irradiance (SKYL), while SKYL has minimal influence leaves. Both decrease at more oblique solar zenith angles (SZA). Higher values occur concrete backgrounds larger higher angles. that typically 6–9% than up 14% = 0. differences also depend on health condition leaves, such content. improve understanding fAPAR/fIPAR facilitate development protocols field measurements.