where Pdiffuse and Pbeam are proportions of incident seasonal photosynthetically
active radiation (PAR) reaching the top of the canopy
as diffuse and direct radiation, respectively, and Tdiffuse and Tbeam
are proportions of diffuse and direct radiation reaching the hemispherical
photograph. We assume that Pdiffuse and Pbeam are equal
to 0.5 (Battaglia et al., 2002).