A hybrid geometric optical and radiative transfer approach is used to parameterize the four component spectral signatures （sunlit crown

sunlit background

shaded crown

and shaded background） in geometric optical reflectance models over discontinuous plant canopies. The path scattering parameters （transmittance and reflectance） are estimated using a modified version of the analytical solutions of path scattering parameters （reflectance and transmittance） for a homogeneous medium layer

which includes the effect of the canopy gaps. The spectral component signatures are functions of the transmittance and reflectance for discontinuous plant canopies

the background albedo and the proportions of incident beam and diffuse skylight. The modeled spectral component signatures show good agreement with data collected in a conifer forest in Holland

Maine. Using the parameterized spectral component signatures

estimates from Li and Strahler’s geometric optical mutual shadowing model for directional reflectance over the old jack pine and old black spruce forests in the boreal ecosystematmosphere study （BOREAS）

match well with PARABOLA measurements at different solar and viewing geometry.