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A new approximation to Ross' (1981) radiative transfer theory for small values of leaf area index (LAI) and two new approximations to Li and Strahler's (1992) geometric‐optical mutual shadowing model are derived. These, together with Roujean et al.'s (1992) approximation to Ross' theory for large LAI and their geometric‐optical model of rectangular protrusions, may be used for formulating semiempirical models of the bidirectional reflectance distribution function (BRDF) of the land surface through linear combinations. Because the functions superimposed depend only on viewing and illumination geometry, the BRDF models derived may be called kernel‐driven; but Nilson and Kuusk's (1989) modified version of Walthall et al.'s (1985) model is an example of an empirical model that belongs to this same class. The linearity of kernel‐driven models is advantageous to global BRDF and albedo processing needs in …