An investigation of how linear BRDF models deal with the complex scattering processes encountered in a real canopy

The Botanical Plant Modelling System (BPMS), P. Lewis (1996), P. Lewis et al. (1997), is used to simulate the directional reflectance of a barley canopy. The ability of linear BRDF model kernels to describe the directional reflectance of this canopy relatively accurately is confirmed. Rather than accepting this as a (form of) `validation´ of the simple model, a more interesting line is followed whereby the factors controlling the reflectance field of the canopy (proportion of sunlit/shaded leaves/soil and respective phase functions) are calculated within the BPMS and compared with the way in which they are modelled in the linear model. This is used to investigate the nature of the relationship between the `apparent´ (linear model) canopy parameters (LAI, leaf reflectance etc.) and the `actual´ (BPMS) parameters