Radiative transfer models establish the quantitative relationship between remote sensing signals and physical parameters

including the object properties

the object structures and the observation geometries

on the understanding of the interactions of the electromagnetic wave and the objects. They serve as the theoretical basis for the interpretation of the remote sensing signals and the retrieval of surface parameters. Recently spatial heterogeneity has drawn widespread attention in the field of quantitative remote sensing. The increasing high resolution imagery and Li DAR data provide a strong support for the consideration of heterogeneity. For the radiative transfer modeling process over heterogeneous vegetation scenarios

the component area ratio

the 3D structure and the distribution pattern within the pixel

and the shadowing and scattering effects near the boundary

are important factors that should be considered. The recent progresses on the VIS/NIR BRDF and the TIR directional emission modeling over heterogeneous land surfaces are introduced

respectively. The key scientific issues and future development directions of heterogeneous vegetation canopy modeling are proposed at last.