A microwave signature model based on the vector radiative transfer equation has been developed for a forested canopy. The model is designed to operate over a wide frequency band and to account for the size and orientation distributions of each forest component, the layering effect, and multiple scattering. The average Muller matrix is formulated in terms of the iterative solution of the radiative transfer solution up to the second order in albedo and then used to determine the co-polarized and cross-polarized power returns. Numerical results show that a significant difference exists in the polarimetric signatures of a forested canopy when the crown region is treated as two layers versus one layer with the same leaf and branch distributions. >