We have developed a microwave canopy backscatter model for continuous and discontinuous tree canopies. This model works at P-, L-, and C- bands. Model inputs are stand parameters (stand density, mean stand trunk diameter at breast height, etc.), tree parameters (numbers of branches per unit volume, branch size, etc.), and radar parameters (wavelength, polarization, etc.). Model outputs are the HH, HV, and VV backscatter coefficients, the VV-HH phase difference, and the HH and VV correlation coefficient. All five outputs correspond to five direct measurements of the JPL airborne SAR system. We have studied the L-band model sensitivity to stand data such as branch size and density, needle density, tree crown width and depth, tree size, and stand density. The comparison of the model outputs with JPL airborne SAR data at Mt. Shasta site (obtained in September 1989) are very promising.