Inclusion of a Simple Multiple Scattering Model into a Microwave Canopy Backscatter Model

A simple multiple scattering model has been incorporated into a microwave canopy backscatter model for forest stands with continuous or discontinuous tree canopies. The multiple scattering model was empirically derived using available calculated multiple scattering values and Monte Carlo simulation. All orders of scattering within canopies beyond single scattering were assumed to be isotropic. Multiple scattering was divided evenly among HH, HV, VH, and VV polarizations. The corresponding single scattering term was polarization-sensitive. The effect of the multiple scattering term on modeled canopy backscatter was less at long wavelengths than at short wavelengths. At a given wavelength, the multiple scattering term affected copolarized scattering less than cross-polarized scattering. These predictions were consistent with calibrated SAR observations and with our understanding of microwave scattering in forested environment. Including multiple scattering effects improved the agreement between modeled and measured canopy backscatter particularly for cross-polarized backscatter at short wavelengths.