The commonly used soil moisture retrieval at vegetated area from microwave radiometry data assume a simple model of vegetation

which is characterized by vegetation volume fraction

effective dielectric constant

plant moisture content

etc. This algorithm is successfully applied under lower frequencies and lower vegetation

but the data used in single scattering albedo is simply assigned a fixed value which is independent of frequencies and polarization

sometimes are even set to zero. In this study

a radiative transfer model is used to model the emissivity and transmissivity of forest canopy

which is more realistically characterized as a volumetric medium consisting of discrete scatters （leaves

stems

tree branches

and trunks.） The scattering coefficient is obtained by integrating the Stokes matrix in the whole sphere region

the extinction coefficient is calculated by forward scattering theory. This mode is expected to cover a wider frequency range as well as vegetation species from lower crop to forest canopy. To facilitate the soil moisture inversion from radiometric data

the unknown variables need to be reduced. The possibility of fitting the modeled emissivity and transmissivity of vegetation canopy into simple equations

and the relationships of these parameters between different microwave radiometric frequencies were studied and the results are presented in this paper.