Modeling Active Microwave Remote Sensing of Snow using Dense Media Radiative Transfer (DMRT) Theory with Multiple Scattering Effects

Dense media radiative transfer theory (DMRT) is used to study the multiple scattering effects in active microwave remote sensing. To solve the dense media radiative transfer equation, we decompose the diffuse intensities into Fourier series in the azimuthal direction. Each harmonic is solved by the eigen-quadrature approach. The solution includes full multiple scattering effects within DMRT. Comparisons are made with the first order and the second order solutions. The model is applied to active microwave remote sensing of terrestrial snow. Full multiple scattering effects are important as the optical thickness for snow often exceed unity. The results are illustrated as a function of frequency, incidence angle and snow depth. The results show that cross polarization can be significant and can be only 6 to 8 dB below co-polarization, a result that is consistent with experimental observations. Also we note that even at snow depth of more than one meter, the active 13.5 GHz backscattering coefficients still have significant sensitivity to snow thickness.