Mechanisms for rain effects on Synthetic Aperture Radar

Five possible mechanisms for the rain effects on the spaceborne C-band SAR observations are considered: 1) attenuation and 2) volume backscattering for the microwave transfer in atmosphere; as well as 3) rain - induced damping to the wind waves and 4) rain - generated ring waves on the ocean surface, and 5) diffraction on the sharp edges of rain products. A composite radar scattering model composed of the atmosphere radiative transfer model and the ocean surface Bragg wave theory is employed to analyze the impact of rain on the normalized radar-backscatter cross-section (NRCS) measured in the VV- and cross-polarized C-band Synthetic Aperture Radar (SAR) channels. Our composite model was validated with the matchup of observations of wind speed and rain rate from the SFMR data as well as the NRCSs and incidence angles of C-band VV-polarization SAR data over two hurricanes. Comparisons between the observed NRCSs and the atmosphere part of our model imply that the most important mechanism for the rain effect on the C-band VV polarized SAR hurricane observations is through the influence of waves on the ocean surface. Moreover, the non-Bragg scattering is important for the cross-polarized NRCS simulations.