An algorithm to retrieve soil moisture using synergistic active/passive microwave data on bare soil surface

Synergism of microwave active/passive data can be promising in practical applications and in the understanding of the interaction mechanism between microwave radiation and land surfaces. But compared with many of the microwave scattering and emission models, no more attention has been paid in this field. A database with simulated microwave backscattering coefficients and emissivities has been constructed under various surface roughness and soil moisture conditions by employing the IEM along with other well-known models. At first step, only Gaussian roughness distribution and small to moderate rough surface is considered. Under rougher conditions, shadowing function has been involved. By analyzing this database, we find out that in some certain ranges, microwave emissivities can be deduced from backscattering coefficients through surface rms slope and rms heights, though their relationship may not certainly be linear. And it also been shown this relationship is independent with soil water content. Therefore, by using empirical or semi-empirical passive models, soil moisture can be retrieved from backscattering coefficients with a satisfactory accuracy. Error analysis and verification using field observations is also given in the paper. By doing such a research, we hope to give an insight into the interaction mechanism between active and passive microwave sensing and also a new algorithm to retrieve land surface parameters through synergism.