Electromagnetic scattering from multilayer rough surfaces with arbitrary dielectric profiles for remote sensing of subsurface soil moisture

Radar remote sensing of soil moisture content at low frequencies requires an accurate scattering model of realistic soils, which often involves multilayer rough surfaces and inhomogeneous dielectric profiles. In this paper, a hybrid analytical/numerical solution to two- dimensional scattering from multilayer rough surfaces separated by arbitrary dielectric profiles based on the extended boundary condition method (EBCM) and scattering matrix technique is presented. The reflection and transmission matrices of a rough interface are constructed using EBCM. The inhomogeneous dielectric profile is modeled as a stack of piecewise homogeneous dielectric thin layers. The scattering matrices of an inhomogeneous dielectric profile are computed by recursively cascading reflection and transmission matrices of individual dielectric interfaces. The interactions between the rough interfaces and the inhomogeneous dielectric profile are accounted for by applying the generalized scattering matrix technique. The solution presented in this paper is for the two-dimensional scenario of multilayer rough surfaces. The technique can also be applied in three dimensions. In numerical simulations, the actual field-collected soil moisture data are used. In particular, the dielectric profiles during both dry and wet ground conditions are examined. The numerical simulations are performed to investigate both backscattering scattering coefficients and co- polarized phase difference due to different subsurface roughness parameters and ground conditions. The results show that both backscattering coefficients and co-polarized phase difference at low frequencies are sensitive to the roughness of subsurface interfaces and deep soil moisture. Also, much larger depth sensitivity can be achieved using co-polarized phase difference than scattering coefficients.