Electromagnetic scattering interaction between a dielectric cylinder and a slightly rough surface

In radar remote sensing of vegetation, accurate scattering models that can describe the interaction of electromagnetic waves and vegetation-covered terrain are of great importance. The common approach is to regard the vegetation-covered surfaces as a random collection of dielectric particles with canonical geometries, such as cylinders representing stems and branches and thin dielectric disks representing leaves, above a half-space dielectric medium with rough interface representing the ground. Most scattering models developed for this problem are based on single scattering properties of the scatterers. In these models, the scattering interaction among the vegetation particles and the vegetation particles and the rough surface are ignored. In more advanced models, such as radiative transfer (numerical or second-order iterative solutions), the scattering interaction among scatterers are accounted for assuming that the particles are in the far-field of each other. This is not an accurate model because most vegetation structures contain large particles (tree trunk, long branches, main stem for grasses) whose length are comparable to the vegetation layer thickness and are much larger than the wavelength. In these cases the near-field interaction, as opposed to far-field interaction, must be taken into account. Experimental results indicate that although the first-order scattering models are capable of predicting the co-polarized backscatter adequately, they are not able to predict the cross-polarized backscatter to within a desirable accuracy. In this paper, an analytical solution that can predict the near-field interaction between a scatterer and a rough surface is presented. This solution is derived using a recently developed technique which is based on the reciprocity theorem, K. Srabandi et al. (1994). This approach is very efficient since only the current distribution of isolated scatterers are needed to evaluate the interaction in the far-field region. The second moments of backscatter fields are provided for a circular dielectric cylinder above a slightly rough surface with inhomogeneous dielectric profile. The accuracy of the theoretical formulation is verified by conducting polarimetric backscatter measurements from a lossy dielectric cylinder above a slightly rough surface. Excellent agreement between the theoretical prediction and experimental results are obtained