Numerical calculations of microwave scattering from dielectric structures used in vegetation models.

摘要

Numerical models for electromagnetic scattering from individual components of a vegetation canopy are studied. The models are based on a surface integral representation of the electromagnetic fields on the material bodies representing the vegetation constituents. Surface integral equations are obtained by using the equivalence principles, and their unknowns are equivalent surface currents. From the equivalent surface currents, the bistatic scattering coefficient is evaluated.; The method of moments is applied to solve these integral equations in the case of two-dimensional objects and of axisymmetric scatterers. The particular geometry of these bodies allows a simplification of the numerical solution. The results are validated for a number of shapes, for both perfectly conducting and homogeneous dielectric bodies. The numerical approach is then compared to analytical approximate models for scattering from vegetation components.; In order to take into account the presence of the ground under a vegetation canopy, a semi-infinite half-space is introduced in the modeling, and the surface integral equations are modified to consider its effects. The resulting integral equations contain a dyadic Green's function for the half-space. In particular, axisymmetric objects are considered, and the dyadic Green's function is written in terms of cylindrical waves. The solution by the method of moments requires the calculation of Sommerfeld-type integrals, and a brief discussion of the issues related to their evaluation is included.; The half-space numerical approach is finally applied to the problem of modeling tree trunks over a flat ground. Its results are compared with those of an analytical approach that neglects the near field interaction of the trunk and the surface of the ground.