Electromagnetic detection of buried dielectric targets

Abstrucf-Scattering from subsurface objects is studied using the T-matrix method. The scatterer is represented as a dielectric ellipsoid and the source is assumed to be an electric dipole in a borehole. This approach easily accommodates rotations of the scatterer relative to the source and also permits relaxation of the two-dimensional constraint inherent in some models. In addition, it provides a new framework from which a large number of subsurface scattering problems can be studied. To illustrate how this approach can be applied, the fields scattered from highly eccentric ellipsoids are found. These ellipsoids, which are presented as an approximation to cylindrical tunnels, are nonaxially symmetric. Results demonstrate the importance of using nonaxially symmetric scatterers rather than those that are axially symmetric. In addition, polarization results demonstrate that a method based on the polarization of the scattered field may provide a more robust diagnostic of scatterer location than methods using only a single field component. An experiment based on a scale model of a subsurface tunnel is described. Results from the analytic model compare favorably with those obtained from the experiment. Results from the analytic model are also compared to those from a previously reported two-dimensional theory.