A geometric optics model for high-frequency electromagnetic scattering from dielectric cylinders

The cylinder is a fundamental shape for (2-D) geophysical modeling, and cyl indrical objects (e.g., pipes) are a common target for ground penetrating r adar. This paper presents physical and theoretical model responses for a cy linder which provide insight into responses that can be anticipated in fiel d data. We calculate the exact expressions for the scattered field componen ts of an obliquely incident plane wave over an infinitely long homogeneous dielectric cylinder and express them in the time domain. We project the fie ld on a horizontal plane over the dielectric cylinder and interpret them fo r a large range of permittivity contrasts. The high-frequency approximation presented in this paper includes the processes of specular reflection and critical refraction, which satisfy Snell's law. Assuming the velocity of th e surface waves is equal to the velocity of the fastest medium, and assumin g their travel path is the shortest one possible, we derive a geometric opt ics model which is valid over a wide range of permittivities. We show that the critically refracted response can be separated and measure d from the specular reflections in the received signal. The identification and isolation of these different responses of the bistatic measurements ena ble a characterization of the target's properties, such as its size, orient ation, and formation. We confirm our theoretical results by comparison with measurements using a physical model.