FDTD Computation of Scattering by Buried Objects

A computational approach of scattering by buried objects is presented by using finite-difference time- domain （FDTD） method, the uniaxial perfectly matched layer （UPML）, and reciprocity theorem. The nu- merical performance of this approach is investigated by numerical experiments. The radar cross sections （RCS） of various buried objects with different electrical sizes, shapes, dielectric constants, are computed and ana- lyzed. The results show that for the conducting cube, the RCS curves are fluctuant, but for the sphere shape one, the curves are smooth. Comparing with scattering in the free space, the ground greatly affects the RCS by dielectric targets, but little does by conducting targets. For the buried dielectric objects, iterative steps can be evaluated by four to five round-trip traversals of the Huygens box, but for the conducting ones, the time steps can be reduced to three round-trip traversals. When the ground is lossy, the run-time can be reduced more to two round-trip traversals.

The Electromagnetic Scattering by Buried Complex Objects

The solution of scattering problem of buried complex bodies needs to not only consider the scattering from the complex bodies, but also apply the boundary conditions in two different types of coordinate systems. This paper applies the conversion technique of vector wave functions combined with the three-dimensional unimoment method to effectively solve this type of complex electromagnetic problem. Using the conversion relations between the cylindrical and spherical vector wave functions, two types of boundary-value problems are conveniently jointed. Both the vector wave function expansion and the multipole expansion belong to eigen function expansion methods and have the same convergence rate. But the former is more rigorous in theory and needs to calculate only two types of eigen components while the latter needs to calculate four types.

Study on the optical system for the record of the pulsed acoustic field and the scattering of the cylindrical-like objects buried in underwater sand

The response of the two working mode of the optical systems, the schlieren mode and shadowgraph mode, for taking of optical photograph of the pulsed acoustic field in liquid are studied. It shows that, the response of the optical intensity on the screen to the acoustic pressure is linear for shadowgraph mode and nonlinear for the schlieren mode. Because the function of shadowgraph mode has no limit on working frequency, it is suitable for the studies of the acoustic field of laboratory model of the seabed or the buried objects at low ultrasonic range. The ultrasonic pulse scattered by the cylindrical-like objects buried in underwater sand was studied experimentally by the shadowgraph mode at low ultrasonic frequency. There are five kinds of the scattered waves from the half-buried object and three kinds of the waves from the full-buried objects were recorded. The two kinds of creeping waves (the longitudinal wave and the shear wave of the object) appear in both of the two cases.

Simulation Study of SVM-Based Approach in Extracting Parameters for Electromagnetic Detection of Buried Object

In this paper,a new method for extracting the parameters of buried object is proposed.The center position and dielectric properties of 2-D buried object are estimated by means of a regression technique based on support vector machine（SVM）.The proposed method,after a proper training procedure,is able to reconstruct the center position and dielectric properties of a buried object inside a given investigation domain.Numerical simulation results indicate that SVM-based approach shows higher accuracy than the back-propagation neural networks（BPNN） algorithm.