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In this example a GPR system is modelled consisting of two bow-ties arranged above a planar soil surface with a metal pipe target. The arrangement of the antennas, ground and target are illustrated left. This configuration has been used previously for experimental and computational studies. Smith and Scott[1] published experimental work carried out on a scale model of a GPR system, which was subsequently modelled using the FDTD method by Bourgeois and Smith[2]. This case study repeats the work of Bourgeois and Smith.
The work of Bourgeois and Smith showed that modelling could provide good results for GPR systems. Their model, however, dispensed with transmissive boundaries because the amplitude of the reflection from the boundary was too great and obscured the signal. They had to use reflective boundaries and a large domain to enable time windowing of the returned signal. While this approach is valid it is expensive in terms of computational resources. In the current model the Celia PML RBC is used. This boundary condition reduces the reflection coefficient substantially over other methods and enables the domain boundaries to be located very close to the antennas and target, minimising the volume needed and reducing the computational memory overhead. The computational geometry of the antennas in the geometry editor is shown below, followed by the complete model.
Shown below is a contour plot of electric field amplitude from the Celia post-processor.
The plot shows the transmission of the pulse through the soil medium from the transmit antenna. Geometry is shown in wireframe on this figure.
The graph shown above illustrates the received signal computed using Celia compared to measurements from Smith and Scott for a metal cylinder target. The amplitudes of the signals have been normalised to a peak value of 1.0, as was done by Bourgeois and Smith, as no absolute amplitude information was available from the experimental results.
1 Smith G, Scott W
'A Scale Model for Ground Penetrating Radars'
IEEE Transactions on Geoscience and Remote Sensing
Vol 27, No 4, July 1989, p358
2 Bourgeois J M, Smith G S
'A Fully Three-Dimensional Simulation of Ground-Penetrating Radar: FDTD Theory
Compared with Experiment'
IEEE Transactions on Geoscience and Remote Sensing
Vol 34, No 1, Sept 1996, p36