Three‐dimensional GPR imaging in the horizontal wavenumber domain for different heights of source and receiver antennae

Abstract

ABSTRACTFor imaging ground‐penetrating radar (GPR) data, three of the most important parameters are the wave speed, polarization and amplitude of the propagating electromagnetic wave‐field. Choosing an appropriate forward model that incorporates these three parameters is a critical aspect of imaging. Also, the height of the antennae above the surface influences the scattered field significantly and should be taken into account. As the height of the antennae above the surface is increased, the widths of the antenna patterns decrease, resulting in decreasing horizontal spatial bandwidths of the scattered electric fields. Imaging is carried out in the horizontal wavenumber domain using the spatial bandwidths of the scattered data. Decreased spatial resolution is obtained for increasing heights. The far‐field expressions do not account for geometrical spreading in air above the surface, resulting in anomalously low image amplitudes for elevated antennae. Experimental data measured with 900 MHz antennae also show reductions in spatial bandwidth as the height of the source and receiver antennae is increased. For heights and , similar spatial bandwidths as predicted by the synthetic results are obtained. For , this reduction in bandwidth is not as strong as predicted by the synthetic results, primarily because of limitations of the far‐field expressions. For stability reasons, the imaging could only be carried out using the limited bandwidth for the forward far‐field model. Images of a spherical metal sphere for measurements at and were almost identical, whereas those at were similar to those at low heights. In one direction, a higher spatial resolution was observed for the antennae with zero height and decreasing spatial resolution for increasing height. In the other direction, the difference in spatial resolution was not very obvious.