Limitations in microwave holographic synthetic aperture imaging over a lossy half-space

Abstract

Experimental results are presented which illustrate the capabilitity of a single-frequency microwave holographic scheme to image both metallic and plastic pipes at a depth of 0.33 m in wet soil with a covering layer of concrete paving stones. The data acquisition system utilises a crossed dipole antenna scanning above the interface recording two orthogonal polarisations at each point on a two-dimensional grid, from which improved surface rejection is obtained. Maximum imaging depth is limited primarily by the ratio of soil attenuation to surface and environmental effects on the antenna response, thereby preventing any significant increase in the conditions quoted. Theoretical investigation into the influence of the lossy dielectric half-space on the synthetic aperture in a one-dimensional model has illustrated that scan height is an important consideration for resolution and antenna system design. It is shown that scanning in close proximity (≤0.1 λ) to the interface increase both lateral and depth resolution. To take advantage of this effect, it is concluded that a noncontacting antenna operating in close surface proximity must be insensitive to height fluctuations.