Influence Analysis of Uneven Surface on Landmine Detection Using Holographic Radar

Holographic radar can be used in landmine detection due to its high lateral resolution and sensitivity to the dielectric contrast generated by plastic case landmines. However, radar image of buried objects suffers from artifacts caused by signals generated from an uneven surface. To distinguish the target from background more easily, it is necessary to analyze the influence of uneven surfaces on phase shift and amplitude change that are the two information characteristics of the holographic radar. In this paper, we modeled a monostatic antenna with fixed frequency to transmit and receive electromagnetic signal under the conditions of flat surface and sinusoidal surface. The received signal was modeled as the combination of refraction from a buried point-like target and reflection from the surface above such target. The forward modeling considers an antenna with assigned beam divergence angle γ and a variable height with respect to the surface. According to the simulated data, the antenna height has a remarkable influence on the residual function calculated in the cases with sinusoidal and flat surface. This outcome of the analysis has been also investigated experimentally in laboratory with a sandbox and an antenna mounted on a mechanical scanner. It was proved that the theory “half wavelength” and “concave-convex lens” we named in the paper are useful to reduce the image artifacts and obtain the best data quality for target detection and classification.