Physical limitations on detecting tunnels using Underground Focusing Spotlight Synthetic Aperture Radar

This work studies the concept of Underground Focusing Spotlight Synthetic Aperture Radar (UF-SL-SAR) systems for tunnel detection applications. A general formulation for generating UF-SL-SAR imaging in realistic, randomly rough ground is developed by focusing in space and frequency at subsurface points by considering rays refraction at the nominal ground surface. Imaging results are presented for two soil scenarios: dry sand and moist clay loam. It is demonstrated that the tunnel is successfully imaged only for the sand case.