Electromagnetic sensing of a subsurface metallic object at different depths

Microwave/radar sensors and techniques are widely used for detecting underground or subsurface targets in archeology, geophysics, and civil engineering. Among existing microwave/radar sensors and techniques, synthetic aperture radar (SAR) imaging enables researchers and engineers to conduct surface and subsurface detection of metallic objects with improved detectability. The noncontact, remote sensing feature of SAR imaging provides a safer approach in a dangerous mission, such as demining. The objective of this paper is to investigate the depth (d) effect of a metallic object buried in dry sand. A steel disk specimen of 15-cm diameter was buried inside a box (sandbox) filled up with dry sand at various depths (d = 10 cm, 18 cm, and 26 cm) and scanned by a 10-GHz SAR system. Three ranges (R = 15 cm, 30 cm, and 60 cm) between the SAR antenna and the sandbox were also considered in this research. It was found that the SAR amplitude and its distribution decrease with the increase of buried depth and the increase of range. Distribution of SAR amplitudes representing the buried metal disk specimen also changed with the increase of buried depth. Empirical models were also proposed for range and depth effects of subsurface metallic objects in SAR images.