Methods for detecting buried objects

About the project

Ground-penetrating radar (GPR) detects objects below the surface from the reflections of electromagnetic waves. In this project we develop and compare acquisition modes for an airborne GPR mounted above the ground – as on an unmanned aerial vehicle – and methods that produce a sharp subsurface image from the acquired data.

We used our own modular SFCW (stepped-frequency continuous-wave) radar with a 2 GHz bandwidth starting at 500 MHz and TEM horn antennas 55 cm above the ground. Measurements were carried out on a 3 × 3 × 0.5 m sand test site, where we buried corner reflectors and an anti-personnel mine.

Three acquisition modes

1. Downward-looking: the antennas look straight down and move in a straight line. A buried object appears in the B-scan as a hyperbola; this mode reaches deepest, down to 0.6 m.
2. Side-looking: the antennas are tilted towards the ground and the platform rotates about a vertical axis, illuminating a ring around it.
3. Circular SAR: the platform moves along a circle with the antennas always looking towards the centre. The area is illuminated from all sides, so the focused image is clearest.
4. Back-projection (BP) sums the reflections from all antenna positions for each image point, so the hyperbolas collapse into point targets. With side-looking and circular SAR we achieved a resolution of 0.1 m and detected objects down to 0.3 m below the surface.