Using invariant features with a polarimetric forward-looking ground penetrating radar

We built and tested a forward-looking polarimetric GPR which measured the scattering matrix of targets. The scattering matrix can be transformed to determine the polarizability angle, relative phase angle, and target magnitude. These quantities are invariant to rotations about the sensor-to-target axis. Measurements were made on dry sand without a target, sand with a buried polystyrene cylinder, and sand with a buried styrofoam cylinder. As frequency was swept the relative phase changed more rapidly when either cylinder was present compared to the sand alone. The relative phase may be a useful feature for detecting plastic objects and voids in sand.