Polarimetric invariants for detection by forward-looking ground penetrating radar

The usefulness of ground penetrating radar to detect landmines has been limited because of low signal-to-clutter ratios which result in high false alarm rates. We describe a method using polarimetric radar to measure the polarizability angle, the relative phase, and the target magnitude. These three independent quantities are directly related to target shape and dimensions and are invariant to rotation about the sensor-to-target axis. Data collected on an automobile disk brake rotor over a frequency range of 1.35-2.14 GHz showed that the polariz ability angle and the relative phase varied less with frequency when the rotor was buried than when laying on the surface. The target magnitude showed similarities to interference patterns from scattering centers at the edges of a cylinder.