Ordnance/Clutter Discrimination Based on Target Eigenvalue Analysis

A procedure is described for deriving a quantitative measure of the "ordnance-likeness" of an unknown target from electromagnetic induction data, which thus can be used as a clutter discriminant. This parameter provides a measure of the axial symmetry and aspect ratio of the target and is formed by taking the ratio of the eigenvalues of the target's magnetic polarizability tensor. The eigenvalues are derived by measuring the matrix elements of the polarizability tensor from above-ground spatial data and then performing an eigenvalue decomposition of this tensor. The method is linear, and does not require a nonlinear parameter search. The eigenvalue ratio is smaller than one for objects that are symmetric and long (ordnance-like) and greater than one for objects that are flat and/or irregular in shape (clutter-like). This ratio is independent of the orientation of the target. The procedure is demonstrated using data derived from samples of metallic clutter and ordnance-like objects (i.e., cylinders, sections of pipe and actual ordnance) at different orientations.