Electromagnetic induction data parameterized in time dependent object intrinsic polarizabilities allow discrimination of unexploded ordnance (UXO) from false targets (scrap metal). Data from a cart-mounted system designed for discrimination of UXO with 20 mm to 155 mm diameters are used. Discrimination of UXO from irregular scrap metal is based on the principal dipole polarizabilities of a target. A near-intact UXO displays a single major polarizability coincident with the long axis of the object and two equal smaller transverse polarizabilities, whereas metal scraps have distinct polarizability signatures that rarely mimic those of elongated symmetric bodies. Based on a training data set of known 1 targets, object identification was made by estimating the probability that an object is a single UXO. Our test survey took place on a military base where both 4.2" mortar shells and scrap metal were present. The results show that we detected and discriminated correctly all 4.2" mortars, and in that process we added 7%, and 17%, respectively, of dry holes (digging scrap) to the total number of excavations in two different survey modes. We also demonstrated a mode of operation that might be more cost effective than the current practice.

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[1] Electric and magnetic fields in the (10 −4 -1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California, from 1995. A data window (2002-2005, enclosing the 28 September 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields or changes in ground conductivity occurred before the earthquake. The data were edited, removing intervals of instrument malfunction, leaving 875 days in the 4 year period. Frequent, spikelike disturbances were common but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signal-to-noise amplitude spectra, estimated via magnetotelluric processing, showed the behavior of the ultralow frequency fields to be remarkably constant over the period of analysis. These first-order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the "residual" fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies present in both the electric and magnetic fields from those present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed, suggesting local distortion due to variations in near-surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects were found that can be reasonably characterized as precursors to the Parkfield earthquake.