EMI real-time subsurface target location by analytical dHP

In processing electromagnetic induction (EMI) survey data for UXO discrimination, the nonlinear search for the location of subsurface objects (“targets”) is one of the most onerous and error-producing components. Here we pursue a technique that exploits fundamental analytical electromagnetic relations to extract estimates of a target’s subsurface position. The formulation requires that one be able to estimate secondary field gradients from the data, e.g. by differencing values from multiple, nearby vector receivers. Further, the field in the vicinity of the Rx units is idealized as one structured like that from an infinitesimal dipole responder; this need not restrict the model complexity applied in other aspects of the processing. Once the system is formulated from the data, direct solution of a 3×3 matrix is the only computational burden. Essentially instantaneous results in simulation tests and in processing of some field data locate a hypothetical source point that varies from nominal target position only by a distance on the order of UXO sizes.