Location Of Magnetic Dipoles In Chongcho Lake, Republic Of Korea: An Application Of The Soapfi (Shape-Of-Anomaly Potential Field Inversion) Program

Abstract

The SOAPFI (shape-of-anomaly potential field inversion) program has been previously applied to the inversion of gravity and magnetic data. These earlier applications add rectangular parallelepipeds to a growing model's periphery according to a criterion that minimizes the difference between the shapes of the modeled and observed fields using an L1- or L2-norm. That method is generalized here to the inversion of magnetic fields using one or more magnetic dipoles. In the presence of measurement or geologic noise, both the growing-model and magnetic dipole inversions are improved by the application of spatial filters to the observed and modeled fields. An improved “profile-adaptive” filtering of modeled fields matches the filter applied to the observed field in curvilinear profiles that may intersect and overlap. Approximately 90 km of magnetic-field profiles was recorded in the 1-km2 Chongcho Lake in Sokcho, Kangwon-do, Korea. Magnetic dipoles, including perhaps unexploded ordinance, were located in this lake. Automatic determination of dipole strengths and locations used total magnetic field anomalies. For each data window, one or more dipoles were modeled. To attenuate local anomalies due to broader and deeper sources than the targeted dipoles, spatial high-pass filtering was applied to observed data in profiles.