Approximate modeling of current gathering effects in airborne electromagnetic data

Abstract

Summary Current gathering occurs whenever a target is in galvanic contact with a conductive host or overburden. Models for the static response of a plate in a homogeneous halfspace and in either layer of a two-layered earth, based on concepts from magnetometric resistivity (MMR) have been developed to help assess the importance of current gathering in airborne electromagnetic (AEM) data. For the case of a vertical target in galvanic contact with a conductive overburden, galvanic currents have been found to remain concentrated near the top of the plate at all times, provided the basement is sufficiently resistive. In this case, the galvanic response of a large plate may be modeled by neglecting that part of the plate not in direct contact with the overburden. In order to fit the galvanic responses computed here to field or model transient electromagnetic data (TEM), it is essential to account for the delaying and broadening effect of the conductive overburden on the observed secondary fields.