Filtro de Redução ao Pólo: Potencialidades e Limitações

Abstract

We demonstrate the potentials and the limitations of applying the reduction-to-the-pole filter to the total field magnetic anomaly in the wavenumber domain. We show that the reduction-to-the-pole technique can be a useful and cost-effective tool for transforming a measured magnetic anomaly caused by an arbitrary source into an anomaly that would be measured at the north magnetic pole. We show that this technique centralizes the magnetic anomaly over their causative source, making magnetic interpretation easier. However, the reduction-to-the-pole technique fails in practice in two cases: (1) if the magnetization direction of the source is unknown and (2) if the reduction-to-the-pole technique is applied at low-latitude magnetic anomalies. These limitations of the reduction-to-the-pole technique are illustrated by synthetic magnetic data. We show that the reduced-to-the-pole anomaly using the wavenumber-domain filtering fails if the magnetic latitude is lower than 15o or if the magnetization of the sources is assumed to be induced only but it is caused by the presence of remanent magnetization. The instability of the reduction-to-the-pole filter is illustrated through the amplitude and phase spectra. Finally, we apply the reduction-to-the-pole filter to two real datasets. The first one is over a buried target from the controlled test site at Vassouras (Rio de Janeiro, Brazil), and the second dataset is over the iron ore province of Minas Gerais State, Brazil.