We have developed an equivalent-source method for perform-ing reduction to the pole and related transforms from magneticdata measured on unevenly spaced stations at different eleva-tions. The equivalent source is composed of points located verti-cally beneath the measurement stations, and their magnetic prop-erties are chosen in such a way that the reduced-to-the-pole mag-netic field generated by them is represented by an inverse-dis-tance Newtonian potential. This function, which attenuates slow-ly with distance, provides better coverage for discrete datapoints. The magnetization intensity is determined iteratively un-til the observed field is fitted within a certain tolerance related tothe level of noise; thus, advantages in computer time are gainedover the resolution of large systems of equations. In the case ofinduced magnetization, the iteration converges well for verticalor horizontal inclinations, and results are stable if noise is takeninto account properly. However, for a range of intermediate incli-nations near 35°, a factor tending to zero makes it necessary toperform the reduction through a two-stage procedure, using anauxiliary magnetization direction, without significantly affectingthe speed and stability of the method. The performance of theprocedure was tested on a synthetic example based on a field gen-erated on randomly scattered stations by a random set of magnet-ic dipoles, contaminated with noise, which is reduced to the polefor three different magnetization directions. Results provide agood approximation to the theoretical reduced-to-the-pole fieldusing a one- or a two-stage reduction, showing minor noise arti-facts when the direction is nearly horizontal. In a geophysical ex-ample with real data, the reduction to the pole was used to correctthe estimated magnetization direction that originates an isolatedanomaly over Sierra de San Luis, Argentina.
展开▼
