Improvement of equivalent source inversion technique with a more symmetric dipole distribution model

Abstract

A technique which generates an equal-area distribution model for numerical integration on the surface of a sphere by equally subdividing the faces of a spherical icosahedron was applied to the analysis of polar orbiting geophysical observatory crustal magnetic anomaly data and compared with the longitude-latitude gridding model currently being used. The region in Bangui, Central African Republic, which includes the Bangui anomaly was chosen for comparison of the two models. Using the equivalent source inversion technique and the technique of principal component regression a magnetization function was calculated for each model. With an average dipole spacing of 2.3° for each model the results indicated good correlation of the inverse solution between the models up to 99.99% of the trace retention of the singular value decomposition. At 99.99% of the trace retention, equatorial instabilities begin to arise. Further increase of the percentage of trace retention led to greater equatorial instabilities; however, the severity of the instabilities were less for the proposed model. At 99.99% of trace retention, a 15% smaller standard deviation of magnetization function was found for the proposed model than for the current model, and at 99.9999% at 42% smaller standard deviation of magnetization function was found for the proposed model. The better results seen with this model are thought to be due to the high symmetry and shape consistency of the model's surface area sectors which are qualities lacking in the longitude-latitude distribution model currently in use. The proposed model is, however, limited in that only discrete dipole spacings are possible, as opposed to the currently used model which permits a continuous range of dipole spacings.