TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 57 (No. 8), pp. 681-689, 2005

Can we estimate total magnetization directions from aeromagnetic data using Helbig's integrals?

Jeffrey D. Phillips

U.S. Geological Survey, Denver, Colorado 80225, U.S.A.

(Received January 30, 2004; Revised September 27, 2004; Accepted September 27, 2004)

Abstract: An algorithm that implements Helbig's (1963) integrals for estimating the vector components (mx, my, mz) of the magnetic dipole moment from the first order moments of the vector magnetic field components (ΔX, ΔY, ΔZ) is tested on real and synthetic data. After a grid of total field aeromagnetic data is converted to vector component grids using Fourier filtering, Helbig's infinite integrals are evaluated as finite integrals in small moving windows using a quadrature algorithm based on the 2-D trapezoidal rule. Prior to integration, best-fit planar surfaces must be removed from the component data within the data windows in order to make the results independent of the coordinate system origin. Two different approaches are described for interpreting the results of the integration. In the "direct" method, results from pairs of different window sizes are compared to identify grid nodes where the angular difference between solutions is small. These solutions provide valid estimates of total magnetization directions for compact sources such as spheres or dipoles, but not for horizontally elongated or 2-D sources. In the "indirect" method, which is more forgiving of source geometry, results of the quadrature analysis are scanned for solutions that are parallel to a specified total magnetization direction.
Key words: Aeromagnetic, magnetization, interpretation.

Corresponding author E-mail: jeff@usgs.gov

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