Investigations of the internal geomagnetic field by means of a global model of the earth's crust

A global model of the Earth's crust has been constructed of two-layer blocks of 2° x 2° dimension, with thickness and susceptibility selected from a tenstep classification of the various crustal types.Considering induced magnetization only, the magnetic effect of each block has been approximated by a single dipole in the middle of the block, directed parallel to the field for a given main field model (32 400 dipoles altogether).The magnetic field of this global model of the crust has been calculated for an altitude of 450 km, appropriate for a comparison with anomaly fields from satellite surveys.From field values at 1° x 1° grid points, model anomaly charts for the X, Y, Z-components and for the total intensity can be plotted.The underlying crustal parameters have been prepared for modification towards adjusting the model field to the final Magsat anomaly field.The aim is to construct a truly realistic model of the whole Earth's crust.Based on a global distribution of the Z-component of the model field a spherical harmonic analysis has been made by a direct integral method, up to degree and order 35.The energy density spectrum of the magnetic field, apart from the lowest degree terms, resembles a "white" spectrum in which the level nearly meets that obtained for the crustal part of an actual field model (from n = 15 to 29), except for a factor of less than 3.A supplemental evaluation of the core part of the observed spectrum indicates a source depth of some 100 km below the surface of the Earth's core, supported by a similar result for the secular variation of the core field.