Harrison, C.G.A. and J.R. Southam, Magnetic Field Gradients and Their Uses in the Study of the Earth's Magnetic Field, Journal of Geomagnetism and Geoelectricity, 43, 585-599, 1991.

Abstract

Magnetic field gradient measurements for geophysical purposes have been made with much less frequency than total field observations. Yet there are considerable advantages in gradient measurements, especially if the objective is to study magnetic anomalies produced by magnetization contrasts in the crust and possibly upper mantle of the Earth. This is because gradient measurements enhance short wavelength signals relative to long wavelength signals. The power spectrum of a magnetic gradient measurement along any line is the same as the power spectrum of the field measured along the same line multiplied by wavenumber. This means that signals from crustal sources are greatly enhanced over those from core sources, and also that diurnal variations of the field, which appear as very long wavelength features in most observations, are heavily attenuated compared with the crustal signal. To make full use of gradient measurements it is desirable to orient the gradient instrument. If orientation can be achieved, then it is possible to determine the lineation direction of lineated features using just one profile running at some angle to the feature lineation. This is similar to the technique for determining lineation direction from the measurement of field components, but the requirement for orientation is much less severe. Even if orientation cannot be achieved, there are rotationally invariant quantities which can be formulated from the gradient tensor which are of potential use in the interpretation of magnetic anomaly sources.

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