Journal ArticleDOI
A magnetic profile around the world
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In this paper, an around-the-world profile of magnetic total field intensity has been analyzed and it was concluded that spherical harmonic coefficients of order and degree greater than 10 are probably not required to describe the main part of the earth's field to within limits acceptable for world charts.Abstract:
An around-the-world profile of magnetic total field intensity has been analyzed. Local anomalies are almost totally absent from Lisbon through the Mediterranean Sea, across the Arabian peninsula, and along the coast of the Arabian Sea to Bombay. Magnetic sources appear to be shallow across the entire Pacific Ocean and in the vicinity of the mid-Atlantic ridge. The major sources under continental areas are much deeper. The Fourier coefficients decrease in amplitude very rapidly up to order 7; beyond that, the envelope of the coefficients slowly decreases, reaching a magnitude of approximately 1 γ at the 2000th harmonic. The harmonics are summed according to fixed wavelength-width intervals. This results in a bimodal distribution indicating crustal sources and core sources. If the single around-the-world profile studied here is typical of all great-circle profiles, it is concluded that spherical harmonic coefficients of order and degree greater than 10 are probably not required to describe the main part of the earth's field to within limits acceptable for world charts.read more
Citations
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Journal ArticleDOI
Spatial Power Spectrum of the Main Geomagnetic Field, and Extrapolation to the Core
TL;DR: In this article, it is shown that the spectrum of the main geomagnetic field is composed of two components, long wavelengths being dominated by fields originating in the core and short wavelengths by fields originated in the crust; the cross-over occurs at n ≥ 11, a wavelength ≤ 3600 km.
Journal ArticleDOI
A geomagnetic field spectrum
Robert A. Langel,R. H. Estes +1 more
TL;DR: In this paper, a spherical harmonic model of the earth's internal magnetic field of degree and order 23 is derived from selected MagSat data, and its power spectrum, computed with terms developed by Mauersberger (1956) and Lowes (1974), is found to exhibit a change of a slope at n = 14 which is interpreted as an indication that the core field dominates at values lower than 13 while the crust field dominates above a value of 15.
Journal ArticleDOI
An Evaluation of the Main Geomagnetic Field, 1940-1962
TL;DR: In this paper, a set of survey and observatory annual mean data available for the interval 1940-1963 is used to make a new determination of the geomagnetic field and its secular change.
Journal ArticleDOI
Spherical harmonic analysis of the geomagnetic field: an example of a linear inverse problem
Kathy Whaler,David Gubbins +1 more
TL;DR: In this paper, Parker's method of linear inference has been applied to spherical harmonic series, and the results are similar to least squares but the error bounds are more pessimistic than those of least squares.
Journal ArticleDOI
Seafloor spreading anomalies in the Magsat field of the North Atlantic
TL;DR: In this paper, a simple magnetization model for the crust of the North Atlantic Basin was proposed to explain the major anomalies of the Magsat intermediate-wavelength magnetic field over the basin.
References
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Journal ArticleDOI
The westward drift of the Earth's magnetic field
TL;DR: In this article, the authors investigated the westward drift of the non-dipole part of the earth's magnetic field and of its secular variation for the period 1907-45 and the uncertainty of the results discussed.
Book ChapterDOI
Interpretation of Aeromagnetic Maps
Journal ArticleDOI
Depth to sources of magnetic anomalies
TL;DR: In this article, the characteristics of several long magnetic total field intensity profiles have been determined and the distance between crossover points of the smooth field and the nondipole field was determined and a histogram of the results plotted.
Journal ArticleDOI
NOL vector airborne magnetometer type 2A
E. O. Schonstedt,H. R. Irons +1 more
TL;DR: The NOL vector airborne magnetometer type 2A (VAM-2A) as discussed by the authors measures the direction and intensity of the Earth's magnetic field from aircraft using a pendulously suspended magnetometer mechanism.