The first spherical harmonic analyses of the geomagnetic main field ignored the ellipticity of the Earth. This was not a serious omission, since the radial departures of the Earth's surface from a sphere never amount to more than 0.17%. However, as the quality of data improved, it was thought that they might justify inclusion of a correction for ellipticity.
The Earth's surface is closely approximated by an oblate spheroid with eccentricity 0.082. This affects both the position of an observation and the observation itself, since the horizontal component, for example, is measured tangential to the spheroid rather than perpendicular to the line joining the site to the Earth's center. Early analyses that took account of this ellipticity (Schmidt, 1898; Adams, 1900; Jones and Melotte, 1953) first determined coefficients for a spherical Earth, then adjusted these for ellipticity. A better method (Cain et al., 1963) was based directly on the original observations.
Adjustment from geodetic to...
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsBibliography
Adams, J.C., 1900. Terrestrial Magnetism. Scientific Papers, Vol. 2. Cambridge: Cambridge University Press, pp. 243–640.
Cain, J.C., Daniels, W.E., Hendricks, S.J., and Jensen, D.C., 1965. An evaluation of the main geomagnetic field, 1940–1962. Journal of Geophysical Research, 70: 3647–3674.
Jones, H.S., and Melotte, P.J., 1953. The harmonic analysis of the Earth's magnetic field for epoch 1942. Monthly Notices of the Royal Astronomical Society, Geophysical Supplement, 6: 409–430.
Kahle, A.B., Kern, J.W., and Vestine, E.H., 1964. Spherical harmonic analyses for the spheroidal Earth. Journal of Geomagnetism and Geoelectricity, 16: 229–237.
Malin, S.R.C., and Pocock, S.B., 1969. Geomagnetic spherical harmonic analysis. Pure and Applied Geophysics, 75: 117–132.
Schmidt, A., 1898. Der magnetische Zustand der Erde zur Epoch 1885.0. Archiv der deutschen Seewarte, Hamburg, 21(2): 76 pp.
Winch, D.E., 1967. An application of oblate spheroidal harmonic functions to the determination of geomagnetic potential. Journal of Geomagnetism and Geoelectricity, 19: 49–61.
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2007 Springer-Verlag
About this entry
Cite this entry
Malin, S.R.C. (2007). Main Field, Ellipticity Correction. In: Gubbins, D., Herrero-Bervera, E. (eds) Encyclopedia of Geomagnetism and Paleomagnetism. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4423-6_211
Download citation
DOI: https://doi.org/10.1007/978-1-4020-4423-6_211
Publisher Name: Springer, Dordrecht
Print ISBN: 978-1-4020-3992-8
Online ISBN: 978-1-4020-4423-6
eBook Packages: Earth and Environmental ScienceReference Module Physical and Materials ScienceReference Module Earth and Environmental Sciences