Ellipsoidal topographic potential: New solutions for spectral forward gravity modeling of topography with respect to a reference ellipsoid

Forward gravity modeling in the spectral domain traditionally relies on spherical approximation. However, this level of approximation is insufficient for some present day high‐accuracy applications. Here we present two solutions that avoid the traditional spherical approximation in spectral forward...

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Bibliographic Details
Published in:Journal of geophysical research. Solid earth 2013-11, Vol.118 (11), p.5991-6002
Main Authors: Claessens, S. J., Hirt, C.
Format: Article
Language:English
Subjects:
Approximation
Earth sciences
Earth, ocean, space
ellipsoid
Ellipsoids
Exact sciences and technology
Geophysics
global gravity model
Gravitation
gravity
Harmonics
Mathematical analysis
Mathematical models
Spectra
Spherical harmonics
topographic potential
Topography
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Summary:Forward gravity modeling in the spectral domain traditionally relies on spherical approximation. However, this level of approximation is insufficient for some present day high‐accuracy applications. Here we present two solutions that avoid the traditional spherical approximation in spectral forward gravity modeling. The first solution (the extended integration method) applies integration over masses from a reference sphere to the topography and applies a correction for the masses between ellipsoid and sphere. The second solution (the harmonic combination method) computes topographic potential coefficients from a combination of surface spherical harmonic coefficients of topographic heights above the ellipsoid, based on a relation among spherical harmonic functions introduced by Claessens (2005). Using a degree 2160 spherical harmonic model of the topographic masses, both methods are applied to derive the Earth's ellipsoidal topographic potential in spherical harmonics. The harmonic combination method converges fastest and—akin to the EGM2008 geopotential model—generates additional spherical harmonic coefficients in spectral band 2161 to 2190 which are found crucial for accurate evaluation of the ellipsoidal topographic potential at high degrees. Therefore, we recommend use of the harmonic combination method to model ellipticity in spectral‐domain forward modeling. The method yields ellipsoidal topographic potential coefficients which are “compatible” with global Earth geopotential models constructed in ellipsoidal approximation, such as EGM2008. It shows that the spherical approximation significantly underestimates degree correlation coefficients among geopotential and topographic potential. The topographic potential model is, for example, of immediate value for the calculation of Bouguer gravity anomalies in fully ellipsoidal approximation. Key Points Topographic potential is best modeled in ellipsoidal approximation The newly derived harmonic combination method performs best Topographic potential strongly correlates with EGM2008 at short spatial scales
ISSN:2169-9313
2169-9356
DOI:10.1002/2013JB010457