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| Titel |
Padding of Terrestrial Gravity Data to Improve Stokes-Helmert Geoid Computation |
| VerfasserIn |
Ismael Foroughi, Juraj Janák, Robert William Kingdom, Michael Sheng, Marcelo C. Santos, Petr Vanicek |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106970
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| Publikation (Nr.) |
 EGU/EGU2015-6655.pdf |
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| Zusammenfassung |
| The Stokes-Helmert method is a well-known method of geoid computation that has been
implemented in the University of New Brunswick’s SHGeo software and is used around the
world. The SHGeo implementation applies Stokes’s integration in spatial form to gravity
anomalies in the Helmert space, after continuing them down to the geoid. A spherical
harmonic model of the global gravity field is used to generate and remove reference Helmert
anomalies before Stokes’s integration is done, and also to generate and add the reference
Helmert spheroid after Stokes’s integration. The same model is used to evaluate, in spectral
form, the far-zone contribution in Stokes’s integration. The boundaries of the near zone for
Stokes’s integration depend on the degree/order of this reference field, so the choice of
optimal integration cap size and degree of reference field is critical and can change the result
significantly.
Larger cap sizes also require larger buffers of data surrounding the computation area to
accurately capture all wavelengths, and because of convergence of the meridians, the
width of this buffer must be larger in longitude degrees than in latitude degrees.
Terrestrial gravity data from these buffer regions are often unavailable, as neighboring
countries may not wish to share their gravity data, or it may be unreliable. This data
deficiency problem may be addressed either by increasing the degree of reference field
and thus decreasing the integration cap size or by padding the regions outside the
geoid computation area by data from global gravity field models and retaining the
preferred larger integration cap. The latter approach is to be advocated, as it avoids
misplaced over-reliance on the accuracy of the higher degrees of existing global
models.
While testing the Stokes-Helmert technique in the Auvergne (France) area with limits of
-1Ë < λ |
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