The gradiometric-geodynamic boundary value problem
ABSTRACT The role of gravity gradients is investigated in the framework of geodetic-geodynamic boundary value problems. The time variation
of the Eötvös tensor can be separated into three parts. The first part is a surface movement term, the second is the time
variation of the gravity field in the original point, and the third is a coupling term. The first and third terms can be computed
by a third order derivative tensor of the gravity potential. These terms can be formulated in spherical and planar approximation.
Gravity gradients have the advantage over gravity measurements that certain gravity gradient combinations are insensitive
to site movements, thereby allowing the time variation of the gravity field to be determined without repeated height measurements.
The solution of the corresponding gradiometric-geodynamic boundary value problem is shown with repeated gravity gradient measurements
of the torsion balance.
Several test computations with a simple mass density model were performed in order to analyze the time variation of gravity
gradients and give estimates of their respective magnitudes.
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ABSTRACT: Spherical harmonic synthesis (SHS) of gravity field functionals at the Earth’s surface requires the use of heights. The present study investigates the gradient approach as an efficient yet accurate strategy to incorporate height information in SHS at densely spaced multiple points. Taylor series expansions of commonly used functionals quasigeoid heights, gravity disturbances and vertical deflections are formulated, and expressions of their radial derivatives are presented to arbitrary order. Numerical tests show that first-order gradients, as introduced by Rapp (J Geod 71(5):282–289, 1997) for degree 360 models, produce cm- to dm-level RMS approximation errors over rugged terrain when applied with EGM2008 to degree 2190. Instead, higher-order Taylor expansions are recommended that are capable of reducing approximation errors to insignificance for practical applications. Because the height information is separated from the actual synthesis, the gradient approach can be applied along with existing highly efficient SHS routines to compute surface functionals at arbitrarily dense grid points. This confers considerable computational savings (above or well above one order of magnitude) over conventional point-by-point SHS. As an application example, an ultra-high resolution model of surface gravity functionals (EurAlpGM2011) is constructed over the entire European Alps that incorporates height information in the SHS at 12,000,000 surface points. Based on EGM2008 and residual topography data, quasigeoid heights, gravity disturbances and vertical deflections are estimated at ~200m resolution. As a conclusion, the gradient approach is efficient and accurate for high-degree SHS at multiple points at the Earth’s surface.Journal of Geodesy 09/2012; 86(9). DOI:10.1007/s00190-012-0550-y · 3.92 Impact Factor
Acta Geodaetica et Geophysica Hungarica 06/2007; 42(2). DOI:10.1556/AGeod.42.2007.2.2 · 0.35 Impact Factor