Abstract
During the last few years, the determination of high-resolution global gravity field has gained momentum due to high-accuracy satellite-derived observations and development of forward gravity modelling. Forward modelling computes the global gravitational field from mass distribution sources instead of actual gravity measurements and helps improving and complementing the medium to high-frequency components of the global gravity field models. In this study, we approximate the global gravity potential of the Earth’s upper crust based on ellipsoidal approximation and a mass layer concept. Such an approach has an advantage of spectral methods and also avoids possible instabilities due to the use of a sequence of thin ellipsoidal shells. Lateral density within these volumetric shells bounded by confocal lower and upper shell ellipsoids is used in the computation of the ellipsoidal harmonic coefficients which are then transformed into spherical harmonic coefficients on the Earth’s surface in the final step. The main outcome of this research is a spectral representation of the gravitatioal potential of the Earth’s upper crust, computed up to degree and order 3660 in terms of spherical harmonic coefficients (ROLI_EllApprox_SphN_3660). We evaluate our methodology by comparing this model with other similar forward models in the literature which show sub-cm agreement in terms of geoid undulations. Finally, EIGEN-6C4 is augmented by ROLI_EllApprox_SphN_3660 and the gravity field functionals computed from the expanded model which has about 5 km half-wavelength spatial resolution are compared w.r.t. ground-truth data in different regions worldwide. Our investigations show that the contribution of the topographic model increases the agreement up to ~ 20% in the gravity value comparisons.
Highlights
With the launch of the dedicated satellite gravity missions, GOCE, GRACE, and GRACEFO, extensive improvements in the quality of global gravitational field models have been obtained by analysing high–low and low–low satellite tracking, accelerometry, and gradiometry
The gravity is computed based on the shape of the topography and the mass-density knowledge
Assuming that the high-frequency gravity field components are mainly caused by the topography, such models can be used to complement high-resolution combined static gravity field models for the very high-frequency components of the gravity field as well as to fill in information into regions lacking terrestrial gravity measurements such as Antarctica
Summary
With the launch of the dedicated satellite gravity missions, GOCE, GRACE, and GRACEFO, extensive improvements in the quality of global gravitational field models have been obtained by analysing high–low and low–low satellite tracking, accelerometry, and gradiometry. The integral transformation of Newton’s law of gravitation is performed in the spectral domain This requires global coverage of the source masses which are represented in terms of harmonic series. A new technique has been developed to model the topographic potential and retrieve high-resolution constituents of the gravity field from masssource information that is provided by the latest Earth’s relief model Earth2014 (Hirt and Rexer 2015). Using the elevation and density information of different layers introduced by Rexer et al (2016), we calculate the gravitational potential of the topography that is reduced for the internal masses below the lowermost reference ellipsoid identified (Fig. 2) and expand the resolution of the latest EIGEN series and other static global gravity field models.
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