Gravity Field Modeling Using Tesseroids with Variable Density in the Vertical Direction

Miao Lin,Jürgen Müller,Heiner Denker

doi:10.1007/s10712-020-09585-6

Abstract

We present an accurate method for the calculation of gravitational potential (GP), vector (GV), and gradient tensor (GGT) of a tesseroid, considering a density model in the form of a polynomial up to cubic order along the vertical direction. The method solves volume integral equations for the gravitational effects due to a tesseroid by the Gauss–Legendre quadrature rule. A two-dimensional adaptive subdivision technique, which automatically divides the tesseroids near the computation point into smaller elements, is applied to improve the computational accuracy. For those tesseroids having small vertical dimensions, an extension technique is additionally utilized to ensure acceptable accuracy, in particular for the evaluation of GV and GGT. Numerical experiments based on spherical shell models, for which analytical solutions exist, are implemented to test the accuracy of the method. The results demonstrate that the new method is capable of computing the gravitational effects of the tesseroids with various horizontal and vertical dimensions as well as density models, while the evaluation point can be on the surface of, near the surface of, outside the tesseroid, or even inside it (only suited for GP and GV). Thus, the method is attractive for many geodetic and geophysical applications on regional and global scales, including the computation of atmospheric effects for terrestrial and satellite usage. Finally, we apply this method for computing the topographic effects in the Himalaya region based on a given digital terrain model and the global atmospheric effects on the Earth’s surface by using three polynomial density models which are derived from the US Standard Atmosphere 1976.

Highlights

An accurate forward modeling method for the computation of gravitational potential (GP), vector (GV), and gradient tensor (GGT) based on a given mass distribution is highly required in many geodetic and geophysical applications
Especially in physical geodesy (Heiskanen and Moritz 1967), it is widely applied in computing mass reductions for geoid determination, as the gravitational effects due to the topographic or atmospheric masses are usually removed before the geoid modeling and added back to the geoid heights after the modeling (e.g., Forsberg 1984; Denker 2013)
Forward gravity modeling is commonly used for geophysical interpretations by removing the complete Bouguer effect from terrestrial or satellite measurements to isolate the gravity signals related to the geological structure inside the Earth (e.g., Álvarez et al 2012; Braitenberg 2015)

Summary

Introduction

An accurate forward modeling method for the computation of gravitational potential (GP), vector (GV), and gradient tensor (GGT) based on a given mass distribution is highly required in many geodetic and geophysical applications. The gravity records are disturbed by temporal signals caused by oceanic and atmospheric mass variations. Forward gravity modeling is commonly used for geophysical interpretations by removing the complete Bouguer effect from terrestrial or satellite measurements to isolate the gravity signals related to the geological structure inside the Earth (e.g., Álvarez et al 2012; Braitenberg 2015). In the inversion of gravity data, an accurate forward solver is crucial for imaging subsurface density anomalies for resource exploration (e.g., Li and Oldenburg 1998) and investigating crust–mantle structures inside the Earth or other planets (e.g., Liang et al 2014; Uieda and Barbosa 2017)

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