Global spectral model of the geoid

The coefficients of the Global Gravitational Models (GGMs) define the external gravitational field of the Earth. In many geoscience applications and gravity interpretations these coefficients are routinely used to represent the geoid surface and related gravitational field quantities without taking into consideration the internal convergence domain for computing the gravitational field inside the Earth's masses. In this study we discuss this issue and present the numerical approach for computing the gravitational field quantities on the geoid. The proposed numerical approach utilizes spectral expressions for the gravimetric forward modelling of topographic mass density distribution and the indirect gravimetric modelling of mass density heterogeneities inside the geoid. In the numerical realization we demonstrate that for precise applications the differences between the potential values computed at the topographic surface and on the geoid should be taken into consideration especially in mountainous regions with complex geology as well as in polar regions, where these differences in absolute values reach 40 m 2 s −2 (or more), which translates into vertical displacements between the geoid and the quasigeoid of about 4 m.