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.

中文翻译：

---

前向重力建模以增强高分辨率组合重力场模型

近年来，由于卫星衍生的高精度观测和前向重力建模的发展，高分辨率全球重力场的确定取得了进展。正向建模根据质量分布源而不是实际重力测量来计算全球重力场，有助于改进和补充全球重力场模型的中高频分量。在这项研究中，我们基于椭球近似和质量层概念来估算地球上地壳的全球重力势。这种方法具有光谱方法的优点，并且还避免了由于使用一系列薄椭球壳而可能导致的不稳定性。这些由共焦下壳和上壳椭球包围的体积壳内的横向密度用于计算椭球谐波系数，然后在最后一步将其转换为地球表面的球谐系数。这项研究的主要成果是地球上地壳引力势的光谱表示，根据球谐系数 (ROLI_EllApprox_SphN_3660) 计算到 3660 次和阶。我们通过将该模型与文献中的其他类似正向模型进行比较来评估我们的方法，这些模型在大地水准面起伏方面显示亚厘米一致性。最后，EIGEN-6C4 由 ROLI_EllApprox_SphN_3660 增强，并且从具有约 5 公里半波长空间分辨率的扩展模型计算的重力场函数与全球不同地区的地面实况数据进行了比较。我们的调查表明，地形模型的贡献使重力值比较中的一致性增加了约 20%。