The primary task of the IAG Sub-Commission on Gravity and Geoid in Africa is the development of the vertical reference surface (the geoid) for the entire African continent. For the practical solution of this boundary value problem, the available, arbitrarily distributed boundary data (gravity values) must be interpolated onto a regular grid for numerical reasons. In this paper it is explained in detail how to create this grid from the irregularly distributed point-gravity data. It is worth mentioning that this gravity database is not only used for geoid computation; it is also a stand-alone product used in earth sciences, as it reflects interesting geophysical signals. The gravity data available in this project are land and shipborne point gravity values as well as altimetry-derived gravity anomaly data. One challenge of preparing the homogeneous grid of gravity anomalies is caused by the inhomogeneous distribution of the observations and a lot of data gaps, especially on land. At these data gaps, gravity anomalies are provided on a so-called underlying grid from the GOCE DIR_R5 global reference model. One challenge in the framework of the least-squares prediction technique used is the determination of an empirical covariance function representing the behaviour of the irregularly distributed data points and the individual weights of the land, shipborne, and altimetry data and the underlying grid entering the process. A sophisticated filtering of the available gravity data is carried out to meet this challenge. The preprocessed data from the remove step are predicted to an equiangular $$5^{'} \times 5^{'}$$ 5 ′ × 5 ′ grid. Finally, a consistent restore step leads to the AFRGDB_V2.2 gravity database. The precision of the developed gravity database has been studied to assess the quality of the new product. The new AFRGDB_V2.2 gravity database is compared to the preceding one (AFRGDB_V2.0), which was generated using the window remove-restore technique.

中文翻译：

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新的 AFRGDB_V2.2 非洲重力数据库

IAG 非洲重力和大地水准面小组委员会的主要任务是开发整个非洲大陆的垂直参考面（大地水准面）。对于此边界值问题的实际解决方案，出于数值原因，必须将可用的、任意分布的边界数据（重力值）插值到规则网格上。在本文中，详细解释了如何从不规则分布的点重力数据创建这个网格。值得一提的是，这个重力数据库不仅用于大地水准面计算；它也是地球科学中使用的独立产品，因为它反映了有趣的地球物理信号。该项目中可用的重力数据是陆地和船载点重力值以及测高得出的重力异常数据。制备重力异常均匀网格的挑战之一是观测分布不均匀和大量数据缺口，尤其是在陆地上。在这些数据缺口处，重力异常是在来自 GOCE DIR_R5 全球参考模型的所谓底层网格上提供的。所使用的最小二乘预测技术框架中的一个挑战是确定一个经验协方差函数，该函数代表不规则分布的数据点的行为以及陆地、船载和高度测量数据的各个权重以及进入过程的底层网格. 为了应对这一挑战，我们对可用的重力数据进行了复杂的过滤。来自删除步骤的预处理数据被预测为等角 $$5^{'} \times 5^{'}$$ 5 ′ × 5 ′ 网格。最后，一致的恢复步骤导致 AFRGDB_V2.2 重力数据库。已研究开发的重力数据库的精度以评估新产品的质量。新的 AFRGDB_V2.2 重力数据库与使用窗口移除-恢复技术生成的前一个 (AFRGDB_V2.0) 进行了比较。