Quasigeoid modelling through FFT methods and different types of gravity anomaly grids
Keywords:
Quasigeoid modeling, Spherical FFT, 1D FFT, residual gravity anomaly gridding, ArgentinaAbstract
One of the main strategies for the establishment of the International Height Reference Frame (IHRF) is based on determining high-precision quasigeoid models. The most widely used scheme for quasigeoid modelling is called remove-compute-restore (RCR). Among the multiple stages of RCR, the “compute” stage consists of an integration of the residual gravity anomalies. This integration can be done with FFT methods, which require that residual anomalies be arranged on a grid, which must be obtained from gravity data. Two methodologies for determining the regular grids and the spherical FFT and 1D FFT integration methods are discussed in this paper. In the first case, residual gravity grids were interpolated onto each node. The second grid was determined by interpolating the complete Bouguer anomalies. Afterwards, the gravimetric effect of the topography was computed and restored to obtain a free-air anomaly grid. Finally, the effects of a global geopotential model (GGM) and of residual terrain model (RTM) were removed from each node. Each grid was used as input in both integration methods separately, resulting in four quasigeoid models, which were validated against GNSS/Levelling data. The results show that models generated using the grid constructed with the second strategy are 1 cm more accurate than those constructed with the first strategy. At the same time, the differences between the models built with spherical FFT and 1D FFT are of the order of mm and, therefore, not significant.
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