| Summary: | 博士 === 國立交通大學 === 土木工程學系 === 101 === With consideration of the height dependent Green’s functions for the Newtonian and elastic effects, this research utilizes a regional and a global tide model to account separately for near (inner) and far (outer) zone contributions, and optimizes the inner-zone region and the grid interval for numerical convolution. A set of computer programs coded in FORTRAN, has been successfully developed to model the gravity and displacement effects due to ocean tide loading (OTL), especially for coastal stations with large ocean tides. The coastline is not only defined by the full-resolution shoreline but optionally a digital elevation model (DEM). We model the gravity effect due to OTL in a computer program SGOTL. A case study using gravity observations at the Hsinchu superconducting gravity station and some offshore islands around the Taiwan Strait suggests that SGOTL outperforms some selected global OTL programs (GOTIC2, g7.0 and BS). The gravity due to OTL at the Hsinchu superconducting gravity station can be up to 11 μgal in amplitude and achieves an accuracy of 0.1 μgal .
In addition, the horizontal and vertical displacements due to OTL can be modeled in a computer program DISOTL. Based on the GPS sites of MOI (at HCHM and MZUM), OTL-induced displacements from DISOTL, GOTIC2 and BS model differ at 1 mm level in amplitude. The displacements at 13 IGS stations in the western Pacific can be up to 8.5 cm in amplitude (KWJ1, Marshall Islands); At stations around Taiwan, the vertical displacements can be up to 5.5 cm (at MZUM). Such large OTL effects (over 1 cm) will have a profound influence on the precise positioning techniques such as VLBI (Very Long Baseline Interferometry), SLR (Satellite Laser Ranging) and GPS (Global Positioning System). A case study at coastal and offshore-island GPS continuous stations suggests that DISOTL can model the OTL corrections and reduce the coordinate variations by up to 35% .
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