The Modeling Of Ocean Tide Loading Displacments In The Coastal Area Of China

The elastic response of the solid Earth due to ocean tides is known as ocean tide loading (OTL), and the effects of the OTL displacement must be taken into account in high-precision geodetic and geophysical data processing. The OTL displacements are modeled by convoluting global ocean tide model with Green’s function which calculated from Earth model. For a long time, the resolution and accuracy of ocean tide models are considered to be the largest error source of the modeled OTL displacements. It is necessary to analyse the effects of different global ocean tide models on the modeled OTL displacements. Currently, GNSS-observed OTL displacements can provide important data for studying the Earth’s crust and upper mantle structure. Thus, the modeled OTL displacement differences caused by different Earth models should be first studied.In my study, the discrepancies of the modeled OTL displacements using different ocean tide models (the regional model NAO99Jb and five recent global ocean tide models,) and different Earth models (Crust2.0 and five Earth models) are investigated. Ocean is divided into near and far-field zones using the modeling area of the regional ocean tide model NAO99Jb, and the discrepancies of the modeled OTL displacements due to near and far-field zones are analysed for different ocean models. Besides, the effects of different ocean tide models and different Earth models on the modeled OTL displacements are also discussed at GNSS stations in Continental Tectonic Environmental Monitoring Network of China (abbreviated as continental network). The main results are shown as follows.(1) The modeled OTL displacements have systematical biases among global ocean tide models at China’s eastern coast. The discrepancies of the modeled M2 OTL displacements using TPXO72ATLAS against other global ocean tide models can reach the millimeter level in the horizontal directions and several millimeters in the up direction in the central coast of Jiangsu Province, also HAMTIDE11A and FES2004 against other global ocean tide models for S2 constituent and NAO99Jb regional ocean tide model against other global ocean tide models both M2 and S2 constituents at Hangzhou Bay coast, mostly due to the effects from ocean tide models in the near-field zones. The discrepancies of the modeled OTL displacements in the northern coast of the Beibu Gulf, the western and northern coast of the Bohai Sea result from the effects of ocean tide models in the far-field zones. The discrepancies of the OTL displacement modeling between TPXO72ATLAS and other global ocean tide models for K1 and O1 constituents can reach the millimeter level in the up direction at the northern coast of the Beibu Gulf, also M2 constituent in the western and northern coast of the Bohai Sea. The accuracy of ocean tide model still plays a key role on modeling OTL displacement at the present.(2) The discrepancies of the modeled M2 OTL displacements only between PREM and AK135 models are relatively large among all Earth models. The discrepancy can close to the millimeter level in the east direction at the northwest coast of Taiwan, and also in the up direction at Fujian Provinces’ coast. The effects of Crust2.0 on the modeled M2 OTL displacement using AK135 model can reach the millimeter level in the up direction and near to the millimeter level in the east direction at Fujian Provinces’ coast. The modeled OTL displacements for the semidiurnal constituents are most sensitive to Earth models in China’s southeast coastal areas, where the GNSS technology can be used to detect the discrepancies of the modeled OTL displacements caused by different Earth models.(3) For GNSS stations, the root mean square (RMS) errors of the modeled M2 OTL displacements using different ocean tide models can reach the millimeter level in the up direction at China’s eastern coast, but smaller at China’s southeast coast. The RMS errors of the modeled M2 OTL displacements using different Earth models are at the sub-millimeter level at all stations. The modeled OTL displacements are sensitive to PREM (PREMhard) model in China’s southeast coastal areas, which may be the preferred region to constrian crustal and upper mantle structure using GNSS-observed OTL displacements.The results of this study can provide a useful reference to constrain the crustal and upper mantle structure of China coastal regions using GNSS-derived OTL displacements. The deficiency of the study is that there is no systematic analysis of the influences of earth structural parameters on Green’s function and modeled OTL displacements, which is worth further study.