Modeling And Precision Analysis Of Ocean Tide Loading Displacments In Taiwan

Solid earth produces an elastic deformation response to ocean tide loading(OTL),due to the redistribution of mass of water caused by ocean tides.The effects of OTL must be taken into account in high-precision geodesy.Theoretically there are some methods to get the response of OTL displacements,like forward-modeling and extracting from GPS.Studies have revealed that ocean tide modes have long been considered a dominant source of error in predicting Earth's response to OTL,particularly near the coast,therefore this thesis focuses on the modeling of OTL displacement in Taiwan,and assessing precision further.To analyze the discrepancies of different ocean models and earth models on the result of modeled OTL displacements in Taiwan,here the author compares sets of modeled predictions directly for combinations of four global ocean models EOTlla,Fes2004,GOT and TPX072atlas,and four earth models PREM,IASP91,AK135 and 1066A.The vector differences of semidiurnal(M2)and diurnal(01)harmonics reveal a good coherence in this area.The modeling of OTL displacements is more sensitive to earth models,the vector differences of M2 constituent caused by different earth models reach respectively 0.89 mm in east and 0.56 mm in north,which are bigger than the value in vertical.It also proves that there are no apparent vector differences between forward-modeled predictions using different ocean models,even between which are corrected by the regional ocean model—NA099Jb.Furthermore,the observations of OTL displacements from GPS using precise point positioning(PPP)in Taiwan,which can offer a standard,can assess the precision of forward-modeled predictions above with the root mean square(RMS)errors.Taking M2 and O1 harmonics as examples,the result of RMS shows that forward-modeled predictions using ocean model EOT11a and earth model PREM is more accurate,however,the residuals still exist with 0.5 mm in horizontal and 1.5 mm in vertical respectively.The residuals reveal that forward-modeled predictions using various ocean-tide and Earth-model in this area lack precision,which mainly caused by the earth model.The observations of OTL displacements from GPS can offer restriction for exploring the Earth's crust and upper mantle structure.