Ocean Tides And Ocean Tide Loading In Antarctica Studied Using GPS

Tidal signals permeate the entire Earth system.An accurate knowledge of tides is consequently needed for geophysical studies such as the research on the orbit of Moon or the inversion of the solid-earth internal structure.Another important application for tides is providing corrections to various measurements so that smaller nontidal signals may be studied.To reach accuracy of 1-mm or 0.1 ?Gal,ocean tides or ocean tide loading must be taken into accounts.Much progress has been achieved in recent years in improving global tide models in open deep water,but the accuracy in shallow seas or polar seas is still low,as well as the corresponding ocean tide loading.Over the past 20 years,Global Positioning System(GPS)technology has been widely used in the fields of geodesy and geophysics.The GPS observations with high precision and continuity are of greatly scientific and practical importance in improving our understanding of ocean tides and ocean tide loading.Antarctic seas,where sea ice and ice shelves interfere with satellite altimeter detection of the ocean surface,have lower densities of high-quality satellite and in-situ data for validation and assimilation.The accuracy of local tides predicted by global ocean tide models is not as good as in low-and mid-latitude regions.In this paper,ocean tides and ocean tide loading are studied comprehensively using GPS.Chapter 1 briefly addresses the present research state and future development tendency on ocean tides and ocean tide loading.Chapter 2 introduces the basic theory of ocean tide generation,as well as the analysis techniques of ocean tides and ocean tide loading.Chapter 3 assesses the accuracy of several state-of-the-art global ocean tide models,and derives the harmonic constants of ocean tides in Prydz Bay using floating GPS observations.Chapter 4 studies the ability of using GPS to extract harmonic parameters of ocean tide loadings in the Antarctic Peninsula.Chapter 5 analyzes the aliasing effects of un-modelled or mis-modelled(sub-)daily signals on GPS time series.The main contents and results of this paper include:(1)The accuracy of state-of-the-art global ocean tide models in 4 regions of Antarctic seas(Antarctic Peninsula,Ross seas,Weddell seas and Prydz seas)is assessed.TPX08 shows the best accuracy in regions of Antarctic Peninsula,Ross seas and Weddell seas.HAMTIDE12 shows the best accuracy in Prydz seas.Due to the assimilation of some in-situ observations,TPXO outperforms other models in Antarctic seas in general.(2)The harmonic constants of ocean tides in Prydz Bay is derived by using floating GPS observations.The root-sum-square for the eight major constituents(O1,Ki,P1,Qi,M2,S2,N2,K2)is about 3 cm.To obtain reliable tide estimates and neglect the filter edge effects,continuous observation longer than 30 days is necessary.Our results show that this kind of "GPS buoy" is an effective and accurate alternative to tidal gauges in Antarctica.(3)The harmonic parameters of ocean tide loading of 13 GPS stations in Antarctic Peninsula are successfully extracted using kinematic PPP mode.The convergence time of using kinematic PPP method to estimate ocean tide loading is short,but the results are robust and contain all interesting signals.GPS-derived estimates are highly consistent to the computed values of TPX08,with RMS of 5 mm.Using GPS-derived estimates as corrections,the RMS of high-frequency kinematic time series of GPS shows a reduction of 30%.(4)Study the aliasing effect of GPS time series in Antarctic Peninsula.The subdaily Ki 'error' in the solid Earth tide will not only affects the estimates of ZTD,but also propagates into annual signals in the GPS daily time series,with mean admittance of 5.6%.The TPX08 is used to assess the harmonic parameters obtained by kinematic PPP mode.The power spectral analysis can separate the aliasing signals in GPS time series with accuracy of 0.1 mm.It provides additional method to evaluate the accuracy of ocean tide models.