Analysis Of Time Series Characteristics Of GPS Coordinates System Around Bohai Sea Region

GPS is widely used in the research fields such as crustal deformation,seismology and geodynamics due to its high precision,real-time and all weather.With the continuous improvement of China's continental tectonic environment monitoring network(abbreviated as"land state network"),the dense layout of GPS continuous stations and the continuous improvement of GPS data accuracy provide abundant data for China's crustal movement.Based on the six years observation data of the GPS base station in the Bohai sea region from 2013 to 2018,this research analyzed the noise characteristics,common mode error,station speed and velocity field,which in order to obtain the more accurate crustal movement law in the Bohai Sea region.The specific work and results are as follows:1.Based on different noise models,the maximum likelihood estimation method was used to estimate the noise magnitude and time series parameters of 27 time series of coordinate stations in the Bohai Sea area.By comparing the different station data,the result indicated that there was colored noise in the station,and it processed the main component.The magnitude of white noise would overestimate just considering the white noise modeland the uncertainty of time series parameters were underestimate,which brought errors to time series analysis.Therefore,the influence of colored noise cannot be ignored when estimating time series parameters.As for the determination of the optimal noise model,the spectral index method and the maximum likelihood estimation method were used to determine the optimal noise model from aspects of qualitative and quantitative.The results shown that the best noise model of the station mainly had two models of WN+FN and WN+FN+RWN.The optimal noise model for most stations was WN+FN,and the WN+FN+RWN model was mainly distributed on the base station with the bedrock type as the soil layer.The WN+FN model was mainly distributed on the base station with the bedrock type as the bedrock.2.The influence of common mode error on coordinate time series analysis was analyzed.The method of principal component analysis was used to extract the common mode error of 27 reference stations in the Bohai Sea area,and the common mode error was calculated by the first principal components in the three directions of N,E and U.The contribution rate of the eigenvalues of the first principal component to the three-coordinate component(N,E,U)is 47.28%,48.94%,and 64.16%,respectively.The maximum likelihood estimation method and the least square spectrum analysis method were used to estimate the noise and coordinate time series parameters of the station before and after the common mode error was removed.The results shown that the magnitude of white noise,flicker noise and random walk noise in all directions was significantly reduced after the common mode error is removed.The noise level of white noise is reduced by 20.07%,13.74%and 26.17%in the N,E and U directions,the noise level of flicker noise is reduced by 49.35%,37.74%,and 40.71%in the N,E,and U directions,which indicating that the common mode error has both white noise and colored noise characteristics.The average improvement of the standard deviation of the relative coordinate time series in the N,E,and U directions was 21.17%,22.5%,and 23.47%,respectively,and the uncertainty of velocity,annual amplitude,and initial phase decreased significantly,with an average decrease of 19.03%,16.35%,and 29.38%.The results shown that the rejection of common mode error effectively improved the accuracy of coordinate time series analysis.And the fast fourier transform was used to analyze the common mode error.3.The law of crustal movement in the Bohai Sea region was studied.The method of estimating the station velocity by combining empirical mode decomposition and least squares fitting was used to estimate the velocity of the coordinate time series after the common mode error was removed,and the station speed with higher precision was obtained.And the horizontal and vertical motion velocity fields in the Bohai Sea area was given.Finally,the EEMD was used to extract the nonlinear trend term and obtain the instantaneous velocity in the vertical direction of each station to obtain real-time status of the crustal movement in the Bohai Sea.At present,the vertical motion rate in the Bohai Rim region was generally slowing down and gradually becoming stable.However,some stations were active,such as HECX,HELY,HETS,SDYT,TJBH,TJWQ,etc.,which need to be monitored especially.