| International global satellite navigation system service organization was founded in 1994.IGS provides free,high precision of the coordinates of IGS reference station time series,which provides a great convenience to study the earth's tectonic movement.Research shows that the vast majority of IGS reference station coordinates time series contains linear movement,at the same time include nonlinear motion.The linear motion of base station reveals the continental plate movement.nonlinear movement include the anniversary of the movement,half an anniversary of the movement and other movement,may relate to environmental load to the surface of the earth,moon and tidal forces,ocean circulation,GPS system technical error.Study the nonlinear change of IGS reference station is currently a hot research topic,and has important theoretical significance.On one hand,this can get precise station position and speed,has contribution to establish a high precision and dynamic reference frame.At present,even the latest international earth reference frame ITRF2008 reference frame is merely gives the IGS station relative to the position of the reference epoch and station own linear velocity,This is obviously not enough,along with various scientific research field of geodesic precision demand is higher and higher,the further research,how to introduce the nonlinear change to earth's frame of reference will be a hot issue nowadays.International experts and scholars began to pay attention to this problem,and has oBTained a series of research results.On the other hand,this can be more reasonable to fully explain the structural movement,so as to explain the nonlinear impact of the various possible factors,the study found that almost all the IGS stations,especially elevation direction,contain obvious anniversary,half-anniversary of the movement.The anniversary,half-anniversary of the movement have relevant to the surface of the earth environment load and ice after springback,the moon and the tides cause there is some connection between sea level changes need to be further research.At present,the nonlinear analysis of time series of GPS coordinates are mainly concentrated in both time domain and frequency domain,on frequency domain the traditional research method mainly depends on the Fourier transform.But based on Fourier transform power spectrum estimate potential assumption:there is a time series data extrapolation of zero.This is likely to cause the deviation of the power spectrum estimation and maximum entropy spectrum analysis method is very good to avoid the problem,In this paper,the maximum entropy method has taken for GPS coordinate time series spectrum estimation,the main research content includes1)Firstly compares four kinds of power spectrum analysis method of BT,Lomb-Scargle,Welch method,maximum entropy method.Then the maximum entropy spectrum analysis method is used to analyze the Australia around 10 IGS stations coordinate time series of power spectrum,which in accordance with the previous basic conclusions are drawn that the maximum entropy spectrum analysis method applied to the GPS coordinates time power spectrum analysis can achieve good results.First of all,analyse the power spectral differences by comparing the simulation of GPS coordinates time series analysis four plus window function in the periodogram method-rectangle,triangle window and harming window,blackman window under different time sequence length,signal-to-noise ratio.Results shows that the four kinds of adding window function are affected by sequence length and signal to noise ratio,the longer the time sequence,the higher the resulting power spectrum resolution,Under the condition of signal-to-noise ratio SNR= OdB,and the time sequence for one year,four types of adding window function are not properly identify cycles.Under the condition of the signal-to-noise ratio SNR= OdB and the time series for three years,four kinds of window function can correctly identify the anniversary of the term and half anniversary,but rectangular window is easy to form a false cycle.The higher sigal-to-noise ratio,the greater the resolution,the less likely the form false cycle.Under the condition of the sequence length is 3 years and the signal-to-noise ratio SNR=-20dB cannot properly identify cycle.Secondly compare the difference of the time series of power spectrum through simulation comparison of the four kinds of power spectrum analysis method in the time series length and signal to noise ratio of different cases.Results show that regardless of the length of the sequence changes,or signal-to-noise ratio change,under the same conditions,the maximum entropy spectrum analysis method are better than the other three methods from the resolution to accuracy.Finally using the maximum entropy method to analyze the internal and surrounding Australia power spectral characteristics of 10 IGS stations,the results show that the anniversary of the movement is one of the main features of the station,part of the station also has obvious half-anniversary of the movement,which is consistent with the previous conclusion.2)Study the influence of the GPS precision not modeling error in the data processing to station coordinate time series,by adapting China and the surrounding area 10 IGS stations from 2000 to 2014 years of observation data.Study the changes of power spectrum by using the maximum entropy spectrum analysis methods to analyze the earth radiation pressure correction,selection of troposphere projection function for IGS stations.The earth radiation pressure correction is firstly analyzed to reveal the impact of the change of IGS reference station coordinates time series,explores the power spectral differences by choosing different earth radiation pressure model of time series of IGS reference station coordinates.Results show that whether choose the earth radiation pressure correction or not,vertical direction of the south to north direction,east to west direction are presented similar characteristics,all have significant anniversary,half peak appeared anniversary.Especially in vertical direction,no matter whether correct signal shows strong anniversary,half anniversary.When NCLE model correction,IGS reference station three directions of anniversary of the signal has a certain degree of diminihed.Therefore,NCLE model after correction,the anniversary of the characteristics of the station as a whole is abate,the earth radiation pressure can partly explain the coordinate time series in the part of the anniversary of the signal,as for the specific order of magnitude,we need to further research.Secondly,two common troposphere delay model are analyzed using the projection function model of VMF1 and GMF models of IGS reference station coordinate time series.Through analysis,we can draw the conclusion:choose different troposphere projection function may does not affect the GPS coordinates of time sequence of periodic signal detection.3)Select 20 base station of the crustal movement observation network of China(CMONOC)from 2004 to 2014,10 years of data as the experimental data.Area stack filtering method is used for Crustal movement Observation network of China time series.At first trend term,gross error,data interpolation and a series of data preprocessing,Then adapt function fitting method to remove cycle,get coordinates residual time series,the last area stack filter algorithm is utilized to extract and eliminate common-mode error,at last analyst the change of power spectrum by using the maximum entropy method.By comparing 20 datum stand out the common-mode error before and after the power spectrum,it almost all of the benchmarks in north-south and east-west directions standing in front of eliminate common-mode error is 4.16cpy short periodic motion.After eliminate common-mode error this kind of periodic motion disappeared or reduced,illustrate the common-mode error is the main factors affecting the periodic motion.In the vertical direction in almost all of the base station have 2.08cpy periodic motion,after eliminate common-mode error,according to the power spectrum of the common-mode error after excluding the 2.08cpy periodic motion disappeared or reduced,illustrate the common-mode error at the same time effect on vertical direction the 2.08cpy periodic motion. |
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