| Since its construction,GNSS stations have provided a wealth of valuable fundamental data for geodetic research,thanks to the rapid development of GNSS technology and its increasingly extensive coverage.The time series of coordinates contain a large amount of information,which not only reveals the inherited tectonic motion of the station under the action of the stress field at the same location,i.e.linear variation,but also contains non-linear variation.It is of great importance to investigate the causes of the non-linear deformation,to improve the noise processing models and methods,to accurately separate out the non-linear deformation and to obtain the precise linear motion of the stations,which is of great importance for the study of plate motion and the construction of the Earth’s reference frame.This paper investigates the removal of common mode error and environmental loading from GNSS station coordinate time series in North China,and uses the removed coordinate time series for the construction of velocity fields in North China to provide a data study basis for the plate motion in North China.The conclusions of this paper are as follows:(1)The coordinate time series data of 37 GNSS stations in North China were pre-processed,and stations with more than 25% of the original data missing were eliminated.10 stations were finally eliminated,leaving 27 stations.These 27 stations were subjected to coarse error removal using the interquartile spacing method,and the missing values in the coordinate time series were completed using the KKF method to obtain a complete GNSS station coordinate time series without coarse error.(2)To remove the common mode error from the GNSS station coordinate time series,the number of stations used was 20,and the IC-PCA method used in this paper was tested against the traditional PCA method and ICA method,and it was found that the RMS values of the N,E and U directions were reduced by 1.93%,1.92% and 7.60%after IC-PCA filtering.The residual RMS values were reduced by 1.93%,1.92% and7.60%,indicating that the IC-PCA method can reduce the information loss caused by the PCA method to the original series,and the filtering results are also more in line with the change trend of the original time series compared to ICA.(3)To remove the environmental load(non-tidal atmospheric load,non-tidal ocean load,hydrographic load,total environmental load)contained in the GNSS station coordinate time series,this paper uses the combination of ICEEMDAN and environmental load correction method and compares it with the combination of EMD and environmental load correction method,and finds that the RMS variation caused by the combination of ICEEMDAN method and environmental load correction is significantly smaller than that caused by the combination of EMD method and environmental load.It is found that the RMS variation caused by the combination of ICEEMDAN and environmental load correction is significantly smaller than that caused by the combination of EMD and environmental load correction,indicating that the high frequency stratification selected by the ICEEMDAN method contains less effective raw information and therefore the RMS variation caused by the combination of correction with environmental load is smaller;moreover,the correction effect of the total environmental load is better than that of the three environmental loads separately.(4)Using the time series of GNSS station coordinates with common mode error and environmental load removed for the inversion of the velocity field in North China,the estimation of the optimal noise model(white noise + power-law noise)reveals that the amplitudes of the noise components in the N,E and U directions are different;the white noise components in the N,E and U directions are relatively small and negligible at many stations;the power-law noise components in the N and The power-law noise components in the N and E directions are more or less similar,all around 10 mm/year,and the power-law noise components in the U direction are larger,all around 50 mm/year;the motion direction of all stations in the same direction is the same,and the motion rate is more or less the same,which is consistent with the motion change of the same plate;the motion direction of stations in different directions is different,and the motion rate of stations in the U direction is obviously smaller than that in the N and E directions,and the The uncertainty is also significantly smaller,which is in line with the rule that the vertical direction is more influenced by non-linear motion.It is also found that in North China the plate is moving horizontally towards the south-east,and the average rate of motion of the stations is more than 30mm/year,while in the vertical direction,most of the area in North China shows an uplifting trend without subsidence,and the average rate of motion of all stations is 2.17mm/year. |
