| Global navigation satellite systems was applied to the field of deformation monitoring as early as the 1980 s.The stations are divided into reference stations and monitoring stations,and the reference stations are built in the more stable areas outside the deformation body to provide reference for calculating the displacement of the monitoring stations.However,the reference station location is not completely stable in geologically complex regions such as Sichuan-Tibet and Qinghai-Tibet.Based on this,this paper solves the network of reference stations with unknown stability,takes the initial coordinates as reference,solves to get the reference station displacement time series,uses the control chart principle to model and analyze the time series,identifies the abnormal displacement reference stations and abnormal displacement time periods,and realizes the stability detection of reference stations.The research contents of this paper are as follows:(1)The factors affecting the stability of the reference station in the complex tectonic region were analyzed,including the geological structure of the survey area,station distribution and different leveling methods,and the results showed that the difference in the accuracy of the points obtained by different leveling methods was less than 2 mm,and the time series change trend was basically the same.Regression analysis model,time series model and gray prediction model were used to fit the time series of benchmark station displacement,and the results showed that the fitting accuracy of polynomial regression model and time series analysis model was higher,and the residual difference between the predicted and real values was less than 2mm except for some abrupt change points.(2)The CUSUM control chart is applied to the anomaly detection of displacement time series,and the CUSUM statistic is constructed using the residuals of model values and real data.The results show that the CUSUM control chart can effectively detect the anomalous data with an offset greater than one times the standard deviation and obtain the time periods in which the anomalous displacements occur.(3)Add modules for calculation of different leveling methods,displacement field,and automatic solution.Five CORS stations data(including Beidou III data)in the CORS network of Sichuan province were used to test the system solution accuracy.The results show that: the medium error of the baseline vectors obtained by the baseline maintenance software is better than 2mm,4mm and 3mm respectively;the accuracy of internal conformity of the leveling results is better,horizontal direction is better than vertical direction,statistical accuracy and repetition accuracy is better than 1mm in horizontal direction and better than 2mm in vertical direction.(4)Based on the CORS station data at the southwest end of the Longmenshan Fault Zone,the stability analysis of the regional datum network is carried out.The maximum coordinate repeatability indexes of N,E and U directions in the reference network are 8.21 mm,4.30 mm and 25.11mm;under the center of gravity reference,the maximum displacement velocities of N and E directions are 15.26±0.95mm/yr and 12.26±0.81mm/yr,respectively,and the station with the largest velocity field is drifting to the northeast relative to other stations,while the displacement velocities of the remaining stations are relatively small.velocity is relatively small;the baseline length changes across faults and blocks are analyzed,and the baseline length increases at a rate of 24.59mm/yr from 2013.01.01 to 2013.06.28,and after 2013.06.28,the baseline length fluctuates but the overall trend shortens at a rate of 6.62mm/yr;using the residuals of the displacement actual sequence model constitutes CUSUM statistics,the analysis obtained that the baseline station anomalous displacement periods coincide with the time series offset periods,which provides a solution to ensure the stability and reliability of the baseline station position. |
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