The Establishment Of Regional Coordinate Reference Frame Based On Shanghai CORS

ITRF2014 is currently recognized as the most accurate global reference frame,however,due to its distribution in China or the surrounding areas is not sufficient,it is difficult to obtain the high-precision GNSS station coordinates from international terrestrial reference frame(ITRF).The paper use the well-distributed global IGS stations,together with the high-density SHCORS stations to establish a high-precision Shanghai regional geodetic reference frame,which can provide an accurate,reliable and stable reference frame basics for regional large-scale long-period basic scientific research and national economic construction.The following are the main research results of this paper:(1)Deduct stations with large gross errors through radial component detection,then calculate the horizontal residual error deviation index by equal weight fitting of rotation,and use the ratio of station residuals and deviation coefficients as the relative weight of each internally constrained station to fit the weighted rotation component.Finally,the optimal internal constraint scheme for establishing the Shanghai regional geodetic reference frame was determined: 37 evenly distributed global IGS core stations + 10 highly stable IGS stations with good geometric distribution in and around China + 6 high precision reference stations in SHCORS,meanwhile,the station relative weight was determined.(2)Based on the optimal internal constraint scheme,estimate the alignment coordinate of each station connected to ITRF through the method of instantaneous alignment by each epoch.Then estimate the annual and semi-annual seasonal signals of each site by performing time series analysis on each site,and use principal component analysis for regional filtering to eliminate the common mode errors which is ubiquitous in regional stations and ambiguous in geophysical mechanism,the result shows that the regional filter can significantly improve the accuracy of station coordinates,after filtering,the NRMS value of the coordinate sequence in the three directions of E,N and U is reduced by 36%,20% and 43%.(3)Complete the establishment of Shanghai regional reference frame and extract the horizontal and vertical velocity fields in Shanghai,the east-west velocity of each station is about 31.0 mm/yr,the north-south velocity is between-10.0 mm/yr and-12.4 mm/yr,and the vertical velocity is-4.9 mm/yr-3.3 mm/yr.At the reference epoch,the horizontal accuracy of each SHCORS stations reaches 0.75 mm-1.25 mm(East)?0.5 mm-1 mm(North),the vertical accuracy reaches 3 mm-5 mm,the speed accuracy reaches 0.132 mm/yr.(4)Assess the quality and stability of the regional reference frame qualitatively by quantitative analysis of origin offset,scale factor and station coordinate time series.The research found that the RMSE in origin increased from 2.5 mm before March 2011 to 2.5 mm-5 mm;the amplitude of the RMSE time series of scale factor began to show an increasing trend after March 2011.The Japan's 9.1 magnitude earthquake in March 2011 is one of the main reason leading to poor accuracy and stability of the Shanghai regional reference frame,and the influence continues to the last epoch of our analysis.The innovation of this research:(1)Use the minimum constraints to realize the connection between the regional terrestrial reference frame and international terrestrial reference frame,innovatively propose and explore different minimum constrained combinations and relative weights of stations on the establishment of the regional terrestrial reference frame,and then determine the optimal constraint plan.(2)Ignoring the correlation between the stations,using instantaneous alignment,time series analysis and principal component analysis to establish a regional reference frame,solving more flexibly and efficiently,and it is easy to incorporate various nonlinear changes and eliminate common mode errors.