The Systematical Error Analysis of Baseline Processing in GPS Network

In the paper,the systematical errors of baseline processing in GPS network were analyzed,and were classified into positon,scale and rotaion systematical errors.Based on the analysis,the methods to eliminate and reduce the systematical errors were studied. In the GPS baseline processing,the impact of the systematical errors should be taken into account.The systematical errors are caused by the orbit error,the coordinate error of the fiducial station,the difference of the processing methods,the software using in baseline processing,the troposphere refraction,and so on. The orbit quality is considered as one of the primary limiting factor in GPS baseline processing.To eliminate the effect of orbit error,the method that fiducial stations are strongly constrained and satellite orbits are to be improved is adopted in the data processing.The coordinate error of the fiducial station also has effect on the precision of the baseline vector.It causes the whole network rotation or the scale of the network.To eliminate the effect of the error,the GPS network should be observed with high precision station such as IGS tracking station simultaneously.Because the datum of GPS relative positioning are determined by both the ephemeris and the fiducial station,the coordinates of fiducial stations should be in the same frame and the same epoch with the pre-cise ephemeris.If not,the coordinates of the fiducial stations should be translated into instanta-neous coordinates in the same frame and the same epoch with the precise ephemeris. Besides,the troposphere refraction is one of the main limiting factors in GPS positioning.The piece-wise constant functions are used for model the troposphere refraction.According to the result of data processing and using the way of analysis and comparison,it is found that the tropospheric refraction bias has influence of scale on the middle length baseline.It may be divided into two parts:fixed error and scale error,but the main is scale error.It is very important to reduce the influence of tropospheric refraction on the GPS network scale and to improve vertical accuracy.