Relativistic Theory Of Time Transfer And Techniques Of Clock Synchronization

Time is one of the basic physical variables to describe object movements. With the development of science and technology, the accuracy of time measurement increases continuously. The long stability of a modern atomic clock is up to10-17. Then the theoretical foundation of time measurement changes from Newtonian theory to the General Relativity Theory (GRT).A single clock is not sufficient to realize a coordinate time scale. We must synchronize a set of clocks located in different places and integrate the data to get a time scale which is more accurate and more stable than any single clock. At the same time, it is required to establish relations between clocks and the time scale in order to maintain the synchronization in some degree. Then relativistic theory of time transfer and techniques of clock synchronization are systematically discussed in this paper.Relativistic time delay should be taken into account in the time transfer between different clocks. The relation between proper time and coordinate time is derived in details. Then the basic transfer models for both portable clock and electromagnetic signal are given. The adjustment schemes for the clocks on the ground and the different type satellite clocks are discussed. The weakness of usual portable clock model is pointed out and a new model considering the rate between portable clock and standard clock is given.Atmosphere delay is one of the major error sources, which affects the accuracy of time transfer in the near Earth space between users with the electromagnetic wave signal. Several usual models for troposphere delay and ionosphere delay are discussed and their influences to different time transfer methods are analyzed.Several time transfer methods of electromagnetic signal-one-way satellite time transfer,TWSTFT(Two-way Satellite Time and Frequency Transfer), LASSO(LAser Synchronization from Stationary Orbit) and pseudo-code and laser ranging are carefully analyzed. The calculation models in the geocentric non-rotating coordinate system are derived, with which other classical models have been compared. The comparison results show that the models of LASSO and TWSTFT in this paper have the higher accuracy and other models are the approximation of them to some extent. The fact that the accuracy of the Petit calculation model can not achieve lps but only 10ps is discoved. Then the influences of major error sources are analyzed and the correction terms are given for different transfer accuracy.The basic model of GPS Common View (GPSCV) is discussed. The satellite ephemeris errors and the station location errors are analyzed in details and then some cautious problems in GPSCV are given. The examples of different baselines are also tried out and the reasons causing the result errors are investigated. Based on our geostationary satellite positioning system, a new time transfer method named GEOSAT Common View (GEOSATCV) is presented. The calculation models in both the geocentric non-rotating and Earth-fixed coordinate system are derived. Then the major errors in GEOSATCV are also analyzed. In view of the disadvantages of present ionosphere delay model using in the geostationary satellite positioning system, a newionosphere delay model is also presented, which can remove systematic errors of the satellite transform equipment and avoid random errors of the special differential receiver placed in the center station and the mapping function used in the present ionosphere delay model.Three basic methods of least square, Kalman filter and AR model, which are used to predict the time deviation of atomic clock, are discussed. The relations between prediction accuracy and prediction models, observable arc and the sampling datum for short- and long-term prediction are computed and analyzed, using the running data of different type satellite clocks in continuous and incontinuous measurement status.