Datum Transformation Parameters Estimation and Longterm Evolution Analysis of WGS84 and ITRS

For in-orbit GPS satellites，we adopted the NUA precise ephemeris in WUS84 from NGA and ITRS from IGS，using the severrparameter Bursa model combined with different satellite-borne atomic clock stabilities at the same time to transform the parameters between WGS84 and ITRS using the least squares criterion.We eliminated the trend term based on the time sequence of the transformation parameters and at last we used spectral analysis to explore its cyclical nature. We use NGA and IGS precise ephemeris，from January 1，2009 to J une 2012，a total of 1 306 d，collecting every coordinate transform parameter to analyze long-term evolution characteristics:three translational the parameters have the 345 d，690 d and 345 d periodic terms，while three rotation parameters，with the 459 d，172 d and 459 d cycle item scale parameter respectively，are found not to be not periodic terms.