Update China geodetic coordinate frame considering plate motion

China Geodetic Coordinate System 2000(CGCS2000),as the formal national coordinate reference frame,has been used for 20 years.The coordinates of all Global Navigation Satellite System(GNSS)stations in China need referring to this system.To this end,the first step is to align the coordinates of all stations,usually included in a regional GNSS network,with a given International Terrestrial Reference Frame(ITRF),then these coordinates are corrected to the CGCS2000 in consideration of plate movement.For a better alignment result,regional control stations are needed and their coordinates were estimated from the combination of constraint-free normal equation systems provided by several International GNSS Service(IGS)analysis centers.The effect in using these refined coordinates,which deter-mine a regional coordinate datum,on the alignment result should be evaluated by the coordinate corrections of the regional control stations to the regional coordinate datum,i.e.smaller corrections mean better alignments of the two associated frames.The test results show that the refined coordinates are more accurate than the ones calculated from the station’s velocity,and are well aligned with the ITRF2005.Moreover,for obtaining the coordinates of GNSS stations in an updated CGCS2000 frame,a gridded linear velocity field based on the estimated velocities at 1025 CGCS2000 stations was generated for China's Mainland using the optimal interpolation method,the inverse distance weighting,which is selected from five interpolation methods.The overall precisions of the constructed velocity field at all stations in the East(E)and,North(N)directions are 0.78 mm/a and 0.95 mm/a,respectively.For evaluating the accuracy of the updated CGCS2000 frame,monthly solutions for the coordinates of some CGCS2000 CORS stations in the ITRF2014 during the period from 2000.0 to 2018 were obtained and the Root Mean Square(RMS)of the differences between the coordinates corrected to the CGCS2000 and the known coordinates at these stations are about 2-3 cm.