Abstract: To unit of Guangzhou CORS reference station network and BeiDou ground-based monitoring station network coordinate datum,and explore the feasibility of using the BeiDou system to maintain the surveying datum of regional CORS station network,we carry out GAMIT high-precision baseline solution and 3D constrained adjustment for 6 sets of dual-frequency data from 27 stations in the Greater Bay Area.The results show that normalized root mean square error(NRMSE) of the baseline solutions is better than 0.25,and the ambiguity resolution success rate of GPS,GLONASS,and Galileo baseline solutions exceeds 90%.The plane direction of baseline repeatability is better than the elevation direction,the fixed error of linear fitting is in the order of millimeter,and the scale error is better than the GNSS Class B 10^-8 accuracy requirements.The baseline adjustment accuracy of the four systems is the highest,and average RMSE of the single system adjustment coordinate difference is 1.1 mm in the north direction and 1.5 mm in the east direction.There is inconsistency in the elevation direction,and the maximum difference in the elevation of Galileo and GLONASS adjustment coordinates is more than 20 mm.This paper verifies the feasibility of GAMIT processing BDS data to independently maintain regional CORS coordinate datum.On the whole,the accuracy of BDS new signal frequency B1C/B2a and B1C/B3I is equivalent to that of GPS L1/L2 dual-frequency combination,and superior to BDS B1I/B3I and Galileo E1/E5a dual-frequency combination.The accuracy of various indicators of the GLONASS G1/G2 dual-frequency combination is relatively low.

Key words: BDS, coordinate datum, baseline repeatability, coordinate consistency, precision analysis