Periodic Variations of BeiDou Satellite Clock Offsets Derived from Multi-satellite Orbit Determination

Multi-satellite orbit determination based on global tracking network can generate satellite orbit and clock products for BDS at the same time. The errors in the two resulting products, however, are difficult to be decoupled completely. There might be periodic fluctuations existing in the satellite clock offsets. Restricted by current imperfect global tracking network, loses of navigation files and software settings, there exist a lot of data gaps in the BeiDou satellite orbit and clock products. A spectrum analysis method applicable to data with gaps was used, and the main periodic items of BeiDou satellite clock offsets were extracted with it. Two improved clock prediction models augmented with periodic corrections were proposed and the prediction accuracy within 24 hours was evaluated. The tested results with nearly one-year-long data showed that the three main periods in BeiDou GEO and IGSO satellite clock offsets are 12, 24 and 8 hours, respectively, while those for MEOs are 12.91, 6.44 and 24 hours. Compared with the conventional clock model of quadratic polynomial, the improved model can increase the prediction accuracy of BeiDou GEO and IGSO satellite clock offsets by 20 to 40 percent at spans less than 24 hours