The Method Of Refining Satellite Clock Reference Bias And Its Application Of Precision Timing

Since Allan and Weiss proposed the GPS common view method in the 1980s,Precise timing by geodesy method has been a hot issue in recent years.With the improvement of accuracy and effectiveness of IGS precise products,the time transfer method based on precise point positioning?PPP?is more accurate and wider coverage than the common view method,even the full view method.At present,PPP time transfer is more and more widely used in the high-precision field such as time datum maintenance and GNSS timing service.However,high-precision error correction is one key point to realize high-performance PPP timing service.The accuracy of PPP time transfer is negatively affected by various GNSS errors,such as tropospheric delay,ionospheric delay,satellite clock offset and so on.In general,the precision of PPP time and frequency transmission with IGS final products can achieve about 0.1 ns,but it can't satisfy for the real-time time transfer and timing service due to the delay of IGS final products.At present,IGS can provide ultra-fast product?IGU?for real-time processing application.The precision of satellite orbit products has reached the same level as the final product,while the clock products can't satisfy the precision requirements of PPP time transfer.In general,the real time satellite clock products exist a reference bias,and the influence of the deviation term on PPP time transfer and timing performance has not been systematically analyzed and discussed.Therefore,it is an interest research topic about the influence of satellite clock bias on real-time PPP time transfer and timing service,and how to establish correction models.This thesis discusses the deviation terms of real-time satellite clock products,and analyses the impact of deviation terms on PPP time transfer and precise timing.Then a new method is proposed to refine time reference of real-time satellite clock products The specific research works are as follows:Based on the algorithm of PPP time transfer and real-time satellite clock offset estimation,this thesis analyses the effects of initial satellite clock bias,time reference bias and relative clock bias on PPP time transfer and GNSS timing.In order to solve the bias of time datum in real-time satellite clock product,a"two-step method"is proposed in this thesis.Firstly,the stability of atomic clocks equipped by different IGS stations and Allen variances of different time intervals are analyzed to establish state model and stochastic model.Then,based these mathematic models,the network solution method is used to separate the initial clock offset term,the frequency offset term and the deviation of the time reference from each receiver clock offset,and refined time reference is obtained.The test of one week is carried out to compare the refined time reference with IGST.The results show that the STD?Standard Deviation?value of the satellite clock offset with refined time reference can reach 0.1 ns or less,and the accuracy is increased by 37%to 93%.At the same time,the long-term stability at 10000s can reach the level of10^-15,which is ten times more than that of unrefined time reference.The PPP time transfer of different IGS stations equipped with hydrogen atomic clocks is used to further verify the performance of refined time reference of real time satellite clock.Compared with the station clock offset provided by IGS,the single-day difference of AMC2,IENG,MEDI,MGUE,NRC1 and PTBB are less than 0.2 ns.,and the improvement is between 55.08%and 83.78%.So,it demonstrates the time reference refinement method of this thesis is effective.