Preliminary Study On International Time Transfer Based On Beidou PPP

Time transfer technology based on Precise Point Positioning(PPP)is one of the main ways of carrying out long distance high accuracy time comparison,which could realize the accuracy of sub-nanosecond level.According to the Circular T issued by Bureau International des Poids et Measures(BIPM),by January 2017,among the 76 time laboratories participating in International atomic time(TAI)comparison,there are 28 time keeping laboratories carrying out time transfer through using GPS PPP,which is 37% of the total;there are 10 combing satellite two-way with PPP,which is13% of the total.Above time keeping laboratories which using PPP technology to carry out time transfer are all internationally important time laboratories.Therefore,the time transfer method based on PPP technology plays an important role in international time comparison.However,GNSS link in current TAI routine international time comparison is only carried out based on GPS or GLONASS system observation data.Since December 2012,the BeiDou navigation system(in the following would be called BeiDou or BDS for short)independently developed by our country formally provides service of navigation,positioning and time service.Though it is only regional system at present,and the promised service range only covers Asia-Pacific region,in places like Europe,parts of the BeiDou satellite could be observed as well.Carrying out research on TAI international time comparison based on BeiDou could promote application of BeiDou regional system in international time frequency field,and accumulate technological reserves for future application of Beidou global system in international time comparison,at the same time,could further improve the stability,accuracy and reliability of TAI international time comparison.This dissertation selects the BeiDou/GNSS observation data from three important international time laboratories,which are National Time Service Center(NTSC),Physikalisch-Technische Bundesanstalt(PTB)and Observatoire Royal de Belgique(ROB),and based on the Bernese 5.2 software independently adapted by National Time Service Center(NTSC),feasibility analysis of BeiDou PPP in international time comparison is carried out.Concrete work includes:(1)Software verification.In TAI time comparison,BIPM adopts the PPP link results calculated by NRCan-PPP software,and this dissertation adopts Bernese5.2software.In order to obtain software difference,with solution strategy of BIPM as the reference,GPS PPP time transfer results of the same link based on two different software are calculated.The RMS of various software PPP results difference is within0.2ns,which verifies the reliability of carrying out PPP time transfer based on Bernese5.2 software which is adapted independently.(2)Products verification.GPS PPP time transfer experiments are conducted with62-day data sets from two international time links,PTB-NTSC and PTB-ROB.Four different precise satellite orbit and clock product sets,including IGS rapid and final GPS single system products,and GBM,COM products from IGS Multi-GNSS Experiment pilot project,are used respectively.The results show that,the results difference RMS of applying different products to carry out time transfer is about0.1ns,which is lower than the international uncertainty level of GPS PPP time transfer,which verifies that the GNSS multi-system products could be used in GPS PPP time transfer,and lay foundation for following BDS PPP time transfer.(3)Comparison and analysis of Bei Dou PPP international time comparison strategy.One Europe-Asia international time comparison link is selected to carry out BDS PPP time transfer experiment,with the GPS PPP results published by BIPM as the reference,analyze BDS PPP international time comparison strategy from various perspectives like solution parameters,elevation mask setting and sampling interval.