Research On Multi-system Data Product Evaluation And Clock Error Short Term Prediction Method Of IGMAS

At present,China's Beidou system has been fully completed,and provides services to the world.This system will provide global services.The performance of BDS-3 satellites and the acceptance of iGMAS tracking station for BDS-3 satellites need to be further explored.The accuracy of orbit and clock products,and the consistency and correlation between orbit and clock products in each analysis center of iGMAS also need to be analyzed comprehensively.In the clock prediction,how to optimize the grey model for the problem of low accuracy of clock prediction.Each analysis center of iGMAS can provide GPS/GLONASS/BDS/Galileo satellite clock products,but the clock synthesis method currently adopted by its integrated center has not taken into account the periodic difference of satellite operation between different satellite navigation systems.In view of the above problems,this paper does the following research.(1)Based on the observation data of iGMAS tracking station,this paper analyzes the observation data of BDS-3 satellite and iGMAS tracking station by using quality analysis software,tests the performance of BDS-3,and proves that the observation data quality of BDS-3 satellite is equivalent with the accuracy of GPS and Galileo satellite,and can meet the requirements of global positioning service of Beidou satellite navigation system.At the same time,it is found that the data integrity rate of tracking station equipped with GNSS-GGR receiver is poor,the difference between different stations is obvious,and there is a situation that BDS-3 part of satellite data can not be received.CETC-54-GMR-4016 receiver has the worst performance in suppressing multipath effect.The inhibition ability of various receivers to the multi-path effect of B2 a frequency points is better than that of B1 C.UB4B0-13478 receiver has the worst performance in weakening ionospheric delay.The frequency point of B1C/B2 a of CETC-54-GMR-4011 receiver is prone to cycle jump.(2)Based on the orbit products and clock products provided by the analysis centers of iGMAS,this paper mainly analyzes the products from four aspects,including product accuracy,consistency,relevance and periodicity.The accuracy analysis shows that the accuracy of orbit and clock products provided by WHU and BAC analysis center is the best,while the other analysis centers is basically the same order,slightly worse than that of WHU and BAC.The results of the orbit/clock product consistency analysis show that the accuracy of orbit and clock has more influence on the results of PPP positioning than the consistency of the two.And the result slso shows that the product consistency of WHU is the best among the selected analysis center products.The correlation analysis between orbit products and clock products shows that there is negative correlation and periodic characteristics between orbit radial deviation and clock deviation.The periodic analysis of clock products shows that BDS,GPS and GLONASS have obvious 12 h and 24 h cycle terms,Galileo has obvious 12 h cycle term,but 24 h cycle term is not obvious;besides,BDS has 48 h,8h and 6h cycle term,GLONASS has obvious 8h cycle term.The main cycle terms of clock difference are about 12 h for BDS and Galileo,while that of GPS and GLONASS is about 24 h.(3)For the problem that the accuracy of clock prediction with grey model is not high,this paper presents a clock forecasting model which combines the autoregression and grey model.The experimental results show that the modeling data quantity affects the prediction results of GM(1,1)model.In the case of large amount of modeling data,the prediction effect of GM(1,1)model is poor,but after the results of GM(1,1)model are modified by AR model,the prediction results of single GM(1,1)model are improved and the prediction accuracy of clock is improved.For GPS satellite,the prediction accuracy can be improved by about 1.5 times.(4)For the problem that the clock synthesis method currently used in iGMAS integrated center does not take into account the periodic difference of satellite between different satellite navigation systems,this paper proposes a clock synthesis model based on polynomial additional periodic term fitting.The experimental results show that: for BDS/GPS/GLONASS/Galileo four satellite navigation systems,the selected models for satellite clock error synthesis are slightly different,BDS/GPS/GLONASS system adopts quadratic polynomial + 4 cycles model for clock synthesis,Galileo system adopts quadratic polynomial + 3 cycles model for satellite clock synthesis.The RMS of BDS and GLONASS is the best and more stable.The RMS of GPS and Galileo is slightly worse than that of ISC,but better than that of CHD,NTS,WHU and XRS.The results of BDS single system static PPP are similar to ISC,and the position accuracy is about 3cm.Through the verification of the method proposed in this paper,it is clear that this method can effectively consider the periodicity between different satellites,so as to improve the accuracy of integrated clock.Therefore,the clock synthesis method based on polynomial additional periodic term fitting proposed in this paper can be a useful supplement to the clock synthesis method of iGMAS analysis center.