Regional TEC Modelling Based on Combined GPS/BeiDou

Hongzhou Yang and Yang Gao

Abstract:	Many researches on ionosphere reconstruction and mitigation have been carried out based on GPS or GLONASS. Apart from Total Electron Content (TEC) reconstruction with a single satellite system, some investigations have been made to the improvement of regional TEC modeling by combining GPS/GLONASS with more visible satellites and better coverage of Ionosphere Pierce Point (IPP). The results show that the TEC can be reconstructed more accurately with the aid of GLONASS. Since the first launch in October 2000, the Chinese BeiDou satellite navigation system has now become an important and popular member of GNSS community with a good coverage in Asian-Pacific area. The capacity of the BeiDou to monitor the TEC is of great interest to the GNSS community and some reported results show that the BeiDou alone is able to provide comparative performance where GPS system has an error levelled at several TECU within China. But there are still limited investigations on combined GPS/BeiDou for regional TEC monitoring. The main objective of this paper is to investigate the performance of the regional TEC determination by combined GPS/BeiDou in both positioning and TEC domains, including both TEC reconstruction and validation. Several challenges must be addressed in using GPS/BeiDou for precise TEC modeling with a regional network, such as the totally separation of TEC parameters and Inter-Frequency Bias (IFB) of receivers and satellites and the additional IFB datum constraint. For the TEC reconstruction, the Geometry Free (GF) pseudorange code (P4) and carrier phase (L4) combinations for both GPS and BeiDou are formed firstly to eliminate unrelated variables such as geometry and troposphere. A window based phase levelling method is then proposed to smooth the pseudorange data with carrier phase data. An advantage of the window based phase levelling is that it will be able to effectively reduce the effect of outliers. After the above data pre-processing, a Kalman Filter (KF) is developed based on the combined GPS/BeiDou regional network and the state parameters to be estimated include TEC model (polynomial function) parameters and IFB of receivers and satellites, and one IFB datum which is added as virtual observation to solve the problem of Matrix rank defect, in this part, different order of polynomial function and different IFB datum are utilized to test their effect on the separation of TEC parameters and IFB parameters. For the TEC validation, the estimated TEC will be investigated both in the TEC and positioning domains. In the TEC domain, the TEC interpolated from GIM is used as the external reference, which is independent to the regional network. In the positioning domain, on the other hand, the Precise Point Positioning (PPP) solution of the station data is used as the external reference and the Single Frequency Standard Point Positioning (SF-SPP) is carried out to verify the TEC estimates generated by the combined GPS/BeiDou regional network. Numeric analysis has been conducted to assess the performance of the proposed method for regional TEC modelling based on combined GPS/BeiDouTo investigate regional TEC modelling based on combined GPS/BeiDou, the network stations are divided into two groups: reference stations and user stations. The references stations are used to generate the TEC estimates while the data from the user stations are used for independent performance analysis of the regional TEC modelling based on combined GPS/BeiDou in both positioning and TEC domains. According to the initial results in the TEC domain, the combined GPS\BeiDou system can obtain more accurate TEC parameters than those derived from single system, and fit well with those from the Global Ionosphere Map (GIM) provided by the Center for Orbit Determination of Europe (CODE). When comes to the positioning domain, the result from the SF-SPP demonstrates that the TEC value from the combined GPS/BeiDou benefits more in positioning accuracy improvement than using a single system, the positioning accuracy can reach 1.19m, 1.47m and 1.76m in east, west and vertical direction correspondingly.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3589 - 3598
Cite this article:	Yang, Hongzhou, Gao, Yang, "Regional TEC Modelling Based on Combined GPS/BeiDou," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3589-3598.
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