Evaluation And Improvement Of The BDS Broadcast Ionosphere Model

Ionospheric delay is one of the most significant error sources in the current satellite navigation and positioning system,which has an impact on satellite timing,positioning,navigation and other applications.Dual frequency users or multi frequency users can correct ionosphere delay by combining observations.But for real-time single frequency GNSS users,ionosphere model is needed to correct ionospheric delay.In order to meet the needs of users and researchers of real-time single frequency BDS,Beidou navigation system broadcasts ionosphere model to correct ionosphere delay.At present,BDS broadcasts Klobuchar model and BDGIM model simultaneously(It should be noted that BDS Klobuchar model is broadcast by beidou-2 and beidou-3 satellites at the same time.The modeling algorithm of them is the same,but the model parameters are significantly different.So they are seen as two models while evaluating BDS model).In order to evaluate and promote the accuracy of Beidou broadcast ionosphere model,a series of research work has been carried out in this paper.The main work of this paper is as follows:1.The broadcast status of three broadcast ionosphere models provided by Beidou satellite navigation system is introduced in detail,and the abnormal broadcast situation of Beidou ionosphere model is discussed.The results show that i GMAS observation station can receive at most 12 sets of different ionospheric model parameters in the same epoch,and the correction error caused by using the abnormal model can reach 855 TECU at most,which has a significant impact on the positioning accuracy.In view of the broadcasting anomaly of Beidou ionosphere model,this paper proposes the majority voting method to merge the ionosphere model in ephemeris file,which gets better correction performance after evaluation.2.Based on the VTEC information at the puncture point obtained from code model,the correction performance of three Beidou broadcast ionosphere model in 2017-2019 is evaluated.The results show that in the Asia Pacific region,BDGIM is slightly better than BDS K8,while BDS-2 K8 and BDS-3 K8 model have similar accuracy.Globally,BDGIM model is superior to BDS K8 model in all latitudes.Besides,BDS model is evaluated based on the TEC information derived from the observation station and the evaluation results of uere of the station,the results are consistent with this conclusion.3.Taking the solar storm on September 6,2017 as an example,this paper analyzes the disturbance of the ionosphere Tec during the solar storm and the response of the Beidou ionosphere model to the solar storm.The results show that during the solar storm,the global ionospheric Tec is significantly positively disturbed,with the maximum disturbance of 53 tecu.The performance of BDS K8 model and BDGIM model are significantly reduced,while BDGIM model is more affected by the model.The results of further evaluation based on the TEC and ROT derived from observation station and the model show that BDS K8 model can make a certain response to the solar storm,but the response time is delayed compared to the real time,while BDGIM model basically does not respond to the solar storm at all.It shows that BDS K8 model has a better response to solat storm than BDGIM model.4.In view of the shortcomings of BDS K8 model,this paper improves BDS K8 model by analyzing the parameters of time variation of ionosphere and the parameters of the original Klobuchar model,through parameter reconfiguration and without adding new parameters.In the process of modeling,ionospheric characteristic parameters are extracted by constructing loss function,and new model parameters are obtained by fitting characteristic parameters with least square method.The evaluation results show that the accuracy of the new model in high latitude area is promoted obviously.