Establishment Of NTCM Broadcast Ionosphere Model And Performance Evaluation In China

Ionospheric delay is the main error source affecting the accuracy of navigation timing and positioning.With the development of global satellite navigation system,GNSS observation data become more and more abundant,which provides an important data source for establishing a convenient and effective ionospheric correction model.For real-time single-frequency users,the ionospheric delay error can not be eliminated by using dual-frequency observations.The ionospheric delay can be corrected mainly by using broadcast ionospheric correction model to obtain ionospheric information.The NTCM model has simple structure,few parameters and high precision,which provides an ideal choice for the establishment of broadcast ionospheric delay correction model.In this paper,different ionospheric delay correction models are summarized,and the principle and method of ionospheric inversion using GNSS data are studied in depth.The performance of NTCM broadcasting ionospheric model in different scenarios is comprehensively analyzed.Meanwhile,the NTCM model(NTCM-CN model and MNTCM-CN model)suitable for China and its surrounding areas is established by using the GNSS observation network in China,and its correction effect is analyzed in depth.The specific research work of this paper is as follows:1)The theories and methods of ionospheric delay correction are summarized and analyzed,including classical empirical model,dual-frequency correction model and VTEC model based on GNSS observation data.2)A method and strategy of establishing VTEC model based on GNSS observation data is realized.The rationality and correctness of this method are verified by experiments,and a software for ionospheric delay correction is developed.3)The performance of NTCM broadcasting model is evaluated from three aspects: time domain,space domain and location accuracy.The performance of NTCM broadcasting model is compared with that of BDGIM,the third generation broadcasting model of Beidou.The calculation results of a solar activity cycle are compared with those of GPS Klobuchar model and NTCMKlobuchar model.The results show that NTCM global broadcasting model has the highest accuracy and can improve 3~10 TECU compared with GPS Klobuchar model,The accuracy of NTCM-Klobuchar model is between NTCM global broadcasting model and GPS Klobuchar model.NTCM global broadcasting model has good performance in most stations,especially in the elevation direction,the positioning accuracy can be improved by about 38% compared with GPS Klobuchar model.And the accuracy of NTCM global broadcasting model is about 1.2 TECU higher than that of BDGIM model.4)The NTCM model suitable for China and its surrounding areas is established and verified by experiments.In the peak solar activity period,the accuracy of NTCM-CN model and MNTCM-CN model is about 8 TECU higher than that of GPS Klobuchar model,and about 7 TECU higher than that of GPS Klobuchar model in the calm solar activity period.The performance of GPS Klobuchar model,Beidou Klobuchar model,BDGIM model,NTCM-CN model and MNTCM-CN model in China is analyzed based on the data of one month in 2018.The results show that the VTEC predicted by NTCM-CN model is in the best agreement with the post-CODE VTEC products.The results of this paper also prove that NTCM-CN model has a good performance in positioning.