Ionospheric Modeling Based On Multi-frequency And Multi-mode GNSS Observations

Ionospheric delay error is one of the most difficult problems in satellite navigation.The ionospheric research based on Global Satellite Navigation System(GNSS)technology mainly focuses on two aspects.The first is the monitoring and modeling of total Ionospheric Electron Content(TEC).Second,application research based on high-precision ionospheric model,such as ionospheric error correction,the coupling relationship between ionosphere and strong convection weather,such as earthquake,typhoon,tsunami,heavy rainfall,etc.Currently,GNSS systems are stepping up their efforts to upgrade and improve their navigation and positioning performance and application service level.In the construction,upgrading and improvement of GNSS system,new requirements are also put forward for the ionospheric model performance and modified technical indicators.Meanwhile,various global and regional multi-gnss tracking station network observations provide rich data resources and platform opportunities for improving the performance of GNSS ionospheric model.Based on this,this paper mainly studies the establishment of high-precision ionosphere model based on GPS+BDS+GLONASS+GALILEO four-system observation data,focusing on solving the ionosphere model accuracy problem in the sparse high-latitude area of the survey station and the ionosphere modeling accuracy problem in China.To achieve this goal,this thesis first discusses the basic principles and methods of GNSS inversion of ionospheric delay.Then,how to build global and regional ionospheric models using GNSS observation data is studied,and the parameters of satellite terminal hardware delay(DCB)are precisely determined.Aiming at the problems of less distribution of GNSS tracking stations in high latitude areas and lower modeling accuracy,the inequality constraint algorithm is adopted to improve the modeling accuracy.Finally,China regional ionospheric model is established based on GNSS observation data of China ground-based enhancement system.The main work of this paper is as follows:(1)The basic characteristics of ionosphere are introduced in detail,the basic principle and method of ionospheric delay inversion based on GNSS are elaborated,and the influence of error of extracting ionospheric TEC using GNSS is deeply analyzed.Finally,the expression and calculation methods of the ionospheric mathematical model are summarized.(2)The global and regional ionospheric models based on GNSS observations are studied and realized.The whole process from data preprocessing to mathematical model fitting is discussed in detail.And the ionospheric grid products released by CODG are used as a reference to evaluate the accuracy and reliability of the ionospheric model studied in this paper.(3)The inequality constraints algorithm is studied in the ionosphere modeling application,through to the ionosphere modeling process of negative grid join non-negative non-zero constraints to improve the singular values of the ionosphere model,and carried on the test,the result showed that join the inequality constraints optimization algorithm to improve the high latitudes ionosphere modeling accuracy,but also improved the precision of global ionospheric model.(4)The regional ionospheric TEC model in China is established based on the observation data of beidou foundation reinforcement system framework network,and the model is used for precise positioning test after ionospheric delay correction.The test results show that the accuracy and reliability of the regional ionospheric model are better than that of the global ionospheric model.In conclusion,this paper improves the global/regional ionospheric modeling accuracy from the perspective of multi-modeling of ionospheric modeling data sources and improvement of ionospheric modeling algorithm.The modeling results show that the improved models have high accuracy and reliability.