Research On Ionospheric Modeling Methods And Applications In Chinese Region

When the satellite navigation signal passes through the ionosphere,it will be refracted,reflected,scattered and absorbed,so that there is a certain time delay for the signal reaching the receiver.Such time delay could be several meters to tens of meters,even hundreds of meters in extremely harsh conditions.It will affect the positioning accuracy of GNSS(Global Navigation Satellite Systems)seriously.Based on the refraction theory and dispersion effect of the ionosphere,the multi-frequency combination method can minimize the its effect on positioning.In addition,the global or regional ionospheric model can be established to further correct the ionospheric delay and to improve the accuracy of navigation and positioning.Many works have been done on the researches of ionospheric model.The study found that,different models have their own characteristics.For example,the polynomial model is suitable for calculating the ionospheric VTEC(Vertical Total Electron Content)in a short time accurately,the spherical model is more suitable for fitting large or global-area,and the multi-surface function can reflect the irregular changes of the ionosphere.The comprehensive completion of BDS(Bei Dou Navigation Satellite System)and establishment of CMONOC(Crustal Movement Observation Network of China)provide strong conditions for the establishment of China's regional ionospheric model.However,China has a vast territory,a large span of latitude and longitude,and the ionosphere has obvious local and regional characteristics.For our country,it is necessary to use the GNSS observation data within our country,provide the appropriate regional model,and generate high-precision ionospheric TEC(Total Electron Content)products independently,and then improve the positioning accuracy of users in the service area effectively,which is also the key to the development of our country's satellite navigation industry.The specific works are as follows:(1)This thesis summarizes the research background and current status of ionosphere research and the principle and method of extracting ionospheric delay by using dual-frequency GNSS observation data based on the basic characteristics of the ionosphere are discussed.Then,the different projection functions and reference coordinate systems in the calculation of the ionosphere are analyzed.(2)After studying the basic theory,function,calculation process,advantages and disadvantages of polynomial function model,spherical model and multi-surface function,we provide the corresponding improving models.(3)A regional ionospheric model in China by using the CMONOC data is established.Comparing the satellite and receiver different code bias results and the ionospheric TEC grid results with the products released by CODE(Center for Orbit Determination in Europe),the accuracy and stability of the regional ionospheric model are evaluated from two aspects: internal and external accuracy.Besides,analyze the influence of ionospheric delay correction on PPP(Precise Point Positioning)and SPP(Single Point Positioning).