| Recently,according to the requirements of some important GPS research subjects in the fields of Geodesy,Geophysics,Space-Physics and navigation in China,we studied systematically how to correcting the effects of the ionosphere on GPS,with high-precision and accuracy. As the parts of the main contributions,the research projects focus mainly on How to improve GPS surveying by reducing ionospheric delay for dual/single frequency kinematic/static users:high accuracy correction of ionospheric delay for single/dual frequency GPS users on the earth and in space,China WAAS ionospheric modeling and the theory and method of monitoring of ionosphere using GPS.The main contents of this Ph.D paper consist of two parts:Fisrt part-the outline of research background and the systematic introduction and summarization of the previous research results of this work.Second part-the main contribution and research results of this paper are focused on as follows:(1) How to use the measurements of a dual frequency GPS receiver to determine the ionospheric delay correction model for single frequency GPS of a local range;(2) How to separate the instrumental biases with the ionospheric delays in GPS observation;(3) How to establish a large range grid ionosphere model and use the GPS data of Chinese crust movement observation network to investigate the change law of ionospheric TEC of China area;(4) How to improve the effectiveness of correcting ionospheric delays for WAAS's users under adverse conditions.(5) How to establish the basic theory and the corresponding framework of monitoring the stochastic ionospheric disturbance using GPS(6) How to improve the modelling ability of ionospheric delay according to its diurnal,seasonal,annual variations based on GPS;(7) How to meet the demand of correcting the ionospheric delay of high-precision orbit determination for low-earth satellite using a single frequency GPS receiver1 Extracting (local) ionospheric information from GPS data with high-precisionThe factors are systematically described and analyzed which limit the precision of using GPS data to extract ionospheric delays. The precision of determining ionospheric delay using GPS is improved based on the further research of the related models and methods. The main achievements of this work include the some aspects as follows:(1) Based on a simple model with constant number of parameters,which consists of a set of trigonometric series functions,a generalized ionospheric model is constructed whose parameters can be adjusted. Due to the property of selecting the different parameters according to the change law of ionospheric delay,the new model has better availability in the field of the related theoretic research and engineering application. The experimental results show that the model can indicate the characteristic of ionospheric actions,improves further the modeling ability of local ionosphere and may be used to correct efficiently ionospheric delay of the single frequency GPS uses serviced by DGPS.(2) Different calculating schemes are designed which are used to analyze in detail the characteristics of the effect from instrumental bias (IB) in GPS observations on determining ionospheric delays. IB is different from noise in GPS observations. The experimental results show that the effect of IB is much larger than that of the noise on estimating ionospheic delay,and IB can cause ionospheric delaymeasurements to include systematic errors of the order of several meters. Therefore,one must significantly take notice of IB and remove its negative effect,and should not casually consider IB as part of noise whenever GPS data are used to fit ionospheric model or to directly calculate ionospheric delay.(3) Stability of IB is studied with a refined method for separating it from ionospheric delay using multi-day GPS phase-smoothed code data. The experimental results show that,by using averaging of noise with phase-smoothed code observation,the effect of noise on separating IB from ION can be effic...
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