| Ionosphere is an important part of the space environment, understanding the structure of ionosphere and the rule of the ionospheric activity is an important basis to better understand human living environment. The research on ionosphere has very important value for the study of the relationship between solar-terrestrial space environment and atmosphere, and improving speed, positioning, timing and navigation system’s precision.Compared to the traditional ionosphere detection technology, GNSS detection technology can achieve continuous operation and high density. At present, the situation of the four Global Navigation Satellite System (GNSS) coexistence and development has been initially formed. With the improvement of multimode CNSS continuously tracking station number and observation data quality, the research on different characteristics of multimode GNSS system is conducted. It is necessary to carry out ionosphere modeling based on multimode GNSS system.Due to the inaccurate ionosphere model and pseudorange observation accuracy, it can only achieve decimeter to meter accuracy for single frequency single point positioning. Through the combination of different frequencies observations, double-frequency users can eliminate more than99%of the ionosphere error. But the linear combination observations magnified observation noises; it needs more time to implement dual-frequency PPP convergence. Improving the ionosphere model accuracy can help to improve positioning precision accuracy and accelerate convergence speed.Ionospheric delay has great influence on single frequency user, but the effect of real-time ionospheric delay correction provided by the navigation system is limited, it’s difficult to get high precision positioning results in this case. Therefore, using real-time observation data streams based on regional or global tracking station network, to build real-time ionospheric model can effectively improve ionospheric model accuracy. At the same time, using real-time ionospheric model can help to monitor the ionosphere, which is useful for the research on ionospheric disturbance and irregular change.In this paper, some problems in the ionosphere two-dimensional chromatography are discussed, such as observation pretreatment, ionosphere extracting method and so on; China regional ionospheric model is built based on observed GPS/Beidou data, and the multimode system impact on the ionosphere model, hardware delay estimation precision is analyzed; Through the analysis of numerous GLONASS observations, GLONASS pseudorange deviations between different frequency are analyzed; we put forward a prior correction method, which can effectively eliminate the pseudorange frequency deviation of GLONASS satellites in ionospheric modeling. For the local area with dense reference stations, we build the ionospheric model based on single satellite, and put forward a double-frequency PPP fast convergence algorithm. Based on Chinese real-time data stream, we develope a real-time ionospheric model system, which can provide real-time ionospheric delay for the regional user products in China. In this paper, the main research contents include:1. Against the clock jump problem, we use satellite single-difference MW combination together with undifference MW and GF to detect cycle slips; we analyze the difference of phase smoothed pseudorange method and combined observations decomposition method and their effects on ionospheric delay extracting; the stations selected strategies for modeling ionospheric delay is analyzed in China, experimental results show that using60uniformly distributed tracking stations can achieve considerable accuracy.2. We use the measured Beidou/GPS dual mode data to establish a Chinese regional ionospheric model; under the current satellites and stations distribution situation, the accuracy of ionosphere model using single Beidou system is low at high and low latitudes, especially for the edge region, and is slightly lower than single GPS system in middle latitudes; Beidou satellites hardware delay are relatively stable, the average monthly variation is less than1.8ns.3. We use numerous GLONASS observations to analyze the pseudorange deviations between different frequencies, the results show that GLONASS pseudorange ICB is very stable but with significant differences from each other, we put forward a new multi-mode ionospheric modeling algorithm considering the impact of inter-frequency bias;, which can effectively eliminate the pseudorange frequency deviation of GLONASS satellites in ionospheric modeling.4. In order to reduce accuracy losses in regional ionospheric modeling, we build the ionospheric model for each satellite in regional area; meanwhile, we propose a new PPP rapid convergence algorithms based on the ionosphere refined products, wide lane UPD and residual SD hardware delay. Using the refined products, the single-frequency PPP users can obtain precision positioning results, for the N, E, U directions, the average RMS values are3.8,4.3and9.2cm; using the fast convergence algorithm, dual PPP users significantly reduce the convergence time, about50%of the rovers can converge to2dm within5minutes.5. We build real-time ionospheric estimated service system based on Chinese real-time data stream, and discuss the weight, robust, hardware delay processing strategy and background field in real-time modeling. Compared with the self-assessment products, CODE afterwards products and other means, in the high and middle latitudes, the real-time model accuracy is about2-3TECu and slightly in lower latitudes, around3-4TECu. Using the real-time ionospheric products, for the single frequency SPP users, the3D deviation is less than1.2m, for the lower latitudes is than2.2m; the single frequency PPP users can achieve0.2m for the horizontal,0.5m for the vertical direction accuracy. We use the real-time products to analyze the electron density magnetic storms impact on the China’s regional ionosphere at DoY076,2013. |
PDF Full Text Request