Theory And Method On Real Time Monitoring Of Ionospheric Delay Using Ground Based GNSS Data

GNSS single frequency terminal user suffered from ionospheric delay a lot, while the ionospheric delay provided by system is not very precise like Klobuchar. So, the main mothod to provide precise ionospheric delay information is to building a monitoring station network and doing ionospheric delay modeling using the real time observation. The ionosphere delay would be then sent to the single frequency terminal user.This paper would concentrate on function based regional and global ionospheric delay modeling. The reason for using function based method is the number of state increasing with the grid number and could lead to transport burden. While the resolution of grid and interplot precision would largely impact the correction precision in user position.The detailed method to realize real time function based ionospheric delay modeling is a constrained Kalman filter combined with spherical harmonic function which can solve the model's parameters and both satellites and receivers'DCB. As the spherical harmonic function can be used in both regional and global ionosphere modeling, this method gives a way to realize real time regional and global ionospheric delay monitoring.For neglecting the vertical variation of electron density, two dimensional method using a thin shell to samplize the modeling structure, but this would introduce some error term. So, in order to improve the precision of ionospheric modeling, a EOF based tomography method is tested for regional ionospheric delay correction and its'result is better than two dimensional spherical harmonic function model.The main content of this paper could be summarized as below:1. Conclude and analysis the theory and method on two dimentional ionosphere modeling. With the strategy and detail coincident with IGS standard, the result of this paper has shown to be in small defference with respect to the product of IGS.2. A real time ionosphere monitoring strategy combining the Kalman filtering and Spherical Harmonic function is proposed. The constrained Kalman filter is used to estimate both ionosphere model parameters and DCB. By using IGS global rinex file as a simulation, the result is shown to be valid and precise.3. Ionosphere tomography theory and method is illustrated. Based on the analysis of advantage of different method, the empirical orthogonal function base tomography is used to build an ionosphere model. The experiment shows the result of this tomography is better than the two dimensional thin slap model.4. Based on the analysis above, a real time ionosphere monitoring system is built using real time data stream from national CORS. The key point of real time system is analyzed and the positioning precision using the ionosphere correction from this real time system shows that this system is useful for single frequency user.