Research On Ionospheric Delay Model Based On Regional CORS

In Global Positioning System, one of the major error sources is ionosphericdelay error. Since2000May, the ionospheric delay has become the largest errorsource which influence the accuracy of GPS positioning after the USA declared offthe SA policy. The paper introduces the principle and method of establishing theionospheric model using GPS. The paper focuses on the polynomial model andestablishes the single and multiple station area ionospheric delay polynomial modelusing GPS data. The paper mainly focuses on the following four aspects:（1）Based on higher difference method and phase minus pseudorange methodand ionospheric residual method and M-W method, a cycle slip detection and repairmethod was proposed. For post-processing data, the joint detection and searchingmethod of ionospheric residual method and M-W method wad proposed. Theexperimental results show that the method which can detect and repair thedual-frequency data is greater than or equal to1cycle slip. It effectively eliminatesthe influence of the cycle slips and prove clean data for the calculation of TEC.（2）The paper detailed the formula of calculating TEC. It focused on thealgorithm of carrier phase smoothing pseudorange. The experimental results showthat different sampling rate data need different smoothing factor. If the sampling rateis one second, the smoothing factor will be50to100. If the sampling rate is thirtysecond, the smoothing factor will be10to20.（3）The paper describes in detail what establishing polynomial model need, itincludes the calculation of the satellite position and satellite elevation angle andsatellite azimuth angle and puncture point and so on. When calculating the satelliteposition, the paper chooses the lagrange sliding interpolation method. Because theinterval of the lagrange sliding interpolation method is fixed. The accuracy is verylow at both ends of the interpolation interval. The formula of the ionospherepolynomial model was given. The ionosphere single and multiple station polynomialmodel in small area was set up with the HK CORS station datas. And it calculatedthe model coefficients and combined hardware delay. The experimental results showthat the fitting effect is getting better and better with the in the increase of the modelorder selection. And the solution of the single and multiple station of the combinedhardware delay is different. When the model point and station are far nearly, thecombined hardware delay value is within one TECU. By contraries, the combined hardware delay value is more than three TECU.（4）Based on calculated hardware delay satellite to receiver, monitoring theseasonal variations and the variations in different latitudes using GPS. Theexperimental results show that there is a significant correlation between theionospheric active degree and the sun active degree. The seasonal variations trend isfound to be the same in different years. And if the latitude is different, theionospheric active degree is different. The lower latitude, the higher ionosphericactive degree.