Research On Ionospheric Delay And Prediction Model Based On Ellipsoidal Harmonic Function

The use of GPS for ionosphere monitoring and prediction is an important work and research direction.The VTEC fitting model of regional ionosphere and the short-term prediction model of regional ionosphere VTEC are focused on in this paper.Finally,the reference for the realization of the relative accurate and real-time ionospheric correlation service can be provided.In this paper,an example of ionospheric empirical model is selected for the analysis.And then,we also use the data downloaded from RTKLIB to develop the VTEC model research of ionosphere.We also use the ionosphere VTEC data downloaded from WHU'S satellite navigation and positioning center to study on prediction model of regional ionosphere.The main contents and conclusions are as follows:1)In this paper,an example is used to analyze the fitting effect of three ionosphere empirical models which include IRI model,Klobuchar model and NeQuick model.The following conclusions are got.On the one hand,the data correction effect of the model in high latitudes is generally better than that of lower latitudes.On the other hand,among the three models,the IRI model is best modified.The modified effect of Klobuchar model is worse than the IRI model.The effect of the NeQuick model is the worst.2)In this paper,data downloaded from RTKLIB is used to study the fitting effect of the three conventional ionospheric fitting models which include polynomial model,spherical harmonic model and grid model.When the three models are used to model the vertical electron content in the regional ionosphere,the polynomial model is more accurate in describing the trend of electronic content in the described area.The accuracy of the ionospheric model established by the spherical harmonic function is slightly lower than that of the polynomial model.And then,The effect of the grid model is the worst.3)The theory of ellipsoid harmonic series and ellipsoidal coordinate system are introduced deeply and the practical form of ellipsoidal harmonic function is described in this paper.A modified ionospheric VTEC model based on the ellipsoidal harmonic function theory is established.We take advantage of the previous data to model the fitting mode and the harmonic function model is compared and analyzed.In the end,compared to the spherical harmonic function model,the ellipsoidal VTEC model improved by about 9.3%in the fitting precision.4)The theory of BP neural network technology is analyzed systematically in this paper.Using BP neural network technology,an ionospheric VTEC fusion model based on ellipsoidal harmonic function is established.By calculating,the overall accuracy of combined model improved by 15.5%compared with spherical harmonic model respectively.5)Based on the theory of BP neural network technology and ellipsoidal harmonic function,the VTEC regional prediction model of ionosphere is established.We use the ionosphere VTEC grid data downloaded from WHU'S satellite navigation and positioning center to study in this research.Compared with the single-point prediction model,the regional prediction model is not much different from the single-point prediction model in the mean and middle error indexes.The absolute error average goes down 1.21TECU.And because the modeling effort is only a fifth of the single-point model,the work efficiency is greatly improved under the premise of guarantee accuracy.