Study On Regional Ionosphereic Modeling By Combining Space-based And Ground-based GNSS Data

The ionosphere is an important part of the space environment.With the rapid development and wide application of aerospace and wireless communication technology,the influence of ionosphere on them can not be ignored.Especially for the GNSS system,the refraction of the ionosphere caused by the ionosphere is the main error source.The direct factor affecting radio wave refraction is the electron content and its distribution in the ionosphere.The ionospheric characteristics are extremely complex and difficult to describe accurately on the physical level.In practice,one of the effective research means is to use all kinds of detection methods to obtain the measured information of electronic content,and then establish the ionospheric TEC and electronic density distribution model with appropriate mathematical functions.The high precision ionospheric model can improve the navigation and positioning accuracy of GNSS users,and also provide data reference for the monitoring and prediction of space environment.Furthermore,it has important scientific significance for the ionospheric basic theory research.Among a large number of ionospheric detection techniques,on the one hand,the ground-based GNSS technology is the most accurate method to measure TEC.On the other hand,the space-based GNSS ionospheric occultation technology can obtain electronic density profiles with high precision.This paper combines the ground-based and space-based GNSS data to model the ionosphere,giving full play to the advan-tages of the ground-based GNSS technology which is able to do long-term continuous monitoring,and the advantage of space-based Occultation Technology which has high vertical resolution and can observe in all-weather.The main contents of this paper are as follows:1.The present situation of the ionosphere research and the general condition of GNSS are briefly introduced.The stratification and variation characteristics of the ionosphere are analyzed.The basic principle of obtaining the ionospheric TEC through the ground-based GNSS and obtaining the electron density through the space-based occultation is described.Then the ionosphere modeling is studied from the following three aspects:2.2-D reginoal VTEC modeling based on ground-based single-station GNSS data.Using uncombined PPP technology instead of conventional carrier smoothing pseudo range method,the extended Calman filter is applied to estimate slant ionospheric delay,taking into account the influence of DCBs.Then,according to the measured data of single-station TEC,the VTEC region polynomial model is established,and the precision of inner coincidence of each time interval is evaluated.At the same time,the IGS ionospheric grid product is used to evaluate the precision of the external coincidence.The test results show that the VTEC model has a good fitting effect,and the VTEC results of several stations have good consistancy with those of IGS products.3.Inversion of the electron density profile in the vertical direction of the iono-sphere.A new model combining Chapman and QP function are proposed to provide an electronic density vertical inversion method using the measured data of radio occul-tation.A number of data from several stations in East Asia are selected to carry out experiments.The results of the electron density profile and the F2 peak parameter es-timation are compared with the occultation and IRI.The results show that the electron density profile obtained by this method is consistent with occultation and IRI results,and the accuracy of F2 layer peak parameters is slightly better than that of IRI model.4.Study on the modeling of regional three-dimensional electron density.On the basis of single-station vertical profile,the horizontal distribution of foF2 and hmF2 is fitted by low order spherical harmonic function according to the measured data of the radio occultation and several ground-based stations in the region.The test results of the in European regional show that the peak parameters of the F2 layer obtained by the three-dimensional model are more consistent with the actual situation than the IRI model.In order to further evaluate the reliability of the model,this paper presents an experiment to test the coincidence between the STEC observations and the calculated values of the models.It is found that the accuracy of STEC is high in addition to the edge of the survey area.Compared with the pixel based tomography model,the three-dimensional electronic density model of this paper reduces the number of parameters to be estimated.The calculation is more convenient and concise,and has a certain reference value.