| The ionosphere at the distance of 60-2000 km from the ground,which is an insurmountable area for ground-space interactive communication.It will cause some interference to the passing radio waves.At the same time,due to the reflection of the ionosphere on high-frequency radio waves,it plays an important role in applications such as short-wave communication and trans-horizon radar.Therefore,research on the ionosphere and its applications has been one of the hot topics of scholars at home and abroad.With the continuous development and improvement of the Global Navigation Satellite System(GNSS),ionospheric modeling using GNSS data has become a hotspot in ionospheric research,and more and more ionospheric modeling methods are being proposed.In short-wave communication,the state change of the ionosphere is an important factor affecting the efficiency and reliability of short-wave communication.This paper focuses on the problems of high complexity and low operation efficiency of current algorithms in 3D ionosphere modeling,the International Reference Ionosphere(IRI)model is used to extract the empirical orthogonal functions(EOFs)as the vertical basis function,which reduces the number of unknown inversions and improves the inversion efficiency,and for the problem of insufficient data in the three-dimensional ionospheric modeling,the observation information is added by adding virtual observations to improve the accuracy of the ionospheric inversion.At the same time,the application of the ionospheric model in the short-wave communication link prediction was analyzed,and the short-wave link prediction was performed using the ionosphere empirical model and ionospheric tomography model combined with ray tracing technology.The main research contents are as follows:1.The pre-processing technology of ionospheric modeling using GNSS data is studied,which mainly includes the use of GNSS dual-frequency data to extract the total electron content(TEC)and carrier phase smoothing ionospheric TEC observations.And the steps and principles of using spherical harmonic model to estimate the differential code bias(DCB)and thin-shell ionospheric model parameters were described.Ensured that high-precision ionospheric information is obtained from the GNSS observation data.2.The regional three-dimensional ionospheric tomographic inversion was performed using the European regional GPS dual-frequency observation data,and for the problem of low efficiency of traditional algorithm inversion,EOFs was extracted as the vertical basis function from the IRI2016 model,which greatly reduced the number of unknowns and improved the efficiency of inversion.Experimental results show that the solution time is greatly shortened,and the accuracy is slightly better than the traditional method.3.Aiming at the problem that insufficient data in traditional ionospheric tomography caused some grids not to be effectively corrected,a method of adding virtual rays to expand observation data was proposed.In this method,some virtual observation stations is set up in the areas lacking observation station,and then virtual rays are added.The ionospheric observation value of the virtual rays is obtained by a previously established thin-shell ionosphere model combined with the projection function,so that the grid coverage of the rays is increased by nearly 30% compare to the original method.The experimental results show that this method can effectively invert the electron density of the grid that originally lacked rays to pass through without influencing the accuracy of the inversion of the actual observed rays-rich areas.4.A ray-tracing technology and a three-dimensional ionospheric model were used to build a short-wave communication link prediction program,and a short-wave link prediction was performed in combination with the IRI2016 empirical model and ionosphere tomographic model,respectively.The influence of the short-wave emission elevation angle and frequency on the propagation distance was analyzed. |
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