Ionospheric Tomographic Model Restrained By EOFs And VTEC

Ionospheric tomography based on Global Navigation Satellite System(GNSS)is a popular technique for ionosphere imaging.However,the limited and uneven distribution of GNSS receivers makes the ionospheric tomography is an ill-posed problem.Though many models have been proposed in the past decades,their inflexibilities in constraints,dependencies on background and lacks of constraint on dark voxels remain headache.In this study,the Vertical total electron(VTEC)and Empirical Orthogonal Function(EOF)were used to constrain the tomography model,and then improve the quality of ionospheric tomography.The main achievements and work are as follows:(1)A function-based tomographic model restrained by VTEC and principal EOF(FVPE)is proposed.First,the Slepian function and EOFs were used to describe the horizontal and vertical changes of electron density to construct the tomography model.Then,the cost function is established applying the VTEC and EOF principal components as constraints to the model,in order to improve the inversion accuracy of the dark voxels and enhance the stability and constraint of the model.Finally,experiments are carried out to validate the FVPE method,compared with the Farzaneh method and IRI-2016 model.Results show that compared with the other two methods,the FVPE is closer to the true in the electron density profile,and has better performance in F2 layer peak data verification,STEC cross verification and VTEC verification,with an average improvement rate of 10.20%,22.57% and 49.38%,respectively.(2)On the basis of FVPE,a EOF-based multiscale tomographic model(EMST)is proposed.In this method,a series of sub-models characterized by different scales are established.A new scale is continuously added to the previous model to capture the structures of different scales by taking each EOF as a new scale.The captured structures are then consolidated by using them to restrain the subsequent models.This ensures a rigid but also a flexible model.Experiments were carried out to verify the accuracy of the model under the multi-scale EOFs constraint and compare with FVPE.Results show that the increase of EOF scale can improve the accuracy of the inversion results slightly,but large scale will introduce observation noise and reduce the tomographic accuracy.In addition,Further experiment was designed to discuss the effect of VTEC constraints.The results show that VTEC constraint can improve the accuracy of electron density with dark voxels,and has no effect on regions with sufficient observations.