Tomographic Inversion of the Ionospheric Electron Density Driven by the Scales of Empirical Orthogonal Functions

Ionospheric tomography is a popular technique for ionosphere imaging. Though dozens of models have been proposed in the past decades, their inflexibilities in constraints, dependencies on background and lacks of constraint on dark voxels remain headache. Several means were taken in our developed model, named EOF-based multiscale tomographic model (EMST). In EMST, 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. Then, the background dependency problem is alleviated by an initial model that can give a rough estimation on the ionosphere without any background. Finally, the VTEC map is used to additionally restrain the voxels, especially the dark voxels, in EMST. A few tests were conducted to validate our model, compare it with the Frazaneh model, and discuss the means. Results show that our model outperforms the reference model in vertical profile, F2 layer peak density (NmF2), slant total electron content (STEC) and vertical total electron content (VTEC) comparisons. Its average improvements over the Farzaneh model reach to 4.93%, 28.69% and 40.89% in NmF2, STEC and VTEC, respectively. Besides, evidences also show that the EMST model is less dominated by the prior model and can be benefited from the multiscale strategy and the VTEC constraint.