| dc.description.abstract | Abstract
Resolution of the traditional ionospheric tomography is limited to the pixel size for discretizing the domain of interest. Specifically, with limited number of propagation paths between the ground stations and the satellite orbit, the reduction of the pixel size for improvement on the resolution often leads to artifacts in the results retrieved from the standard algorithms, such as the algebraic reconstruction technique (ART), the multiplicative algebraic reconstruction technique (MART), and the simultaneous iteration reconstruction technique (SIRT). This issue is mainly related to the ill-posed nature of the system equations from the ionospheric tomography. In this thesis, a local pixel-refinement technique is proposed for resolving this issue. The proposed technique exploits an inhomogeneous domain discretization. That is, in the domain of interest, the regions with high density gradient are dicretized using fine pixels, whereas the ones with low density gradient are dicretized using coarse pixels. With this discretiztion technique, the number of pixel is relatively reduced compared to the one form entire-domain fine discretization. With this technique, it is shown that the resolution of the reconstruction results is improved, and there is no observation of the aforementioned artifacts. The proposed technique is validated through the US-TEC data. Several events are used to demonstrate the effectiveness of the proposed technique. Indeed, with the proposed technique, the ionospheric irregularities, such as sporadic E layers and plasma bubbles, are identified in the reconstruction data using the standard ART, MART, and SIRT tomography algorithms. Indeed, the classical tomography algorithms with the proposed discretization technique are shown the effective tools for monitoring the ionospheric fine structures. | en_US |