Resolution degradation parameters of ionospheric tomography

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Abstract
Tomographie reconstruction of the electron density structure in the ionosphere has generated much interest due to the possibility of high‐resolution two‐dimensional image reconstruction using total electron content (TEC) data. An algorithm based upon the filtered backprojection algorithm of X ray tomography that provides such two‐dimensional reconstructions has been developed; however, the resolving capability is limited by the nature of the ionospheric system. In ionospheric tomography, each piece of data contains information similar to a sample on a projection in X ray tomography. Collectively, however, the information content of ionospheric data sets is significantly different from a set of tomographic projections. These differences are the result of characteristics of the data acquisition system and are directly related to the resolution limits of the reconstructed images. In this paper the data acquisition system is analyzed to determine the sources of this degradation. Two key parameters of nonuniform sample spacing and angular reindexing error are analyzed to determine their effect upon the reconstruction process. A method of evaluating sampling schemes to measure the information content of the resulting projections is presented. Finally, a relationship between the angular reindexing error and the point spread function of the imaging system is derived.