Ionospheric Imaging Using GNSS: A New Approach for Canadian Polar Regions

O. al-Fanek and Susan Skone

Abstract:	Three-dimensional ionospheric modeling using tomography techniques has been applied previously to investigate the vertical extent of electron density variations. In such methods the GNSS observations (often within ground-based networks) are manipulated to estimate line integrals of a parameter known as Slant Total Electron Content (STEC). These integrated quantities are then expressed in terms of unknown values of ionospheric electron density. For example, some approaches divide the ionosphere into voxels and assume the electron density to be constant within each cell. Inversion algorithms are used to estimate the electron density values. However, this problem is mixed-determined; that is there are regions where the data overdetermines parts of the solution but underdetermines other parts. Also, the ray paths are not available in all directions. For example there are no horizontal ray paths for Global Positioning System (GPS) signals observed in a ground-based network; therefore the vertical resolution is not as good as the horizontal resolution. In this paper, a novel Computerized Ionospheric tomographic (CIT) reconstruction technique based on Empirical Orthogonal Functions (EOF) and Spherical Cap Harmonics (SCH) is developed. This model divides the ionosphere into voxels and the ionospheric parameter is assumed to be constant within a cell. To reduce the number of unknowns, a functional based model is used to represent the electron density in space. The functional based model uses EOF and SCH to describe the vertical and horizontal distribution of the electron density, respectively. The underlying model is obtained from the International Reference Ionosphere (IRI) model and the necessary measurements are obtained from earth-based and satellite-based GPS databases. Based on the IRI-2007 model, a basis set is formed using EOF for the required location and time of interest. Selecting the first few basis vectors corresponding to the most significant singular values and combining them with SCH, the three-dimensional CIT is formulated as a least squares estimation problem of the SCH coefficients.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	643 - 653
Cite this article:	al-Fanek, O., Skone, Susan, "Ionospheric Imaging Using GNSS: A New Approach for Canadian Polar Regions," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 643-653.
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