Tomographic Imaging of Ionospheric Electron Density over Ethiopia Using Ground Based GPS Receivers

Zewdie, Gebreab Kidanu (2012) Tomographic Imaging of Ionospheric Electron Density over Ethiopia Using Ground Based GPS Receivers. Masters thesis, Addis Ababa University.

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Abstract

The Total Electron Content (TEC) from a spatially distributed network of Global Positioning System (GPS) receivers can show the temporal, seasonal, latitudinal and longitudinal variations of the ionospheric electron distribution. However, it does not convey any information about ionospheric electron density structure along the vertical direction. Computerized Ionospheric Tomography (CIT) is a method to investigate vertical ionospheric electron density profile in two or three dimensions. In this work, ground based GPS receivers over Ethiopia have been used to record signals transmitted from GPS satellites and the computed pseudoranges and phase values are used to calculate Total Electron Content (TEC). In two dimensions (2D), the vertical plane along 40:02610E longitude is discretized into pixels and the distance traveled in each pixel crossed by GPS signals to four receivers located close to the vertical plane is calculated in a selected reference frame. Using TEC from these stations a 2D, altitude versus latitude, distribution of electron density is inverted with in each pixel. In three dimensions (3D), the volumetric ionosphere over Ethiopia is discretized in to numerous small voxels and the distance traveled by GPS signals in each voxel is calculated from the precise position of the GPS satellites to find the coefficient matrix in an appropriate reference frame. A 3D ionospheric electron density distribution is then obtained using TEC data from GPS stations located all over the country. In both 2D and 3D tomographic reconstructions damped least square inversion algorithm with second order Tikhonov regularization has been employed. We used the L-curve method to determine the regularization parameter. The performance of the inversion algorithm has been numerically validated with a simulated TEC from IRI2007 model. The numerical experiments show that the algorithm produced results with 2-norm relative reconstruction errors 0:04 and 0:02 for the 2D and 3D inversions respectively.

Item Type: Thesis (Masters)
Subjects: Q Science > Q Science (General)
Q Science > QC Physics
Divisions: Africana
Depositing User: Selom Ghislain
Date Deposited: 19 Nov 2018 13:15
Last Modified: 19 Nov 2018 13:15
URI: http://thesisbank.jhia.ac.ke/id/eprint/7305

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