Tomographic Imaging of Ionospheric Electron density over Ethiopia using Ground based GPS receivers
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Date
2012-06
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Addis Ababa University
Abstract
The Total Electron Content (TEC) from a spatially distributed network of Global Posi-
tioning System (GPS) receivers can show the temporal, seasonal, latitudinal and longi-
tudinal 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 iono-
spheric electron density pro le in two or three dimensions. In this work, ground based
GPS receivers over Ethiopia have been used to record signals transmitted from GPS satel-
lites 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 den-
sity 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
nd the coe cient 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 inver-
sion 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
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Keywords
Ethiopia using Ground based GPS receivers