K.N.Toosi University of Technology
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Khajeh Nasir Univ.
Ionospheric tomography is a method to investigate the ionospheric electron density in two or three dimensions. In this study, the function-based tomographic technique has been used for regional reconstruction of a 3D tomographic model of the ionospheric electron density using the GPS measurements of the Iranian Permanent GPS Network. Two-dimensional Haar wavelets and empirical orthogonal functions are used as base functions to model the horizontal and the vertical structure of the electron density, respectively. Sparseness of data and data gaps make ionospheric tomography an ill-posed inverse problem. The truncated singular value decomposition (TSVD) method is used to come up with solution. The data analysis results show that the latitudinal sections of the electron density in ionosphere obtained from the tomographic technique supports the expected time and height variations in the electron density. Moreover, these findings show that the height of maximum electron density is changed during the day. This confirms the efficiency of the developed multilayer model in comparison to the traditional single-layer ones. The relative error between the reconstructed electron density and the electron density obtained from ionosonde data varies between 5 to 35 percent. The difference between the reconstructed electron density (as well as the corresponding estimations of the IRI-2001 model) and the direct estimates of this quantity increases when the electron density reaches to its maximum value. Assuming that the ionosonde station in Tehran produces reliable results, this proves that the reconstructed image as well as the IRI-2001 model does not efficiently constraint the electron density during this period of time.