Fundamental analysis of the tomographic imaging system for reconstructing ionospheric distributions
Na, Helen Ru-Lin
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https://hdl.handle.net/2142/19515
Description
Title
Fundamental analysis of the tomographic imaging system for reconstructing ionospheric distributions
Author(s)
Na, Helen Ru-Lin
Issue Date
1991
Doctoral Committee Chair(s)
Lee, Hua
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Physics, Atmospheric Science
Language
eng
Abstract
Ionospheric tomography has generated great interest due to the possibility of two-dimensional imaging of electron density profiles. Traditional methods have, thus far, been capable of only one-dimensional imaging. Tomographic reconstructions are possible from existing one-dimensional data and can be enhanced by knowledge gained through traditional imaging methods. In this thesis, a complete ionospheric imaging system is presented.
The ionosphere is a plasma of ionized gas formed by ionization of the upper atmosphere by solar radiation and high-energy particles from the sun. Regions of irregular electron concentration exist within this layer of plasma, which interfere with the propagation of radio signals as they are reflected around the earth's surface by the ionosphere. Although there are well-accepted theories on the formation of the ionosphere, there are no corresponding theories for the formation of these irregularities. As a result, imaging the electron density is the best method of determining the location and nature of these irregularities.
In this thesis, the ionospheric system will be analyzed and modeled as a tomographic imaging system. The complete ionospheric imaging system is formulated in three segments: the ionospheric data acquisition system, the system model, and a reconstruction algorithm. The fundamental resolution limits of this system are then analyzed in several ways. The resolution of the imaging system based upon controllable parameters will be examined followed by a quantitative measure of the complete imaging system's resolving capability. The effect of the various resolution degradation factors will then be isolated and methods of compensation will be investigated. Once the resolving capabilities of the system have been thoroughly determined, a variety of methods for enhancing the reconstruction algorithm will be developed. These methods will take advantage of existing knowledge of the ionosphere. A new Orthogonal Decomposition Algorithm will then be developed. This algorithm removes some of the resolution degradation factors found in the original reconstruction algorithm by using orthogonal decomposition. A generalized development is given, and an interesting example of choosing Fourier kernels as the set of basis functions is presented. Finally, the future of ionospheric imaging will be discussed.
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