Limitations of ionospheric imaging by tomography

The potential of imaging large ionospheric structures by applying tomographic techniques has only been proposed recently and has already received interest and increasing attention by workers in ionospheric research. In the combined case of an idealized plane geometry and complete and continuous data extending to {plus minus} infinity the inversion is exact and unique. This is no longer the case if any of the idealized conditions are removed. Specifically, the limitations are investigated that arise from limited angles, sampled data of finite receiving aperture and circular geometry. Under these various nonidealized but more realistic conditions, fidelity of the reconstructed image is investigated by computing the response to an impulse-source function. The deterioation of the reconstructed image, the sensitivity to the position in the image plane, and the possible existence of ghost images are all numerically investigated and illustrated. Possible methods of improvement are suggested. 23 refs.

[1]  Dale A. Ausherman,et al.  Developments in Radar Imaging , 1984, IEEE Transactions on Aerospace and Electronic Systems.

[2]  S. Lang,et al.  An Introduction to Fourier Analysis and Generalised Functions , 1959 .

[3]  K. Yeh.  Second-order Faraday rotation formulas , 1960 .

[4]  H. Scudder.  Introduction to computer aided tomography , 1978, Proceedings of the IEEE.

[5]  E. Bramley.  Fluctuations in direction and amplitude of 136 MHz signals from a geostationary satellite , 1974 .

[6]  G. N. Ramachandran,et al.  Three-dimensional reconstruction from radiographs and electron micrographs: application of convolutions instead of Fourier transforms. , 1971, Proceedings of the National Academy of Sciences of the United States of America.

[7]  B. F. Logan,et al.  The Fourier reconstruction of a head section , 1974 .

[8]  E. C. Titchmarsh.  Introduction to the Theory of Fourier Integrals , 1938 .

[9]  J. Klobuchar,et al.  Application of computerized tomography to the investigation of ionospheric structures , 1990 .

[10]  G. W. Swenson,et al.  Ionospheric electron content and its variations deduced from satellite observations , 1961 .

[11]  Jeffrey Robert Austen,et al.  Ionospheric imaging using computerized tomography , 1988 .

[12]  K. Yeh,et al.  Comparison of Faraday and Doppler methods of obtaining ionospheric electron content , 1968 .

[13]  K. Davies,et al.  Recent progress in satellite radio beacon studies with particular emphasis on the ATS-6 radio beacon experiment , 1980 .

[14]  S. Deans.  The Radon Transform and Some of Its Applications , 1983 .

[15]  R. Bracewell.  Strip Integration in Radio Astronomy , 1956 .

[16]  R. Lewitt.  Reconstruction algorithms: Transform methods , 1983, Proceedings of the IEEE.

[17]  O. Garriott,et al.  A comparison of methods used for obtaining electron content from satellite observations , 1963 .