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Poster Session 1
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Computerized Ionospheric Tomography Using the GPS/MET and NNSS Data
Raymund(1994) reviewed the CIT reconstruction algorithms proposed by various investigators. One of the most commonly used algorithms is Algebraic Reconstruction Technique, or ART, having an additive correction and first introduced in CIT by Austen et al. (1988). This is an iterative procedure for solving the equation (2). A modified version of ART is the so-called multiplicative ART (MART) algorithm in which the correction in each iteration is obtained by making a multiplicative modification to X as
shown as the following equation (Raymund et al., 1990).
where lk are relaxation parameters such
that 0 < lk < 1. In this paper, the MART algorithm has been applied to the data (absolute slant TECs) to reconstruct the ionosphere as the examples of Figures 3 and 4.
Figure 3. The electron density contour reconstructed by LITN on Aug. 28, 1995.
Figure 4. Ionospheric tomography by GPS/MET from 05:00 to 06:39 UT on the 10th of Feb., 1997. We note that the period of GPS satellite orbiting the Earth is about 100 minutes. Furthermore, the left part of this figure
(-90°~90° at the x-axis) is dayside tomography; and the right part
(90°~-90° along) is night side tomography.
5. Conclusion and future work
We note that, using the GPS/MET to reconstruct the ionosphere, it is hard to observe the Es layer. One of the probable reason is the LEO's GPS signal observation using a low sampling rate at 0.1 Hz. Furthermore, the initial guess in MART algorithms is very important. The initial value in LITN is used to adopting the prediction of IRI-90 model. However, the GPS/MET occultation observation gives us another way to retrieve the initial electron densities from the Abel integral transform. We hope to get more accurate reconstruction of the ionosphere by the assistant of GPS/MET.
References
- C. R. Huang, C. H. Liu, H. C. Yeh and W. H. Tsai, The low-latitude ionospheric tomography network (LITN)-initial results, Journal of Atmospheric and Solar-Terrestrial, 1997
- C. R. Huang, C. H. Liu, K. C. Yeh, K. H. Lin, W. H. Tsai, H. C. Yeh, and J. Y. Liu, A study of tomographically reconstructed ionospheric images during a solar eclipse, Journal of Geophysical Research, VOL. 104, NO. A1, pages 79-94, January 1,1999
- T. D. Raymund, J. R. Austen, S. J. Franke, C.H. Lin, J. A. Klobuchar, and J. Sralker, Application of computerized tomography to the investigation of ionospheric structures, Radio Science, Volume 25, Number ³, Pages 771-789, September/October 1990
- T. D. Raymund, S. J. Franke, and K. C. Yeh, Ionospheric tomograph: its limitations and reconstruction methods, Journal of Atmospheric and Terrestrial Physics, Vol. 56, No. 5, pp. 637-657, 1994
- Antonio Rius, Giulio Ruffini, and August Romeo, Analysis of Ionospheric Electron Density Distribution from GPS/MET Occultations, Transactions on Geoscience and Remote Sensing, Vol. 36, No. 2, March 1998
- William S. Schreiner, Sergey V. Sokolovskiy, Christian Rocken, and Douglas C. Hunt,Analysis and Validation of GPS/MET radio occultation data in the ionosphere, Radio Science, Volume 34,Number 4, Pages 949-966, July-August 1999
- L.-C. Tsai, W. H. Tsai, W. S. Schreiner, F. T. Berkey, and J. Y. Liu, Comparisons of GPS/MET Retrieved Ionospheric Electron Density and Ground Based Ionosonde Data
- Sergey V. Sokolovskiy, Inversions of Radio Occultation Amplitude Data, Radio Science, Volume 35, Number 1.Pages 97-105, January-February 2000.
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