Ionospheric imaging using computerized tomography
Ionospheric imaging using computerized tomography
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DOI：
10.1029/rs023i003p00299
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发表时间：
1988-05
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通讯作者：
J. Austen
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作者：
J. Austen
计算机断层扫描技术可用于产生电离层电子密度的二维图像。必要的数据是在多个地面站同时记录的跨电离层卫星信标总电子含量数据。电离层成像的情况下提出了一个困难的问题，由于大量的数据丢失。这是发射器（在轨）和接收器（地面）的位置造成的结果，并导致重建算法无法正确重建背景密度分布。尽管存在这种限制，但已经开发出一种方法，该方法成功地重建了轮廓中的不规则和变化。计算机程序模拟了数据采集和图像重建过程。这使得该方法可以用几个电子密度模型，发射器和接收器的位置，以及非迭代和迭代重建算法进行测试。模拟是假设一个1000公里高度的极地轨道卫星和几个地面站。成像区域宽3500公里，高800公里。提出了一种新的算法，它是离散反投影算法的一种改进，适用于非均匀采样几何。在未修改的算法无法产生可用结果的情况下，它会产生高质量的结果。模拟进行测试图像和现实的电离层模型，以证明这种技术的能力和局限性。通过这些模拟，发现改进的CT算法的组合产生良好的结果。由于用于重建的数据不完整，用于迭代算法的初始估计非常重要。将其他数据，如高度剖面从电离层探测仪，到重建过程中，以消除这个问题的方法提出了建议。第一章包括绪论、问题的陈述、动机和类似的研究。第2章包含TEC测量理论、CT理论以及几种CT算法的描述。第三章描述了仿真过程、所用模型和仿真结果。第4章包括对结果的讨论、对程序的评论、改进建议和结论。附录记录了模拟程序，给出了数据结构的细节，并提供了算法列表。
Computerized tomography (CT) techniques can be used to produce a two-dimensional image of the electron density in the ionosphere. The necessary data are transionospheric satellite beacon total electron content (TEC) data recorded simultaneously at multiple ground stations. The ionospheric imaging case presents a difficult problem due to large amounts of missing data. This is a consequence of the locations of the transmitter (in orbit) and receivers (ground-based) and causes the reconstruction algorithm to fail to correctly reconstruct the background density profile. Despite this limitation, a method has been developed which successfully reconstructs the irregularities and variations in the profile. A computer program simulates the data collection and image reconstruction process. This allows the method to be tested with several electron density models, transmitter and receiver locations, and noniterative and iterative reconstruction algorithms. Simulations are performed assuming a 1000-km-altitude polar-orbiting satellite and several ground stations. The imaged region is 3500 km wide by 800 km high. A new algorithm, which is a modification of the discrete backprojection algorithm, is developed for use with nonuniform sampling geometries. It produces good quality results in cases where the unmodified algorithm fails to produce a usable result. Simulations are performed on both test images and realistic ionospheric models in order to demonstrate the capabilities and limitations of this technique. Through these simulations, a combination of modified CT algorithms was found to produce good results. Because of the incomplete data used for the reconstruction, the initial estimate used for iterative algorithms is very important. Methods of incorporating other data, such as height profiles obtained from an ionosonde, into the reconstruction procedure to eliminate this problem are suggested. Chapter 1 contains an introduction, the statement of the problem, motivation, and similar research. Chapter 2 contains TEC measurement theory, CT theory, and a description of several CT algorithms. Chapter 3 contains a description of the simulation procedure, the models used, and the simulation results. Chapter 4 contains a discussion of the results, comments on the program, suggestions for improvements, and conclusions. The Appendix documents the simulation program, presenting details of the data structures, and providing algorithm listings.