GPS電波掩星法反演電離層散塊E層之模擬

劉忠青(Jong-Ching Liu)

指導教授 ： 朱延祥

國立中央大學/地球科學學院/太空科學研究所/碩士(2015年)

摘要

由GPS電波掩星技術(Radio Occultation)可以反演出訊號強度隨高度剖面資料，而從這些訊號強度資料中可以判別散塊E層的存在與否。在這篇論文中將利用路徑尋覓法，以IRI(International Reference Ionosphere)模式為電離層背景電子濃度，模擬訊號在散塊E層中行進的情況而得到訊號強度隨高度剖面資料。在本研究中會展示若是一個無傾斜(與訊號平行)、均勻的散塊E層，會因為GPS訊號散焦(defocusing)的狀況，加上當訊號重疊時相位的疊加，在訊號強度圖中也可以看出一個U型形狀，可以由此訊號強度隨高度變化圖U型結構中的凹槽判斷此散塊E層的厚度。當把此均勻散塊E層傾斜一個角度，其U型結構會慢慢在訊號強度圖之中消失；亦或當把此散塊E層的水平延展降低至一定的長度，U型結構也會慢慢消失，這兩者皆可說明散塊E層具有遮蔽訊號的能力。而在本論文中也會將以隨機亂數產生器調整散塊E層的散亂程度，觀察其對應的訊號強度圖，以及將前面模擬結果的訊號強度圖與福衛三號(COSMIC)2008年的掩星資料做為比較。

關鍵字

訊號強度 ； 散塊E層 ； 模擬 ； 電波掩星 ； 厚度

並列摘要

he amplitude profile of GPS signal can be calculated by GPS Radio Occultation(RO), and the existence of sporadic-E can be distinguished by the profile. In this thesis, the amplitude profile of GPS signal would be simulated by ray tracing method, and the electron density information as given by IRI model. In the study, it has been shown that U-shape in amplitude profile due to the GPS signal is defocusing considering phasor
when the uniform sporadic-E is parallel with the propagation signal, and the thickness of the sporadic-E could be calculated by trough in the U-shape. When sporadic-E is tilted with the GPS signal direction, the U-shape structure was disappearing with the increase of the tilt angle; when the horizontal extension of sporadic-E is reduce, the U-shape structure was disappearing with the decrease of the horizontal extension, too. Both result can be explained that the sporadic-E is a shelter. The varied amplitude profile was simulated by the sporadic-E including the irregularity produced from different random number generator. All the amplitude profile results were compared with the COSMIC RO data in 2007.

並列關鍵字

model ； sporadic E ； simulation ； radio occultation ； thickness ； Ray Tracing

參考文獻

﹝14﹞吳剛宏，「福衛三號電子濃度分析：電離層E 層」，國立中央大學太

﹝10﹞Yeh, W. H., C. H. Huang, T. Y. Hsiao, T. C. Chiu, C. H.

Kuo, S.Sokolovskiy, J. C. Chang, J. G. Sela, and R. A.

﹝1﹞Appleton, E. V., “Two Anomalies in the Ionosphere”, Nature, 157, pp. 691, 1946.

﹝2﹞Arras, C., J.Wicket, G.Beyerle, S.Heise, T.Schmidt, and C. Jacobi, “A global climatology of ionospheric irregularities derived from GPS radio occultation” Geophys. Res. Lett., Vol. 35, doi:10.1029/2008GL034158, 2008.