低緯度電離層不規則體之結構研究

Study of low-latitude ionospheric irregularity structure based on New LITN

蕭棟元(Tung-yuan Hsiao)

指導教授 ： 蔡龍治

國立中央大學/地球科學學院/太空科學研究所/博士(2007年)

摘要

電離層是無線電衛星訊號傳播到地面接收站的必經介質，當電離層的狀態不穩定的時候，訊號會有閃爍的情況，我們稱之為”閃爍現象”(Scintillation)，閃爍現象可分為訊號的閃爍(Power Scintillation)和相位的閃爍(Phase Scintillation)，且好發在春秋分的季節以及落日之後。 國立中央大學自2006開始建立新的低緯度電離觀測測網(New LITN)用以接收美國海軍(NNSS)和我國福衛三號上酬載的三頻訊號標(TBB)，目前四個站已建設完成，分別是中壢(25.1360N, 121.5390E)，草屯(23.9810N, 120.6970E)，車城(22.7250N, 120.5440E)和南沙太平島(10.060N, 114.3500E)，利用其中兩各頻率的訊號，我們可以推演出其路徑上的全電子含量(TEC)，並利用斜向的全電子含量(STEC)和電離層斷層掃描的演算法產生二維高度和緯度的剖面影像，此方法可以用來觀測大尺度的電離層現象包含電離層赤道異常現象(EIA)等等，在本論文中，我們觀測收集了ㄧ年的資料後，發現低緯度的閃爍現象夜間的好發於午夜前後，且利用簡單的光學幾何模型去推估閃爍現象發生的位置、高度、厚度和長度，並將這些現象和中壢的電離層觀測儀做比較。此外我們亦發現赤道的閃爍現象會先發生，然後延伸到比較高緯度的區域(大約20度)，但地磁場擾動強(KP>3)時閃爍現象的時間和影響的緯度區域會延長，但有趣的是，春秋分季節時只有在低地磁擾動(KP<3)的時候才會發生低緯度的閃爍現象，反而是11~12月份在地磁場擾動強(KP>3)時閃爍現象必較多且明顯。

關鍵字

電離層 ； 電離層斷層掃描 ； 電離層赤道異常現象 ； 電離層不規則體

並列摘要

A radio signal traversing the ionosphere will be modified by irregularities. When received at an antenna, these signals present random temporal fluctuations in both amplitude and phase. Scintillations are particularly severe in the tropical regions around the equinoxes during the evenings. National Central University rebuilt the LITN (Low latitude Ionosphere Tomography Network) in 2006. The scintillation measurements and ionospheric tomography reconstruction of the beacon satellites in this study for three specific low-latitude locations were spaced approximately 350 km apart in the tropics, at Chung-li (25.1360N, 121.5390E), Taotsun (23.9810N, 120.6970E), Checheng (22.7250N, 120.5440E) and Itu Aba Island (10.060N, 114.3500E). The coherent beacon receiving systems receive radio signals from the LEO satellites, including 150/400MHz Navy Navigational Satellite Systems and FORMOSAT-3/COSMIC Satellites. In this thesis, we explore the low latitude scintillation near midnight, and approach correct location within the F region using a simple optical model when the radio signals traveled through them. There are 83 scintillation days from April 2006 to April 2007 (395 days) and occurred usually at 18~05 LT in the night time, especially at pre-midnight or post-midnight. The scintillations have high correlation with months when Kp < 3. The scintillations are happened at May-June and December-February less than the other months. On the contrary, scintillations are normally more frequent during the equinoctial months of August-October and March-April. Meanwhile there are 16 scintillation days happened when Kp > 3

並列關鍵字

ionosphere ； EIA ； ionospheric tomography ； ionospheric irregularity

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