| 摘要: | 本論文主要利用福衛三號衛星掩星資料與中壢特高頻雷達回波資料來研究電離層散塊 E 層 ( Es 層) ，其厚度很窄，約 0.5 ~ 5 km、水平延展很廣，約百公里等級之層狀結構。[劉忠青，2015] 碩士論文中之結果顯示當 GPS 射線接近水平穿過層狀 Es 層時，福衛三號接收到的訊雜比 (SNR) 剖面圖中會出現「U型結構」的散焦 (Defocusing) 現象，並利用路徑覓跡法解釋電波受垂直方向折射指數梯度的影響傳播路徑會發生偏折。首先，分析 2008 與 2011 年兩年的衛星掩星資料，利用 [Chu et. al. , 2014] 之品質控管方法與散焦現象挑選出有「U型結構」的典型層狀 Es 層事件，進而分析層狀 Es 層之形態特徵，包含時間上的季變化、空間上發生高度、厚度的全球分布概況，並利用直方圖統計出確切的發生高度、厚度數值與分布情形，作為本論文中重要的結果。其次，本論文另一個主要目的為驗證 [劉忠青，2015] 碩士論文中之模擬結果，確認是否發生「U型結構」的散焦 (Defocusing) 現象時，GPS 射線都是接近水平穿過層狀 Es 層。要驗證此結果，光靠衛星掩星資料所得到的 Es 層資訊還不足夠，必須再輔以雷達回波資料。處理時，先利用距離-時間-回波功率圖 (RTI) 得到回波強度，並使用互頻譜、雷達干涉法定位出 Es 層中場沿不規則體 (FAI) 回波點，再參考 [楊國峰，2008] 博士論文之方法反演出層狀 Es 層平面的三維姿態。有了 Es 層平面方程式，便能計算 Es 層平面與 GPS 之 L1 訊號傳播方向間的入射角，此外還能確認衛星觀測到的「U型結構」是否在 Es 層平面上。;FORMOSA-3 satellite occultation data and Chung-Li VHF radar echo data will be used to study the ionospheric Sporadic-E layer (Es layer) in this research. The Es layer could be classified from their different three-Dimensional structure but this thesis only discuss layer-structured Es layer, which thickness is very narrow, about 0.5 ~ 5 km, and the horizontal extension is very wide, about hundred kilometers level. [Jong-Ching Liu, 2015] show that when GPS rays nearly horizontally pass through the layer-structured Es layer, the signal-to-noise ratio (SNR) profile received by FORMOSA-3 will be a "U-shaped structure", which called defocusing phenomenon. In additional, Jong-Ching Liu also uses the ray trace algorithms to explain the deflection of the propagation path of the radio wave affected by the gradient of the refractive index in the vertical direction. First, analyze the two years satellite occultation data in 2008 and 2011, and select typically layer-structured Es layer events with a "U-shaped structure" by the quality control method from [Chu et. al., 2014] and the property of defocusing phenomenon. Then discuss the morphological characteristics of the layer-structured Es layer, including the seasonal change in time and the global distribution of height and thickness in space. Use the histogram to quantify the exact height, thickness and their distribution, which are the main result in this research. Secondly, another purpose of this thesis is to verify the simulated results in [Jong-Ching Liu, 2015] to confirm whether the GPS rays almost horizontally pass through the layer-structured Es layer when defocusing phenomenon occurs. To verify this result, the information of Es layer obtained from satellite occultation data is not enough. Also combine with radar echo data to reach the goal. First, get the echo power from the range-time-intensity (RTI) diagram, and use cross-spectrum and radar interferometry to find and locate the field-align irregularity (FAI) echo points in Es layer, and then use the method in [Kuo-Feng Yang, 2008] to retrieve the plane of layer-structured Es layer in three-dimensional space. With this plane equation, the incident angle between the plane of Es layer and the propagation direction of GPS L1 signal could be calculated. Furthermore, it can also be confirmed whether the "U-shaped structure" observed by the satellite is on the plane of Es layer. |
