| 摘要: | 本論文利用全球導航衛星系統(Global Navigation Satellite System, GNSS)地面接收機資料紀錄，推演計算電離層全電子含量(Total Electron Content, TEC)擾動指數(Rate of TEC Index, ROTI)，以探討電離層電子密度不規則體的日、季、太陽活動與全球分佈。分析國際GNSS服務(International GNSS Service, IGS)所公佈地面GNSS接收機L1和L2波段訊號資料，並藉此計算每5分鐘內TEC變化率的標準偏差，即是ROTI，其相當於TEC電波相位擾動。目前全球約有2000座以上的地面接收機台站，其GNSS訊號可用以計算每30秒一筆TEC資料。分別針對太陽極大期(2000年)、太陽極小期(2009年)與太陽中強期(2013年)ROTI研究其日、季、太陽活動、經度與緯度變化。結果顯示中低緯度ROTI主要發生在磁緯度±30 ̊間，日落後1900LT開始出現、夜間2100LT達到最大、最終於子夜後0200LT消失，其於春和秋季至為明顯，且在南美洲上空最為強烈。除了太陽極小期外，磁緯度±30 ̊之ROTI通常會出現明顯雙峰現象，其中心位置集中於20 ̊ N和20 ̊ S。一般而言，極區ROTI會比中低緯度的強烈，尤其是南極地區。此外，結合福衛三號S4閃爍模型經驗，補足ROTI於海上及偏遠地區觀測之不足，可建構ROTI全球模式，以推估地面GNSS訊號相位擾亂和電離層電子密度之擾亂程度與分佈，其除可用於電離層科學研究外，並可提供衛星通訊、定位與導航應用參考。;The thesis goal is to study the diurnal, seasonal, solar activity and geographic variations of ionospheric irregularities by means of Rate of TEC Index (ROTI) derived by measurements of worldwide ground-based GNSS (Global Navigation Satellite System) receivers. Routine observations of the ionospherically imposed propagation effects upon GNSS satellite signals are available online from International GNSS Service (IGS). With data over 2000 ground-based IGS stations of the globe, ionospheric total electron content (TEC) with the 30-sec time resolution can be derived. The standard deviation of TEC variations in a 5-minute interval is further computed to obtain ROTI around each receiving station. Variations in diurnal, seasonal, solar activity and geographic distribution of ROTI are examined during the solar maximum year of 2000, solar minimum year of 2009, and solar median year of 2013. Results show that intense ROTIs frequently appear in the low-latitude ionosphere within ±30-degree magnetic dip; start at 1900 LT (Local Time), reach their maximum at 2000-2100 LT, and vanish by about 0200 LT, especially prominently in the spring and autumn seasons. The region experiencing the most intense ROTI is the low-latitude ionosphere in South America. ROTIs often exhibit a double-peaked structure at 20 ̊N and 20 ̊S geomagnetic except in the solar minimum year. It is interesting to find that ROTIs in high-latitude region, especially in the southern polar region are much more intense than those in low- and mid-latitude region. Based on FORMOSAT-3 S4 data, a global ROTI model is constructed, which can be used not only for ionospheric scintillation scientific researches but also positioning, navigation, and communication applications. |
