| 摘要: | 本篇論文為考慮地球曲率之三維電離層斷層掃描在赤道異常區的模擬研究。實驗採用IRI-90 電離層模型，作為模擬時的原始資料。日期選取10月19日， LT0600、LT1200、LT1800及LT2400四個時段，重建區域為高度125∼1000Km；北緯 0°∼50°；東經116°∼124°，共分為36×101×9個網格。地面接收站設置以每一個經度一個為原則，平均分佈於緯度上，共設置九個地面接收站。 首先模擬衛星飛行的軌道，並經由模擬計算出每個地面接收站所接收到每次事件的相位移資料，以此為原始資料反演出IRI-90 model電離層的結構。首先將九站之相對斜向全電子含量投影到衛星飛行軌道面，使用兩站法求得重建積分常數值。利用back-projection method將重建絕對斜向全電子含量平均分配到射線所通過的網格點。以alpha Chapman layer做垂直方向的分配。由MART演算法得到迭代後之重建電子濃度在三維空間（R，θ，ψ）之分佈。 由於接收站皆不共面造成重建積分常數誤差大，位於赤道異常區之接收站的誤差最大。接收站的數量、衛星軌道與重建區域之相對關係、外插的方法、初始資料的設定、先驗資訊的缺乏•••等等，都造成重建電子濃度的誤差。 The main of this paper is a simulation of three-dimensional (3-D) computerized ionospheric tomography (CIT), which is consider of the earth curvature, in the equatorial anomaly characteristics (EAC) region. We applied IRI-90 model as initial electron density distribution of ionosphere, and choose the date October 19, in the time of LT 0600, LT1800, LT1200, and LT2400. The reconstructed region is over a altitude range of 125 to 1000 km, a latitude range of 0° to 50° N, and a longitude range of 116° to 124° E. There are 36×101×9 pixels. Choose nine ground stations separated at different longitude and equally separated at latitude. The process is started from the simulation of satellite’s trajectories, and we determine the data of Doppler’s phase shift for every receiver station. These are original data of this study, then, we make a projection of the relative STEC to the plane of satellite’s trajectories, and use the two stations method to obtain the reconstructed integer constants. Horizontal distribution is using back projection method. Vertical distribution is using alpha Chapman layer. Then use MART algorithm to reconstruct the 3-D images in the sphere coordinate of ionospheric electron density. The max error is happened in the receiver, which is in the EAC region. The error is come from the number of receiver, the geometry relationship between the satellite and reconstruct region, the interpolation method, the initial data, the lack of prior information, and so on. |
