全球定位系統單雙頻信號用於電離層路徑總電子含量估測及應用

The Estimation of TEC and Its Application by Using GPS Single and Double Frequency Signals

蔡耀霆(Yao-Ting Tsai)

指導教授 ： 王立昇

國立臺灣大學/工學院/應用力學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002368

摘要

隨著全球定位系統(Global Positioning System ,GPS)的使用越來越普及，用戶對定位的精準度要求也日益增加，但大部分使用者都屬於單點單頻定位，而單頻接收機無法像雙頻一樣使用去電離層組合有效的將電離層誤差消除，此一誤差也是影響單頻定位效果的重點之一。
GPS定位受到電離層的影響產生誤差，但也可以反過來利用接收到的觀測量，透過有效的消除其他誤差的方式，來估測電離層的總電子含量(Total Electron Content ,TEC)，而其用處有二。一是探測該區域電離層值，提供有效的物理量，透過長期觀測，可觀察出電離層的時空分布及其變化週期，並加以分析及解釋。二是利用探測出的電離層值提供給單頻接收機，有效的消除訊號傳播過程中造成的電離層誤差，進而增加定位的精準度。
本研究首先介紹全球定位系統及其誤差項，再詳細介紹電離層及其誤差，而後利用三種方法，分別為雙頻CCL(Code-to-Carrier Leveling)、雙頻PPP(Precise Point Positioning)及單頻PPP，利用GPS觀測量透過不同組合來獲得電離層觀測量，最後使用最小平方法來估計出單層電離層模組(Single Layer Model , SLM)所需要的係數，來探測該區域電離層的總電子含量。
實驗方法有二，一是估測整日接收機天頂點的總電子含量(zenith VTEC)，並與IGS提供的最終全球電離層地圖(Final GIM)比較其差異。三種方法皆可進行有效估測，而實驗結果得出雙頻PPP與Final GIM最為接近。二是是透過單頻單點定位來評估其TEC值是否能有效的消除電離層誤差，並以Final GIM做參考，比較四種方法的改善程度。從多日之實驗結果觀察，三種方法皆可得到較廣播星曆所提供之電離層修正量更為精準的定位結果。若與Final GIM提供之修正量相比，在3D定位上，雙頻PPP可得到更穩定且較好的結果。若選取雙頻PPP與Final GIM的整合策略，平面定位的準度上亦可改善。

關鍵字

電離層 ； 總電子含量 ； 單頻單點定位 ； CCL ； PPP

並列摘要

As the use of Global Positioning System (GPS) becomes more and more popular, users have increased requirements for positioning accuracy, but most users are single-point single-frequency positioning. The single-frequency receiver cannot effectively eliminate the ionospheric error by using the ionosphere-free combination as the dual-frequency receiver. This error is one of the main factors affecting the single-frequency positioning.
GPS positioning is affected by the ionosphere, which can cause errors. On the other hand, the received measurements can be used to estimate the Total Electron Content (TEC) of the ionosphere by effectively eliminating other errors. There are two uses for it. One is to detect the ionosphere’s TEC in this area to provide effective physical quantities. Through long-term observation, the spatio-temporal distribution of the ionosphere and its period can be observed, analyzed and explained. The second is to provide the single-frequency receiver with the ionospheric TEC value. The single frequency receiver can then eliminate the ionospheric error caused by the signal propagation process, so as to increase the positioning accuracy.
In this thesis, the global positioning system and its error terms are firstly introduced , and the ionosphere and its errors are described in detail. Then, three methods are used, namely dual-frequency CCL (Code-to-Carrier Leveling), dual-frequency PPP (Precise Point Positioning) and single frequency PPP , such that the GPS measurements are analysed to obtain ionospheric observations. Finally, the least square method is adopted to estimate the coefficients in the single layer model (SLM) to detect the total electron content of the ionosphere in the area.
There are two experimental methods. One is to estimate the total electron content of the zenith of the receiver (zenith VTEC) throughout the day, and compare the difference with the final global ionospheric map (Final GIM) provided by IGS. All three methods are effectively estimated, and the experimental results show that the dual-frequency PPP is more closer to the Final GIM.
The second method is to evaluate whether the TEC value can effectively eliminate the ionospheric error through single-frequency single-point positioning, for which the Final GIM id used as a reference to compare the improvement of the three methods. From the experimental results, the three methods can obtain ionospheric corrections and improved positioning results than those provided by broadcast ephemeris. Compared with the correction provided by Final GIM, dual-frequency PPP can give rise to more stable and better results in 3D positioning. Moreover, If the integration strategy of dual-frequency PPP and Final GIM is selected, the accuracy of plane positioning can even be improved.

並列關鍵字

CCL ； PPP ； ionosphere ； total electron content ； single frequency single point positioning

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