本篇論文的內容是透過福爾摩沙衛星三號所提供的ionPhs (Level 1b)的資料進行GPS無線電波掩星法(GPS Radio Occultation)的計算與比較，分別透過偏折角(Bending angle)與全電子含量(Total Electron Content,TEC)反演出電離層的電子濃度；其演算方式是參考[Antonio Rius,1998]與[Jiu hou Lei,2007]論文中所提到的方式，由ionPhs 中超額相位和衛星的位置和速度的資料可算出偏折角(Bending Angle)，再利用Abel transform 積分法算出折射指數(Index of Refractivity)，進而算出電離層之電子濃度(Electron Density)。另一個方法是直接由超額相位算出TEC，再反演出電子濃度。最後，將會比較和討論福爾摩沙衛星三號之反演法與[Antonio Rius, 1998]論文中其反演法之差異，再跟福爾摩沙衛星三號ionPrf (Level2)之電子濃度做交叉比對，並且討論及誤差之分析。結果與討論之重點會放在模擬的部份，希望可以透過模擬的方式，比較出幾個GPS 掩星反演法演算之準確性。 The excess phase provided by the FORMOSAT3/COSMIC was utilized to retrieve the ionospheric electron density from Global Positioning System (GPS) radio occultation (RO) algorithm that is based on Abel transform under the assumption of the spherical symmetry. In this paper, we compared the different radio occultation techniques for the retrieval of ionospheric electron density, in which the bending angle of the GPS ray and calibrated total electron content (TEC) are used, respectively. The retrieved electron densities from different algorithms are validated by electron density measured by ground base ionosonde for three years from 2008 to 2010. We calculated mean deviation (M0) and root mean square error (RMSE) of the foF2 data for different seasons. The results show the RO-retrieved foF2 from bending angle and calibrated TEC are generally consistent with the COSMIC-retrieved foF2. It appears that the electron densities (with M0 between 0.1 and 0.18%) retrieved from the bending angle are better than those (with M0 between 0.25 and 3.2%) from the calibrated TEC in the daytime. However, for the nighttime data, a comparison shows that the electron densities obtained from piercing methods seem to be better than those retrieved from other methods. Nevertheless, the RMSE values for the different RO algorithms seem to be comparable to each other. The details of the different RO algorithms will be introduced in this paper.
