一個新的三維、連續且基於無線電掩星觀測的電離層模式，稱為台灣自主電離 層數值模式(TWIM)，首次被應用於消除單頻C/A 碼虛擬距離(pseudorange)觀測 中的絕對和差分電離層延遲。為了評估其表現，使用了兩種定位演算法即單獨 定位和差分定位。TWIM 模式產生的垂直全電子含量(VTEC)圖及定位結果也與其 他模式比較，如Klobuchar(KLB)和全球電離層圖(GIM)。研究顯示，使用TWIM 模 式和GIM 產生之全球和區域全電子含量圖能呈現出電離層的詳細結構，特別是在 低緯度區域。而KLB 模式僅提供基本的電離層晝夜及地理特徵。TWIM 模式也提 供了三維電離層電子密度且顯著地改善定位。在使用單獨定位方面，相較於GIM， TWIM 模式提供優良的定位結果，且在低仰角衛星遮蔽下優於KLB 模式。基於平 均表現評價各個包含所有站點與所有天數觀測的模型，TWIM 模式表現良好且能 提供公尺到數十公分等級的準確度，可比擬於使用GIM 的結果。KLB 模式排第三 並甚至在某些時候表現較UNC 差。在差分定位方面，在所有基線上的每日水平方 向平均誤差與水平方向基線因子呈現高度正線性相關。當使用來自電離層模式 的差分電離層校正時，此種效應大幅減少，且在垂直方向上無影響。在跨越所 有季節及各種太陽活動的地磁寧靜條件下，使用單頻接收機進行差分GPS 定位時， TWIM 模式甚至可以提供數十公分到公分等級的準確度。這也說明了，基於兩種 定位演算法，在準確度遞增的一般排序為KLB、TWIM 及GIM 模式。由TWIM 模式 和GIM 表現的類似之處，證明了TWIM 模式適用於提供優良的電子密度和電子密 度梯度，可被推廣應用至其他大地測量學與太空科學。;A new three-dimensional, continuous ionospheric model based on radio occultation observation, called the TaiWan Ionospheric model (TWIM), is used for the first time to remove absolute and differential ionospheric delays in single-frequency C/A code pseudorange observations. To evaluate its performance, two positioning algorithms namely stand-alone positioning and differential positioning are used. The VTEC maps and positioning results using TWIM is compared with results using other models, such as the Klobuchar (KLB) and the global ionospheric maps (GIM). It has been demonstrated that global and regional TEC maps using TWIM and GIM exhibit a detailed structure of the ionosphere, particularly at low-latitude region, whereas KLB only provide the basic diurnal and geographic features of the ionosphere. TWIM can also provide three-dimensional ionospheric electron density and improve positioning significantly. Using the stand-alone positioning, it is shown that TWIM provides very good positioning comparable to GIM and better than KLB even for low satellite elevation masks. Based on the average performance rating of each model across all stations and all days of observation, TWIM performs very well and can provide meter-to-decimeter accuracy and its results is very comparable with the results using GIM. KLB is a far third where occasionally performs even worse than UNC. In differential positioning, daily horizontal mean errors for all baselines show a highly positive linear correlation with the horizontal baseline vector. This effect is significantly reduced when using differential ionospheric correction derived from ionospheric models, and does not take effect along the vertical. TWIM can even provide decimeter-to-centimeter level accuracy in differential GPS positioning for single-frequency receivers during geomagnetic quiet conditions across all seasons and various solar activities. This shows that based on both positioning algorithms the general order of increasing accuracy is KLB, TWIM, and GIM. The similarity of the performance of TWIM and GIM demonstrates the applicability of TWIM in providing quality electron density and electron density gradients, which can be extended to other geodetic and space science applications.
