臺灣博碩士論文加值系統

中華三號衛星（ROCSAT-3）為台灣和美國共同合作發展的氣象衛星，預計西元2003年發射，軌道高度約為800公里，接收穿過大氣層而產生掩蔽效應的GPS衛星訊號，透過掩蔽訊號進而推求產生掩蔽效應路徑部分之大氣層的折射率，再藉由折射率可推求大氣狀態中的濕度、溫度和壓力等資料。將全球近即時的掩蔽訊號同時分析，即可預測全球即時氣象。
欲想藉由掩蔽訊號推求大氣狀態，先決條件須知GPS衛星和中華三號衛星的軌道位置，GPS衛星軌道可由GPS廣播星曆、GPS預估星曆或後處理之精密星曆得知，中華三號衛星軌道即為本論文研究之重點。然而中華三號衛星尚未發射，本文實驗中所使用的資料為中華三號衛星之實驗衛星MicroLab-1衛星資料。對於MicroLab-1衛星軌道位置，本文使用均勻分佈於全球的24個IGS追蹤站，將MicroLab-1衛星視為快速移動的移動站而使用無電離層載波相位三次差分法加以推求，並且加入對流層改正模式，測站之固體潮改正、天線相位中心改正和衛星的質量中心改正以及地球旋轉改正；由於相位三次差分法會有累積誤差的現象，故再引入無電離層虛擬距離二次差分法加以改正累積誤差。實驗結果發現，改正後之無電離層載波相位三次差分法當使用GPS廣播星曆在地心地固坐標系的三軸分量上的精度可達到1.028、1.098、1.613公尺，若使用IGS之GPS預估星曆在三軸上分量上的精度可達到0.942、0.857、1.141公尺。

ROCSAT-3 is a constellation of eight meteorological satellites which is a cooperative project between Taiwan and the U.S. The altitude of ROCSAT-3 satellites is about 800 kilometers and the satellites will be launched in 2003. ROCSAT-3 satellites receive GPS occulted signals that traverse the earth''s atmosphere, and then derives the refractive index of the atmosphere through which GPS signals have passed during occultation events. With the refractive index, one can retrieve the moisture, temperature and pressure of atmosphere. In addition, by analyzing near real-time globally distributed occultations simultaneously, global real-time weather forecast can be implemented.
To retrieve meteorological parameters from occultation observation, one must know the orbits of both GPS satellites and ROCSAT-3 satellites. GPS satellites'' orbit can be obtained from GPS broadcast ephemeris, IGS predicted ephemeris or IGS precise ephemeris. The purpose of this study is to determined the ROCSAT-3 orbit in near real-time. Since ROCSAT-3 satellites will not be launched till 2003, so the data of MicroLab-1, which is the preliminary experiment of the ROCSAT-3 project, is used in this paper. To estimate the orbit position using 24 IGS tracking station distributed uniformly on the earth, we consider MicroLab-1 as a rapid moving station, and apply the ionosphere-free carrier phase third-differential method in this study. Besides, the tropospheric correction model, solid earth tide correction and antenna phase center correction of the tracking stations, mass center correction of satellite and earth rotation correction are incorporated. Since the phase third-differential method will produce accumulative error, the ionosphere-free pseudorange dual-differential method is introduced to reduce the error. The results indicate that the corrected ionosphere-free carrier phase third-differential method and GPS broadcast ephemeris combine achieve to the accuracy of 1.028、1.098 and 1.613 meter on the three-axis components in the earth-fixed coordination system; whereas with IGS''s GPS predicted ephemeris, the method can achieve the accuracy of 0.942、0.857 and 1.141 meter.

摘要……………………………………………………………………1
英文摘要………………………………………………………………2
誌謝……………………………………………………………………4
目錄…………………………………………………………………....5
表目錄………………………………………………………………....7
圖目錄…………………………………………………………………8
第一章 緒 論…………………………………………….…………12
§1-1 前言…………………………………………………..12
§1-2 文獻回顧……………………………………………..…………13
§1-3 研究動機與方法………………………………………14
第二章 中華三號衛星與全球定位系統…………………………...16
§2-1 中華三號衛星與其觀測資料…………………………16
§2-2 全球定位系統…………………………………………19
§2-2-1 GPS衛星的訊號……………………………….20
§2-2-2 GPS衛星軌道星曆…………………………….20
§2-3 GPS觀測量…..…………………………………………21
§2-3-1 虛擬距離觀測量……………………………….22
§2-3-2 載波相位觀測量……………………………….23
§2-3-3 虛擬距離與載波相位觀測量之差分方程式….25
§2-3-4 雙頻觀測量之無電離層效應線性組合………..28
§2-4 無電離層虛擬距離二次差分觀測量………….…….…29
§2-5 無電離層載波相位二次差分觀測量………….……….31
§2-6 無電離層載波相位三次差分觀測量…….…………….33
第三章 中華三號衛星與地面測站之GPS觀測資料的改正模
式……………………………………………..…………..…35
§3-1 對流層改正模式……………………………………..35
§3-2 質量中心與天線相位中心之改正…………………..38
§3-3 固體潮改正…………………………………………..41
§3-3-1 平衡潮和固體潮………………………………42
§3-3-2 固體潮改正量的計算…………………………43
§3-3-3 太陽與月球位置的計算………………………46
§3-4 載波相位中心改正及地球旋轉改正…………………..49
§3-4-1 載波相位中心改正……………………………49
§3-4-2 地球旋轉改正…………………………………50
第四章 實驗成果…………………………………………………..52
§4-1 實驗資料………………………………………………52
§4-2 實驗成果分析………………………………………..54
§4-2-1 無電離層虛擬距離二次差分觀測量的實驗
成果分析…………………………………….…55
§4-2-2 無電離層載波相位三次差分觀測量的實驗
成果分析……………………………………….61
§4-2-3 無電離層虛擬距離二次差分觀測量結合無
電離層載波相位三次差分觀測量的實驗成
果分析……………………………………….…66
第五章 結論與建議………………………………………………78
參考文獻……………………………………………………………..80

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