結合GPS及BDS對於定位效能之提升：應用於大地監測

Combining GPS and BDS to improve positioning performance: application to geodetic monitoring

全球定位系統（Global Positioning System, GPS）精密定位可提供使用者靜態定位以及逐一時刻定位高精度的定位成果，並廣泛的運用在大地監測之上，如：地殼變形監測、控制測量、海嘯早期預警以及估計同震位移等。而若是可改善GPS的定位效能，勢必對大地監測能產生助益。近年來由於中國的北斗衛星導航系統（BeiDou Navigation Satellite System, BDS）正式提供亞太地區服務，並且由於其衛星的軌道特性，使得BDS在台灣地區具有與GPS相當的可視衛星數，此外再加上都是以CDMA的方式傳播訊號，顯示兩者之間有較高的相容性。因此在本研究中希望藉由結合GPS及BDS，增強衛星幾何，達到提升定位效能的目標。在實驗中，蒐集了5條基線（50～265km），並分析加入BDS之後對於靜態定位連續站模式、靜態定位移動站模式以及逐一時刻定位成果的影響。其成果顯示：（1）在靜態定位連續站模式中，GPS與GPS＋BDS會有精度相似的每日解，在平面精度上幾乎一致，而高程精度則是GPS＋BDS會略優於GPS。（2）在靜態定位移動站模式中，當觀測時間在2小時內GPS＋BDS能夠明顯的提升定位精度，而在觀測時間大於4小時之後可以預期GPS＋BDS與GPS會有相似的定位精度。在觀測時間小於2小時，GPS＋BDS可以縮短定位精度達到預設精度門檻值所需的時間。（3）而在逐一時刻定位的部分，GPS＋BDS在平面精度及高程精度上分別約有19％及23％的提升。 GPS (Global Positioning System) precise positioning can provide accurate static and epoch-by-epoch positioning result, and is widely used in geodetic monitoring. The BDS (BeiDou Navigation Satellite System) has been fully-operational in Asia-Pacific region. Currently in Taiwan, BDS can provide as many visible satellites as GPS can provide. Moreover, both of BDS and GPS transmit signal are based on CDMA, which means these two systems are highly compatible. Therefore, we expect to achieve better positioning performance by combining GPS and BDS. In this study, we develop a generalized computation method and use the method to perform GPS-only and GPS+BDS relative positioning and to evaluate the impact of GPS+BDS in continuously operating reference station (CORS) mode, in campaign mode, and in epoch-by-epoch positioning. For data analyses, five experimental baselines which ranging from 50km to 265km were collected. The results indicate that (1) in CORS mode, GPS+BDS has similar horizontal daily solutions as GPS, and is slightly better than GPS in vertical daily solutions; (2) in campaign mode, for data length ≤ 2hr, obvious positioning accuracy improvement could be obtained by GPS+BDS. For data length ≥ 4hr, GPS+BDS would have similar positioning accuracy as GPS. For data length ≤ 2hr, the required occupation time for achieving a predefined accuracy can be significantly reduced by applied GPS+BDS; (3) for epoch-by-epoch positioning, the positioning accuracy can be improved by 19% in horizontal direction and by 23% in vertical direction.