以中距離基線場做GPS定位精度之研究

Abstract

提昇GPS定位之精度一直是使用者所追求的目標，為達此目的，吾人著眼於改善對流層折射效應對GPS定位之影響。在本論文中，即考慮觀測量的雜訊會隨著天頂距愈大（仰角愈低）而放大，故採用觀測量不等權（P=cos2(z)，z為天頂距）的觀念引入低角度衛星的觀測資料，以期能提昇GPS相對定位之精度。 有別於以往大多採用基線重現性或標準偏差來評估GPS靜態測量之內部精度；本研究以工研院量測中心經國家標準實驗室驗證之ME5000精密測距儀為檢定之標準件，其測距準確度為±（0.2mm+0.2ppm）；因為此精度遠優於GPS測量，故可將ME5000所測得之斜距當作參考值，用以評估GPS測量之外部精度。 經本研究證實，衛星最低仰角仍以15°為最佳。而觀測量不等權的處理方法確實可以增進GPS定位之精度，其影響反映在基線的斜距上，一般來說，平均可以提昇1~3mm的精度；此一作法，同時還可以避免低角度雜訊較大的觀測資料影響GPS定位之結果，進而提昇GPS量測之精確度及可靠度。

The enhancement of the precision of the GPS positioning is always requested GPS receivers' user. To get this object, we will focus on improving the tropospheric refraction errors. In this thesis, the observation noise which is proportional to the zenithal angle is considered. Besides, we try to use low angle satellite observations with unequal weight（P=cos2(z)，z is the zenith distance）to improve the precision of GPS positioning. Usually, the baseline repeatability or standard deviation is adopted to evaluate the internal precision GPS positioning. However, in this thesis, ME5000 precise telemeter, which has been examined by National Measurement Laboratory of the R.O.C., is used as the tool to achieve the standard values. The precision of ME5000 precise telemeter is assessed to be ±(0.2mm+0.2ppm), which is better than the GPS measurements. Therefore, this value can be applied as the reference to evaluate the external precision GPS positioning. In this thesis, the best cutoff angle is proved to be 15°. Besides, the GPS positioning precision can be improved by using the method of unequal weight. Generally speaking, the errors of the baseline slope length can be reduced about 1~3mm. Moreover, the low angle observation that the larger noise is avoid can be applied to improve the accuracy and reliability of GPS survey.