全球定位系統 (Global Positioning System, GPS)訊號通過電中性介質大氣層時，會受到對流層效應的影響造成訊號延遲誤差；對流層延遲誤差又可分為乾延遲、溼延遲兩部份；ㄧ般的解決方法是利用氣象經驗模式及參數估計法來修正此對流層誤差，但由於水氣變化的影響，利用經驗模式無法完全表示此部分延遲量。為了有效消除水氣部分造成的溼延遲誤差，內政部引進了兩台水氣微波輻射觀測儀(Wate Vapor Radiometer, WVR)，可直接對大氣作異質性的觀測，求得可降水量、液態水量、及路徑濕延遲量。藉由水氣輻射儀觀測濕延遲量，加上地表壓力所計算求得準確的乾延遲量，可得天頂路徑總延遲量；本研究探討利用水氣輻射天頂延遲觀測量作為修正對流層誤差的外部改正方法，對於高精度GPS相對定位之影響。

本研究採用2006年3月15日到2006年7月10日共118天實驗資料，進行相對定位解算，其成果如下: (1)利用水氣輻射儀驗證GPS技術所反演出的天頂延遲量，將GPS所推演的天頂延遲量與真實WVR觀測值比較，其標準差可達10-23 mm等級。 (2)在陽明山到北港基線計算中，與傳統GPS定位方法(未加入WVR)比較，加入WVR觀測資料於基線解算，可提升北港站坐標在高程方向及速度量估計的精度；但所計算出的高程値及速度量將分別會有數個mm及數個mm/year的差異(Bias)存在。 (3)在網形計算中，只利用兩台WVR儀器無法提供網形內其它各站天頂延遲修正量，因此對於GPS網形解算成果並無太大助益；但可看出水平梯度參數可提升網形解在平面方向上的定位精度。

As Global Positioning System (GPS) signal propagates in the neutral atmosphere, the tropospheric refraction causes the propagation path delay that can be separated into two main components: the dry delay and the wet delay. Theoretically, the path delay can be reduced or eliminated by using an empirical meteorological model and parameter estimation. However, it is difficult to remove the delay effect completely as a result of varied water vapors. In order to cope with the wet delay, the Ministry of the Interior introduced Water Vapor Radiometers (WVR) which can directly measure the inhomogeneous atmosphere and retrieve the precipitable water vapor, integrated liquid water and the radio propagation wet delay. Therefore, the zenith total delay (ZTD) can be estimated by combining the WVR wet delay and the dry delay derived from an empirical meteorological model. This study focuses on the effect of the ZTD derived from WVR as the external corrections to correct the tropospheric delay for high precision GPS relative positioning.

GPS observations, meteorological data and WVR measurements covering 118 days from 15th March to 10th July 2006 are collected for this study. The result shows (1) A comparison of ZTD derived from GPS and WVR respectively shows an excellent agreement at 10-23 mm standard deviation. (2) The vertical positioning and velocity accuracies of the baseline of YMSM-PKGM are improved by applying WVR data, and there are bias of height at several mm and velocity at several mm/yr. (3) The network solutions of Taiwan tracking stations are computed using WVR at two stations. Limited to the number of WVR instruments, which can only provide the zenith total delay corrections at two stations of the regional network in Taiwan, the accuracy is not improved significantly; however, we find out that using gradient parameters can improve the horizontal accuracy.

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