GPS浮標是將一大地測量等級雙頻天線盤裝置於浮體上，利用全球定位系統(Global Positioning System, GPS)進行定位，已被許多學者證實為一種經濟、有效的海水面資料蒐集工具。傳統GPS浮標系統定位時為了消去系統誤差的影響，會在附近架設GPS參考主站，利用差分相對定位(Differential Global Positioning System, DGPS)技術來求解GPS浮標之坐標。近年來由於IGS(International GNSS Service)等國際組織提供了精密星曆及精密衛星時錶改正資料，有學者提出精密單點定位(Precise Point Positioning, PPP)的概念，利用單一GPS接收儀即可求解出測站的絕對坐標，得到高準確度(accuracy)之定位成果，不僅改進了傳統單點定位精度不佳的問題，也使得測量外業操作更具便利性，人力需求、儀器成本降低。

本研究在台南安平潮位站旁進行6次GPS浮標施測，首先利用與GPS浮標距離不同之GPS參考主站來進行差分定位，分析基線距離對GPS浮標定位成果的影響，由實驗結果可得出基線越長則定位準確度(accuracy)越低；再以IGS提供之最終產品(final product)、快速產品(Rapid product)、超快速產品(Ultra-Rapid product)之觀測部分observed half)、超快速產品(Ultra-Rapid product)之預估部分(predicted half)四種不同發布延遲時間的精密星曆與精密時錶改正資料對GPS浮標進行精密單點定位解算，與傳統差分相對定位方法定位結果進行比較後，得出使用最終產品之平面方向均方根誤差(Root Mean Square Error, RMSE)可達3~5公分，而高程方向均方根誤差可達10公分；快速產品之平面方向均方根誤差可達6~8公分，而高程方向均方根誤差可達15公分；超快速產品觀測部分之平面方向均方根誤差可達15~20公分，而高程方向均方根誤差可達30~40公分；超快速產品預估部分之平面方向均方根誤差可達2~3公尺，而高程方向均方根誤差可達3~4公尺。
實驗中也蒐集了安平潮位站的潮位資料，故也將此資料與GPS浮標高程方向定位成果進行比較，而研究中將著重於高程變化量之分析，假設潮位儀觀測海水面高程變化量為參考解，由實驗結果可發現差分相對定位橢球高變化量均方根誤差之平均值約4.5公分；使用最終產品時橢球高變化量均方根誤差之平均值可以達到6公分以內；使用快速產品時橢球高變化量均方根誤差之平均值可以達到10公分以內；使用超快速產品觀測部分於觀測環境理想時橢球高變化量均方根誤差之平均值可以達到25公分左右；使用超快速產品預估部分時橢球高變化量均方根誤差之平均值約1~2公尺。

The GPS buoy is a floating buoy equipped with a geodetic-grade dual-frequency GPS receiver and has been demonstrated to effectively and economically collect sea level data. In order to eliminate the systematic errors of GPS buoy, traditional DGPS (Differential Global Positioning System) techniques is used to provide positional information of GPS buoy, thus an additional GPS receiver is required to set up as a reference station. Because International GNSS Service (IGS) recently provides the precise ephemeris and the corrections of satellites clock, a novel technique, Precise Point Positioning (PPP), is developed to compute a station’s coordinate with acceptable accuracy where its 3D RMSE in kinematic and static modes are smaller than 1 meter and 1 decimeter, respectively by using only one GPS receiver to reduce labor and expense and simplify the data processing scheme.
In this study, six campaigns around Anping tide gauge, Tainan, were successfully performed and the collected GPS buoy data were processed with four types of precise ephemeris provided by IGS, including final product, rapid product, ultra-rapid product (observed half) and ultra-rapid product (predicted half) with the use of PPP technique. Comparing the PPP results with DGPS, the differences reach 3~5 cm in the horizontal and 10 cm in the vertical with final product; 6~8 cm in the horizontal and 15 cm in the vertical with rapid product; 15~20 cm in the horizontal and 30~40 cm in the vertical with ultra-rapid product (observed half); 2~3 m in the horizontal and 3~4 m in the vertical with ultra-rapid product (predicted half). In addition, the collected data were also processed by DGPS techniques using different reference stations to analyze the effect of various baselines. The results show that accuracy degrades when the baselines increase.
Finally, in additional to the comparison of results derived by PPP and DGPS, they were all compared to Anping tide gauge records as well. The aim of this study is the analysis of height variations provided by different methodologies. Comparing to Anping tide gauge records, the differences in height variations can achieve 4.5 cm with DGPS; 6 cm with final product; 10 cm with rapid product; 25 cm with ultra-rapid product (observed half); 1~2 m with ultra-rapid product (predicted half).

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