以GPS決定船姿態角改善船載海面高

Abstract

本研究於船測重力計畫之船上建立一多天線GPS系統獲取取樣間隔1 Hz之觀測資料，以TRACK進行動態差分定位解算，而後進行船隻運動姿態解算，解算方法為姿態角直接解法(Direct Computation Formulas, DCF)；而後以此姿態角成果對天線垂距作改正，得時變天線垂距改正量，再應用時變天線垂距於海面高(Sea Surface Height, SSH)改正。本研究撰寫了一FORTRAN程式，處理資料時間比對、解算天線相位中心間距離、解算船隻運動姿態、使用姿態成果取得時變天線垂距並以其改正海面高。TRACK定位成果在靜態長距離基線中精度可達約1公分；動態船隻基線則可達約2公分。姿態角成果與同時於船上施測之INS/GPS整合系統所得成果進行比較，其成果顯示多天線GPS系統與INS/GPS整合系統之航向角差異甚小，故知此多天線GPS系統搭配姿態角直接解法於求取船隻運動姿態上是可行之方法。時變天線垂距改正海面高成果則以交叉點分析、與DTU10之差值分析進行比較：與平均海水面DTU10之差值，於直線航線上標準差約改善0.7公分，改善比率約為3.45%，於轉向航線上標準差約改善1.4公分，改善比率約為4.07%；交叉點分析方面，方均根值改善約0.5公分，比率為3.31%。

In this research, a GPS multi-antenna system has been built in the campaigns of collecting shipborne gravity with 1-Hz data rate. The positioning package TRACK is used for kinematic relative positioning (KRP). The assessment of baseline length suggests that the accuracy of KRP from TRACK reaches 1cm in a static condition and 2 cm on a ship. A computer program has been built to compute ship attitudes from kinematic baselines by the direct computation formulas (DCF). The estimated attitudes are used to correct for the antenna height to the sea surface due to attitude effect. The comparison between GPS and GPS/INS-derived attitudes suggest that GPS attitude system and DCF function properly. With the attitude effect accounted, the RMS crossover differences of the corrected SSHs are improved by 0.5 cm, or 3.31% relatively, compared to the case of raw SSHs. With the ocean tide corrected, the difference between corrected SSHs and DTU10 modeled values are reduced by 0.7 cm in standard deviation along straight survey lines, and by 1.4 cm along non-straight lines, corresponding to relative improvements of 3.45% and 4.07%, respectively.