用於平均海水面監測之GPS浮標高程推求方法

Height Determination of GPS Buoy for Monitoring of the Mean Sea Level

在潮位站附近海水面上設置GPS浮標，持續量測海水面之變化，並與潮位站共構之GPS連續追蹤站，進行動態相對定位，可解算出GPS浮標瞬間位置，再擷取其橢球高，以時問序列繪製高程分佈圖，此曲線就代表海水面隨時間變化之瞬時位置。但因GPS浮標置於海面上，受波浪高低起伏影響，使其天線傾斜無法正確垂直，造成高程量測不正確，為避免本項誤差，本文將從GPS浮標之設計、姿態測定原理、改正公式之推導，到實地測量實驗，進行深入之探討。結果證實，若將天線設置於GPS浮標表面之幾何重心，在天線高儘量減小之情況下，只要將觀測所得之高程取其平均值即可，無須為測定其姿態而大費周章的設置三個天線，計算其姿態，再進行姿態改正。

To establish GPS buoy above the surface near Tide Gauge for continuously monitoring sea level change and dealing with the dynamic relative positioning of the GPS tracking station integrated with the Tide Gauge, the instantaneous position of GPS buoy can be solved. Then based on ellipsoid height of each point and time series, the curve of height distribution is drawn. The curve can represent the instantaneous position of the sea surface. However, when the GPS buoy drifts on the surface of the sea, the antenna of GPS cannot continuously perpendicular to the buoy due to up and down of the wave. It causes the error of ellipsoid height measured from the GPS receiver. To avoid the error, this article will discuss the design of GPS buoy, the principle of buoy altitude measurement, the derivative of correction formula and the test of field survey. It is proved that if the antenna is set up at the geometry center of the GPS buoy surface and the antenna height is as short as possible (only antenna is preferred. not tripod), the accuracy of mean value of ellipsoid height obtained from the solution of instantaneous position is enough. It is not necessary to establish three GPS antenna for determining the angular orientation of the GPS buoy.