Global Positioning System (GPS)浮標已被證實可用來觀測海水面變化。與傳統六分鐘一筆潮位平均值之潮位站資料相比，GPS浮標可用來觀測高頻的海洋訊號，其週期由數秒到數分鐘不等。本研究利用GPS浮標收集台南安平商港附近海域兩處之海水面資料，並分析求得特定海洋訊號資料：氣象海嘯(meteotsunami)與有效波高(significant wave height)。由於氣象海嘯振幅會受到港灣共振效應而變大，故本研究藉由在台南安平商港內及港外各放置一個GPS浮標，同時分析港內與港外GPS浮標紀錄，進一步探討港灣共振頻率與氣象海嘯頻率之相關性。實驗時於岸上設置一固定站進行相對差分定位，做為GPS浮標定位結果之參考解，利用四種不同GPS解算軟體，分別為GrafNav軟體、RTKLIB軟體、P3軟體以及GAMIT TRACK軟體，搭配International GNSS Service (IGS)所提供之精密星曆進行精密單點定位解算或動態定位解算，之後計算GPS浮標高程變化量與潮位站間差值之標準偏差值(Root Mean Square, RMS)來比較不同GPS解算軟體在不同解算方式下之品質優劣。為了利用GPS浮標觀測之海水面資料進行氣象海嘯與波浪訊號研究，我們利用37個常見的分潮週期與潮位站資料計算出GPS浮標觀測時的潮位高度，將GPS浮標解算之原始資料與擬合後的潮位高度利用移動平均法(Moving average)擷取出氣象海嘯與波浪訊號加以分析。之後，利用零上切法(zero-up crossing)與零下切法(zero-down crossing)定義出波高值，計算前三分之一的波高平均值為有效波高，而前三分之一波高的週期平均值為有效波高之週期，此計算結果可應用於海岸工程或近岸工程建設。最後將港內與港外浮標之差分定位解的海水面時間序列利用Hilbert Huang Transform (HHT)分解成數個Intrinsic Mode Functions (IMFs)分量，大致上分為高頻、中頻以及潮汐分量，藉由HHT分解後的頻譜強度圖判定是否偵測到氣象海嘯的存在。

Global Positioning System (GPS) buoys have been demonstrated to collect sea level data effectively and economically. By comparing to tide gauge records, GPS buoys provide high-frequency oceanic signals with periods of a few seconds to a few minutes that cannot be detected from 6-minute tide gauge records. In the study, GPS buoys were used to measure sea level variations in Aping harbor, Tainan and to study meteotsunami and significant wave height (SWH). Since meteotsunami may be amplified by harbor resonance, two GPS buoys were deployed inside and outside the Aping harbor, respectively to investigate the relationship between the harbor resonance and the frequencies of meteotsunamis. Different softwares including GravNav, RTKLIB, P3 and GAMIT/GLOBK are used to process GPS buoy measurements using Differential GPS (DGPS) with an additional GPS receiver as a reference station on shore and Precise Point Positioning (PPP) technique with the precise ephemerides of the final product provided by International GNSS Service (IGS). In order to verify the processed results, we compare the processed results derived from different softwares with Aping tide gage records. Using 37 tidal periods to fit tide gauge records to obtain the ocean tide, the processed GPS buoy results after removing fitting ocean tide are used to study meteotsunami and SWH by the moving average. Wave heights are defined by the zero-up crossing and zero-down crossing methods and the mean wave height of the highest one-third of wave heights, called SWH, is calculated. The estimated SWH can be provided for guiding the coastal construction. Finally, oceanic signals of different frequencies including high frequency, middle frequency, and tidal components are acquired using GPS buoy derived sea level variations by Hilbert-Huang Transformation (HHT) and then are used to detect the phenomenon of meteotsunami.

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