利用GPS浮標監測氣象海嘯

Monitoring Meteotsunami Using GPS Buoys

全球定位系統（Global Positioning System, GPS）浮標被證實可有效且快速地收集海水面資訊，與傳統六分鐘紀錄一筆之潮位站資料相比，1-100Hz GPS浮標可用於監測更高頻之海洋訊號，例如氣象海嘯和有效波高。本研究同時位於台南市安平商港內與港外進行GPS浮標施測，並於岸上設置一固定站，分別利用GrafNav軟體、RTKLIB軟體、GAMIT/TRACK軟體搭配International GNSS Service（IGS）最終產品精密星曆進行動態相對差分與精密單點定位解算，解算成果與安平潮位站資料相比，驗潮站與差分定位結果差值均方根為3~10公分，與精密單點定位差值均方根為7～12公分。將港內與港外GPS浮標之動態差分定位之海水面時間序列利用希爾伯特-黃轉換（Hilbert Huang Transform, HHT）分解成數個本質模態函數（Intrinsic Mode Functions, IMFs）分量，可以成功偵測到氣象海嘯頻率，且經由比較安平港港內外浮標之IMFs和港灣共振週期計算，發現此氣象海嘯並非由安平港港灣共振引起。 Global Positioning System (GPS) buoys have been demonstrated to effectively and economically collect sea level data. By comparing to traditional tide gauge records, 1-100 Hz GPS records can measure high-frequency oceanic signals with periods of a few seconds to a few minutes; for example, meteotsunami and significant wave height that cannot be detected from 6-minute tide gauge records. In this study, two GPS buoys were deployed inside and outside the An-ping harbor, Tainan, with an additional GPS receiver on shore as a reference station. Different softwares including GravNav, RTKLIB, and GAMIT/TRACK were used to process GPS buoy measurements, with Differential GPS (DGPS) and Precise Point Positioning (PPP) techniques and using the precise ephemerides of the final product provided by International GNSS Service (IGS). By comparing the GPS buoy positioning results derived using different softwares with An-ping tide gauge records, the Root Mean Square (RMS) of differences between tide gauge records and DGPS solution is 3~10 cm and is 7~12 cm when PPP solution is used. Finally, inside and outside of harbor GPS buoy derived sea level variations are decomposed into Intrinsic Mode Functions (IMFs) by Hilbert Huang Transformation (HHT) and the frequency of meteotsunami is successfully detected. After comparing the records of inside and outside GPS buoys and the computation of periods due to harbor resonance, meteotsunami is not amplified by harbor resonance in this area.

Global Positioning System (GPS) buoys have been demonstrated to effectively and economically collect sea level data. By comparing to traditional tide gauge records, 1-100 Hz GPS records can measure high-frequency oceanic signals with periods of a few seconds to a few minutes; for example, meteotsunami and significant wave height that cannot be detected from 6-minute tide gauge records. In this study, two GPS buoys were deployed inside and outside the An-ping harbor, Tainan, with an additional GPS receiver on shore as a reference station. Different softwares including GravNav, RTKLIB, and GAMIT/TRACK were used to process GPS buoy measurements, with Differential GPS (DGPS) and Precise Point Positioning (PPP) techniques and using the precise ephemerides of the final product provided by International GNSS Service (IGS). By comparing the GPS buoy positioning results derived using different softwares with An-ping tide gauge records, the Root Mean Square (RMS) of differences between tide gauge records and DGPS solution is 3~10 cm and is 7~12 cm when PPP solution is used. Finally, inside and outside of harbor GPS buoy derived sea level variations are decomposed into Intrinsic Mode Functions (IMFs) by Hilbert Huang Transformation (HHT) and the frequency of meteotsunami is successfully detected. After comparing the records of inside and outside GPS buoys and the computation of periods due to harbor resonance, meteotsunami is not amplified by harbor resonance in this area.