東沙共站封閉型壓力式潮位計觀測值比對

On the Comparison of Three Self-contained Pressure Tide Gauges in Dongsha

封閉型潮位計將感測器、紀錄器、電源，封裝於一體，安置於水下量測潮位，為蒐集潮位資料時所常用。本研究分析三具安置於東沙潮位站之壓力式潮位計，以了解資料特性。三具潮位計垂直安置於同一具6吋管中之同一支架上，各個潮位計感測零點與潮位站參考點之支距於施作時以捲尺量得。由於三具潮位計為因工作推展，先後採購獲得，前一次壓力常數校正時間有別，分別為2012、2016、2019年。經分析平均潮位，推算潮位計間之支距後，發現前次校正在2012及2016年者，分別產生約0.07m及0.02m之飄移。由潮位時序之相關係數比對，前次校正已久者，波形亦有變異。本研究具體呈現，壓力式潮位計定期檢校之必要性。本研究由海水壓力化算水深時，同時比對簡易公式與UNESCO（1983）公式之差異，在本次蒐集之數據中，最大達0.0066m。

The self-contained type tide gauge has the sensor, logger, power supply and other required units sealed into one container. This type of gauge has been widely deployed into the sea for tide information gathering. This study analyzes the data collected by three gauges deployed at the Dongsha tide station. These three gauges were placed vertically on the same staff in a six-inch pipe. The sensor zero of each gauge is taped at the installation and also at the de-installation. Because the gauges were purchased in different years along with the project’s progress, the most recent calibration of the instrument pressure constants are not the same. They were calibrated in 2012, 2016, and 2019 respectively. From the average of observed tide with each gauge, it is found that there are 0.07 m and 0.02 m drifts with the gauges calibrated in 2012 and 2016. Observed from the correlation coefficients, the form of the tide collected with these two units is also moderately deformed. This study provides evidence on supporting the need for gauge calibration. In the depth conversion from seawater pressure, this study also found that the deviation between the simplified conversion equation and UNESCO (1983) equation reaches 0.0066m in the data processed.