本研究主要目的為利用桑克干涉儀（Sagnac intereometer）的原理，發展光纖感測器（fiber optic sensor）量測土石流發生時所造成的地表振動（ground vibration），或稱為地聲（underground sound）。光纖感測器的元件包含光源單元、感測單元及訊號處理單元；感測單元中含一繞軸式光纖地聲感測裝置。在完成光纖量測系統的架構後，本研究先於實驗室中以此設備量測石頭撞擊礫石底床所產生的地聲，並與一般常用的地聲檢知器（geophone）所量測到的結果比較。在確定光纖感測器的可信度之後，本研究於雲林縣華山土石流示範觀測站之河床，同時以光纖感測器及地聲檢知器量測石頭撞擊河床所產生的地聲。量測結果顯示光纖感測器所感測到的地聲頻率範圍與地聲檢知器的結果一致，且地聲的尖峰頻率相同，因此證實此一感測器的開發成功。

The purpose of this project is to develop a fiber optic sensor for detecting the ground vibrations produced by debris flows, based on the Sagnac interferometer. The ground vibration is sometimes called underground sound. The fiber optic sensor consists of a laser source unit, a sensing unit, and a signal processing unit. The sensing unit contains a vibration sensitized fiber optic coil for detecting the ground vibration. The fiber optic sensor was tested first in the laboratory by applying it to measure the ground vibrations produced by a rock hitting the gravel bed. This ground vibration signal was compared with those detected by a geophone, which has been widely used to measure the ground vibration. Comparison of these signals verified the capability of the new devised fiber optic sensor. The fiber optic sensor and the geophone were then installed at a river bed, where the Hua-Shan Debris Flow Monitoring Station locates, to detect simultaneously the ground vibrations produced by the impact of rocks upon the river bed. Comparison of the ground vibration signals obtained from these two instruments shows that frequency range of the signals are the same, and the peak frequency in both signals are quite similarity.

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