In this paper, we study the debris flow monitoring system. Two kinds of sensing system are studied and compared with
their performance. The first sensor is a traditional geophone, while the second one is a fiber optic sensor. This sensing
system is composed of a fiber optic sensor and a Sagnac interferometer. The optical sensor is constructed by a mandril
wrapped with fiber. We compare the characteristic of those two sensor heads. The results indicate that the fiber optic
interferometric sensor head (fiber optic geophone) has high resolution and its frequency response highly match with the
traditional geophone. The results of experiments show that the performance of fiber optic geophone sensing system work
well for low frequency range. According to our preliminary test, the dynamic range detected by the optic fiber sensor is
45 dB, while the frequency ranges is between 10 ~ 300 Hz.