本研究係於水土保持局建置之華山土石流觀測站，分別以地聲檢知器(Geophone)及麥克風(Microphone)量測重量不同的石塊撞擊河床時所產生之地聲訊號及聲音訊號，再經由快速傅立葉轉換(FFT)及Gabor轉換分析所測得之時域訊號，以求得地聲及聲音訊號的頻率域訊號及時間－頻率訊號。實驗結果顯示，地聲及聲音訊號的頻率範圍介於10Hz~150Hz之間，隨著石頭重量的增加，地聲及聲音訊號的頻率也將隨之降低。地聲訊號的主要尖峰頻率值均在聲音訊號的頻率域中顯現，但地聲訊號在高頻區域較容易衰減，因此在訊號頻率特性的顯現上，並沒有聲音訊號完整。此外，本研究利用實驗時之氣候條件，包括：溫度及溼度，代入聲音能量在大氣中的理論衰減計算後，再和實驗結果的衰減做比較。發現當空氣中的濕度高時聲音能量的衰減相當小，且當訊號的頻率值越低時，聲音能量的衰減也將隨之變小。

In this study experiments were carried out to investigate the difference between the airborne sound and the underground sound (ground vibration) produced by the rock motions on a channel bed near the Huashan Debris Flow Monitoring Station, established by the Soil and Water Conservation Bureau, Taiwan. The airborne and underground sounds were collected simultaneously by three microphones and three geophones, respectively, at the same locations. The sound signals were analyzed using both the Fast Fourier Transform (FFT) and the Gabor transform to represent the signals in both the frequency and time-frequency domains. The experimental data show that the frequency of both the airborne and underground sounds produced by the impact of the rock against the channel bed ranges between 10 and 150 Hz and the peak frequency of the signals decreases as the weight of the stone increases. Furthermore, the higher frequency band of the underground sounds decays much faster than that of the airborne sounds. The spatial decay rate of the airborne sounds was also determined and compared with the values which were estimated based on the available theory. The spatial decay rate of the airborne sounds decreases as the frequency of the sound decreases and the humidity of the air increases.

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