Locating the Ultrasonic Echo Head Wave of Bottom Sediment in Drilling Hole Based on Local SNR

Locating the head wave of ultrasonic echo accurately is the basis of measuring the thickness of sediment in drilling hole precisely. This paper presents a method to locate the echo head wave by local signal-to-noise ratio (L-SNR). The original signal is filtered by a parameters constrained Gabor filter and transformed into frequency domain by windowed Fourier transform firstly, and then the L-SNR is computed. The peaks in L-SNR function just represent and locate the beginnings of echos. The experiments results show that the L-SNR has sharp peaks at the beginnings of the echos indeed and the locating based on these peaks is high precise. This paper has also indicated that the length of the time window should be the 4~8 times of the reciprocal of transducer bandwidth.