Decreasing the influence of dispersive wave modes in long-range ultrasonic rail testing using wavelets

The sensitivity and the resolution of long-range ultrasonic testing (LRUT) are significantly limited by the presence of dispersive wave modes, commonly inherent to the acquired ultrasonic signals. This paper presents a signal processing technique based on the discrete wavelet transform (DWT) for reducing the effect of dispersive wave modes in LRUT of rails. A comparative study of different type of wavelet, thresholding procedures and threshold selection rules is presented. The proposed concept has been evaluated in the presence of high level of additive dispersive waveform at signal to noise ratio (SNR) from -20dB to 20dB. The results show that the effect of dispersion can be reduced in great extent even in the case of extremely high SNR level.