Nondestructive detection method for underground continuous wall using time-scale representation of Morlet wavelet

The properties of Morlet wavelet and its transform were investigated. The good time-frequency regularity and complex analysis characters of Morlet wavelet were used to map one-dimensional detection wave to two-dimensional time-scale representation (TSR), namely Scalogram. The Scalogram carries rich medium information, which is valuable for implementing comprehensive analysis and defects identification on medium. Moreover, by means of the wavelet transform modulus maxima (WTMM) derived from the real part of Morlet wavelet transform, the defects on medium could be accurately located. This method also effectively makes up for the shortages of complex signal analysis (CSA), short time Fourier transform (STFT) and time-frequency representation (TFR). Its feasibility and effectiveness were illustrated by the practical detection for underground continuous wall made of cement and concrete. In addition, the combination of the Morlet wavelet and Dergauss wavelet can avoid the bifurcation of wavelet transform modulus maxima line and further improve the proposed method.