Application Of Wavelet Transform In Detection Of Shallow Cavities By Surface Waves

Application of wavelet transforms in detection of underground shallow cavities is investigated.<br>Wave propagation is simulated by a transient response analysis on an axisymmetric finite element<br>model. Cavities in a homogeneous isotropic half-space of a variety of shapes and embedment depths are<br>considered. The continuous wavelet transform (CWT) is introduced as a new tool for cavity detection.<br>Effects of different types of cavities on power spectral surfaces (power spectral amplitudes versus<br>frequency and receiver location) and wavelet time-frequency maps (wavelet transform coefficients,<br>algebraic or absolute, versus time and frequency) are studied. Strong energy concentrations in power<br>spectral surfaces right in front of a cavity in certain frequency bands are observed. Time and frequency<br>signatures of waves reflected from near and far faces of the cavity can be clearly identified in wavelet<br>time-frequency maps. Those can be effectively used to locate and estimate the size and shape of the<br>cavity.