Wavelet transform reassignment and the use of low-oscillation complex wavelets

In this paper, we explore the use of new time-frequency reassignment tools for the enhancement of prominent features in the time-frequency plane of the wavelet transform. The reassignment method allows for the localisation of time-frequency and time-scale distributions. Here we outline the underlying theory of this relatively new method and apply it to the analysis of test signals. Thereafter the usefulness of the method is demonstrated by application to the analysis of sonic echo signals used in the non-destructive testing (NDT) of foundation piles. We find that the reassignment method, when combined with low oscillation complex wavelet-based transforms, offers potential in identifying highly localised pertinent features that were otherwise difficult resolve when using the standard scalogram/ridge representation.