Application of the overcomplete wavelet transform for underwater transitory signal characterization

In this paper we consider the problem of transitory signal characterization, extracted from the underwater environment. The main difficulty which appears in this field is due to the transient behavior of the received signals and to the noise level of the underwater environment. In fact, in the received signal structure a transient part occupies only a small zone and its capture can be done by an adaptive detection stage. Furthermore, we are interesting to characterize the extracted part in both time and frequency domains. Consequently, we propose an adaptive time-frequency method based on the over-complete wavelet transform concept, in which case an irregular sampling procedure will be involved. This procedure uses a method based on the fourth order moment, applied for each subband, in order to establish the optimal weight for each sample. The obtained results for real data prove the capability of the proposed approach to accurately characterize an underwater transient signal, comparatively with the classical methods (spectrogram, for example).