The energy based characteristics of sperm whale clicks using the Hilbert Huang transform analysis method

In this paper, a unique analysis method for sperm whale clicks based on Hilbert-Huang transform (HHT) is proposed. Four sperm whale click samples with durations of 10 ms (defined as click I), and four sperm whale click samples with durations of 5 ms (defined as click II) were illustrated. These click samples were recorded in the Mediterranean Sea by Centro Interdisciplinare di Bioacusticae Ricerche Ambientali, Università degli Studi di Pavia. The empirical mode decomposition method was used to decompose click I samples into seven intrinsic mode functions (IMFs) and one residue function (RF), and click II samples were decomposed into six IMFs and one RF. The average energy distributions of multiple IMFs and the single RF domain for click I and click II samples were explored using the HHT analysis method. The average energy-frequency representations were also investigated for the same click I and click II samples. The analysis results show that the energy-frequency characteristics of sperm whale clicks can be extracted and understood by applying several IMFs and one RF signal with a high-resolution analysis.