Time-cyclic frequency representation of propeller tonals applied to recordings in the sea of Marmara

Noise produced by the cavitation of the propellers is the main underwater acoustic signature used to detect and classify ships. Propeller noise exhibits cyclostationarity and creates acoustic traces called tonals which depend on the characteristic of the propellers and can be detected by using Integrated Cyclic Modulation Coherence (ICMC) method. ICMC is based on the Cylic Modulation Coherence (CMC) which is basically the Fourier transform of the spectrogram normalized over the spectral frequency. This transform eliminates the temporal information due to duality between time and cyclic frequency which prevents the analysis of propeller tonals over time. We propose a visual tool named ICMC-gram1 The suffix ’gram’ is used similarly to ’spectrogram’ or ’seismogram’, indicating a graphical representation of data over time or frequency -which allows to examine the changes in cyclic frequencies over time- and present ICMC-gram results of real data collected from the Sea of Marmara during Summer 2023.