Detection of amplitude modulation of sea vessel underwater noise emission at rolling and pitching at the background of ultralow frequency fluctuations

Konson A.D., Volkova A.A.

Analysis of the influence of ultralow frequency (up to 0.05 Hz) fluctuations of sea vessel underwater noise emission on the possibility of extraction of signal amplitude modulation existing in the frequency band of sea vessel rolling and pitching on the rough surface (from 0.03 to 0.5 Hz) is carried out. Possible characteristic variants of ultralow frequency fluctuations spectra are determined based on the analysis of signals recorded in natural conditions. Appearance of ultralow frequency signal fluctuations was observed in different frequency bands of the total frequency band of the carrier signal (from 0.5 to 8.0 kHz). Different hypotheses of the nature of ultralow frequency fluctuations formation depending on hydrological acoustic conditions are proposed. It is shown that ultralow frequency fluctuations can have negative effect on the possibility of amplitude modulation detection. Possible circuits of extraction of signal amplitude modulation in rolling and pitching frequency band against ultralow frequency fluctuations are considered. The effective method of compensation of ultralow frequency fluctuations influence for a standard device of detection of amplitude modulation caused by rolling and pitching is presented. The proposed method is implemented as software in the structure of a standard device. Operability of the method has been shown using noise signals of sea vessels recorded in natural conditions.

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