2023_programme: Observation and modelling of underwater noise from far shipping lanes at mid-frequencies

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  • Session: 21. Underwater Noise - Modelling and Measurements
    Organiser(s): Alexander Gavrilov
  • Lecture: Observation and modelling of underwater noise from far shipping lanes at mid-frequencies
    Paper ID: 2067
    Author(s): Nathan Ivkovic, Xavier Cristol, Gaultier Real, Dominique Fattaccioli, Gilles Gaonach
    Presenter: Ivkovic Nathan
    Abstract: Among the different origins of underwater acoustic ambient noise, the contribution from far shipping is generally conceived as essentially low frequency. This is certainly true when considering the signal power density on a single hydrophone, where far shipping is significant below the order of 1kHz, but is masked by sea surface noise at mid-frequencies (from 1kHz to some 10kHz). In this article, we present a model simulating the ambient noise due to both sea surface agitation and shipping, and we compare some of its predictions to measurements performed in the Mediterranean Sea and in the Atlantic Ocean on a 2D antenna in the context of the DGA Naval Systems project ALMA 2018. \nIn presence of a strong thermocline, the sound-speed profile produces the phenomenon classically called “noise notch”, which is an interval in elevation angle, where no ray, hence no noise can arrive from the sea surface. Our model predicts that shipping noise peaks, neatly contrasting with the surface noise, occupy the boundaries of this notch. This is because the main sources of ship noise, namely propellers, are located several meters below the surface, i.e. deeper than the very surficial sources of surface noise (air bubbles below wave breaking). \nWe analysed ambient noise measurements on a 5m x 2m 2D antenna with 128 hydrophones in the Mediterranean Sea (over the continental slope, South of Balearic Islands). We first compensated the array movements (rotations, drift) and adaptively subtracted noise from the towing ship and sperm whale clicks. Then we formed 3D elevation x bearing beams, which finally display unmistakable peaky contributions of a far shipping lane located at more than 200km, at frequencies up to several kHz, at the bounds of a strong noise notch, in accordance with our model predictions.
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  • Corresponding author: Mr Nathan IVKOVIC
    Affiliation: Thales Defence Mission System
    Country: France
    e-mail:

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