Evaluating the performance of ocean gliders’ technology to characterize ship-radiated underwater noise

Abstract

This study uses passive acoustic monitoring techniques to investigate the potential of Autonomous Underwater Gliders for assessing and localizing a controlled vessel through underwater radiated noise. The propagation of noise was investigated through an advanced propagation loss model utilizing oceanography data collected by the glider. Comprehensive sea trials were conducted using a Slocum G3 glider equipped with acoustic capabilities. These trials involved capturing the underwater radiated noise from a specific vessel while simultaneously collecting oceanographic data. The first step involved identifying the noise pattern of the target vessel and assessing the individual noise sources in accordance with ISO standards. Subsequent trials involved using a glider, a hydrophone array, and a seabed-moored hydrophone to further analyze vessel noise signatures. The acoustic performance of the glider was compared to that of other conventional stationary platforms. A study was conducted to evaluate the self-noise produced by the glider in order to ensure the precision of the acoustic data. Furthermore, sound propagation loss was studied using the gathered oceanic data. Propagation loss models were developed in two distinct environmental conditions: 1) a shallow coastal inlet 80 m deep and 2) a deep bay up to 200 m deep during summer and winter, both in the presence and absence of strong surface stratification. A range- and depth-dependent sound speed profile map was created to estimate propagation loss inside the area covered by the glider. This led to the testing and improvement of advanced sound propagation models compared to the ISO standard 17208 formulations. The findings demonstrate that the gliders can characterize and measure ship-based URN and locate the direction of the source relative to the glider, thereby improving the understanding of the spatial and temporal variability of ocean sound sources. The study supports the use of AUGs in marine acoustic monitoring, which has implications for environmental policies and the development of quieter vessels.