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Passive acoustic inversion techniques for measuring gas flux into the water column have the potential to be a powerful tool for the long-term monitoring and quantification of natural marine seeps and anthropogenic emissions. Prior inversion techniques have had limited precision due to lack of constraints on the initial amplitude of a bubble's excitation following its release into the water column ( R ε 0 i ). R ε 0 i is determined by observing the acoustic signal of bubbles released from sediment in a controlled experiment and its use is demonstrated by quantifying the flux from a volcanic CO2 seep offshore Panarea (Italy), improving the precision by 78%. [ABSTRACT FROM AUTHOR]

This work presents the results from a series of bistatic sea surface scattering experiments conducted in shallow water using a parametric acoustic array as a source and a receiver comprising a horizontal linear array. The experiments measured scattering at three frequencies (4, 8, and 15 kHz) and at three incident grazing angles (13º, 20º, and 30º). The measurements were made over a 5 day period during which a variety of environmental conditions were encountered. This paper provides an outline of the experiments and presents some results for the forward scattering strength. The results show that the wave direction has a significant effect on the surface forward scattering. At each incident grazing angle, the fluctuations of scattering strength due to environmental conditions decreases as the frequency increases. [ABSTRACT FROM AUTHOR]

Underwater noise from commercial shipping throughout the oceans has been increasing over the past decades and the environmental impact of this noise remains an area of great uncertainty. This has led to the measurement of noise from commercial vessels in order to understand the impacts that these vessels may engender. Hydrofoils are used by ferries in various locations around the world and locally may be a significant contributing factor of the soundscape. However, the investigation on underwater radiated noise from the activity of hydrofoils in the field has not been widely conducted. This article is an attempt to characterize the noise from hydrofoils in the field. Detailed measurements in the coastal water close to the Panarea port, Italy are reported. The investigation describes the broadband frequency spectrum with the main energy approximately centered on 30–130 Hz but covering frequencies up to tens of kHz. A key result was that the spectrum of the noise varied between the three stages (displacement, transition, and foiling) of the hydrofoils heading into or out of the port. [ABSTRACT FROM AUTHOR]