Monitoring ocean acoustic noise has been the subject of considerable recent study, motivated by the desire to assess the impact of anthropogenic noise on marine life. A combination of measuring ocean sound using an acoustic sensor network and modelling sources of sound and sound propagation has been proposed as an approach to estimating the acoustic noise map within a region of interest. However, strategies for developing a monitoring network are not well established. In this paper, considerations for designing a network are investigated using a simulated scenario based on the measurement of sound from ships in a shipping lane. Using models for the sources of the sound and for sound propagation, a noise map is calculated and measurements of the noise map by a sensor network within the region of interest are simulated. A compressive sensing algorithm, which exploits the sparsity of the representation of the noise map in terms of the sources, is used to estimate the locations and levels of the sources and thence the entire noise map within the region of interest. It is shown that although the spatial resolution to which the sound sources can be identified is generally limited, estimates of aggregated measures of the noise map can be obtained that are more reliable compared with those provided by other approaches.

Seismic interface waves generated by seabed impacts are believed to have biological importance. Previous work on the effects of ocean piling and dredging studied water motion adjacent to the seabed, using sediment measurements as reviewed in the literature. This new modelling work has idealised the sediment data to a simple model with few parameters, and has shown how this leads to filtration of the applied energy to propagate simple seismic vibration wavelets. These special wavelets remain compact with high peak levels of the associated water particle velocity as they ripple outward, and provide a means of assessing the worst-case environmental impact. The form of this wavelet morphs from a hump shape to a dip and back, via intermediate forms which are here described in mathematical terms based on the Ricker form. Whilst the model structure is idealised it is much closer to reality than the Rayleigh and Scholte half-space models, but with only two more parameters required. The resultant wavelet peaks are propagated with values given by the optimal limit case of cylindrical spreading (ignoring absorption) which results in a relatively widespread impact.

A multi-frequency reference vessel (RV-multi) has been established at NPL, with the ultimate aim of establishing a standard source of acoustic cavitation in water. The vessel is a cylindrical cavity and can work at 6 frequencies, from 21 kHz up to 140 kHz, in controlled temperature conditions. RV-multi is capable of self-tuning its driving frequency to lock onto a fixed modal pattern, based on the maximised phase derivative of the driving voltage signal. The ability of system self-locking was tested under various power levels. As part of the validation process for the new reference vessel, its performance has been investigated using various methods. A small hydrophone was used to determine the acoustic pressure distribution along selected planes of symmetry inside the vessel. The generated cavitation distribution was also monitored using sonoluminescence, erosion and acoustic emission. In a novel step, broadband laser vibrometry was used to measure the motion of the vessel wall to investigate the feasibility of a non-invasive method of cavitation detection.