Investigation of sound pressure waveforms helps the selection of appropriate metrics to evaluate their effects on marine life in relation to noise thresholds. As marine animals move farther away from a sound source, the temporal characteristics of sound pressure may be influenced by interactions with the sediment and the sea surface. Sound pressure kurtosis and root-mean-square (rms) sound pressure are quantitative characteristics that depend on the shape of a sound pulse, with kurtosis related to the qualitative characteristic “impulsiveness.” After verifying the propagation modeling approach using selected test cases from the JAM Workshop held in Cambridge, UK, in 2022, the time dispersion values of pressure signals produced by an individual airgun shot across various sediment types are analyzed. The results reveal that there is significant pulse dispersion when the seabed consists of predominantly sand-type sediments: i.e., the airgun signal duration increases considerably over long distances, thus decreasing the kurtosis of a sequence of pulses, whereas the pulse dispersion is more limited for clay and silt-type sediments. The range variations of frequency weighted kurtosis and rms sound pressure differ from those of the unweighted kurtosis, depending on the corresponding lower and upper roll-off frequencies corresponding to different marine animal groups.

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Comparisons are made of sound pressure and particle acceleration predicted by two methods in the vicinity of two arrays of marine-seismic airguns. Data describing the array properties and the environmental conditions are taken from test cases designed to facilitate intermodel comparison. The two propagation approaches, one based on method of images and the other on wave number integration, are shown to be capable of giving line-on-line agreement when the latter method implements the full form of the Hankel transform; when the more approximate Fourier transform is used, predictions are shown to differ at ranges of a few meters from the source.@en

Computer models can be used to predict the sound field near an airgun or airgun array. The accuracy of such predictions can be assessed either by a process of verification (comparison with alternative theoretical solution to the same computational problem) or by validation (comparison with measurement). A set of verification test problems is described, as used originally by participants in the International Airgun Modeling Workshop held in Dublin, Ireland on July 16, 2016, and now by other authors in this special issue. The main inputs specified are the characteristics of the source (array geometry, airgun type and volume, and chamber pressure) and of the propagation medium (mainly water depth and bottom type). Also specified are source waveforms for individual airguns for authors wishing to focus only on the propagation aspects of the problem. The outputs are specified in terms of metrics derived from the sound pressure and sound particle acceleration.@en

The production of underwater sound is more and more considered to be an environmental risk. This has already been the case for military sonar for more than a decade, as sonar was identified as a possible cause of marine mammal strandings. The approach we adapted for military sonar is the following. The risk is characterized by computing the exposure (sound produced by the sonar) in an area around the source and by coupling that information to the effects it causes on a certain animal species. The risk is then quantified by taking into account the probability of the presence of that species in the area. If too large, the risk can be mitigated. We observe a trend of shifting the focus from individual disturbance to more general population consequences. A similar approach is advised to characterize the risks involved in the use of airguns in seismic acquisition.

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