Noise of underwater explosions in the North Sea. A comparison of experimental data and model predictions

Abstract

An analysis is presented of sound measurements performed near two detonations of unexploded ordnance (UXO) in the North Sea, at distances ranging from 1.5 to 12 km. The charge masses of the detonations were 325 and 140 kg TNT equivalent. The objective of the measurements was to improve the accuracy of model predictions of the area where UXO detonations affect harbour porpoises in the North Sea. For the predictions, an explosion emission model is combined with a shallow-water propagation model. The prediction model was previously validated for distances up to 2 km. The measurements reported here allowed validation up to a distance of 12 km. The measured levels and spectra are well explained by the model calculations. The model results depend strongly on the sea sediment layering. The propagation of high-frequency components appears to be affected primarily by the silty top layer, while low-frequency components are affected also by deeper sandy layers. Measured and calculated noise levels are used to determine permanent-threshold-shift effect distances for harbour porpoises (Phocoena phocoena). Values ranging from 2 to 6 km are found for the two detonations.

A Case Study-Based Analysis of Uncertainties on the Assessment of Impulsive Underwater Noise for the Marine Strategy Framework Directive

“…This formula was determined empirically by means of explosion experiments performed in shallow water of 15 m water depth, using measurement distances from 165 m to 950 m and TNT equivalent weights from 0.3 to 6.1 kg. This empirical formula was selected for the comparison here since estimated SEL values derived by this formula were reported [21] to be in good agreement with other measurements of explosions in the order of magnitude of the TNT equivalents considered here, also agreeing with well with empirical formulas derived by Cole [22]. The process of an explosion is strongly nonlinear up to a sufficient distance to the source.…”

Dynamics of cavitation bubbles near granular boundaries

“…2020; Hampton-Smith, Bower & Mika 2021; Salomons et al. 2021). The blast-generated bubble exhibits successive cycles of growth and collapse that produce measurable sonic pulses through the water.…”

“…A thorough analysis and understanding of the bubble dynamics near a granular interface is particularly important for underwater explosions when charges are detonated near the sand bed. Such explosions can have a variety of origins, such as military exercises, detonation of unexploded ordnances or blast fishing, and often have severe effects on the surrounding marine fauna (Dahl et al 2020;Hampton-Smith, Bower & Mika 2021;Salomons et al 2021). The blast-generated bubble exhibits successive cycles of growth and collapse that produce measurable sonic pulses through the water.…”

Hindcasting Soundscapes before and during the COVID-19 Pandemic in Selected Areas of the North Sea and the Adriatic Sea

“…SOPRANO considers bathymetric variations and range-dependent sediment properties. The accuracy of SOPRANO was verified against a detailed multi-model comparison based on the propagation loss calculations of various methods (adiabatic mode theory, coupled modes, ray tracing, parabolic equation, and flux theory) [20] and compared with the measurements for shipping [33] and explosions [34]. These benchmark studies showed that the propagation loss (PL) for a variable sediment type and bathymetry is similar in accuracy to the adiabatic mode theory.…”