Underwater Blast Noise Measurements in Very Shallow Water
Jorge E. Quijano
IEEE Journal of Oceanic Engineering
This article presents measurements and a model-based analysis of the acoustic noise generated by underwater charges (of weights 0.78–13.28 kg TNT equivalent) detonated in very shallow water (≤4-m depth) within a bay with a limited line-of-sight acoustic path toward open and deeper waters. Four bottom-mounted and one mid-water acoustic recorders at ranges 70–1000 m (water depths 4–60 m) were used to measure blast signatures of 48 detonations. Measurements at close range allowed for characterization of the frequency-dependent performance of a bubble curtain mitigation system, and verification of the agreement between the measured data and a theoretical model of an underwater explosion. Measurements at longer ranges provided empirical curves of the peak (PK) level and sound exposure level (SEL) as a function of range, which are more representative for acoustically enclosed locations than current models for confined detonations found in the literature. The measurements indicate strong attenuation outside the bay of the high-frequency oscillations characteristic of the blast shockwave, likely due to the effect of bathymetry features. Modeling of blast noise using the parabolic equation method successfully represented the PK and SEL characteristics of the blasts, but also highlighted the need to refine the seabed geoacoustic model and the bathymetry of the area.