Abstract
Impact pile driving generates intense and impulsive underwater noise, which can have significant effects on marine life. As sound waves propagate away from the pile–water and pile–soil interfaces, their pressure characteristics evolve under the influence of seabed and sea surface reflections. Understanding these sound pressure waveform properties is essential for selecting appropriate metrics to assess noise impact on marine species, particularly in relation to established environmental noise thresholds. Commonly used exposure metrics, such as cumulative sound exposure level (SEL) and peak sound pressure level (Lp, pk), provide important information but may not fully capture the complexity of noise impact across different species. Current impact assessments classify sound into only two mutually exclusive categories: impulsive and nonimpulsive. However, in reality, pulse length can vary with range and strike repetition rate. Given the impulsive nature of impact pile driving noise, this study investigates sound pressure kurtosis as a complementary metric to quantify the impulsiveness of noise signals across various sediment types. Furthermore, the study models the application of a noise mitigation system, specifically an air-bubble curtain, to evaluate its effect on noise emission and subsequent changes in kurtosis. The findings provide insights into the variability of sound pressure kurtosis in both mitigated and unmitigated cases, offering a comprehensive understanding of the acoustic characteristics of impact pile driving noise and its potential effects on marine ecosystems.