On definitions of signal duration, evaluated on close-rangeairgun signals (PDF)

Muller J. A., R, M. A. Ainslie, and M. B. Halvorsen

DOI: 10.1121/10.0019747

Journal of the Acoustical Society of America 153, 3513–3521 (2023)

In impact assessments for underwater noise, the duration of a transient signal is often expressed by the 90%-energy signal duration s90%. Consequently, the rms sound pressure is computed over this duration. Using a large set of measurements on marine-seismic airgun signals, it is shown that s90% is often very close to the interval between the primary and secondary pulse (the bubble period) or a small integer multiple thereof. In this situation s90% is a measure of the duration of the relative silence between primary and secondary peaks, which is not the intended measure. Rarely, s90% quantifies the duration of the main peak, leading to a much lower value of s90%. Since the number of peaks included in s90% is sensitive to the nature of the signal, relatively small differences in the signal lead to large differences in s90%, causing instability in any metric based on s90%, e.g., the rms sound pressure. Alternative metrics are proposed that do not exhibit these weaknesses. The consequences for the interpretation of sound pressure level of a transient signal, and the benefits of using a more stable metric than s90% are demonstrated. VC 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.