Empirical Relationships of Particle Motion and Pressure Soundscapes Along the US Eastern Continental Shelf

Jones, I.T., S.B. Martin, and J.L. Miksis-Olds

The Effects of Noise on Aquatic Life IV. Springer Nature Switzerland, Cham. (2026)

DOI: 10.1007/978-3-031-94229-7_71-1

Acoustic particle motion is the primary sensory cue for fish and aquatic invertebrate hearing, yet underwater soundscape studies usually only report sound pressure levels. In the free field, particle motion magnitudes are often approximated by the ratio of sound pressure to acoustic impedance, which only requires single hydrophone pressure measurements. However, this scaling does not always apply near the seafloor, e.g., within ¼ acoustic wavelength, and never in the near field. This study compared measured sound pressure with measured particle motion from hydrophone arrays near the seafloor, at ten offshore sites on the US Eastern Continental Shelf ranging from the Gulf of Maine to Florida. In a 50 Hz decidecade band, >75% of measured particle motion level data exceeded sound pressure-impedance relationship estimates by over 3 dB, but this relationship was closer for 100 and 400 Hz decidecade bands. These relationships were region-specific, with the difference between measured particle motion and impedance relationship estimates being significantly lower (more negative) in the Gulf of Maine compared to southern sites. The results inform the potential error and overlooked variability of particle motion levels when only relying on sound pressure-impedance relationship estimates of particle motion, particularly over short (60 s) time integrations.