John Ragland

John Ragland

PhD student in Electrical Engineering at the University of Washington

Publications

Exploring surface source contributions to ocean ambient noise interferometry with airgun shots

Published in Journal of the Acoustical Society of America, 2022

A seismic reflection survey conducted directly over two bottom-mounted hydrophones in the north-east Pacific Ocean is used to explore how surface source locations affect ambient noise interferometry for the two hydrophones. The airgun shots are used as an approximation of an impulsive sound source at a discrete location, which allows us to investigate spatial contributions to the cross correlation between the two hydrophones. Simulated and experimental results are presented. The contributions to the cross correlations are explained by different reflections off the surface or bottom of the ocean, and a discussion about what can and cannot be inferred about the emergence to the Green's function is presented.

Recommended citation: Ragland, J., and Abadi, S. (2022).� "Exploring surface source contributions to ocean ambient noise interferometry with airgun shots" The Journal of the Acoustical Society of America, 152, 3069-3077. doi:10.1121/10.0015231 ../files/airgun.pdf

An overview of ambient sound using Ocean Observatories Initiative hydrophones

Published in Journal of the Acoustical Society of America, 2022

The Ocean Observatories Initiative (OOI) sensor network provides a unique opportunity to study ambient sound in the north-east Pacific Ocean. The OOI sensor network has five low frequency (Fs = 200_Hz) and six broadband (Fs = 64 kHz) hydrophones that have been recording ambient sound since 2015. In this paper, we analyze acoustic data from 2015 to 2020 to identify prominent features that are present in the OOI acoustic dataset. Notable features in the acoustic dataset that are highlighted in this paper include volcanic and seismic activity, rain and wind noise, marine mammal vocalizations, and anthropogenic sound, such as shipping noise. For all low frequency hydrophones and four of the six broadband hydrophones, we will present long-term spectrograms, median time-series trends for different spectral bands, and different statistical metrics about the acoustic environment. We find that 6-yr acoustic trends vary, depending on the location of the hydrophone and the spectral band that is observed. Over the course of six years, increases in spectral levels are seen in some locations and spectral bands, while decreases are seen in other locations and spectral bands. Last, we discuss future areas of research to which the OOI dataset lends itself.

Recommended citation: Ragland, J., Schwock, F., Munson, M., & Abadi, S. (2022). An overview of ambient sound using Ocean Observatories Initiative hydrophones. The Journal of the Acoustical Society of America, 151(3), 2085-2100. https://doi.org/10.1121/10.0009836

Long-term noise interferometry analysis in the northeast Pacific Ocean

Published in Journal of the Acoustical Society of America, 2022

Long-term noise interferometry analysis is conducted over six_years of data using two hydrophones on the Ocean Observatories Initiative Cabled Array. The two hydrophones are separated by 3.2_km and are bottom-mounted at 1500_m. We demonstrate the ability of ambient noise interferometry to reliably detect multi-path arrivals in the deep ocean from bottom-mounted hydrophones. An analysis of the multi-path arrival peak emergence is presented, as well as long-term trends of the signal-to-noise ratio of the arrival peaks. Last, we show that long-term ambient noise interferometry provides the opportunity for monitoring directional, coherent ambient sound such as the fin whale chorus.

Recommended citation: Ragland, J., Abadi, S., and Sabra, K. (2022). Long-term noise interferometry analysis in the northeast Pacific Ocean, The Journal of the Acoustical Society of America, 151, 194-204. doi:10.1121/10.0009232