John Ragland

John Ragland

PhD student in Electrical Engineering at the University of Washington

Talks and presentations

Overview of ambient noise research and outreach with OOI hydrophones

December 01, 2022

Poster, American Geophysical Union, Chicago, IL

The ocean observatories initiative has eleven hydrophones that constantly record ambient sound throughout the north-east Pacific Ocean. Nine of the hydrophones are mounted on the seafloor and two of the hydrophones are suspended in the sound fixing and ranging channel. Six of the hydrophones record broadband ambient sound with a sampling rate of 64 kHz. Five of the hydrophones record low frequency ambient sound with a sampling rate of 200 Hz. In this talk, an overview of research and outreach conducted by the Ocean Data Lab at the University of Washington that utilizes this acoustic data will be presented. Some of the research topics that will be presented include trends in ambient sound and using ambient noise interferometry to estimate the Green's function between two hydrophones. For the trends in ambient sound, data from 9 of the hydrophones over six years is visualized, analyzed, and compared to previous results. Data recorded by two low-frequency hydrophones has successfully been used to estimate the Green's function between the two hydrophones by measuring the coherence of the ambient sound. Additionally, data of opportunity has been used to experimentally explore the emergence of the Green's function for bottom mounted hydrophones in the north-east pacific. Lastly, an online, interactive data explorer for the low frequency hydrophones will be presented. This data explorer provides the opportunity for the public to view and explore the low frequency acoustic data measured and provided by the Ocean Observatories Initiative. [work supported by ONR]

Overview of ocean ambient noise interferometry - theory and simulation

December 01, 2022

Talk, Acoustical Society of America, Nashville, TN

[Won 2nd best student paper award] Ambient noise interferometry is a passive acoustic technique for environment characterization. The technique uses coherent ambient sound to approximate the Green's function between two sensors. It has previously been used in ocean acoustics to passively estimate water temperature, sound-speed structure, and mode shapes as well as for sensor localization. Since this technique utilizes the ambient noise field, whose characteristics are often unknown, understanding the effects of non-isotropic ambient sound is important for ambient noise interferometry. In this talk an overview of the theoretical literature for noise interferometry will be presented with a specific emphasis on the effects of non-isotropic ocean noise source distributions. Additionally, simulations that explore the emergence of the Green's function will be presented. Specifically, sound source distributions and environmental parameters such as sound speed profile will be explored. Lastly, the implications of these works on the possibilities and limitations of ambient noise interferometry will be discussed. [work supported by ONR]

Using Coherent Ambient Sound to Learn About the Ocean

November 03, 2022

Seminar Talk, Applied Physics Laboratory - UW, Seattle, WA

With deep oceans absorbing most of the additional heat due to human caused climate change, it is important to be able to monitor the deep ocean. Can ambient sound be used as a tool to monitor the deep ocean? Coherent ambient sound can contain a lot of useful information about the environment that the sound is propagating in. If the distribution of sound sources is favorable, you can even estimate the Green's function between two sensors using just ambient coherent sound. The Green's function estimate could then be used to infer oceanographic variables. This technique is called ambient noise interferometry. In this talk, long-term acoustic data from the Ocean Observatories Initiative is used to explore the possibilities of using ambient noise interferometry in the deep ocean for long-term ocean monitoring. Video of presentation

Long-term ambient noise interferometry in the NE Pacific deep ocean

February 01, 2022

Talk, Ocean Sciences Meeting,

Ambient noise interferometry is the method of using ambient sound to measure the time domain Greene's function (TDGF) between two nodes. Ambient noise interferometry is a well-developed technique in seismic imaging applications, allowing for the measurement of surface wave velocities using microseisms. Ambient noise interferometry has also been used in acoustic oceanography to measure oceanographic variables such as water temperature and flow velocity. Along with measuring the TDGF, ambient noise interferometry can also be used to characterize the directionality of coherent sound in the ocean. In this talk, we use six years of ambient sound data recorded by two bottom mounted hydrophones to investigate ambient noise interferometry in the deep ocean. The hydrophones are separated by 3.2 km and are both at a depth of 1500 m. We show that the TDGF between the two hydrophones can be resolved with averaging times around 200 hours. Additionally, the TDGF contains clear, multi-path arrivals. These multi-path arrivals have not been previously observed with ambient noise interferometry in the deep ocean. We also observe a chorus of fin whale vocalizations originating from near Alaska, that is not visible in data recorded by a single hydrophone. Lastly, the viability of using multi-path arrival times in the deep ocean for passive acoustic tomography will be explored. Multi-path arrival times provide a unique opportunity for ocean observation since they contain information about the entire, deep ocean, water column. We will present ocean acoustic simulations to estimate the expected seasonal fluctuations of the multi-path arrival times due to temperature changes and we will evaluate the viability of using the multi-path peaks measured with ambient noise interferometry for passive acoustic tomography. [work supported by ONR]