–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Of all the ways to sense objects in the ocean, sound reaches the furthest. Light seldom travels more than hundreds of meters in the ocean, but sound can travel thousands of kilometers. For example, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) created a network of just 6 hydrophones (underwater microphones) that can detect a nuclear explosion anywhere in the global oceans (Figure 1).
Figure 1. Map of 6 underwater acoustic sensing stations of the Comprehensive Test-Ban Treaty Organization.
Reproduced with permission from Ainslie, Michael A., et al. “Ocean soundscapes and trends from 2003 to 2021: 10–100 Hz.” The Journal of the Acoustical Society of America 157.6 (2025):4358-4384, Figure 1.
Sound can travel so far that listening has long been selected for detecting threats such as submarines, but the ocean carries acoustic signals of wind, waves, rain and sea ice that are important for monitoring climate change, and the sounds of animals vocalizing underwater tell us about their distribution and about the health of marine ecosystems.
Using sound to understand changes in the ocean requires many years of data to sort out changes on daily, seasonal, and longer-term time scales. The CTBTO hydrophone array is one of few sources of such long time series of ocean sound.
Figure 2. Measured and modeled Sound Pressure Level in the 10-40 Hz band from Wake Island in the Pacific Ocean. Reproduced with permission from Robinson, Stephen, et al. “Impact of the COVID-19 pandemic on levels of deep-ocean acoustic noise.” Scientific Reports13.1 (2023): 4631, Figure 2. Creative Commons Attribution 4.0 International License
Figure 2 shows 12 years of low frequency acoustic data from the Pacific. The strongest pattern in sound level is annual variation, but you can also see a longer-term pattern of increasing variation from 2010 to 2020.
Figure 3. Expanded view of sound level data from figure 2, here from 2018-2020. Reproduced with permission from Robinson, Stephen, et al. “Impact of the COVID-19 pandemic on levels of deep-ocean acoustic noise.” Scientific Reports13.1 (2023): 4631, Figure 4. Creative Commons Attribution 4.0 International License
Analyzing data from before COVID hit in 2020, shown with blue dots in figure 3, makes it possible to estimate what sound levels were expected in 2020 based on earlier years. The data points change color from blue to red once COVID started to affect seagoing activities. You can see that many of the red dots from January to July 2020 are lower than the gray area predicted from pre-COVID data, demonstrating that the reduction in human activities during COVID reduced sound levels around Wake Island.
Excessive sound can also harm wildlife by damaging hearing and by causing stress or disturbance. Recordings from the west coast of the US have shown that increased shipping caused underwater sound energy to more than double each decade from the 1960s to the 1990s. This increase in human-generated ocean noise stimulated concerns about increasing effects of noise on marine life. In June 2025, a coalition of 37 countries declared “ocean noise is intensifying, driven by the ongoing expansion of global shipping activities and development of ocean industries” and formed a high ambition coalition for a quiet ocean (https://www.foraquietocean.org).
Figure 4. Trends in annual mean sound pressure level (SPL) from 2006-2021 at Ascension Island at 5 frequency bands: VLF=9-14 Hz; LF=14-28 Hz, MF=28-56 Hz; HF=56-112 Hz; ADEON B = 9-89 Hz. Reproduced with permission from Ainslie, Michael A., et al. “Ocean soundscapes and trends from 2003 to 2021: 10–100 Hz.” The Journal of the Acoustical Society of America 157.6 (2025):4358-4384, Figure 18.
Analysis of CTBTO data from sites around the world document changes in ocean sound after 2000. This century has not seen significant increases in sound pressure level at any of the CTBTO sites. Figure 4 shows the long term decline in sound level in 4 frequency bands from 2006-2021 at Ascension Island in the Atlantic Ocean. A close look at the acoustic record (Figure 5A) shows that airguns used to prospect for offshore oil and gas along the African and South American coasts were a primary source. Figure 5B shows that the best predictor of sound pressure level there in the MF band is the price of Brent Crude Oil. When the price of oil is low, there are fewer surveys. The major sources of sound energy varied between sites and included natural sounds of earthquakes and whales and sounds of human activities such as shipping.
Figure 5. 5A shows a waveform on the top and spectrogram (plot of frequency against time) of a series of pulses from an airgun source recorded from the CTBTO station at Ascension Island. Figure 5B shows how the sound level recorded there correlates with the price of oil. Reproduced with permission from Ainslie, Michael A., et al. “Ocean soundscapes and trends from 2003 to 2021: 10–100 Hz.” The Journal of the Acoustical Society of America 157.6 (2025):4358-4384, 5A: Figure 16; 5B Figure 20.
Access to long time series of ocean sound data is critical for understanding how changes in sound sources cause trends in ocean sound. This information is not only critical for estimating indicators of climate change and ocean health, but also for managing the effects of sound. Noise from human activities may not have been increasing ocean sound levels globally in this century, but sound produced by more localized activities and the harm it causes to wildlife needs to be measured and managed.
Over the last 50 years, the integration of global weather data with improved computer models has drastically improved our ability to forecast weather. The applications of ocean sound to measure threats, climate change and ecosystem health are so important that we need similar expansion and improvement of our global ocean sound observation networks so that we can forecast and manage these important applications.
New Orleans, May 19, 2025 – More than 400 underwater sites in the United States are potentially contaminated with unexploded ordnance (UXO) — weapons that did not explode upon deployment, which continue to pose a safety concern.
Connor Hodges, a doctoral student at the University of Texas at Austin, studies the changes in the acoustic characteristics of these UXOs after they have been subject to corrosion and biofouling to help detect them underwater.
“Many of these sites are in shallow water, potentially posing a threat to human safety, and date back several decades,” said Hodges. “This long exposure to the environment leads to corrosion as well as encrustation in the form of barnacles or algal growth.”
Corrosion and growth make UXOs difficult to observe with standard sonar imaging techniques, as the objects begin to lose resemblance to their original appearance and blend into their environment over time. These changes also alter how acoustic signals scatter from the objects, and the changes can become more severe over time as corrosion or organic growth gets worse.
Clockwise from bottom left: photo of corroded bomblet, X-ray CT scan of the same bomblet, acoustic fingerprint of the bomblet with corrosion signature cross section of the bomblet (inset). Credit: Kevin Lee, Connor Hodges, and Preston Wilson
Hodges will discuss the use of acoustics for corroded UXO recovery on Monday, May 19, at 8:00 a.m. CT as part of the joint 188th Meeting of the Acoustical Society of America and 25th International Congress on Acoustics, running May 18-23.
Hodges and his collaborators tested a collection of AN-Mk 23 practice bombs — miniature bombs used for dive-bombing practice — in various stages of corrosion, which had been buried in a brackish pond on Martha’s Vineyard for about 80 years. They compared the acoustics of these samples to those of pristine AN-Mk 23, monitoring the scattering response at different directions and angles.
The researchers found the change in size, shape, and material makeup of a bomb as it corrodes changes its acoustic resonance and leads to a different, weaker scattered acoustic signal than pristine bombs. The changed acoustic signature could result in the object being misclassified or undetected.
“Acoustic scattering techniques give an insight into the internal structure of the object imaged, as well as a method to ‘see’ into the seafloor,” said Hodges, noting that using sonar to map the seafloor and detect munitions is also faster and cheaper than other techniques.
Many former military sites used for practice bombs are shifting toward public use, making UXO identification a timely endeavor.
“There is a risk of detonation if they are stepped on or otherwise disturbed,” Hodges said. “This poses a larger risk to human safety in shallow waters, and UXO identification and recovery becomes vital as old sites are transitioned away from military use.”
He hopes the work can help provide better predictive tools for finding UXOs in civilian environmental demining efforts and plans to study other types of munitions as well as other types of corrosion and biofouling phenomena.
“Underwater UXO can be tricky to find and recover, so it is important that this can be done safely and effectively,” said Hodges. “We hope this work will ultimately help save lives.”
ASA PRESS ROOM In the coming weeks, ASA’s Press Room will be updated with newsworthy stories and the press conference schedule at https://acoustics.org/asa-press-room/.
LAY LANGUAGE PAPERS ASA will also share dozens of lay language papers about topics covered at the conference. Lay language papers are summaries (300-500 words) of presentations written by scientists for a general audience. They will be accompanied by photos, audio, and video. Learn more at https://acoustics.org/lay-language-papers/.
PRESS REGISTRATION ASA will grant free registration to credentialed and professional freelance journalists. If you are a reporter and would like to attend the meeting and/or press conferences, contact AIP Media Services at media@aip.org. For urgent requests, AIP staff can also help with setting up interviews and obtaining images, sound clips, or background information.
ABOUT THE ACOUSTICAL SOCIETY OF AMERICA The Acoustical Society of America is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.
ABOUT THE INTERNATIONAL COMMISSION FOR ACOUSTICS The purpose of the International Commission for Acoustics (ICA) is to promote international development and collaboration in all fields of acoustics including research, development, education, and standardization. ICA’s mission is to be the reference point for the acoustic community, becoming more inclusive and proactive in our global outreach, increasing coordination and support for the growing international interest and activity in acoustics. Learn more at https://www.icacommission.org/.
Monterey Bay Aquarium Research Institute, Moss Landing, CA, 95039, United States
Popular version of 4aUW7 – Wind-driven movement ecology of blue whales detected by acoustic vector sensing
Presented at the 188th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0038108
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
A technology that captures multiple dimensions of underwater sound is revealing how blue whales live, thereby informing whale conservation.
The most massive animal ever to evolve on Earth, the blue whale, needs a lot of food. Finding that food in a vast foraging habitat is challenging, and these giants must travel far and wide in search of it. The searching that leads them to life-sustaining nutrition can also lead them to a life-ending collision with a massive fast-moving ship. To support the recovery of this endangered species, we must understand where and how the whales live, and how human activities intersect with whale lives.
Toward better understanding and protecting blue whales in the California Current ecosystem, an interdisciplinary team of scientists is applying a technology called an acoustic vector sensor. Sitting just above the seafloor, this technology receives the powerful sounds produced by blue whales and quantifies changes in both pressure and particle motion that are caused by the sound waves. The pressure signal reveals the type of sound produced. The particle motion signal points to where the sound originated, thereby providing spatial information on the whales.
A blue whale in the California Current ecosystem. Image Credit: Goldbogen Lab of Stanford University / Duke Marine Robotics and Remote Sensing Lab; NMFS Permit 16111.
For blue whales, it is all about the thrill of the krill. Krill are small-bodied crustaceans that can form massive swarms. Blue whales only eat krill, and they locate swarms to consume krill by the millions (would that be krillions?). Krill form dense swarms in association with cold plumes of water that result from a wind-driven circulation called upwelling. Sensors riding on the backs of blue whales reveal that the whales can track cold plumes precisely and persistently when they are foraging.
The close relationships between upwelling and blue whale movements motivates the hypothesis that the whales move farther offshore when upwelling habitat expands farther offshore, as occurs during years with stronger wind-driven upwelling. We tested this hypothesis by tracking upwelling conditions and blue whale locations over a three-year period. As upwelling doubled over the study period, the percentage of blue whale calls originating from offshore habitat also nearly doubled. A shift in habitat occupancy offshore, where the shipping lanes exist, also brings higher risk of fatal collisions with ships.
However, there is good news for blue whales and other whale species in this region. Reducing ship speeds can greatly reduce the risk of ship-whale collisions. An innovative partnership, Protecting Blue Whales and Blue Skies, has been fostering voluntary speed reductions for large vessels over the last decade. This program has expanded to cover a great stretch of the California coast, and the growing participation of shipping companies is a powerful and welcome contribution to whale conservation.
Seoul National University, Gwanak-ro, Gwanak-gu, Seoul, Republic of Korea, Seoul, Seoul, 08826, South Korea
WOOJAE SEONG
Professor of Seoul National University
http://uwal.snu.ac.kr
Popular version of 2aEA9 – A study of the application of global optimization for the arrangement of absorbing materials in multi-layered absorptive fluid silencer
Presented at the 187th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0035138
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Underwater Radiated Noise (URN) generated by naval vessels is critically important as it directly impacts survivability. Underwater Radiated Noise (URN) refers to the sound emitted by objects, like ships or submarines, into the water. This noise is generated by various sources, including the vessel’s machinery, propellers, and movement through water. It can be detected underwater, affecting their ability to remain undetected. So various studies have been conducted to reduce URN for submarines to maintain stealth and silence.
This study focuses on the ‘absorptive fluid silencer’ installed in piping to reduce noise from the complex machinery system. An absorptive fluid silencer is similar to a car muffler, reducing noise by placing sound-absorbing materials inside.
We measured how well the silencer reduced noise by comparing sound levels at the beginning and end of the silencer. Polyurethane, a porous elastic material, was used as the internal sound-absorbing material, and five types of absorbent materials suitable for actual manufacturing were selected. By applying a ‘global optimization method,’ we designed a high-performance ‘fluid silencer.’.
The above graph shows a partial analysis result, It can be observed that using composite absorbing materials provides superior sound absorption performance compared to using a single absorbing material.
Florent Le Courtois – florent.lecourtois@gmail.com
DGA Tn, Toulon, Var, 83000, France
Samuel Pinson, École Navale, Rue du Poulmic, 29160 Lanvéoc, France
Victor Quilfen, Shom, 13 Rue de Châtellier, 29200 Brest, France
Gaultier Real, CMRE, Viale S. Bartolomeo, 400, 19126 La Spezia, Italy
Dominique Fattaccioli, DGA Tn, Avenue de la Tour Royale, 83000 Toulon, France
Popular version of 4aUW7 – The Acoustic Laboratory for Marine Applications (ALMA) applied to fluctuating environment analysis
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0027503
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Ocean dynamics happen at various spatial and temporal scales. They cause the displacement and the mixing of water bodies of different temperatures. Acoustic propagation is strongly impacted by these fluctuations as sound speed depends mainly on the underwater temperature. Monitoring underwater acoustic propagation and its fluctuations remains a scientific challenge, especially at mid-frequency (typically the order of 1 to 10 kHz). Dedicated measurement campaigns have to be conducted to increase the understanding of the fluctuations, their impacts on the acoustic propagation and thus to develop appropriate localization processing.
The Acoustic Laboratory for Marine Application (ALMA) has been proposed by the French MOD Procurement Agency (DGA) to conduct research for passive and active sonar since 2014, in support of future sonar array design and processing. Since its inception in 2014, ALMA has undergone remarkable transformations, evolving from a modest array of hydrophones to a sophisticated system equipped with 192 hydrophones and advanced technology. With each upgrade, ALMA’s capabilities have expanded, allowing us to delve deeper into the secrets of the sea.
Figure 1. Evolution of the ALMA array configuration, from 2014 to 2020. Real and Fattacioli, 2018
Bulletin of sea temperature to understand the acoustic propagation
The campaign of 2016 took place Nov 7 – 17, 2016, off the Western Coast of Corsica in the Mediterranean Sea, located by the blue dot in Fig.2 (around 42.4 °N and 9.5 °E). We analyzed signals from a controlled acoustic source and temperature recording, corresponding approximately to 14 hours of data.
Figure 2. Map of surface temperature during the campaign. Heavy rains of previous days caused a vortex in the north of Corsica. Pinson et. al, 2022
The map of sea temperature during the campaign was computed. It is similar to a weather bulletin for the sea. From previous days, heavy rains caused a global cooling over the areas. A vortex appeared in the Ligurian Sea between Italy and the North of Corsica. Then the cold waters traveled Southward along Corsica Western coast to reach the measurement area. The water cooling was measured as well on the thermometers. The main objective was to understand the changes in the echo pattern in relation to the temperature change. Echos can characterize the acoustic paths. We are mainly interested in the amplitude, the time of travel and the angle of arrival of echoes to describe the acoustic path between the source and ALMA array.
All echoes extracted by processing ALMA data are plotted as dots in 3D. They depend on the time of the campaign, the angle of arrival and the time of flight. The loudness of the echo is indicated by the colorscale. The 3D image is sliced in Fig. 3 a), b) and c) for better readability. The directions of the last reflection are estimated in Fig. 3 a): positive angles come from the surface reflection while negative angles come from seabed reflection. The global cooling of the waters caused a slowly increasing fluctuation of the time of flight between the source and the array in Fig. 3 b). A surprising result was a group of spooky arrivals, who appeared briefly during the campaign at an angle close to 0 ° during 3 and 12 AM in Fig. 3 b) and c).
All the echoes detected by processing the acoustic data. Pinson et. al, 2022
Figure 3. Evolution of the acoustic paths during the campaign. Each path is a dot defined by the time of flight and the angle of arrival during the period of the campaign. Pinson et. al, 2022
The acoustic paths were computed using the bulletin of sea temperature. A more focused map of the depth of separation between cold and warm waters, also called mixing layer depths (MLD), is plotted in Fig 4. We noticed that, when the mixing layer depth is below the depth of the source, the cooling causes acoustic paths to be trapped by bathymetry in the lower part of the water column. It explains the apparition of the spooky echoes. Trapped paths are plotted in the blue line while regular paths are plotted in black in Fig. 5.
Figure 4. Evolution of the depth of separation between cold and warm water during the campaign. Pinson et. al, 2022
Figure 5. Example of acoustic paths in the area: black lines indicate regular propagation of the sound; blue lines indicate the trapped paths of the spooky echoes. Pinson et. al, 2022
Overview
The ALMA system and the associated tools allowed illustrating practical ocean acoustics phenomena. ALMA has been deployed during 5 campaigns, representing 50 days at sea, mostly in the Western Mediterranean Sea, but also in the Atlantic to tackle other complex physical problems.
Popular version of 2pAB8 – Moving Cargo, Keeping Whales: Investigating Solutions for Ocean Noise Pollution
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0027065
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Figure 1. Image Courtesy of ZoBell, Vanessa M., John A. Hildebrand, and Kaitlin E. Frasier. “Comparing pre-industrial and modern ocean noise levels in the Santa Barbara Channel.” Marine Pollution Bulletin 202 (2024): 116379.
Southern California waters are lit up with noise pollution (Figure 1). The Port of Los Angeles and the Port of Long Beach are the first and second busiest shipping ports in the western hemisphere, supporting transits from large container ships that radiated noise throughout the region. Underwater noise generated by these vessels dominate ocean soundscapes, negatively affecting marine organisms, like mammals, fish, and invertebrates, who rely on sound for daily life functions. In this project, we modeled what the ocean would sound like without human activity and compared it with what it sounds like in modern day. We found in this region, which encompasses the Channel Islands National Marine Sanctuary and feeding grounds of the endangered northeastern Pacific blue whale, modern ocean noise levels were up to 15 dB higher than pre-industrial levels. This would be like having a picnic in a meadow versus having a picnic on an airport tarmac.
Reducing ship noise in critical habitats has become an international priority for protecting marine organisms. A variety of noise reduction techniques have been discussed, with some already operationalized. To understand the effectiveness of these techniques, broad stakeholder engagement, robust funding, and advanced signal processing is required. We modeled a variety of noise reduction simulations and identified effective strategies to quiet whale habitats in the Santa Barbara Channel region. Simulating conservation scenarios will allow more techniques to be explored without having to be implemented, saving time, money, and resources in the pursuit of protecting the ocean.
Figure 1. Map of 6 underwater acoustic sensing stations of the Comprehensive Test-Ban Treaty Organization.
Figure 1. Map of 6 underwater acoustic sensing stations of the Comprehensive Test-Ban Treaty Organization.
Figure 4. Trends in annual mean sound pressure level (SPL) from 2006-2021 at Ascension Island at 5 frequency bands: VLF=9-14 Hz; LF=14-28 Hz, MF=28-56 Hz; HF=56-112 Hz; ADEON B = 9-89 Hz. Reproduced with permission from Ainslie, Michael A., et al. “Ocean soundscapes and trends from 2003 to 2021: 10–100 Hz.” The Journal of the Acoustical Society of America 157.6 (2025):4358-4384, Figure 18.
Figure 4. Trends in annual mean sound pressure level (SPL) from 2006-2021 at Ascension Island at 5 frequency bands: VLF=9-14 Hz; LF=14-28 Hz, MF=28-56 Hz; HF=56-112 Hz; ADEON B = 9-89 Hz. Reproduced with permission from Ainslie, Michael A., et al. “Ocean soundscapes and trends from 2003 to 2021: 10–100 Hz.” The Journal of the Acoustical Society of America 157.6 (2025):4358-4384, Figure 18.
A blue whale in the California Current ecosystem. Image Credit: Goldbogen Lab of Stanford University / Duke Marine Robotics and Remote Sensing Lab; NMFS Permit 16111.
