Unlocking the Secrets of Ocean Dynamics: Insights from ALMA

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

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.

Moving Cargo, Keeping Whales: Investigating Solutions for Ship Noise Pollution

Vanessa ZoBell – vmzobell@ucsd.edu
Instagram: @vanessa__zobell

Scripps Institution of Oceanography, La Jolla, California, 92037, United States

John A. Hildebrand, Kaitlin E. Frasier
UCSD – Scripps Institution of Oceanography

Twitter & Instagram: @scripps_mbarc
Twitter & Instagram: @scripps_ocean

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.

The expected sonic transformation of the Arctic Ocean under Climate Change

Giacomo Giorli – Giacomo.Giorli@cmre.nato.int

NATO STO CMRE, Viale S. Bartolomeo, 400, La, Spezia, 19126, Italy

Aniello Russo
La Spezia, Italy

Sandro Carniel
La Spezia, Italy

Popular version of 2pAO2 – Noise levels in a changing Arctic Ocean and its implications for security
Presented at the 185th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0023028

Please keep in mind that the research described in this Lay Language Paper may not have yet been peer reviewed.

Global warming is rapidly driving a substantial transformation of the oceanographic characteristic of the Arctic Ocean and its cryosphere. The Arctic region is in fact warming up much faster than the rest of the planet, and recent studies and reports have highlighted its major consequences. In much of the ice-free Arctic Ocean, the mean sea surface temperature continued its warming trend observed since 1982 and ice sheets in Greenland receded for the 25th consecutive year. According to NASA reports, this year the annual sea-ice minimum extent was the sixth lowest on record. Such an observation implies a significant sea ice retreat and reduction of ice longevity, which will most likely turn the future Arctic in a giant Marginal Ice Zone. Storm and rain patterns are also changing, having Arctic precipitations significantly increased since the 1950s across all seasons. Moreover, increased heat fluxes injected by  warmer Atlantic waters  are preventing the formation of new ice, as well as reducing the thickness and longevity of multi-year ice. The resulting atmosphere- ocean interactions under these new forcing create more turbulent mixing (heat) between the deep Atlantic waters and the upper Arctic Ocean, hence a positive feedback mechanism usually referred to as “Atlantification”, that is, a climatic shift driving the Arctic Ocean towards new and different oceanographic characteristics. Moreover, an ice-free Arctic will open up new possibilities for deep-sea resources extraction, new commercial and military routes and activities. All these environmental modifications are already affecting the Arctic Ocean underwater soundscape. An example is provided by the underwater noise at low frequencies, expected to increase due to the openings of new routes for maritime shipping resulting from nearly ice-free seas (Figure 1). In addition, the more frequent storms and intense precipitation would affect the sea state generating bubbles and spray associated with breaking waves, hence increasing the underwater noise. Additional contributions are due to changes affecting marine life, marine food industries and coastal economies.

Figure 1: Main maritime routes across the Arctic Ocean with minimum sea ice extension. Source: US Navy Arctic Roadmap 2014-2030.

In the lights of this ongoing transformation of the Arctic, CMRE conducted a series of studies and sea-trials (funded by the NATO Allied Command Transformation) of the new Arctic oceanographic conditions and ambient noise. In 2021 and 2022, a series of moorings equipped with passive acoustic recorders and oceanographic sensors were deployed in the region of Fram Strait. In 2023, with the additional support of the NATO Office of the Chief Scientist, CMRE started a long-term scientific endeavor to address how climate change might affect the Alliance’s security in the maritime domain. In June-July 2023, CMRE deployed three deep moorings for monitoring the acoustic-oceanographic conditions in the long term.

Results contribute to create a long-term database of acoustic measurements and to understanding how sounds from different sources (biological, man-made and natural) will change in the next decade.

The loss of an F35 fighter aircraft and the search for Malaysian Airlines flight MH370

Alec Duncan – a.j.duncan@curtin.edu.au

Centre for Marine Science and Technology, Curtin University, Bentley, WA, 6102, Australia

David Dall’Osto
Applied Physics Laboratory
University of Washington
Seattle, Washington
United States

Popular version of 1pAO2 – Long-range underwater acoustic detection of aircraft surface impacts – the influence of acoustic propagation conditions and impact parameters
Presented at the 185th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0022761

Please keep in mind that the research described in this Lay Language Paper may not have yet been peer reviewed.

In the right circumstances, sound can travel thousands of kilometres through water, so when Malaysian Airlines flight MH370 went missing in the Indian Ocean in 2014 we searched recordings from underwater microphones called hydrophones for any signal that could be connected to that tragic event. One signal of interest was found, but when we looked at it more carefully it seemed unlikely to be related to the loss of the aircraft.

Fast-forward five years and in 2019 the fatal crash of an F35 fighter aircraft in the Sea of Japan was detected by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) using hydrophones near Wake Island, in the north-western Pacific, some 3000 km from the crash site1.

Fig. 1. Locations of the F35 crash and the CTBTO HA11N hydroacoustic station near Wake Island that detected it.

With the whereabouts of MH370 still unknown, we decided to compare the circumstances of the F35 crash with those of the loss of MH370 to see whether we should change our original conclusions about the signal of interest.

Fig. 2. Location of the CTBTO HA01 hydroacoustic station off the southwest corner of Australia. The two light blue lines are the measured bearing of the signal of interest with an uncertainty of +/- 0.75 degrees.

We found that long range hydrophone detection of the crash of MH370 is much less likely than that of the F35, so our conclusions still stand, however there is some fascinating science behind the differences.

Fig. 3. Top: comparison of modelled received signal strengths versus distance from the hydrophones for the MH370 and F35 cases. Bottom: water depth and deep sound channel (DSC) axis depth along each path.

Aircraft impacts generate lots of underwater sound, but most of this travels steeply downward then bounces up and down between the seafloor and sea surface, losing energy each time, and dying out before it has a chance to get very far sideways. For long range detection to be possible the sound must be trapped in the deep sound channel (DSC), a depth region where the water properties stop the sound hitting the seabed or sea surface. There are two ways to get the sound from a surface impact into the DSC. The first is by reflections from a downward sloping seabed, and the second is if the impact occurs somewhere the deep sound channel comes close to the sea surface. Both these mechanisms occurred for the F35 case, leading to very favourable conditions for coupling the sound into the deep sound channel.

Fig. 4. Sound speed and water depth along the track from CTBTO’s HA11N hydroacoustic station (magenta circle) to the estimated F35 crash location (magenta triangle). The broken white line is the deep sound channel axis.

We don’t know where MH370 crashed, but the signal of interest came from somewhere along a bearing that extended northwest into the Indian Ocean from the southwest corner of Australia, which rules out the second mechanism, and there are very few locations along this bearing where the first mechanism would come into play.

Fig. 5. Sound speed and water depth in the direction of interest from CTBTO’s HA01 hydroacoustic station off Cape Leeuwin, Western Australia (magenta circle). The broken white line is the deep sound channel axis.

This analysis doesn’t completely rule out the signal of interest being related to MH370, but it still seems less likely than it being due to low-level seismic activity, something that results in signals at HA01 from similar directions about once per day.

[1] Metz D, Obana K, Fukao Y, “Remote Hydroacoustic Detection of an Airplane Crash”, Pure and Applied Geophysics,  180 (2023), 1343-1351. https://doi.org/10.1007/s00024-022-03117-6

Acoustical Society of America Announces Winners of Science Communication Awards

Acoustical Society of America Announces Winners of Science Communication Awards

Acoustical Society of America (ASA) LogoMelville, June 28, 2023 – The Acoustical Society of America (ASA) is pleased to announce the winners of the Science Communication Awards, recognizing excellence in the presentation of acoustics related topics to a popular audience.

Each non-ASA member award includes a $2,500 cash prize and a $1,000 reimbursement to attend the awards ceremony at the 186th ASA Meeting taking place in Ottawa, Canada, 13-17 May 2024. Each ASA member award includes a $1,000 cash prize. The winners of the 2023 ASA Science Communication Awards are as follows:

Non-acoustic Expert Multimedia Winner
In the SciShow episode, “5 Places with Amazing Acoustics from Thousands of Years Ago,” show host Hank Green captivates the audience with insightful exploration of acoustics in historical settings. Viewers are transported to ancient venues renowned for their exceptional soundscapes and learn about what acoustic phenomena are taking place. Through engaging storytelling and accessible explanations, this SciShow episode brings the wonders of acoustics to life, inspiring viewers to appreciate the acoustic marvels of the past.

Honorable mentions in this category go to Bartosz Ciechenowski’s interactive science blog, Sound and the Short Wave podcast episode, Experience The Quietest Place On Earth, hosted by Margaret Cirino, Regina G. Barber, and Gabriel Spitzer.

Acoustic Expert Multimedia Winner
The Rest is Just Noise Podcast stands out as a remarkable audio journey into the realm of acoustics. With deep knowledge and captivating storytelling, co-hosts Dr. Andrew Mitchell, Dr. Francesco Aletta, and Dr. Tin Oberman explore various acoustical phenomena and their impact on our lives. Through interviews with experts and immersive soundscapes, this podcast educates and entertains listeners, creating a space where the beauty and significance of acoustics are celebrated.

Honorable mentions go to the Listen Lab video, What should Ant-Man’s voice sound like when he changes size?, created by Matthew Winn and the documentary, Fathom, directed by Drew Xanthopoulos and featuring Ellen Garland and Michelle Fournet.

Long Form Print Winner
David George Haskell’s Sounds Wild and Broken: Sonic Marvels, Evolution’s Creativity, and The Crisis of Sensory Extinction emerges as a thought-provoking exploration of the intricate relationship between sound, nature, and human existence. Haskell masterfully weaves together scientific research, personal anecdotes, and philosophical reflections to highlight the urgency of preserving our sonic ecosystems. With eloquence and depth, this book challenges readers to reconsider their relationship with sound and the natural world.

Honorable mentions go to Karen Bakker’s The Sounds of Life: How Digital Technology Is Bringing Us Closer to the Worlds of Animals and Plants and Nina Kraus’ Of Sound Mind, How Our Brain Constructs a Meaningful Sonic World.

Short Form Print Winner
Ute Eberle’s captivating Knowable Magazine article, “Life in the Soil Was Thought to Be Silent. What If It Isn’t?,” shines a light on the often-overlooked acoustic richness beneath our feet. Eberle’s insightful exploration uncovers the hidden symphony of the soil, revealing the vital role sound plays in the ecosystem. Through her meticulous research and engaging prose, Eberle challenges preconceptions, opening a new realm of wonder and discovery.

Honorable mentions go to the Scientific American article, What Birds Really Listen for in Birdsong (It’s Not What You Think) by Adam Fishbein and Speaking in whistles by Bob Holmes, another Knowable Magazine article.

The 2023 award cycle reviewed content created between 2021 and 2022. A total of 73 nominations were received for the ASA Science Communication Awards, showcasing the breadth and depth of acoustics communication endeavors. The ASA extends its congratulations to the winners and honorable mentions for their exceptional contributions to acoustics communication. These projects have successfully bridged the gap between complex scientific concepts and the public, fostering a greater understanding and appreciation for the fascinating world of acoustics. The next award cycle will review content created between 2023 and 2024, with the call for nominations in the spring of 2025.

———————– MORE INFORMATION ———————–
The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its worldwide membership represents 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, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

Turning Up Ocean Temperature & Volume – Underwater Soundscapes in a Changing Climate

Freeman Lauren – lauren.a.freeman3.civ@us.navy.mil

Instagram: @laur.freeman

NUWC Division Newport, NAVSEA, Newport, RI, 02841, United States

Dr. Lauren A. Freeman, Dr. Daniel Duane, Dr. Ian Rooney from NUWC Division Newport and
Dr. Simon E. Freeman from ARPA-E

Popular version of 1aAB1 – Passive Acoustic Monitoring of Biological Soundscapes in a Changing Climate
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018023

Climate change is impacting our oceans and marine ecosystems across the globe. Passive acoustic monitoring of marine ecosystems has been shown to provide a window into the heartbeat of an ecosystem, its relative health, and even information such as how many whales or fish are present in a given day or month. By studying marine soundscapes, we collate all of the ambient noise at an underwater location and attribute parts of the soundscape to wind and waves, to boats, and to different types of biology. Long term biological soundscape studies allow us to track changes in ecosystems with a single, small, instrument called a hydrophone. I’ve been studying coral reef soundscapes for nearly a decade now, and am starting to have time series long enough to begin to see how climate change affects soundscapes. Some of the most immediate and pronounced impacts of climate change on shallow ocean soundscapes are evident in varying levels of ambient biological sound. We found a ubiquitous trend at research sites in both the tropical Pacific (Hawaii) and sub-tropical Atlantic (Bermuda) that warmer water tends to be associated with higher ambient noise levels. Different frequency bands provide information about different ecological processes (such as fish calls, invertebrate activity, and algal photosynthesis). The response of each of these processes to temperature changes is not uniform, however each type of ambient noise increases in warmer water. At some point, ocean warming and acidification will fundamentally change the ecological structure of a shallow water environment. This would also be reflected in a fundamentally different soundscape, as described by peak frequencies and sound intensity. While I have not monitored the phase shift of an ecosystem at a single site, I have documented and shown that healthy coral reefs with high levels of parrotfish and reef fish have fundamentally different soundscapes, as reflected in their acoustic signature at different frequency bands, than coral reefs that are degraded and overgrown with fleshy macroalgae. This suggests that long term soundscape monitoring could also track these ecological phase shifts under climate stress and other impacts to marine ecosystems such as overfishing.

A healthy coral reef research site in Hawaii with vibrant corals, many reef fish, and copious nooks and crannies for marine invertebrates to make their homes.
Soundscape segmented into three frequency bands capturing fish vocalizations (blue), parrotfish scrapes (red), and invertebrate clicks along with algal photosynthesis bubbles (yellow). All features show an increase in ambient noise level (PSD, y-axis) with increasing ocean temperature at each site studied in Hawaii.