June 2025

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June 2025 | Oceanography

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directional passive acoustic dataset and associated environmen­

tal time series from an acoustically undersampled region of the

United States Exclusive Economic Zone along the southeast­

ern OCS. Data collected are applicable to marine spatial plan­

ning and ecosystem-based management, and they also pro­

vide a mechanistic understanding of cumulative impacts on

marine resources. ADEON acquired measurements and devel­

oped objective metrics that enabled a quantitative assessment

of the Mid- and South Atlantic Ocean region soundscape, with

consideration of ecosystem conditions, as they may be linked

to extant biologic, geophysical-chemical, and/or anthropogenic

processes. Consideration was also given to resolving periodic­

ities in regional processes over long timescales to establish an

acoustic baseline for extracting trends and for comparing to his­

torical oceanographic time series in the region.

ADEON MULTI-PLATFORM APPROACH

The backbone of the measurement program was the ALTO

lander developed by JASCO Applied Sciences specifically for

the ADEON program (Figure 1b). The lander sensors included

a passive, four-channel autonomous acoustic recorder (AMAR),

a four-frequency echo sounder (Acoustic Zooplankton Fish

Profiler – AZFP by ASL Environmental Sciences, Canada), a

VEMCO VR2W fish tag receiver, and a Sea-Bird-37 CT-DO

unit. This combination of technology is transferable and relo­

catable and has been successfully deployed by other projects and

in additional regions since the conclusion of ADEON, including

AEON (Acoustic and Environmental Observation Network in

the NW Atlantic; https://eos.unh.edu/aeon), multiple projects to

monitor the movement of marine mammals around oil and gas

developments off Canada and Australia, and many wind farm

developments in the United States, Scotland, and Australia.

Lander sites were selected by considering ecological rele­

vance, diversity of anthropogenic activities, 200–900 m target

depth range (with three sites less than 400 m deep to accommo­

date the echosounder depth maximum), sufficient along-shelf

and across-shelf comparisons, and locations of other known

observation assets to support the analysis of soundscape por­

tability (Figure 1c,d). Five University-National Oceanographic

Laboratory System (UNOLS) cruises were devoted to servic­

ing lander deployments, turnarounds, and recovery and also

supported vessel-based, biological net tows performed during

fine-scale acoustic surveys (FSASs) of water column backscat­

ter, marine mammal surveys, full water column CTD casts,

and acoustic propagation characterization at each lander loca­

tion. Kowarski et al. (2022) present the details of the deploy­

ment dates, durations, and AMAR lander passive acoustic

array parameters.

The landers were deployed from November/December 2017

to December 2020. The four-channel AMARs sampled approx­

imately 45 minutes of each hour, alternating between a single

channel at 16 kHz sampling rate for 20 minutes, all four channels

at 16 kHz for 20 minutes, and a high frequency 512 kHz sam­

pling rate for a total of five minutes. The echo sounder system

sampling for 10–12 minutes each hour occurred during the por­

tion of the hour when the AMAR was sleeping to eliminate con­

tamination of the passive acoustic recordings. The AZFP emitted

a 750 μs ping every four seconds during the 10–12 minute sam­

pling period. The CT-DO unit sampled every 30 minutes.

To link the long-term measurements to environmental con­

ditions, the network design included remote sensing of oceanic

and atmospheric variables to be used as covariates in the eco­

system and soundscape models. These data included: (1) auto­

mated identification system (AIS) ship tracks, (2) sea sur­

face temperature (a combination of data from the NASA Jet

Propulsion Laboratory [JPL] and Copernicus), (3) chlorophyll a

concentrations obtained from the NASA-NOAA Visible Infrared

Imaging Radiometer Suite (VIIRS) onboard the Suomi National

Polar-orbiting Partnership (SNPP) satellite, (4) net primary pro­

ductivity derived from NASA using the Vertically Generalized

Production Model (VGPM) by Behrenfeld and Falkowski (1997),

(5) mixed layer depth derived from the Hybrid Coordinate

Ocean Model (HYCOM), (6) wind speed and direction from

the Advanced SCATterometer (ASCAT) real aperture sensor

onboard the meteorological operational platforms of the French

Institute for Ocean Science (IFREMER), and (7) upper surface

current speed and direction from the Ocean Surface Current

Analysis Real-time (OSCAR) project at JPL. The final element of

the network design incorporated mobile measurements that pro­

vided a broader context for the long-term measurements. These

consisted of data from the FSASs performed by the lander ser­

vice vessel, a horizontal array of hydrophones towed by a drifting

sailboat, and an autonomous sailboat that measured variability

of the soundscape between lander locations and across the Gulf

Stream—the dominant regional oceanographic feature.

ADEON STANDARDS

The standardization component of ADEON increased the value

of its data by providing products comparable to data from other

national and international acoustic programs. ADEON adopted

the international standard for underwater acoustical terminol­

ogy ISO 18405 Underwater acoustics – Terminology (ISO 18405,

2017; Ainslie et  al., 2021), compatible with the International

System of Units (BIPM 2019) and the International System of

Quantities (ISO 80000-8 Quantities and units – Acoustics). A

dictionary of terms was created to facilitate internal commu­

nication among project team members as well as with exter­

nal stakeholders. The ADEON Project Dictionary: Terminology

Standard (https://doi.org/10.6084/m9.figshare.12436199.v2) was

also used by the Joint Monitoring Programme for Ambient Noise

in the North Sea (JOMOPANS; Robinson and Wang, 2021), the

EU’s SATURN program (Ainslie et al., 2024), and ISO/DIS 7605

Underwater Acoustics—Measurement of Underwater Ambient

Sound

(https://www.iso.org/standard/82844.html).

ADEON

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