Oceanography | Vol. 38, No. 2
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terminology was also adopted in recommendations from two
international workshops, one in Dublin in 2016 (Ainslie et al.,
2019) and one in Berlin in 2022 (Martin et al., 2024), and it
served as the basis for the new ISO project 23990 Underwater
Acoustics—Bioacoustical Terminology via the SATURN
terminology standard.
For passive acoustic processing bands, ADEON adopted inter
national standard decidecade band terminology (IEC 61260-
1:2014) whereby multiple decidecade bands can be combined
into a single decade band or user selected bands (https://doi.
org/10.6084/m9.figshare.6792359.v2). To achieve high frequency
resolution over a wide frequency range, the ADEON Data
Processing Specification (https://doi.org/10.6084/m9.figshare.
12412610.v1) introduced hybrid millidecade bands, with mil
lidecade bands used at high frequency and 1 Hz bands at low
frequency (Martin et al., 2021). Finally, two further standards
describe ADEON’s choice of hardware (https://doi.org/10.6084/
m9.figshare.6809711) and calibration and deployment guidelines
(https://doi.org/10.6084/m9.figshare.6793745).
ADEON RESULTS
Passive Acoustics
A total of 116 TB of passive acoustic data were recorded during
the three-year data collection phase of ADEON. All data were
retrieved, except for August–November of 2019 and 2020 at site
VAC, which were lost due to commercial trawling; these land
ers were successfully retrieved thanks to their satellite beacons
(Figure 1). Figure 2 summarizes this extensive dataset using
the monthly empirical probability density functions (EPDF) of
the one-minute sound pressure levels (SPL) in various decide
cade frequency bands. The broadband SPL was computed from
the high-frequency sampling rate data and covers four ADEON
decade bands, which are sum of the decide
cade bands centered from 10 Hz to 80,000 Hz,
with edge frequencies of 8.91–89,100 Hz. The
peak of the EPDFs for the broadband SPL at
all stations was near 100 dB re 1 µPa². The
two stations closest to shipping lanes (VAC
and HAT) had the highest peak SPLs in their
broadband EPDFs.
The EPDFs for four decidecade bands
shown in Figure 2 present some of the key
features of the OCS soundscape. The 20 Hz
decidecade band had higher levels in win
ter than in summer due the mating cho
rus of fin whales, showing that this biologi
cal contribution is often the most notable part
of the soundscape at 20 Hz. The 20 Hz and
125 Hz decidecade bands at CHB had dis
torted EPDFs due to the strong effect of flow-
induced noise on the results. In general, the
125 Hz decidecade band exhibited substantial
contributions from two sources—vessels and
minke whales. The differences between the
summer and winter sound levels at the south
ern stations (WIL, CHB, SAV, JAX, and BLE)
were caused by the mating chorus of minke
whales in winter. The two northern stations
(VAC and HAT) showed little difference
between summer and winter months due
to the frequent presence of vessels. The two
higher frequency decidecade bands (630 Hz
and 3,150 Hz) both show higher SPLs in
winter and lower levels in summer, associ
ated with higher mean wind speeds in winter
than in summer.
Several studies of the ADEON soundscape
have provided insight into the contributions
FIGURE 2. An overview of the ADEON soundscape using monthly empiri
cal probability density functions of one-minute sound pressure levels aver
aged over all years. The columns are different frequency bands: broadband
(8.91–89,100 Hz) sound pressure level (in dB), and the 20, 125, 630, and 3,150 Hz
decidecade bands. The seven rows are for the seven recording locations. The
colors represent the month, as shown by the legend on the right. A dashed line
at 90 dB provides a reference for comparison between frequency bands and
stations. At VAC, the lander was picked up by fishers in July of 2019 and 2020,
so only data from 2018 are available for August to November. The reference
sound pressure is 1 µPa.