Although this study provides valuable insight into tran- 
siting noise emissions from CTVs, future work should focus 
an expanding the dataset to include a wider range of individ- 
ual vessels and, importantly, other operational states 
Measuring CTVs during operations within offshore wind 
farms—particularly during crew transfers—will be crucial 
for a complete assessment of their underwater noise impact. 
V. CONCLUSION 
This study presents the first dedicated measurements of 
RNLs from CTVs and demonstrates that transiting CTVs, 
although relatively small, emit noise levels comparable to 
:hose of much larger commercial vessels, reaching or 
exceeding a representative large-vessel reference spectrum 
in several frequency bands, particularly above 1kHz. The 
generally low variability in RNLs allows the derived spectra 
:o be used as viable input for numerical models that aim to 
include transiting CTVs. Within the observed transit speed 
range, the main source of variability was found to be vessel- 
specific and not be explained by speed and length alone. 
Although residual distance-related effects at high frequen- 
cies remain evident in the data, the application of SSCI- 
based propagation loss correction including frequency- 
dependent absorption proved to be a robust and practical 
approach for the present measurement configuration. In this 
sxtended form, the ISO-17208-3 framework provides a fea- 
sible approach for opportunistic ship noise measurements— 
an area still lacking standardized methodology—and is com- 
patible with ongoing national monitoring efforts. 
SUPPLEMENTARY MATERIAL 
See the supplementary material for Figs. S1-S5, includ- 
ing Fig. S1 for vessel-specific RNL spectral probability den- 
sities for all 13 CTVs, Figs. S$2 and $3 for comparisons of 
SSCI and the image source propagation-loss model 
highlighting the contribution of the absorption term, Fig. S4 
for additional scatterplots (speed, length, and distance vs 
RNL), and Fig. S5 for trend summaries of effect strengths 
and feature importances from the GAM and RF analyses. 
ACKNOWLEDGMENTS 
This research was funded under the DEMASK Project 
by the North Sea Region of the European Regional 
Development Fund (Interreg) of the European Union. We 
would like to thank the crews of the BSH research vessel 
WEGA and the WSV vessel Neuwerk, without whom data 
zollection would have been impossible. 
AUTHOR DECLARATIONS 
Conflict of Interest 
The authors have no conflicts to disclose 
3414 
J. Acoust. Soc. Am. 159 (4), April 2026 
https:/doi.org/10.1121/10.0043324 
JASA 
Ethics Approval 
This study did not involve human participants or live 
animals. Ethics approval was therefore not required. 
DATA AVAILABILITY 
The raw hydrophone recordings and high-resolution SPL 
time series used in this study are subject to third-party restric- 
tions and cannot be made publicly available due to national 
data protection regulations. The authors are not permitted to 
distribute these data. Processed data products that support the 
findings of this study, including aggregated decidecade-band 
SPL statistics at 20s temporal resolution and derived spectral 
metrics, will be deposited in the ICES Continuous Noise 
Database (https://underwaternoise.ices.dk/continuous). 
Bechtold, B. (2016). “Violin plots for Matlab,” GitHub, https://github.com/ 
bastibe/Violinplot-Matlab. 
3randt, M., Diederichs, A., Betke, K., Matuschek, R., and Nehls, G. (2011). 
“Responses of harbour porpoises to pile driving at the Horns Rev II offshore 
wind farm in the Danish North Sea,” Mar. Ecol. Prog. Ser. 421, 205-216. 
Breiman, L. (2001). “Random forests,” Mach. Learn. 45, 5-32. 
JEMASK Project (2025). “The DEMASK Project, Interreg North Sea,” 
https://www.interregnorthsea.eu/demask (Last viewed 13 April 2026). 
Juarte, C. M., Chapuis, L., Collin, S. P., Costa, D. P., Devassy, R. P., 
Eguiluz, V. M., Erbe, C., Gordon, T. A. C., Halpern, B. S., Harding, H. 
R., Havlik, M.-N., Meekan, M. G., Merchant, N. D., Miksis-Olds, J., 
Parsons, M., Predragovic, M., Radford, A. N., Radford, C. A., Simpson, 
S. D., Slabbekoorn, H., Staaterman, E., van Opzeeland, I., Winderen, J., 
Zhang, X., and Juanes, F. (2021). “The soundscape of the Anthropocene 
ocean” Science 371, eaba4658. 
Erbe, C., Dunlop, R. A., and Dolman, S. J. (2018). “Effects of noise on 
marine mammals,” in Effects of Anthropogenic Noise on Animals, edited 
by H. Slabbekorn, R. Dooling, A. Popper, and R. Fay (Springer, New 
York), pp. 277-309. 
Hawkins, A. D., and Popper, A. N. (2017). “A sound approach to assessing 
the impact of underwater noise on marine fishes and invertebrates,” ICES 
J. Mar. Sci. 74(3), 635-651. 
Termannsen, L., Ladegaard, M., Tennesen, P., Malinka, C., Beedholm, K., 
Tougaard, J., Rojano-Donate, L., Tyack, P. L., and Madsen, P. T. (2025). 
“High-frequency vessel noise can mask porpoise echolocation,” J. Exp. 
Biol. 228(6), jeb249963. 
EC (2014). “IEC 61260-1:2014—Electroacoustics—Octave-band and frac- 
tional-octave-band filters—Part 1: Specifications” (International 
Electrotechnical Commission, Geneva, Switzerland). 
‚EC (2016). “IEC 61260-3:2016—EBElectroacoustics—0Octave-band and frac- 
tional-octave-band filters—Part 3: Periodic tests” (International 
Electrotechnical Commission, Geneva, Switzerland). 
EC (2019). “IEC 60565-2:2019—Underwater acoustics—Hydrophones— 
Calibration of hydrophones—Part 2: Procedures for low frequency pres- 
sure calibration,” Ist ed. (International Electrotechnical Commission. 
Geneva, Switzerland). 
SO (2016). “ISO 17208-1:2016/Amd 1:2024—Underwater acoustics— 
Quantities and procedures for description and measurement of underwater 
sound from ships—Part 1: Requirements for precision measurements in 
deep water used for comparison purposes [includes Amendment 1: 2024]” 
(International Organization for Standardization, Geneva, Switzerland). 
ISO (2019). “ISO 17208-2:2019—Underwater acoustics—Quantities and pro- 
cedures for description and measurement of underwater sound from ships— 
Part 2: Determination of source levels from deep water measurements” 
(International Organization for Standardization, Geneva, Switzerland). 
ISO (2025). “ISO 17208-3:2025—Underwater acoustics—Quantities and 
procedures for description and measurement of underwater sound from 
ships—Part 3: Requirements for measurements in shallow water” 
(International Organization for Standardization, Geneva, Switzerland). 
JOMOPANS Project (2020). “Joint Monitoring Programme for Ambient 
Noise in the North Sea (TJOMOPANS), Interreg North Sea,” https://north 
searegion.eu/jomopans/ (Last viewed 13 April 2026). 
Basan et al.