Some studies, like Haver et al 2019 use broadband measurements between 50 Hz - 1.5 kHz, but Haver et al 2020 looked for shipping noise in median power spectral densities between 10 Hz - 2 kHz, and Bittencourt et al 2020 used a variety of third-octave-levels. How do you choose which soundscape metric is best to monitor shipping noise?
$\begingroup$
$\endgroup$
Add a comment
|
3 Answers
$\begingroup$
$\endgroup$
We attempted to provide meaningful feedback to this question with the JOMOPANS project, were we employ the sound pressure level (SPL) of third-octave level (TOL) bands from different stations around the North Sea to build our modeled noise maps. Ward et al., 2021 put out an EU report detailing what standards we used when processing our data.
However, in the GES Tool that we created for the project (https://jomopansgestool.au.dk/en/), we limited our users to view both the 63 and 125 Hz TOL bands, as they are important for historical and practical reasons, and then we provided decade bands of a broader scope.
How do you choose? I think it depends on your question. What types of vessels are you interested in investigating? What impact are you trying to measure? Looking at the 125 Hz TOL will allow you to have a broader comparison with older publications, but as you mentioned, increasingly studies want to include higher frequencies as not all boats are built the same. As Hermannsen et al., 2019 pointed out, smaller, recreational vessels impact the higher frequencies.
References
Hermannsen, L., Mikkelsen, L., Tougaard, J., Beedholm, K., Johnson, M., & Madsen, P. T. (2019). Recreational vessels without Automatic Identification System (AIS) dominate anthropogenic noise contributions to a shallow water soundscape. Scientific reports, 9(1), 1-10.
Ward, J., Wang, L., Robinson, S., & Harris, P. (2021). Standard for Data Processing of Measured Data. Report of the EU INTERREG Joint Monitoring Programme for Ambient Noise North Sea (Jomopans).
$\begingroup$
$\endgroup$
This is tricky because a method of estimation that works for one environment, might not be as accurate in another. In Haver 2021 we adopted the 1/3 octave bands (63 and 125 Hz) method from the European Marine Strategy Framework Directive and found that method to be an acceptable proxy for cargo and tanker activity at a handful of deep (>500 m) sites in U.S. waters. More detailed detectors may be more precise but at high cost of analyst time and computing resources.
It also depends on the question. In our 2019 paper, we were specifically targeting noise in the primary communication frequencies for humpback whales, but those frequencies might not be as relevant for a different species.
$\begingroup$
$\endgroup$
On top of other specialized metrics to cover for example whale call bands, I suggest that third octave (or decidecades as we should now call them) level should always be reported as most other broad band metrics can be deduced from those by readers in the future.
answered Jul 7, 2022 at 6:52