Monthly Archives: January 2016

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With our ship source level paper (pre-print) finally revised in Overleaf and accepted by PeerJ, it’s time to get ready to help translate the manuscript (which ended up on the long side) into simpler formats to convey our key findings to the public and press.  My first impulse was to use this as an opportunity to do something I’ve long-desired for my teaching: create a table and/or info-graphic that communicates the (very confusing) difference between underwater and in-air decibel scales.

A more urgent goal for today — with press phone calls/interviews looming — is distilling some simple facts from the paper and articulating them without scientific jargon.  These same highlights and summary statistics are destined for a blog post at Beam Reach that will convey the key findings, potential implications — both for killer whale communication and echolocation masking, and for mitigation of underwater noise pollution from ships.

How “loud” is ship noise?

Build tables that extract key results from the paper and contextualize them for the public, with attention to the confusion about underwater vs in-air decibels. First confirmed via DoSiTs that we subtract 62 when converting underwater decibels to in-air decibels (NOAA’s underwater acoustics page is not clear [and maybe wrong] on this topic!?). (Erbe, 2010) also could be improved by being explicit about how to do and derive this conversion…

Ship source levels (broadband)

 

Ship class Underwater broadband source level In-air broadband source level Familiar noise source of equivalent intensity
dB re 1 microPa @ 1 meter dB re 20 microPa @ 1 meter (from various Googled decibel scale images)
“Max” (mean+4sigma) 201 138 Jet take-off
Max of center 95% (mean+2sigma) 187 124 Jack hammer @ 1 m
Mean of all ships in study 173 +/- 7 ~110 Rock concert (or earbuds at full volume? or auto horn)
Max of center 95% of container ships (loudest class, mean+2sigma) 186 124 Jack hammer @ 1 m
Mean of container ships (loudest class) 178 +/- 4 116 Ambulance siren
Mean of military ships (one of quietest classes) 161 +/- 10 99 Chain saw

Received levels (broadband)

Of course, the killer whales are typically at least 100-1000 meters from these ships and we measured frequency-independent spreading rates at study site of about -18 log (R), so we should present a table of receive levels that depicts what ship noise experience is typical for SRKWs…

Receiving situation Underwater broadband source level In-air r broadband source level Familiar noise source of equivalent intensity
dB re 1 microPa dB re 20 microPa
Typical background level at Lime Kiln
Typical ship passing Lime Kiln
“Loud” ship passing Lime Kiln
1 m from “loudish” ship 175 113 Rock concert
10 m from “loudish” ship (175-18) 157 95 Lawn mower
100 m from “loudish” ship (175-18*2) 139 77 Busy street
1,000 m from “loudish” ship (175-18*3) 121 59 Vacuum cleaner
10,000 m from “loudish” ship 103 41

Broadband levels associated with the quantiles

Email with Val and Wikipedia remind us that Gaussian distributions hold 95% of their values in a range of the mean +/- twice the standard deviation (s.d., or “sigma”, or σ).  Here’s a comparison that Val ran down in Portland:

quantile(data_1_3_BB_noNA$ddB_SL_Emp,probs = c(0.025,0.05,0.25,0.5,0.75,0.95,0.975))
    2.5%       5%      25%      50%      75%      95%    97.5%
155.6082 160.8810 169.6775 174.4650 178.3650 183.5545 184.8073
> mean(data_1_3_BB_noNA$ddB_SL_Emp)
[1] 173.5007
> sd(data_1_3_BB_noNA$ddB_SL_Emp)
[1] 7.403251
Mean - 2 sigma
 173.5 - 2*7.4
[1] 158.7      compare with 155.6   (2.5% quantile above)

Mean + 2 sigma
 173.5 + 2*7.4
[1] 188.3	this one is about 3 dB above the 97.5% quantile above

So the 2*sigma estimates in the table are close enough, but may be slight (3 dB) over-estimates of the broadband levels associated with the  97.5% quantiles…

Erbe, C. (2010). Underwater acoustics: Noise and the effects on marine mammals. Pocketbook, printed by JASCO Applied Sciences, Brisbane, QLD, Australia. Retrieved from http://oalib.hlsresearch.com/PocketBook%%203rd%%20ed.pdf