Monthly Archives: April 2014

Ship noise paper progress: spectral figures

Back on 3/4/14, Val and I decided to bounce this strategy off Jason: rather than using only night-time data (to exclude the 50 kHz spike and hump we see in the 95% (and to a lesser extent 75%) quantiles of ship and background RL, present quantiles for the whole population and then underlay a “nighttime-only” 95% quantile curve to show how the 50kHz humps go away… If he balks (or reviewers do down the line), then we ~halve data set by only using nighttime data..

Working with Val in Seattle on final details of receive level figure:

  • Hz with sci notation in x-axis, rather than kHz (for ship noise audience)
  • Increase horizontal grid lines to make it easier to read off values and differences between background and ship levels.
  • Work out how to get a legend in ggplot (involves “melting” data series into single column of data with variable name in adjacent column) and position it inside the plot

We sketched out Tufte-ian solution to the ship population source level plot that will show per Hz, 1/12-octave band, and 1/3-octave band levels.

Scott's sketch of what a plot comparing spectrum, 1/12-, and 1/3-octave levels of ship noise.

Scott’s sketch of what a plot comparing spectrum, 1/12-, and 1/3-octave levels of ship noise.

About a month later, we’ve got that figure finalized and are working on the last piece of the paper: whether there’s anything interesting to say about acoustic outliers within a particular class of ships.  Here are notes I took as I visually analyzed plots Val made of noise spectrum levels for each of our ship classes.  Each plot has 25, 50, and 70% quantiles from the population within that class, as well as clouds of data points for each ship measurement made within that class.

Scanning through the DropBox folder called SL_by_Class, here are some highlights:

1) First a data processing sanity check: What are the diagonal features/artifacts (with slope of ~10 dB/decade) showing up in the densest of data point clouds in the 1/12 (but not 1/3!) octave level plots, e.g.–

ddB_abs_vs_ 1_12_octave band _ Bulk carrier __.png
ddB_abs_vs_ 1_12_octave band _ Container ship __.png

See this example at HF end in this zoomed screen grab  —
HF artifacts?

and more worrying example at LF because of the reflection of the slope in the 1/12 octave levels, along with what may be steps in the population distribution of levels near 25 Hz and 45 Hz –Screen Shot 2014-04-11 at 11.43.58 AM

2) Here is a list of per Hz (with absorption) png files that show *really* interesting outliers which I’ve grouped into a couple “categories of interest” —

ddB_abs_vs_ hz _ Bulk carrier __.png
1 super-high, 2 high, and 1 low outliers at HF
The super-high and unusually low outliers define a huge range from lowest to highest at uppermost HFs — about 60 dB for bulk carriers!
Other classes have less variability, e.g. Cargo ships and tankers ~30 dB, Container and military ships ~40 dB, Vehicle carriers ~45 dB, Tugs ~50 dB
For perspective, Ross (Ross, 1976) shows a plot of WWII sub cavitation inception raising levels in a 10kHz-30kHz band 50 dB as the speed of a sub:
(at 7m) increased from ~3kt to ~5kt…
(at 16m) increased from ~4kt to ~6kt…
(at 91m) increased from ~8kt to 12kt.

ddB_abs_vs_ hz _ Cargo __.png
1 high outlier at HF

ddB_abs_vs_ hz _ Container ship __.png
2 similarly high outliers at HF

ddB_abs_vs_ hz _ Tanker __.png
1 of upper outlier at HF shows some very interesting wiggles, akin to those that Hildebrand captured from the Hanjin
Here they are looking very wiggly (in the no-abosorption, per Hz version of the plot) –Screen Shot 2014-04-11 at 12.27.37 PM

ddB_abs_vs_ hz _ Tug __.png
2 high outliers at HF, one or both of which have some wiggles

ddB_abs_vs_ hz _ Vehicle carrier __.png
1 particularly high outlier

3) Other random nifty observations

Different fisheries boats show cool peaks near common transducer frequencies (e.g. 38 and 50 kHz):
Screen Shot 2014-04-11 at 11.53.47 AM

There was more variability in HF levels for military boats than I expected.  I wonder if this is different ship/prop designs or different speeds — maybe a good class in which to look for correlations?
Screen Shot 2014-04-11 at 11.56.35 AM

Ross, D. (1976). Mechanics of underwater noise. Pergamon Press.