mcbem-2014-01-submission-wwf-en

Pressure amplitude
rms amplitude = 0.7
peak amplitude = 1
peak to peak amplitude = 2
There are no widely accepted international standards for reporting sound pressure levels (SPL, units are
dB re 1 µPa) and depending on how the pressure or energy is calculated or measured, the numerical
value associated with a sound can vary significantly (by 20 dB or more). Peak amplitudes, peak-to-peak
amplitudes and root mean square (rms) may all be used (Figure 2, and Table 1). Sound exposure levels
(SEL) measure the total energy of a signal over time, and in water, the sound exposure units are dB re 1
µPa ·s. They can be used to compare sounds that are continuous, single, or multiple pulses, and can also
be used to describe the cumulative exposure of a sound over the duration of a specified time period
(Table 1). It is also important to note whether the sound energy is reported at the source (usually 1 m
from the actual source), or is a received level. For sound sources larger than a few cm, the sound is
produced over a distance greater than 1 m, so sources levels are modeled.
1
0.5
0
-0.5
-1
0 Time (s) 1
Time (s)
Figure 2. A waveform showing several ways of expressing the amplitude of a continuous sound. The root
mean square (rms) amplitude is 0.8, the peak amplitude is 1 and the peak to peak amplitude is 2.
Courtesy of Kathy Heise.
There are many naturally occurring loud sources of sound in the ocean, ranging from biological ones,
such as sperm whale codas or blue whale calls, to abiotic sources such as wind and waves and
underwater earthquakes. Whether a sound is considered noise depends on the perspective of the
listener. For the purpose of this workshop, noise is considered to be anthropogenic (man-made) sounds
that potentially may impact marine mammals, invertebrates and fish. Sources of noise on the BC coast
include shipping, seismic surveys, military activities (e.g., sonar, torpedoes), vessel sonar, new and
emerging technologies (e.g., AUVs, modems) and harbour activities (e.g., pile driving and dredging).
Anthropogenic noise can interfere with the ability of marine animals to forage, reproduce, avoid
predators, communicate and navigate. It may cause behavioural changes, although these are often
difficult to detect or interpret. It can mask important communication and echolocation signals and
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