Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
and rain (90-100 dB) are important. Wind, rain and solid precipitation will
dominate background noise at frequencies above 1000 Hz, with levels of 95-
105 dB to be expected for heavy wind and precipitation conditions.
3.2.8 Airborne ambient noise
In a coastal area near the shoreline, surf noise is the dominant
contributor to the airborne ambient. The overall airborne noise level and
spectrum shape are related not only to the local wind speed but also to the
height of the swell which may be influenced by distant storms at sea. Beyond
100 to 200 m offshore the airborne noise level is influenced primarily by
local breaking wave crests and may become quite low during calm sea
conditions. Some surf noise data reported for moderate wind speed conditions
(about 10 kts) are shown in Fig. 3.10. The surf noise spectra reported for
two different areas can be seen to be similar except at 50 Hz where the BBN
data show a considerably higher level. This may be the result of higher swell
conditions (swell height was not reported). The spectrum labeled voffshoretl
was measured for the same sea conditions as the surf noise spectrum but at a
point about 200 m from the beach. The sea state was given as "choppy with
some breaking crests". The band levels shown for the offshore spectrum
correspond to those measured on land in rural areas and thus represent
relatively quiet airborne noise conditions.
3.3 Man-Made Noise
This section contains a summary of the characteristics of man-made noise
sources which are active in the Alaskan marine environment. The sources are
organized into three general categories: industrial, transportation, and
cultural. The information is presented in the form of tables of principal
parameters and graphs showing selected source level spectra. The data base
1/3 octave spectra for all of the examples shown in this section is included
in Appendix A.
The significant parameters selected for comparison in the tables are:
Type - Fixed, Local, or Moving. A llfixedll source remains stationary at
one location, a "local" source is not fixed but moves at a slow rate of
less than 0.3 krn/hr, and a "movingt1 source travels at a higher rate of
speed.
Dominant Bandwidth - The frequency band including the 1/3 octave band
with the highest sound level and bounded by the 1/3 octave bands with
levels within 10 dB of the maximum. The reported data spectra were
sometimes truncated within the dominant bandwidth as defined here. This
is noted by the statement "Bandwidth limited by available data".
Maximum 1/3 Octave Band - The band with the highest sound level.
Temporal Pattern - Continuous, Fluctuating, Intermittent, or Impulsive
(see definitions in Sec. 3.1.2).