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

BBN Systems and Technologies Corporation
may be found operating in Alaska, but is thought to be representative of the
prevalent sizes used in industrial and transportation applications.
The Bell 205 helicopter, used for both cargo and passenger carrying, can
be seen from the table to produce a source level of 165 dB for the loaded
cruise condition. This is comparable to the takeoff source level of the
Boeing 737-300 as shown in Table 3.3B. The Bell 222, a newer and somewhat
smaller helicopter, produces an approach source level of 161 dB. The takeoff
source level of 152 dB shown in the table for this aircraft is undoubtedly too
low as a result of the reported data not including the lower frequency noise
components, e.g., from the main rotor, which are a significant part of the
overall noise output. The Sikorsky S61, a larger model often used for search
and rescue as well as oil industry operations, can be seen to produce a cruise
source level of 156 dB which is comparable to the takeoff source level of the
Cessna 172 single-engine propeller aircraft. This relatively low source level
may be aided by the 5-bladed main and tail rotors used on the S61 helicopter.
The Bell 206B, a 5-passenger light helicopter, is seen to produce a cruise
source level of 151 dB which is similar to that of a Cessna 185 at cruise
power, as shown in Table 3.3B.
The source level spectra for the selected helicopter examples are shown
in Fig. 3.16. All of the spectra are similar with the exception of the Bell
205 and Bell 222 helicopters having band levels below 1.25 kHz which are 5 to
10 dB higher than those of the Bell 206B and the Sikorsky S61. Comparison of
the general range of the helicopter spectra in Fig. 3.16 with the examples of
fixed wing aircraft spectra in Fig. 3.15 shows that the group of helicopters
selected produces source levels which are comparable to the lowest range of
fixed wing aircraft spectra. With the probable exception of noise from the
large two-bladed helicopters such as the Bell 205 and 212, the potential noise
impact of helicopter operation is thus not expected to be much different from
that for fixed wing aircraft operation for comparable aircraft sizes.
However, since helicopters are typically operated at lower altitudes, there
may be an increase in noise exposure at ground level for helicopters as a
result of usual operating procedures.
3.3.3 Cultural and recreational sources
The acoustic source examples included in this category have been selected
from vehicles and tools used for cultural and recreational fishing, hunting,
camping, and other activities not performed for industrial or commercial
purposes. Smaller boats have been included in this category rather than under
industrial or transportation sources even though many small boats are used for
commercial fishing. Table 3.4 contains source level data for the examples'
selected. The format is identical to that used previously in Tables 3.2 and
3.3. Representative estimated underwater source level spectra are shown in
Fig. 3.17.
The most widely distributed recreation-related underwater acoustic
sources in Alaskan waters are outboard motor powered boats. They produce a
wide range of source levels depending on the motor horsepower and propeller
type used. Outdrive and inboard power cruisers are also widely distributed.
Examples of these sources are shown in Table 3.4. The dual 80 HP outdrive