Аннотация
The erection of wind turbines is preceded by an environmental assessment
of the impact of wind turbines on people living nearby. One impact
to be assessed is sound. It is thus important to have scientifically
based knowledge of how wind turbine sound will be perceived in order
to ensure that this sound does not adversely affect the health of
residents in the area. This report presents an analysis of the results
from two previous field studies investigating the relation between
sound levels from wind turbines at dwellings and the perception of
the sound. It also describes the factors influencing this relationship.
In a diary study the participants reported how often they were home
and, if so, whether they were outdoors, and whether they could hear
the turbines. The objective of this study was to describe how often
the sound from wind turbines was heard and in which meteorological
conditions. A complementary field study investigated the accuracy
of the sound propagation model used today by comparing longterm
sound measurements with the values calculated using different models.
This study also investigated whether variations in meteorological
factors influenced sound propagation to such a degree that they should
be included in the calculation of sound levels.The joint analyses
of the two field studies confirm and strengthen previously reported
data. The percentage of respondents who noticed wind turbine sound
as well as the percentage annoyed by the noise, increased with increasing
sound levels. The probability of being annoyed was greater in rural
areas and if the turbines were visible from the dwelling. However,
differences in terrain had no statistical effect. The only association
between sound levels and healthrelated variables other than annoyance
was disturbed sleep.Participants in the diary study more often reported
hearing sound from the wind turbines when the electrical power increased
(i.e. when electricity production increased). A statistically significant
relationship between how often the sound was heard and the calculated
sound level at the dwelling was found, even though the amount of
time the participants spent outdoor varied substantially; the higher
the calculated sound level, the more often the sound was heard. The
diary study also gave some insight into the relationship between
audibility and wind speed. The results indicate that wind turbine
sound could still be heard at relatively high wind speeds, when it
would have been expected to be masked.
Longterm measurements of wind turbine sound at about 550 meters from
a modern turbine showed that the calculated and measured levels agreed
well. Sound levels calculated using a parabolic equation model, which
takes into account variations in meteorological factors, did not
give a better prediction than the model commonly used at environmental
permit proceed
ings Naturvårdsverket 2001. Meteorological variations are probably
only of importance for sound propagation at longer distances. Meteorological
circumstances could, however, be important for estimation of the
source sound levels, the largest element of uncertainty in the calculations.
The studies show that the sound levels vary at the same wind speed,
and that wind turbine sound could still be heard at wind speeds when
it should be masked by other windinduced sounds. This implies that
the description in the environmental impact assessment of the sound
that neighbours will possibly hear should be extended, even though
the sound propagation model used today is adequate. Further studies
regarding the possibility of hearing the sound at high wind speeds
are needed, as the number of participants in the
diary study was small. The data also suggest that the risk of sleep
disturbance should be further explored.
Линки и ресурсы
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