Page 30 - Spring 2009

Fig. 4. Assumed distribution of aircraft-produced, outdoor Sound Exposure Level values at approximately 3 1⁄2 miles from the airport.
The analyses of these two data variables (Sound Exposure Level and time since retiring) provided results of the form:
(3)
(4)
Table 1 lists the values of the constants from the standard for when one has only SEL data and for when one has both SEL and time since retiring data.
Table 1: Values of Eq. (4) constants for the two methods used to compute awakenings
Application to realistic scenarios
By using the probability of awakening method and the two different dose-response relationships defined by Eq. (3) and Eq. (4), the percent of people awakened can be comput- ed for different realistic scenarios. For this article, the awak- enings are computed at a single point with assumed distri- butions of noise events. The assumptions include a realistic distribution of A-weighted SEL values, three different num- bers of night-time aircraft noise events, and three different outdoor-to-indoor noise reductions.
Figure 4 gives the assumed distribution of aircraft-pro- duced outdoor A-weighted SEL. This distribution was meas- ured by a permanent noise monitor located about 31⁄2 statute miles from the airport (at the approximate location of the 65 dB day-night sound level for that airport).
Three different distributions of nighttime noise events are assumed, see Table 2. For purposes of this comparison, these events are grouped into thirds of the night. These dis- tributions are intended to represent what might occur when
increases in operations are not matched by increases in air- port capacity. If distribution #1 represents an existing condi- tion, then distribution #2 and distribution #3 might both be the result of a significant increase in operations at the air- port, with no increase in capacity—operations arrive later at night (distribution #2) or leave earlier in the morning (dis- tribution #3).
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