Collected data from 33 noise monitors summarizes Day-Night Average Sound Level (DNL) that is a 24-hour, time-averaged sound exposure level with a 10 decibel (dB) nighttime (10 p.m. to 7 a.m.) weighting to account for the lower background noise levels during nighttime hours.
The measured aircraft DNL for each month is compared to the same month of the previous year and to a 12-month average. The report identifies noise from existing aircraft operations at O’Hare.
Modeled values for each noise monitor are shown for 1997, 2000 and the O’Hare Modernization Full Build-Out noise contours.
Aircraft noise levels for each monitor vary from month to month because runways are utilized differently under changing wind conditions which affect where aircraft fly.
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