§ 4191.024. Day-night sound level (Ldn).

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"Day-Night Sound Level" [abbreviated as (Ldn)] means a cumulative aircraft noise index which estimates the exposure of an area to aircraft noise and relates the estimated exposure to an expected community response.

Decibels of noise [abbreviated as (dB)] are measured by an A-weighted sound-level meter. In the Ldn procedure, noise exposures are accumulated for a typical 24-hour period. A weighing factor equivalent to a penalty of ten decibels (10 dB) is applied to aircraft operations or other noise sources between 10:00 p.m. and 7:00 a.m. to take into account the increased sensitivity of people to night-time noise. The Ldn values are expressed graphically on maps using contours.

(Ord. 1138-94.)

                    
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