Agenda - 06-27-1983 - Laserfiche WebLink

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41 NOISE DESCRIPTORS IN THE FAA'S INTEGRATED NOISE MODEL Actual airport noise environments are defined using more complex descriptors than those we discussed earlier. During the next segment of the Seminar, we shall examine the methods used to describe the airport noise environments. Airport community noise is made up , primarily , of a series of separate events . Between events , the environment may b!e relatively quiet . Over the years , various noise descriptors have beeb developed to describe the noise environment . These descriptors can be,divided into two basic kinds : ( 1 ) those that reflect in a single numbO• the amount of sound energy during a 21 -hour day and (2) those that reflect in a single number how much of the time a noise level is exceeded . In the following pages, we describe five airport descriptors , fourlof which are in the first category, and one in the second : • Noise Exposure Forecast • Equivalent Sound Level Category • Day-Night Sound Level ( Cumulative Energy Measures) 410 • Community Noise Equivalent Level . Time Above Threshold Category 21 ( Cumulative Time Measure) Noise Exposure Forecast (NEF) Noise Exposure Forecast (NEF) is a cumulative energy measure of noise exposure . It represents a technical upgrading of a land use planning tool developed for airports in the early 1960 's - the Composite Noise Rating ( CNR) . NEF uses Effective Perceived Noise Levels (EPNL) . Calculations of EPNL not only weight frequencies according to the sensitivity of the human ear , they also account for higher-ithan-normal annoyance at the presence of pure tones in aircraft noise silgnals ( such as the chacrac ter ist Jo compressor whine of a jet engine during landing) , and they account for greater annoyance at a sound that h4s a longer duration . 410 18