Getting to Grips with Aircraft Noise

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9 - A BIT OF THEORY It was introduced in the early 1970's by the State of California for community noise exposure, with particular emphasis on airport noise. 9.5.6. NOISE AND NUMBER INDEX (NNI TERMED LNNI) This index corresponds to an average sound level (in PNLmax) of all the events that occurred in a given period. N max( ) ⎡ LPN i 1 ⎡ ⎤⎤ LNNI = 10log * 10 ⎢⎣ ⎢⎣ ∑ 10 ⎥⎦ ⎥⎦ + 15log( N ) − 80 N i= 1 where: LPNmax(i) is the PNLmax for a procedure N corresponds to the number of procedures 80 is a normalized constant It was originally devised by the Wilson Committee on Noise in Britain (1963). The Noise and Number Index scale runs from 0 to 60 and following the results of social surveys, the Wilson Committee assigned values of annoyance to the index as shown in the graph below. The Wilson Committee considered that exposure to aircraft noise reaches an unreasonable level in the range 50 - 60. A difference of 10 NNI corresponds either to an increase of the peak level of 10 PNdB or to a quadrupling of the number of flights in the period. 76 Flight Operations Support & Line Assistance Getting to grips with aircraft noise
Flight Operations Support & Line Assistance Getting to grips with aircraft noise 9 - A BIT OF THEORY 9.5.7. WEIGHTED EQUIVALENT CONTINUOUS PERCEIVED NOISE LEVEL (WECPNL TERMED LWECPN) This index is relative to a cumulated noise level of all the events over a given period. Each noise event is weighed depending on the period of the day and the season of its occurrence. L WECPN = L WECPN ( hotmonths ) + L WECPN ( temperatemonths ) 1, 2or3 + L WECPN ( coldmonths ) The computation of WECPNL requires using two intermediate indices. 9.5.7.1. TOTAL NOISE EXPOSURE LEVEL (TNEL TERMED LTNE) This index describes the noisiness produced by a succession of aircraft flyovers. L TNE ⎡ 10log ⎢⎢⎣ ⎤ ⎡T + 10log⎢⎣ ⎥⎥⎦ t n LEPN ( i ) 10 0 = ∑ 10 i= 1 0 Where: LEPN(i) is the EPNL for the procedure i n is the number of movements T0 is a constant equal to 10 s t0 is a constant equal to 1 s 9.5.7.2. EQUIVALENT CONTINUOUS PERCEIVED NOISE LEVEL (ECPNL TERMED LECPN) In the same way we have defined EPNL, we design the equivalent cumulative perceived noise level as follows: = L LECPN TNE ⎡T ⎤ − 10log⎢⎣ ⎥ , t0 ⎦ Where: T corresponds to the exposure time 9.5.7.3. WECPNL CALCULATION 9.5.7.3.1. Considering two periods in a day L WECPN = ⎡5 ⎛ 10 log 10 ⎢⎢ 8 ⎜⎜ ⎣ ⎝ L ECPNday ( 0700− 2200) 10 ⎞ + ⎟⎟ ⎠ ⎤ ⎥⎦ 3 ⎛ 10 8 ⎜⎜ ⎝ L ECPNnight ( 2200− 0700) 10 + 10 ⎞⎤ + S ⎟⎟ ⎠⎥⎥ ⎦ 77
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Getting to Grips with Aircraft Noise

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