Commission Directive (EU) 2015/996Dangos y teitl llawn

1.

First the reference spectrum is corrected to remove the SAE AIR-1845 atmospheric attenuation α _n,ref :

Ln(dref) = Ln,ref(dref) + αn,ref · dref

(D-1)

where L_n(d_ref) is the unattenuated spectrum at d_ref = 305 m and α _n,ref is the coefficient of atmospheric absorption for the frequency band n taken from Table D-1 (but expressed in dB/m).

2.

Next the corrected spectrum is adjusted to each of the 10 standard NPD distances d_i using attenuation rates for both (i) the SAE AIR-1845 atmosphere and (ii) the user-specified atmosphere (based on SAE ARP-866A).

(i)

For the SAE AIR-1845 atmosphere:

Ln,ref(di) = Ln(dref) – 20,lg(di/dref) – αn,ref · di

(D-2)

(ii)

For the user atmosphere:

Ln,866A(T,RH,di) = Ln(dref) – 20,lg(di/dref) – αn,866A(T,RH) · di

(D-3)

where α _n,866A is the coefficient of atmospheric absorption for the frequency band n (expressed in dB/m) calculated using SAE ARP-866A with temperature T, and relative humidity RH.

3.

At each NPD distance d_i the two spectra are A-weighted and decibel-summed to determine the resulting A-weighted levels L_A,866A and L_A,ref — which are then subtracted arithmetically:

(D-4)