Division: Calculations in homogeneous conditions - Commission Directive (EU) 2015/996 of 19 May 2015 establishing common noise assessment methods according to Directive 2002/49/EC of the European Parliament and of the Council (Text with EEA relevance)

The attenuation due to the ground effect in homogeneous conditions is calculated according to the following equations:

if G_path ≠ 0

A_{ground,H} = \max (- 10 \times \lg [4 \frac{k^{2}}{d_{2}^{p}} (z_{2}^{s} - \sqrt{\frac{2 C_{f}}{k}} z_{s} + \frac{C_{f}}{k}) (z_{2}^{r} - \sqrt{\frac{2 C_{f}}{k}} z_{r} + \frac{C_{f}}{k})], A_{ground,H,min})

(2.5.15)

where

fm is the nominal centre frequency of the frequency band considered, in Hz, c is the speed of the sound in the air, taken as equal to 340 m/s, and C_f is defined by:

C_{f} = d_{p} \frac{1 + 3 {wd}_{p} e^{- \sqrt{{wd}_{p}}}}{1 + {wd}_{p}}

(2.5.16)

where the values of w are given by the equation below:

(2.5.17)

Ḡ_w may be equal to either G_path or G′_path depending on whether the ground effect is calculated with or without diffraction, and according to the nature of the ground under the source (real source or diffracted). This is specified in the following subsections and summarised in Table 2.5.b.

(2.5.18)

is the lower bound of A_ground,H .

For a path (S_i,R) in homogeneous conditions without diffraction:

Ḡ_w = G′_path
Ḡ_m = G′_path

With diffraction, refer to the section on diffraction for the definitions of Ḡ_w and Ḡ_m .

if G_path = 0: A_ground,H = – 3 dB

The term – 3(1 – Ḡ_m ) takes into account the fact that when the source and the receiver are far apart, the first reflection source side is no longer on the platform but on natural land.

Division Calculations in homogeneous conditions