# 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), Division: Accounting for topography

Extent: E+W+S+N.I.

In cases where topography has to be taken into account (see Section 2.7.6), the aircraft height coordinate z has to be replaced by z′= z – zo (where zo is the z-coordinate of the observer location O) when estimating the propagation distance d. The geometry between aircraft and observer is shown in Figure 2.7.d. For the definitions of d and ℓ see Sections 2.7.14 to 2.7.19.
Figure 2.7.d
Ground elevation along (left) and lateral (right) to ground track
(The nominal ground plane z = 0 passes through the aerodrome reference point. O is the observer location.)

---
Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.10/division/4 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.10/division-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.