# 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: Geometric parameters

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

Figures 2.7.j to 2.7.l show the source-receiver geometries when the observer O is (a) behind, (b) alongside and (c) ahead of the segment S1S2 where the flight direction is from S1 to S2 . In these diagrams
O is the observer location
S1 , S2 are the start and end of the segment
Sp is the point of perpendicular closest approach to the observer on the segment or its extension
d 1, d 2 are the distances between start, end of segment and observer
ds is the shortest distance between observer and segment
dp is the perpendicular distance between observer and extended segment (minimum slant range)
λ is the length of flight path segment
q is the distance from S1 to Sp (negative if the observer position is behind the segment)
Figure 2.7.j
Flight path segment geometry for observer behind segment
Figure 2.7.k
Flight path segment geometry for observer alongside segment
Figure 2.7.l
Flight path segment geometry for observer ahead of segment
The flight path segment is represented by a bold, solid line. The dotted line represents the flight path extension which stretches to infinity in both directions. For airborne segments, when the event metric is an exposure level LE , the NPD distance parameter d is the distance dp between Sp and the observer, called the minimum slant range (i.e. the perpendicular distance from the observer to the segment or its extension, in other words to the (hypothetical) infinite flight path of which the segment is considered to be part).
However, for exposure level metrics where observer locations are behind the ground segments during the takeoff roll and locations ahead of ground segments during the landing roll, the NPD distance parameter d becomes the distance ds , the shortest distance from the observer to the segment (i.e. the same as for maximum level metrics).
For maximum level metrics, the NPD distance parameter d is ds , the shortest distance from the observer to the segment.

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.7/division/2.7.18/division/1 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.7/division-2.7.18/division-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.