# 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), Appendix C: Modelling of lateral ground track spreading

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

It is recommended that, in the absence of radar data, lateral ground track dispersion be modelled on the assumption that the spread of tracks perpendicular to the backbone track follows a Gaussian normal distribution. Experience has shown that this assumption is a reasonable one in most cases.
Assuming a Gaussian distribution with a standard deviation S, illustrated in Figure C-1, about 98,8 percent of all movements fall within boundaries of ± 2,5·S (i.e. within a swathe of width of 5·S).
Figure C-1
Subdivision of a ground track into 7 subtracks
(The width of the swathe is 5 times the standard deviation of the ground track spreading)
A Gaussian distribution can normally be modelled adequately using 7 discrete sub-tracks evenly spaced between the ± 2,5·S boundaries of the swathe as shown in Figure C-1.
However, the adequacy of the approximation depends on the relationship of the sub-track track separation to the heights of the aircraft above. There may be situations (very tight or very dispersed tracks) where a different number of subtracks is more appropriate. Too few subtracks cause ‘fingers’ to appear in the contour. Tables C-1 and C-2 show the parameters for a subdivision into between 5 and 13 subtracks. Table C-1 shows the location of the particular subtracks, Table C-2 the corresponding percentage of movements on each subtrack.
Table C-1
Location of 5, 7, 9, 11 or 13 subtracks
(The overall width of the swathe (containing 98 % of all movements) is 5 times the standard deviation)
Subtrack number
Location of subtracks for subdivision into
5 subtracks
7 subtracks
9 subtracks
11 subtracks
13 subtracks
12/13
± 2,31·S
10/11
± 2,27·S
± 1,92·S
8/9
± 2,22·S
± 1,82·S
± 1,54·S
6/7
± 2,14·S
± 1,67·S
± 1,36·S
± 1,15·S
4/5
± 2,00·S
± 1,43·S
± 1,11·S
± 0,91·S
± 0,77·S
2/3
± 1,00·S
± 0,71·S
± 0,56·S
± 0,45·S
± 0,38·S
1
0
0
0
0
0
Table C-2
Percentage of movements on 5, 7, 9, 11 or 13 subtracks
(The overall width of the swathe (containing 98 % of all movements) is 5 times the standard deviation)
Subtrack number
Percentage of movements on subtrack for subdivision into
5 subtracks
7 subtracks
9 subtracks
11 subtracks
13 subtracks
12/13
1,1 %
10/11
1,4 %
2,5 %
8/9
2,0 %
3,5 %
4,7 %
6/7
3,1 %
5,7 %
7,1 %
8,0 %
4/5
6,3 %
10,6 %
12,1 %
12,1 %
11,5 %
2/3
24,4 %
22,2 %
19,1 %
16,6 %
14,4 %
1
38,6 %
28,2 %
22,2 %
18,6 %
15,6 %

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