Division Ground track data

Aircraft ground tracks shall be described by a series of coordinates in the (horizontal) ground-plane. The source of ground track data depends on whether relevant radar data are available or not. If they are, a reliable backbone track and suitable associated (dispersed) sub-tracks shall be established by statistical analysis of the data. If not, backbone tracks are usually constructed from appropriate procedural information, e.g. using standard instrument departure procedures from Aeronautical Information Publications. This conventional description includes the following information:

• Designation of the runway the track originates from

• Description of the track origin (start of roll, landing threshold)

• Length of segments (for turns, radius and change of direction).

This information is the minimum necessary to define the core (backbone) track. But average noise levels calculated on the assumption that aircraft follow the nominal routes exactly can be liable to localised errors of several decibels. Thus lateral dispersion shall be represented, and the following additional information is necessary:

• Width of the swathe (or other dispersion statistic) at each segment end

• Number of subtracks

• Distribution of movements perpendicular to the backbone track.