Construction of Ground Subtracks for Aircraft Noise Calculations Using an Estimate of Lateral Flight Dispersion

In the absence of position data such as radar data, aircraft noise calculations usually rely on the definition of flight geometries in terms of flight track and flight profile data. Typically, the ground track is constructed as a backbone track with a number of subtracks accounting for the lateral flight dispersion. Depending on the nature of the tracks, for instance when considering diverging tracks compared to very narrow tracks, the number of subtracks needs to be such that smooth noise contours and footprints are computed, putting a requirement on the minimum number of subtracks needed. In practice however, as the tracks need to be digitized by expert hand, the number of available subtracks is often limited. Furthermore, the location of the subtracks is often unknown, requiring corridor boundaries to be estimated and to be translated into subtrack locations. This paper presents a method for the construction of the required number of subtracks based on an estimate of lateral flight dispersion. Two cases are envisioned: the first being an estimate of the lateral flight dispersion using a set of three pre-existing subtracks (one backbone track and left/right subtracks), the second being an estimate using a backbone track and corridor boundaries. The method uses geometric matching of the original tracks, followed by an estimation of the local lateral track dispersion. The lateral distribution function is then used for the construction of new subtracks. A series of aircraft noise calculations using diff erent numbers of subtracks are shown, showcasing the influence of the number of subtracks on the noise contours, depending on the nature of the tracks (e.g.situations with tight turns).