Effects of meteorology on predicted levels of aircraft noise Free

Calculation of average noise (e.g., Ldn) around airports generally ignores the effects of atmospheric gradients as these effects are assumed to average out over the course of a year. The validity of this assumption was tested through a numerical study using the aircraft noise simulation model NMSIM. Specifically, NMSIM was extended to account for three‐dimensional refraction by wind and temperature gradients, plus refraction and scattering into shadow zones, as well as ground impedance effect. Five years of meteorological data at a number of airport locations was obtained, and divided into hourly conditions. A nominal airport, based on a major air carrier airport, was defined. NMSIM was run for hourly operations and weather conditions at each airport location. The resultant Ldn contours were compared to each other by season and location, and also to contours computed for the baseline assumption of no gradients. [Work supported by NASA Langley Research Center.]