Application of atmospheric absorption models for aircraft enroute noise

Propagation of aircraft enroute noise for flights above 18 000 ft above ground level (AGL) (5.49 km AGL) is important for estimating noise impact in U.S. National Parks and other quiet areas. One key to the accurate estimation of noise impact is atmospheric absorption. In our atmosphere, it turns out that the absorption coefficient is dependent on altitude as well as frequency. The altitude dependent parameters include mean pressure, temperature, and relative humidity as well as the concentration of molecular species. This altitude effect can be important for certain frequency bands, and this point will be emphasized in this paper. In addition, an improved atmospheric absorption model for high altitudes of Sutherland and Bass [J. Acoust. Soc. Am. 115, 1012–1032 (2004)] shows slightly different values of atmospheric absorption in important frequency bands for aviation noise at altitude compared to the typical ANSI Standard S1.26-1995 (R 2009). For certain situations, the updated atmospheric absorption coefficient could produce different enroute noise predictions on the ground. [Work supported by FAA/NASA/Transport-Canada PARTNER Center of Excellence.]