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The effect of atmospheric pressure on measured aircraft noise levels.

Payne, R C (1994) The effect of atmospheric pressure on measured aircraft noise levels. NPL Report. RSA(EXT) 48

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Noise certification of subsonic jet aeroplanes, heavy propeller-driven aeroplanes and helicopters is carried out using the procedures described in the hlternational Civil Aviation Organization (ICAO) document Annex 16. Measured noise levels are corrected to reference atmospheric conditions to allow for differences in air attenuation resulting from variations in ambient temperature and relative humidity. The attenuation is calculated using the Society of Automotive Engineers standard ARP 866A. This procedure does not include the effect of ambient atmospheric pressure.
This Report discusses the influence of atmospheric pressure on the attenuation of sound transmitted to the ground during noise certification tests carried out using airfields at altitude. ARP 866A and three alternative procedures that include the effect of atmospheric pressure are assessed, and calculations are made of air attenuation rates based on reference atmospheric pressure and pressures that are representative of those that occur at airfields located at altitudes of up to 10000 feet (3048 m). Comparison of these attenuation rates shows differences that are dependent on temperature, relative humidity, frequency and altitude. For combinations of low temperature/low humidity or high temperature/high humidity, attenuation rates calculated using ARP 866A are greater than those predicted using the other three procedures. For combinations of temperatures less than about 10 °C and relative humidities less than about 70%, attenuation rates are larger at altitude.
The effect of these differences on EPNL evaluation is difficult to assess as it is dependent not only on meteorological conditions, but also on spectral shape and propagation distance. The effect is likely to be small. However, in order to draw defInitive conclusions about EPNL evaluations and the significance of neglecting the effect of atmospheric pressure on attenuation rates, further work is required using a representative sample of certification test data.

Item Type: Report/Guide (NPL Report)
NPL Report No.: RSA(EXT) 48
Subjects: Acoustics
Last Modified: 02 Feb 2018 13:19
URI: http://eprintspublications.npl.co.uk/id/eprint/90

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