This report presents the results of a test program conducted to measure the effect of varying meteorological conditions on aircraft flyover noise levels. Detailed temperature and humidity data were obtained using an instrument system carried by a light aircraft. High and low altitude inversions as well as standard lapse rate atmospheres were investigated. Level flyovers were conducted, using a DC-9-10 aircraft operated at a thrust of 6,000 lbs., as a constant noise source. Measured noise levels varied up to 4 EPNdB depending upon the absorptive properties of the atmosphere. Several analysis procedures were investigated in an effort to correct noise data for weather conditions. Weather correction procedures based on single point meteorological data were inadequate to normalize, to reference conditions, the noise data for those conditions with non-uniform temperature and humidity profiles. A layered analysis procedure, however, normalized all flyover noise levels to those levels taken under near reference conditions. The layered analysis procedure incrementally adjusts the measured peak spectra based on the acoustic absorption in each increment. These results indicated that noise certification testing under non-uniform temperature and humidity conditions could, if allowed, be conducted provided that frequent and detailed meteorological data is available and the layered weather correction procedure is used.

"TRB's Airport Cooperative Research Program (ACRP) Synthesis 9: Effects of Aircraft Noise: Research Update on Select Topics includes an annotated bibliography and summary of new research on the effects of aircraft noise. The report is designed to update and complement the U.S. Federal Aviation Administration's 1985 Aviation Noise Effects report"--Publisher's description

An analysis has been performed of measured and predicted aircraft noise levels around Denver International Airport. A detailed examination was made of 90 straight-out departures that yielded good measurements on multiple monitors. Predictions were made with INM 5, INM 6 and the simulation model NMSIM. Predictions were consistently lower than measurements, less so for the simulation model than for the integrated models. Lateral directivity ("installation effect") patterns were seen which are consistent with other recent measurements. Atmospheric absorption was determined to be a significant factor in the underprediction. Calculations of atmospheric attenuation were made over a full year of upper air data at seven locations across the United States. It was found that temperature/humidity effects could cause variations of up to +/-4 dB, depending on season, for the sites examined. It was concluded that local temperature and humidity should be accounted for in aircraft noise modeling.Plotkin, Kenneth J. and Shepherd, Kevin P. (Technical Monitor)Langley Research CenterNOISE PREDICTION; AIRCRAFT NOISE; ACOUSTIC PROPAGATION; SOUND PROPAGATION; NOISE INTENSITY; MODELS; TEMPERATURE EFFECTS; DIRECTIVITY

Noise certification of subsonic jet aeroplanes, heavy propeller-driven aeroplanes and helicopters is carried out using the procedures described in the International 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 degrees Celsius 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.