Effects of excess ground attenuation on aircraft noise contours
Keywords:acoustic noise, acoustic wave absorption, atmospheric acoustics, airport noise prediction programs, expected noise level contours, ground attenuation, aircraft noise source, acoustical impedance, aircraft fly-by, ground-to-ground propagation, air-to-ground propagation
AbstractVarious airport noise prediction programs are used to calculate expected noise level contours around airports based on the details of the aircraft operations. One of the major factors influencing these contours is the excess attenuation of the sound from the aircraft when the sound is propagating at near grazing incidence to the ground. When considered in detail, this excess attenuation is a complex phenomenon, but airport noise prediction programs use quite simple approximations to estimate the effect of excess ground attenuation. The attenuation of sound from an aircraft traveling close to the ground will depend on a number of factors that will vary as the aircraft passes by. The attenuation will be influenced by the spectrum and directionality of the aircraft noise source and these effects will vary with time as the aircraft passes an observation point. The resulting attenuation will also be influenced by the acoustical impedance of the ground as well as various meteorological effects. Thus, to accurately predict the attenuation of the sound from an aircraft, quite complex calculations would be required on a point by point basis as the aircraft passes an observation point. Most airport noise prediction programs include only quite simple approximations to these complex effects. The influence of each aircraft fly-by is typically only calculated for the point of closest approach to the observation point and not as a complete point-by-point calculation for the complete fly-by. Usually, only overall A-weighted or PNL-weighted levels are considered. The excess ground attenuation is usually calculated in two separate parts: (a) ground-to-ground propagation, and (b) air-to-ground propagation
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