Experimental study of air-to-ground lateral attenuation using results of long-term noise monitoring at Narita airport

This paper describes a result of examination on the validity of equations for calculating lateral attenuation for air-to-ground sound propagation of aircraft flyover noise under various meteorological conditions, using long-term unattended noise monitoring at Narita Airport. It is indispensable to take account of lateral attenuation when modeling airport noise. Thus, we have examined whether existing equations such as SAE/AIR 5662 and our 1751M can correctly evaluate lateral attenuation for flyover noise of recent aircraft, using results of long-term noise monitoring and repeated short-term noise measurements. Our study sixteen years ago showed that air-to-ground lateral attenuation rapidly decreased when elevation angle of sound arrival direction became higher than about 10-15°. As a result, we proposed a modified equation (1751M) available under various meteorological conditions expressed in vector wind and temperature gradient. Since then, however, long time passed and a lot of new types of aircraft were introduced. Having compared noise predictions with measurements for recent aircraft, we suspected that 1751M gives a bit underestimation of lateral attenuation. On the other hand, SAE issued a new equation AIR 5662 as a reformulation of AIR 1751 in 2006. It gives a positive value of lateral attenuation at elevation angles of about 10-30°, differently from 1751M. Therefore, we decided to examine which of the two equations AIR 5662 and 1751M gives a more reliable estimation of ATG lateral attenuation. We carried out examination of air-to-ground lateral attenuation, applicable to various meteorological conditions, from noise observations of middle and small sized aircraft installed with twin engines, by using data of long-term noise monitoring at Narita. This paper also shows a comparison of lateral attenuation obtained from measurement with that calculated using AIR 5662.