AD-A262 600 SPEAKMAN DTICSELECTE C MODELING LATERAL ATTENUATION OF AIRCRAFT FLIGHT NOISE

to. 0L Airbase and/or airport noise prediction models • such as the Air Force NOISEMAP computer program are used to forecast the long term noise exposure from aircraft flight and ground activity at a facility. Noise contour maps from these calculations are used to assess the potential adverse effects such noise may have on the environ and to assist nearby communities in performing compatible land use planning. To calculate the noise exposure at any specified ground position located to the side of a flight path, a variety of noise attenuation mechanisms must be accounted for if the-=del is to predict levels that are in reasonable agreement with! field noise measurements. For such locations, the attenuation effects are usually grouped as being due to: (1) wave divergence (spherical spreading)', (2) atmospheric absorption, and (3) lateral attenuation (the combined attenuation due to ground, meterological, forward flight, and engine/airplane installation effects). Because of the complexity of the frequency dependentinteraction of these phenomena affecting lateral attenuation, most attempts in recent years (Ref 1,2,3,4,5,6) to improve the technical basis of the simplified algorithms used in airbase/airport noise "models have defined lateral attenuation as a function of elevation angle in terms of a variety of single event measures such as the Sound Exposure Level. For civil aircraft the lateral attenuation model developed by the Society of Automotive Engineers, Inc. A-21 Committee on Aircraft Noise (Ref 5) is commonly used. Since it was derived mainly from measured lateral attenuation data on civil aircraft, the predicted results generally show good agreement when compared with actual measurements. However, th