Abstract:

ESDU 04011 can be used to predict sound attenuation in a turbulent atmosphere with wind and temperature gradients. A Fast Field Program is implemented to perform the prediction. The Item can be used to predict the ground reflection correction relative to free-field levels allowing the user to convert a frequency spectrum measured at a location to a free-field spectrum, or to infer a measured spectrum from a free-field spectrum. The effects of wind and temperature gradients are considered through the resulting variation of sound speed with height. The user is offered the choice between a linear or a logarithmic sound speed profile or may opt to enter specific sound speed values at different heights. Three computer programs are provided, A0411, M0411 and B0411. Programs A0411 and M0411 can be used to predict sound attenuation. Program B0411 allows the user to generate input files easily.