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. Two computer programs are provided@ A0411 and B0411. Program A0411 can be used to predict sound attenuation. Program B0411 allows the user to generate input files easily.