A Method for Determining the Radiation Characteristics of Aircraft in Flight Free

Information on the basic characteristics of aircraft noise sources during flight requires that a methodology be established which can adequately determine total acoustic power, directivity, and frequency characteristics from sound pressure measurements. A procedure is presented for transposing from sound‐pressure‐time information received at a stationary ground point to information on the radiation characteristics of the moving source. Included are such physical mechanisms as propagation time lags, energy losses through a diverging sound field, atmospheric absorption losses, and Doppler shifts in frequency. A graphical approach is utilized wherever feasible to facilitate calculation. The method is equally applicable to cases where the microphone is in motion parallel to the axis of an axially symmetrical sound source at rest.