A new procedure has been developed for determining the absorption experienced by pure-tone sound waves propagating through the atmosphere. The procedure, which accounts for classical absorption processes (viscosity and heat conduction) as well as molecular energy transfer mechanisms, has a firm theoretical basis, has been extensively verified by laboratory experiment, and has been issued recently as an American National Standard ANS 1.26-1978. To apply the procedure of ANS 1.26 to determination of atmospheric absorption losses experienced by wideband random noise required development of a method that took into account the slope of the power spectrum of the sound pressure at the microphone. An important application of the method would be to adjust a measured 13-octave-band sound-pressure-level spectrum for differences in atmospheric absorption occurring under test and reference meterological conditions. Development and verification of the method are described for application to measurements of aircraft flyover noise. [Work supported by the Federal Aviation Administration.]