Acoustic pulse propagation through stable atmospheric boundary layer: Theory and experiment

Abstract

Mesoscale wind speed and temperature fluctuations with periods from 1 min to a few hours significantly affect a variability and turbulent regime of stable atmospheric boundary layer (ABL). Their statistical characteristics are still poorly understood, although the knowledge of such statistics is required when modeling sound propagation through stable ABL. Several field experiments have been conducted to study the influence of mesoscale wind speed fluctuations on acoustic pulse propagation in stable ABL. The results of these experiments are presented in this work. A special acoustic source was used to generate acoustic pulses due to a detonation of air-propane mixture with a repetition period of 1 min or 30 s. The mean wind speed profiles and mesoscale wind fluctuations were measured by Doppler sodar up to a height of 300 m, and by anemometers placed on a 56-mast. From the measurements of the pulse travel time fluctuations at different distances from the source the statistical characteristics of the mesoscale wind fluctuations such as frequency spectra, coherences, horizontal phase speeds and scales have been obtained. Some of the obtained results are interpreted with a recently developed model of internal wave spectrum in a stably stratified atmosphere.