Inclined acoustic sounding of the atmospheric boundary layer

Abstract

The method of inclined acoustic sounding of the atmospheric boundary layer has been proposed and realized experimentally. The method is based on the phenomena of the waveducted sound propagation along ground surface under the presence of the positive wind shear. In the experiment the wind velocity profiles and their large-scale time fluctuations were continuously controlled with the SODAR up to the height of 300 m and with the anemometers placed at the mast of 56 m height. The fluctuations of the acoustic pulse travel time with the periods in the range of 3–30 min were measured between the special pulse generator and the three receivers placed on the ground surface 2.5 km apart from each other, forming a horizontal triangle antenna. The obtained cross coherence and phase spectra between the pulse travel time and the wind velocity fluctuations show a peak of coherence with the maximum of about 0.8 to 0.9 for the period of 8 min. Such low-frequency wind velocity fluctuations near the ground surface are thought to be caused by the gravity wave modes propagating in the stable stratified troposphere with the periods close to the Brunt–Vaisalla period. The inclined acoustic sounding is proposed to be used for the acoustic tomographic monitoring of the three-dimensional wind field in the atmospheric boundary layer.