Operation of a monostatic acoustic sounder on the campus of The University of Calgary for the period March to September, 1976, has provided data on the atmospheric boundary layer over Calgary. The formation and dissipation of the nocturnal temperature inversion layer leaves a clear signature in the sounder records. A trend is discerned in which the nocturnal layer tends to form at sunset, whereas convective instability is established some 2-3 hours after sunrise. Comparison of sounder records with an extensive set of radiosonde temperature profiles has shown that the height of the inversion layer can be determined reliably when a single, dark, ground-based return is visible on the sounder charts. On many occasions, however, the sounder detects multiple structures in the atmosphere. In these cases, it is difficult to establish a systematic correspondence of the turbulent structure as observed in the sounder records with the temperature profile as observed by the radiosonde.

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An experimental investigation of the propagation of sound in the presence of an elevated temperature inversion has been conducted on a farm site in southern Alberta. The refractive focusing of sound in the inversion layer was observed to cause shadow zones and regions of sound enhancement in which sound levels were up to 20 dB lower and 20 dB higher, respectively, than during normal afternoon conditions. Fluctuations of 35 dB in the sound intensities at microphones 1730 and 2180 m from the source have been witnessed as the location of the focusing region changed. Ray tracing analysis for meteorolgical data acquired predicts excess attenuations of sound consistent with those recorded. The use of a monostatic acoustic sounder proved useful in correlating anomalous sound levels with the appearance of temperature inversions.

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An acoustic sounder array located on a rural site 20 km west of Calgary is described. The array is designed to sense atmospheric turbulence with a working vertical range of 2 km and also to provide information on the vertical wind profile up to 800 m above the site. The array consists of a central, vertically directed, monostatic array (output acoustic power ∼ 100 W), and four passive inclined receivers, each acting as a bistatic receiver for the central monostatic transmitter. The bistatic receivers are arranged along two mutually perpendicular horizontal baselines. On-line microprocessors are used to retrieve Doppler shift data from all receiver channels, and hence to calculate the wind profile. Typical results from the Doppler acoustic sounder array are presented. It is hoped that by the time of presentation, soundings will have been made during at least one Chinook event (a foehn-type wind associated with airflow over the nearby Rocky Mountains).