ACOUSTIC PULSE-PROPAGATION ABOVE GRASSLAND AND SNOW - COMPARISON OF THEORETICAL AND EXPERIMENTAL WAVE-FORMS

Theoretical predictions are made of the effect of an absorbing ground surface on acoustic impulsive waveforms propagating in a homogeneous atmosphere for frequencies below 500 Hz. The lower frequencies of the pulse are enhanced as the effective flow resistivity of the ground surface decreases and as the propagation distance increases. The pulse waveforms and peak amplitude decay observed for propagation distances of 40 to 274m over grassland were satisfactorily matched by calculations using an assumed effective flow resistivity of 200 kNs m~4. Measurements over snow gave much greater amplitude decay rates, and the waveforms were radically changed in appearance, being dominated by the lower frequencies. These waveforms were satisfactorily matched only when a layered ground was incorporated into the calculations; then, an assumed surface effective flow resistivity of 20 kN sm-4gave good agreement with the observed waveforms and peak amplitude decay. © 1990, Acoustical Society of America. All rights reserved.