Michael R. Stinson
Inst. for Microstructural Sciences, Natl. Res. Council, Ottawa, ON K1A 0R6, Canada
The influence of the vertical sound-speed profile on sound propagation in an acoustic shadow has been investigated. For upwardly refracting conditions with both source and receiver near the ground, the profile in the first couple of meters nearest the ground can be critically important in determining the sound-pressure level in the acoustic shadow. A meteorological tower has been used to determine sound-speed profiles, in conjunction with acoustical propagation experiments. Wind speed and direction measured at a 10-m height and temperatures measured at heights of 8.7 and 2 m are used with similarity scaling expressions [L'Esperance et al., Appl. Acoust. 40, 325--346 (1993)] to obtain predicted vertical profiles for wind speed, temperature, and sound speed. These predicted profiles can be tested using additional measurements of wind speed and temperature at other heights. It is found that the similarity-based profiles do not always describe the actual profiles close to the ground. The implications for the prediction of sound fields in an acoustic shadow are investigated numerically using a fast, parabolic equation approach that includes profile, atmospheric turbulence, and ground impedance effects.