Sound-speed profiles determined from outdoor sound propagation measurements

Measurements of sound propagation over distances up to 1000 m were carried out with a plasma impulse sound source generating reproducible, short time signals of high peak level. The measured travel time difference between direct and ground reflected wave allows for determination of the sound-speed profile in the atmospheric surface layer. A simple relationship was found between measured travel time difference and the scaling parameter of a logarithmic sound-speed profile. According to Monin–Obukhov similarity theory a logarithmic-linear profile can be used to describe the refraction profile for stable conditions (i.e., positive temperature gradient). In this case, two travel time measurements at different heights are necessary to determine the profile parameters. The acoustically derived profiles show good agreement with those deduced from wind speed and temperature measurements made at several heights above ground in conjunction with the acoustic measurement. Ray tracing is used for the discussion of meteorological effects on sound propagation in profiles with a positive gradient of refraction (i.e., sound speed increasing with height).