Air-ground interaction in long range propagation of low frequency sound and vibration-field tests and model verification

An extensive program of intermediate and long range impulsive sound propagation field tests have been conducted. The test program and the performed measurements are presented. Particular focus is given on the air-ground interaction and its effect on low frequency sound and vibration propagation. It is found that the pressure wave interaction with the viscoelastic Rayleigh wave in the ground may have a significant effect on the ground impedance and the sound and vibration propagation. This introduces an important mechanism not covered in commonly used ground impedance models. Numerical simulation models have been developed and verified against the test data. The ground impedance does not only effect the sound pressure propagation. If either acoustically induced ground vibration, or ground to building transmitted vibration, is to be considered, the acousto-seismic impedance has a dramatic effect on the level of ground vibration induced by a given sound pressure. For a site where Rayleigh wave interaction appears at the dominant frequencies of the sound pressure, the ground vibration may be greater than a factor 100 (40 dB) than at a site with ground conditions not making the interaction happen.