Experiments on surface waves over a model impedance plane using acoustical pulses

Experiments studying the propagation of acoustical pulses above a model surface are described. Under appropriate conditions, sound waves traveling in the horizontal direction above an impedance plane consist of a body wave and a surface wave. The body wave propagates at the speed of sound in air c while the surface wave is characterized by phase velocity nu<c and an amplitude that decreases exponentially with vertical height above the surface. Calculations of acoustical pulses propagating above an idealized impedance plane confirm these characteristics and show the surface wave as a distinct arrival from the body wave. Measurements have been made of pulses generated from a point source above a model surface consisting of a square lattice of cavities. The impedance of the surface was measured and theoretically modeled. The impedance values were used to compute predicted pulses. There is good agreement between the measured and predicted acoustical pulses.