EFFECTIVE FLOW RESISTIVITY OF GROUND SURFACES DETERMINED BY ACOUSTICAL MEASUREMENTS

It is shown that a single-parameter theory can be used to predict the measured transmission spectra between a source and receiver located above ground surfaces having a wide range of acoustic impedance, or effective flow resistivity. Surfaces behaving essentially as locally reacting range from new-fallen snow, effective flow resistivity sigma equals 10 - 30 cgs rayls, through grass-covered ground, sigma equals 150 - 300 rayls, to mature asphalt, sigma equals 30,000 rayls. The thermal-conduction and viscous boundary layer of the surface limits the effective flow resistivity of even the hardest and most impervious surface to the range 10**5 - 10**6 rayls, depending on frequency: this value is appropriate to evaluate the complex reflection coefficient of the paint-sealed surface of a thick slab of reinforced concrete.