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Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficientIn atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.
Document ID
19910007372
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Daigle, Gilles
(National Research Council of Canada Ottawa Ontario, Canada)
Embleton, Tony
(National Research Council of Canada Ottawa Ontario, Canada)
Date Acquired
September 6, 2013
Publication Date
December 1, 1990
Publication Information
Publication: NASA, Langley Research Center, 4th International Symposium on Long-Range Sound Propagation
Subject Category
Acoustics
Accession Number
91N16685
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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