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Ground Impedance Measurement Over a Range of 20 m

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In the course of aircraft signal measurements on the military airport at Jever, Germany, the surface impedance of the grass-covered ground was determined from c. 60 Hz to 2.2 kHz. Complex transfer functions were measured over ranges of up to 20 m using (quasi-)white noise and a numerical inversion of the spherical wave reflection factor. The relatively long range enables to determine an effective surface impedance, which is an average over a patch of the ground within the measurement set-up. The resulting normalised impedance shows a real part, i.e. the resistance, decreasing from around 6 to around 2 at frequencies from around 100 Hz to around 1.2 kHz and increasing again above c. 1.2 kHz. Its imaginary part, i.e. the reactance, decreases from around 8 to around 2 in the same frequency range and increases again above c. 1.2 kHz. The increase beyond c. 1.2 kHz may be due to the influence of turbulence.

A comparatively simple two-parameter model has been fitted to the measured impedance. It results in an effective flow resistivity e = 100 kPas/m2 and an effective rate of porosity decrease with depth of αe = 9 m−1.
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Document Type: Research Article

Publication date: September 1, 1999

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  • Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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