title: The near-ground structure of the nocturnal sound field.
abstract: The near-ground behavior of the low-frequency (100 Hz to 500 Hz) sound field in the nocturnal sound duct is studied theoretically and experimentally. In the first few meters of the atmosphere, narrow-band sound fields are found to have a characteristic vertical structure. The sound field is the superposition of a "surface mode," whose magnitude decreases monotonically with altitude, with a sum of "higher modes," each of whose magnitudes has a pronounced minimum a few meters from the ground at approximately the same height. The surface mode attenuates to negligible levels after a few hundred meters from the source. Consequently, more than a few hundred meters from a narrow-band source, there is a "quiet height" at which the sound level is reduced by 10 to 15 dB relative to its value on the ground. The narrow-band quiet height is shown to be a robust feature of nocturnal sound propagation.
authors.affiliation: National Center for Physical Acoustics, University of Mississippi, University, Mississippi 38677, USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Waxler
authors.forename: Carrick L
authors.initials: CL
authors.lastname: Talmadge
authors.forename: Shantharam
authors.initials: S
authors.lastname: Dravida
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Gilbert