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Nov 1976

Volume 60, Issue S1, pp. S1-S125

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back to top Session UU. Physical Acoustics VII: Atmospheric Acoustics/Physical Acoustics
Contributed Papers
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Study of the behavior of radiational inversions with a calibrated acoustic sounder (A)

B. R. Kerman, H. E. Turner, R. E. Mickle, and W. Clink

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S114 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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A calibrated acoustic sounder developed by the Atmospheric Environment Service of Canada is compared to an in situ sensor measuring the acoustic backscatter cross‐section directly, Some deficiencies in the calibration technique and discrepancies with the in situ sensor are analyzed. The vertical structure of the acoustic backscatter cross‐section during various stages of a radiational inversion is examined in conjunction with supporting temperature, humidity and velocity data taken from a tethered balloon system.
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Antennas for sodar systems (A)

U. I. Kurze

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S114 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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The remote probing of the thermal structure and the wind velocity in the lower atmosphere requires highly directive antennas, which should have a half‐power beam width of about ± 6° (3‐dB points), a 90°‐side‐lobe suppression of at least 40 dB, little volume reverberation, low wind sensitivity, and be made of weather‐proof material. Various off‐axis parabolic horn antennas have been built and acoustically evaluated, considering additional requirements of mobility. The performance of shielding tubes and their absorbent lining, the transmission loss of the antenna walls and the influence of antennas of different size have been evaluated both theoretically and experimentally. Detailed studies of antenna elements are supplemented by field applications of sodar systems.
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Observation of upper atmosphere warmings with the use of natural infrasound (A)

D. Rind and W. L. Donn

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S114 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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Natural infrasound of 5 sec period is generated by interfering ocean waves in the Atlantic Ocean to the east of our location. Our normal amplitude pattern of infrasound in winter is characterized by semidiurnal and diurnal oscillations associated with reflecting tidal winds in the lower thermosphere [W. L. Donn and D. Rind, J, Atmos, Sci, 29, 156–172 (1972); D. Rind and W. L. Donn, J. Atmos. Sci. 32, 1694–1704 (1975)], Occasionally an amplitude pattern featuring continuously strong signal throughout the day is observed. Eight of these cases were investigated and it is shown, with the use of observations at Wallops Island, that seven of these coincide with observed stratospheric warmings during which east winds replace west winds, allowing for reflection of signal from the east at 40–50 km. The continuously high amplitudes result from reflection in the stratosphere where strong dissipation and tidal winds are minimal. Conversely when stratospheric westerlies diappear at times of warmings, infrasound from the Pacific diminishes at western stations, Continuous high‐amplitude patterns not associated with an observed upper air warming are discussed as perhaps signifying unnoticed mesophere and lower thermosphere warmings.
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Leaking modes in the propagation of atmospheric acoustic‐gravity waves (A)

W. A. Kinney and A. D. Pierce

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S114 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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Attempts to predict the transient acoustic pressure pulse at long horizontal distances from large explosions in the atmosphere have adopted a model atmosphere bounded above by a halfspace of finite sound speed and have represented the waveform as a superposition of contributions from dispersively propagating guided modes. Certain modes at low‐frequency decay exponentially (leaking modes) with increasing distance of propagation. Until now, the practice has been to neglect the contributions from leaking modes at low frequency. The theory associated with leaking modes at low frequency. The theory associated with leaking modes has been previously discussed in detail [V. A. Kinney, A. D. Pierce, and C. Y. Kapper, J. Acoust. Soc. Am. 58, S108(A) (1975)]. Examples of numerically synthesized transient waveforms are now exhibited with and without the inclusion of leaking modes. The inclusion of leaking modes results in waveforms each having a marked beginning rather than a low‐frequency oscillating precursor of gradually increasing amplitude as previously obtained. Also, the revised computations indicate that waveforms invariably begin with a pressure rise; a result supported by other theoretical considerations and experimental data. [Work supported by Air Force Geophysics Laboratory.]
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Upper atmosphere circulations as observed with the use of natural infrasound (A)

D. Rind

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S114 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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Natural infrasound of 5‐sec periods is generated continuously by ocean waves to the east of our location. The amplitude characteristics and horizontal phase velocity are functions of the acoustic reflection characteristics of the upper atmosphere. The monthly patterns of the observed acoustic parameters, culled from eight years of continuous observations, are reviewed and compared to the existing knowledge of 30–120‐km winds and temperatures. Included in the discussion are (1) the percentages of observed semidiurnal and diurnal amplitude oscillations for each month, related to the reliability of these tides in the upper atmosphere; (2) annually repeating oddities in each month such as a late March increase in semidiurnal tidal strength and varying meridional wind influences from summer to winter; and (3) the failure of current atmospheric models to correctfy predict the observed lower thermosphere sound velocity at 0400 which is much greater from the east then predicted.
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Sound reflection from locally reacting surfaces of finite extent (A)

W. James Hadden, Jr., Robin A. Vidimos, and Philip M. Sencil

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S114-S115 (1976); (2 pages)

Online Publication Date: 11 Aug 2005

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An approximation for the scattering of spherical waves by a rectangular patch with finite acoustic impedance is presented. Comparisons are made with laboratory experiments in which sound pressure levels were measured in the direction of specular reflection. Particular attention is given to the way in which both the theoretical and experimental results approach the limiting case of a plane surface with finite acoustic impedance.
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Acoustic/seismic coupling phenomenology (A)

J. G. Constantine and R. B. WaLker

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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This paper summarizes the results of a recent experiment that was designed to characterize the signal generation and propagation media in order to develop an acoustic/seismic signal propagation model. Specifically, this paper discusses the coupling of acoustic energy in the soil as a function of frequency; the observation of signal amplitude variations as a function of distance and frequency; and the measurement of signal distortion through the calculation of the normalized correlation and coherence function. It has been found that acoustic/seismic cross properties provide good discrimination parameters and that seismic and acoustic differential propagation velocity and seismic multimode propagation velocity can be used to provide ranging information; that the signal amplitude is a direct function of the soil coupling properties and soil inhomogeneities; and that the acoustic/seismic, as well as the seismic propagation channel, is nonlinear and can be best characterized through the application of Weiner's nonlinear theory.
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Radiation in a random medium (A)

Alan R. Wenzel

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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A theoretical investigation of the wave field radiated by a point source in a random medium is described. The analysis, which is based on the smoothing method, deals specifically with time‐harmonic waves in a medium which is statistically homogeneous and isotropic. Approximate results are obtained for the special case in which the wavelength is much less than the correlation length of the medium. These results show that, in a mean‐square sense, the randomness of the medium leads to a slight amplification of the wave field. [Work supported by NASA.]
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Acoustically induced instabilities of control valves (A)

Uno Ingard

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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Recent theoretical and experimental studies of acoustically induced axial oscillations of control valves are reviewed, and a mechanism for acoustically induced lateral oscillations is proposed. Possible methods of quenching the instabilities are also discussed. [Work supported by ONR.]
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Mechanical response of the lung at high frequency (A)

J. J. Fredberg and A. Hoening

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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For the purposes of learning about pulmonary structure, interpretation of high frequency impedance of branching airway systems may be facilitated by a theoretical prediction of input impedance. We have developed ways of treating special classes of asymmetry in branching structures which simulate a variety of observations unaccounted for in current symmetric models. This self‐consistent analysis, which assumes that small sub‐units can be joined in an appropriate manner to simulate ever‐larger branching structures, also incorporates the geometric and dynamic properties of the airway walls and enclosed gas. This analysis has been successfully applied to models of adult and infant lungs, and mirrors trends found in existing data. The model also suggests quantitative and qualitative dependences of system impedance responses to certain airway system characteristics, such as wall properties, branching asymmetry, and central and peripheral airway obstructions. Modal overlap and clumping are observed. Wall properties and branching asymmetry are both found to be important at low frequencies (≲1 kHz), while the asymmetric nature of the structure predominates at higher frequencies (≳3 kHz). The effect of central airway obstructions is most marked at higher frequencies (>2 kHz) where the number of apparent modes has decreased as modal regularity increases. Peripheral airway obstructions, in contrast, have small effect at high frequency.
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Acoustic nonspecular scattering from a plate with line impedance discontinuities (A)

Peter R. Stephanishen

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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An approach is presented to investigate the acoustic nonspecular bistatic scattering of an incident acoustic plane wave by a fluid loaded plate with line impedance discontinuities. The approach is based on the extension of a method which was presented in an earlier paper [P. R. Stepanishen, J. Acoust. Soc. Am. 59, S32(A) (1976)] to investigate the effect of a single discontinuity on the acoustic transmission and scattering from a plate. The total scattered field is expressed as a sum of a specular reflected plane wave and a sum of scattered cylindrical waves which originate at the discontinuities on the plate which is described by Timoshenko‐Mindlin plate theory. The scattering strengths of the cylindrical waves can exhibit highly directional characteristics and are expressed, using Fourier transform methods, as the solution of a linear set of coupled equations. Several special cases are investigated and discussed. In particular, it is noted that when the effects of the acoustic‐elastic interactions between the scatterers or impedance discontinuities can be neglected, the nonspecular scattered field can be expressed as a product of two terms, i.e., the nonspecular scattered pressure from a single discontinuity times an equivalent scattering array factor.
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Edge mode radiation due to a fluid‐loading discontinuity (A)

M. Pierucci

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S115-S115 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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Edge mode radiation is determined for an infinite membrane with a discontinuous fluid loading condition. The membrane is assumed to be line driven. The lower portion of the membrane (y < 0) is exposed to a very light fluid which imposes no fluid leading on the structure. The upper half of the membrane (y > 0) is split up into two regimes (x < 0 and x > 0). The x < 0 regimes imposes fluid loading conditions on the membrane vibration while the x > 0 region is assumed to be a vacuum. The two upper regimes are separated by an acoustic anechoic surface. The radiated acoustic intensity as a function of frequency for different surface tensions and angular positions is derived and results are presented. [Portion of this work was sponsored by NAVSEA.]
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