Instrumentational Rôle in the Observation of Geoacoustical Phenomena from Artificial Sources

Fehr, Uri

doi:10.1121/1.1910708

Cited by 7 publications

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is claimed 21 that with acoustic filters hot-wire microphones could be used to detect sounds inaudible to the unaided ear. The thermistor microphone 22 has been used to detect long-range infrasound from rockets, 23 and has a frequency range from about 0-001 Hz upwards.…”

Section: Microphones For Infrasoundmentioning

confidence: 99%

Noise measurement and evaluation

Tempest¹,

Bryan²

1976

Proc. Inst. Electr. Eng. UK

View full text Add to dashboard Cite

This review outlines the history of noise measurement in the 'pre-electronic' era, and then goes on to describe current practice. The first five Sections are devoted to the 'engineering' aspects of the subject, i.e. the methods used to make physical measurements of noise parameters viewed as a series of pressure fluctuations in the air. As well as measurements at normal levels in the normal audio-frequency range, special techniques for unusually high and low frequencies and pressure levels are described,'together with integrating techniques to determine the total sound output from sources. The second half of the review is devoted to techniques of noise evaluation. This subject, which is currently an area of more activity than the physical measurement side, deals with the relationship between the measurable physical parameters of the noise and its effects on the human organism. These effects include annoyance, discomfort, interference with communication, and damage to hearing, they are due not only to noise in the audible-frequency range, but also to low-frequency and infrasonic noise. Those areas are indicated where present knowledge is limited and further research and standardisation are required.

show abstract

Section: Microphones For Infrasoundmentioning

confidence: 99%

Noise measurement and evaluation

Tempest¹,

Bryan²

1976

Proc. Inst. Electr. Eng. UK

View full text Add to dashboard Cite

show abstract

Energy propagation in the lower ionosphere and atmosphere produced by artificial disturbances, 1

Fehr¹,

McGahan²

1969

J. Geophys. Res.

View full text Add to dashboard Cite

A series of medium‐size explosions are monitored by a variety of ground sensors. A preliminary study of one typical explosion at 250 meters above the ocean surface has revealed many interesting results; from the acoustical signal the effects of the atmosphere on infrasonic waves generated as a pulse have been identified both as a function of frequency and as a function of distance. VLF and ELF electromagnetic signals have been observed by stations more than 100 kilometers from the explosion center. The signals are described fully, and the experimental objectives are summarized.

show abstract

1- to 16-Hz infrasound associated with clear air turbulence predictors

Posmentier¹

1974

J. Geophys. Res.

View full text Add to dashboard Cite

The 1-to 16-Hz infrasound detected by a four-element array of microphones was recorded for 75 s six times daily from April through June 1971. The spectra of these records are diurnally variable but stationary on a shorter time scale. The spectral slopes are inconsistent with theoretical spectral slopes of turbulent pressure fluctuations and of sound radiated by incompressible aerodynamic turbulence. It is hypothesized that the infrasound is radiated by a mechanism involving compressibility in aerodynamic turbulence. Four records were selected as being representative of extremely low amplitude conditions. Four other records were chosen as being representative of highly coherent strong amplitude records. These latter four records all exhibited very high horizontal phase speeds, implying near-vertical incidence. A search was made for meteorologic parameters that varied consistently with the acoustic data. It has been found that all four low amplitude records were from periods during which nonturbulent conditions probably existed between altitudes of 6 and 12 km. The four strong amplitude records coincide with times of high probability of clear air turbulence. The turbulence judgments are based on the wind speed, the directional shear, and Richardson's number, calculated from nearby rawinsonde data. It is concluded that 1-to 16-Hz infrasound may be radiated by clear air turbulence and may be a basis for a remote passive detection system. If this conclusion were confirmed, it would have significant implications for both practical and theoretical problems associated with clear air turbulence.Of the entire spectrum of infrasound the highest frequencies, those that are closest to audible frequencies, have probably been least subjected to scientific inquiry. The purpose of the study that is the subject of this report has been to explore the general nature of this higher-frequency infrasound, and the essential finding of the study has been the association of this infrasound with clear air turbulence (CAT) in the lower stratosphere.Wescott [1964] measured the spectra from 0.2 to 200 Hz of pressure fluctuations detected by balloon-borne acoustic probes at altitudes of 17-22 km. The median values of his spectra at 5 Hz were about 9 dB above those of our spectra, discussed below. Since his measurements were taken at high altitudes (and the pressure amplitude of a plane acoustic wave varies as the square root of the ambient pressure as it propagates vertically), they would normally be expected to be about 12 dB below ours. There is a net excess therefore of 21 dB. This is probably a real difference in observations, resulting from geographic, seasonal, or other effects, if it is assumed that we did not observe entirely different phenomena. 5 "' 0 4 ß -r I o z z I0 • i0 z 95% ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß X ß ß ß ß ß ß ß ß ß ß ß ß X o --ß --X X ß ß X ß _ X X ß ß ß ß _X X S x X X X X X ß ß ß

show abstract

Instrumentational Rôle in the Observation of Geoacoustical Phenomena from Artificial Sources

Cited by 7 publications

References 0 publications

Noise measurement and evaluation

Noise measurement and evaluation

Energy propagation in the lower ionosphere and atmosphere produced by artificial disturbances, 1

1- to 16-Hz infrasound associated with clear air turbulence predictors

Contact Info

Product

Resources

About