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Showing papers on "Noise (radio) published in 1985"


PatentDOI
TL;DR: In this paper, an improved noise suppression system (400) was proposed which performs speech quality enhancement upon speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification.
Abstract: An improved noise suppression system (400) is disclosed which performs speech quality enhancement upon speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification. The noise suppression system of the present invention includes a background noise estimator (420) which generates and stores an estimate of the background noise power spectral density based upon pre-processed speech (215), as determined by the detected minima of the post-processed speech energy level. This post-processed speech (255) may be obtained directly from the output of the noise suppression system, or may be simulated by multiplying the pre-processed speech energy (225) by the channel gain values of the modification signal (245). This technique of implementing post-processed signal to generate the background noise estimate (325) provides a more accurate measurement of the background noise energy since it is based upon much cleaner speech signal. As a result, the present invention performs acoustic noise suppression in high ambient noise backgrounds with significantly less voice quality degradation.

331 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of a dual-detector optical heterodyne receiver was analyzed and compared with that of a conventional singledetector HetNOMA receiver.
Abstract: The performance of a dual-detector optical heterodyne receiver was analyzed and compared with the performance of a conventional single-detector heterodyne receiver. The dual-detector receiver is found to offer two main advantages over the single-detector receiver-1) increased performance in the presence of local oscillator intensity fluctuations that might severely degrade single-detector receiver performance, and 2) decreased local oscillator power requirements. These two advantages are particularly important in a communication system which uses semiconductor laser diodes as local oscillators. Such lasers suffer from intrinsic wide-band intensity fluctuations and can also impose strict power constraints on receiver design. Based on the analysis, suggestions for the optimal design of a dual-detector heterodyne receiver are made. Also, several experiments were performed to demonstrate the improved performance of the dual-detector receiver-both for unguided- and guided-wave receivers.

248 citations


Journal ArticleDOI
TL;DR: In this article, the size and statistical nature of the drift noise element is discussed for two kinds of measured substances, and a theory is developed and compared to data from Greenland and Canadian Arctic ice cores.
Abstract: Because of snow drifting, two time series of any variable derived from two adjacent ice cores will differ considerably. The size and statistical nature of this noise element is discussed for two kinds of measured substance. A theory is developed and compared to data from Greenland and Canadian Arctic ice cores. In case 1, the measured substance can diffuse and the seasonal cycle degrade with time and depth, e.g. δ(18O). In case 2, the measured substance cannot diffuse, e.g. microparticles. The case 2 time series contain drift noise proportional to that in the accumulation series. For accumulation series, the spectral power is concentrated at the high frequencies, i.e. is “blue”. Such noise can be easily reduced by taking relatively short time averages. The noise in the case 1 time series, however, starts out “blue” but quickly diffuses to have a “red” character with significant power at longer wavelengths, and many decades of such series must be averaged to reduce the noise level. Because the seasonal amplitude of any given variable is an important input to the drift noise and because the seasonal amplitudes of some variable types are latitude-dependent, some sites have inherently less drift noise than others.

186 citations


Journal ArticleDOI
18 Jul 1985-Nature
TL;DR: The X-ray flux of the bright galactic bulge source GX5 -1 shows intensity-dependent quasi-periodic oscillations between 20 and 40 Hz, appearing as a broad peak in the power spectrum whose centroid frequency, width, and integrated excess power strongly depend on the source intensity.
Abstract: The X-ray flux of the bright galactic bulge source GX5 - 1 shows intensity-dependent quasi-periodic oscillations between 20 and 40 Hz, appearing as a broad peak in the power spectrum whose centroid frequency, width, and integrated excess power strongly depend on the source intensity. The strength and steepness of low-frequency noise present in the power spectra below 15 Hz also depend on the source intensity. No evidence is found for coherent X-ray pulsations between 0.5 and 2000 Hz. Possible mechanisms to explain these new phenomena are discussed.

184 citations


Journal ArticleDOI
TL;DR: In this paper, the initial boundary layer state can significantly affect the radiated noise from an axisymmetric jet and it is found that planes with initially laminar boundary layers emit more noise.
Abstract: The initial boundary-layer state can significantly affect the radiated noise from an axisymmetric jet. Jets with initially laminar boundary layers are found to emit more noise. Thus, 'cleaner' far-field noise characteristics are achieved in tripped jets. Data suggest that the additional noise in the initially laminar case partly originates from the first stage of pairing of the coherent shear-layer vortices.

144 citations


Journal ArticleDOI
TL;DR: The results support the conclusion that the light‐sensitive pore is opened by an internal transmitter that acts as an agonist and that both open and closed states of the pore may be blocked by external Ca2+.
Abstract: In cell-attached recordings from rods in the intact lizard retina, light decreased a standing inward membrane current with a reversal potential approximately 60 mV more positive than the resting potential. The peak amplitude of saturating responses depended upon the area of recorded membrane and varied from cell to cell over approximately 100-fold range. Small patches of membrane gave variable responses to identical moderately intense flashes. Whole-cell voltage-clamp recordings were obtained on isolated frog rods with intact ellipsoids. Peak whole-cell photocurrent was related to flash intensity by a Michaelis equation with saturating response amplitudes ranging up to 30 pA in 0.1 mM-Ca2+ Ringer solution. In darkness the steady-state current-voltage relation, determined with whole-cell voltage clamp, showed outward rectification. Photocurrent had nearly constant amplitude between -80 and -10 mV, a mean reversal potential of +8 mV and recovered from flashes more slowly at positive holding potentials. Although it was not possible to resolve light-sensitive single-channel current events, power spectral analysis revealed both low- and high-frequency components of the light-sensitive noise in both cell-attached and whole-cell recordings. The low-frequency component was described by the product of two Lorentzians using time constants derived from the kinetics of the dim flash response. The high-frequency component of the light-sensitive noise was described by a single Lorentzian with a half-power frequency of 62 Hz in lizard and 212 Hz in frog. The half-power frequency was not appreciably affected by steady illumination. The Lorentzian nature of the noise suggests that the light-sensitive channel is a pore rather than a shuttle-type carrier. In cell-attached recordings the high-frequency component declined monotonically with increasing light intensity, suggesting that less than one-half of the channels are open in darkness. Furthermore, the ratio of the variance of the high-frequency noise to the mean photocurrent was independent of light intensity. Changing external Ca2+ from 0.1 to 0.5 mM reduced the ratio from 19.7 to 9.0 fA without a significant effect on the cut-off frequency of the noise. The results support the conclusion that the light-sensitive pore is opened by an internal transmitter that acts as an agonist and that both open and closed states of the pore may be blocked by external Ca2+. The conductance of the light-sensitive pore in the absence of external Ca2+ is estimated to be 1.25-2 pS.(ABSTRACT TRUNCATED AT 400 WORDS)

141 citations


Journal ArticleDOI
TL;DR: In this article, the role of large-scale coherent structures in broadband jet noise suppression and amplification under controlled excitation is studied experimentally, and it is found that suppression occurs only at low Reynolds and Mach numbers, when the boundary layer at the jet exit is laminar.
Abstract: The role of large-scale coherent structures in broadband jet noise suppression and amplification under controlled excitation are studied experimentally. It is found that suppression occurs only at low Reynolds and Mach numbers, when the boundary layer at the jet exit is laminar; the optimum St(Theta) (St, based on the initial shear-layer momentum thickness) value is 0.017, at which the excitation results in a quick roll-up and transition of the laminar shear-layer vortices, yielding coherent structures similar to those existing at high speeds. At the asymptotic level the broadband jet noise can only be amplified by the excitation. The amplification is inferred to be maximum for excitation in the St(D) (St based on the jet diameter) range of 0.65-0.85. Finally, it is noted that the pairing process induced by the excitation is at the origin of the broadband noise amplification.

141 citations


Journal ArticleDOI
TL;DR: In this article, the electron and hole impact ionization coefficients in (100) GaAs have been determined using photomultiplication measurements performed on specially fabricated p+-n diode structures having active region carrier concentrations from 1.1 X 1017 to 2.2 X 1015 cm-3.
Abstract: The electron and hole impact ionization coefficients in (100) GaAs have been determined using photomultiplication measurements performed on specially fabricated p+-n diode structures having active region carrier concentrations from 1.1 X 1017 to 2.2 X 1015 cm-3. These structures are designed to permit pure electron and hole injection in the same diodes. In diodes having heavy p+ doping, the effects of electron dead space have been observed. This dead-space region corresponds to the distance required for an injected carrier to accelerate ballistically to the impact ionization threshold energy, and a method to include this phenomenon in the calculation of α and β from the experimental multiplication data is presented. Agreement among the results from all these structures is obtained with an electron threshold energy of 1.7 eV, and the corrected data are also in agreement with data obtained from device structures designed to eliminate dead-space effects. The measured ratio of α/β in GaAs is found to decrease from 2.4 at 2.2 X 105 V/cm to 1.0 at 6.25 X 105 V/cm. Avalanche noise measurements performed at 30 MHz on the same devices under both electron and hole injection yield a keff of 0.6 and a k'eff of 1.7, respectively, in agreement with the values of these parameters obtained from the photocurrent results.

138 citations



Journal ArticleDOI
TL;DR: Several mechanisms by which bubbles can contribute to ambient noise in the ocean are described and their effectiveness estimated in this paper, where the efficiency of all these mechanisms is estimated on the basis of an adaptation of Lighthill's theory of aerodynamic noise.
Abstract: Several mechanisms by which bubbles can contribute to ambient noise in the ocean are described and their effectiveness estimated. At low frequency, up to a few tens of Hz, bubbles are driven into oscillation by oceanic turbulence. The normal quadrupole radiation mechanism of turbulence thus acquires a monopole character. At frequencies from around 1 to a few kHz single bubbles formed by breaking waves radiate in free oscillation. In the range of hundreds of Hz the acoustic emission may be due to collective oscillations of systems composed of many bubbles. The efficiency of all these mechanisms is estimated on the basis of an adaptation of Lighthill's theory of aerodynamic noise. Finally, at frequencies above several kHz, drop impact and free oscillations of bubbles thereby produced appear to be responsible for the ambient noise. [Work supported by SACLANT ASWR, La Spezia, Italy.]

108 citations


Journal ArticleDOI
TL;DR: A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS), which is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements as mentioned in this paper.
Abstract: A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS). The RF coupling is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements. In this preliminary version the double sideband receiver noise temperature rises from 205 K at 116 GHz to 375 K at 349 Ghz, and to 815 K at 466 GHz. This is the most versatile and sensitive receiver yet reported for sub-mm wavelengths.

Patent
15 Jul 1985
TL;DR: In this article, a high frequency (HF) frequency-management system for automatically selecting optimum HF frequency is presented, where a frequency management means controlling the operation of a regular HF radio communications transmitter and receiver at each station.
Abstract: A high frequency (HF) frequency-management system for automatically selecting optimum HF frequency. A frequency management means controls the operation of a regular HF radio communications transmitter and receiver at each station. The frequency-management means transmits sounding signals synchronously and repeatedly over a finite group of HF frequencies, from a first radio communications station to a second radio communications station. Link quality evaluation (LQE) is carried out at the second station. Sounding signals are transmitted synchronously and repeatedly back to the first station. Optimum HF frequencies are selected based on the sounding signals and LQE. An HF communications path is automatically established between stations. The system performs the scanning of the HF frequencies, the detection and measurement of signals, noise and interferences on each frequency and the timing synchronization as required for the frequency management operation.

Journal ArticleDOI
TL;DR: Compared to film-screen systems used in general radiography, mammographic systems have similar DQE values at low frequencies, but are superior at higher frequencies.
Abstract: The signal‐to‐noise ratio (SNR) and the detective quantum efficiency (DQE) have been experimentally determined as a function of spatial frequency for several mammographic film–screen systems. These two parameters were determined from our measurements of noise power spectra and sensitometric properties of each system along with modulation transfer function(MTF) data for the screens which were obtained from others. From the noise power spectra, it was found that film noise contributes significantly to the total noise of mammographic film–screen systems, comprising 30%–50% of the total noise at 1 cycle/mm and as much as 75% at 5 cycles/mm. All systems had approximately the same SNR below 1.5 cycles/mm, but differed at higher frequencies due to differences in screen MTF and in the gradient of the film’s sensitometric curve. The DQE curves varied between systems at all frequencies, however, due to differences in system speed, MTF, and gradient. Generally, the DQE of mammographic film–screen systems is between 10%–30% at frequencies below 1 cycle/mm and decreases to about 1% between 8 and 12 cycles/mm. Compared to film–screen systems used in general radiography,mammographic systems have similar DQE values at low frequencies, but are superior at higher frequencies.

Journal ArticleDOI
TL;DR: In this article, the influence of the main technological parameters on the noise figure and associated gain for operating frequencies up to 60 GHz is given for TEGFET's and MESFETs.
Abstract: Noise modeling in TEGFET's which provides good results in agreement with the experimental findings is presented. The influence of the main technological parameters on the noise figure and associated gain is given for operating frequencies up to 60 GHz. A comparison between TEGFET's and MESFET's is carried out. A new method for calculating the noise and gain performances of FET's is then proposed.

Journal ArticleDOI
TL;DR: A survey of the recent literature on 1/f noise in p-n junction diodes can be found in this article, where the authors compared the agreement between experiment and calculated relations.
Abstract: A survey is given of the recent literature on 1/ f noise in p‐n junction diodes. Two models for the explanation of 1/ f noise are discussed: Hooge’s model assuming mobility fluctuations and McWhorter’s model assuming number fluctuations. Relations for the magnitude of the 1/ f noise based on Hooge’s model are presented for several types of diodes: diffusion current dominated diodes, GR current dominated diodes, long and short diodes, and illuminated photodiodes. These relations are compared with experimental results obtained from diodes made of Si, GaP, and (HgCd)Te. The agreement between experiment and calculated relations is often found to be satisfactory, both for forward and reverse‐biased diodes and for illuminated diodes. 1/ f noise relations based on McWhorter’s model are scarce, moreover, they do not sufficiently describe the 1/ f noise in diodes.

Journal ArticleDOI
TL;DR: In this article, a method is presented for predicting the broadband noise spectra of horizontal axis wind turbine generators, including contributions from such noise sources as the inflow turbulence to the rotor, the interactions between the turbulent boundary layers on the blade surfaces with their trailing edges, and the wake due to a blunt trailing edge.
Abstract: A method is presented for predicting the broadband noise spectra of horizontal axis wind turbine generators. It includes contributions from such noise sources as the inflow turbulence to the rotor, the interactions between the turbulent boundary layers on the blade surfaces with their trailing edges, and the wake due to a blunt trailing edge. The method is partly empirical and is based on acoustic measurements of large wind turbines and airfoil models. The predicted frequency spectra are compared with measured data from several machines, including the MOD-OA, MOD-2, WTS-4, and U.S. Windpower Inc. machine. The significance of the effects of machine size, power output, trailing-edge bluntness, and distance to the receiver is illustrated. Good agreement is obtained between the predicted and measured far-field noise spectra.

Journal ArticleDOI
TL;DR: In this paper, the one and two ion beam instability is considered as a possible explanation for the observations of broadband electrostatic noise in the plasma sheet region of the geomagnetic tail.
Abstract: The one and two ion beam instability is considered as a possible explanation for the observations of broadband electrostatic noise in the plasma sheet region of the geomagnetic tail. When only hot streaming plasma sheet boundary layer ions are present, no broadband waves are excited. Cold, streaming ionospheric ions can generate electrostatic broadband waves propagating in the slow beam acoustic mode, but the growth rates of the waves are significantly enhanced when hot boundary layer ions are present. (Both the slow and fast beam acoustic modes can be excited, depending on the relative ion drift.) This model predicts that the wave intensity of the broad band noise should peak in the plasma sheet boundary layer. Observations of less intense electrostatic waves in the lobes and plasma sheet are likely a result of the absence of hot ion beams or large ion temperatures, respectively, which result in smaller growth rates. The ion beam instability may play an important role in the formation of the central plasma sheet.

Journal ArticleDOI
TL;DR: Handel's theory of quantum 1/f noise is applied to the Hooge parameters of bipolar transistors and various types of FET's in this article, where the experimental data seem to agree with the predicted theoretical limit.
Abstract: Handel's theory of quantum 1/f noise is applied to the Hooge parameters of bipolar transistors and various types of FET's. Very low values for the Hooge parameters α Hn and α Hp for electrons and holes are obtained. For several cases the experimental data seem to agree with the predicted theoretical limit whereas in other cases the mobility 1/f noise is masked by other noise sources. In good GaAs devices the predicted quantum limit for α Hn is reached within a factor 5-10. The theory is also applied to the Hg 1-x Cd x Te materials and devices. Because of the very low effective masses involved, the theory predicts values as high as 2 × 10-4-2 × 10-5, depending on x . What remains presently unexplained are the high values of α H for semiconductor resistors and long p-n diodes.


PatentDOI
TL;DR: In this article, an adaptive shaping filter and a summer, in conjunction with a directional reference sensor and a primary sensor which have at least a common sensing element there between, is proposed for reducing noise from a near-field noise source sent together with signals from a far-field source.
Abstract: A method and apparatus for reducing noise from a near-field noise source sent together with signals from a far-field source. The method uses an adaptive shaping filter and a summer, in conjunction with a directional reference sensor and a primary sensor which have at least a common sensing element therebetween. The directional reference sensor situated between the near-field noise source and the far-field signal source, rejects the broad-band signal but accepts the broad-band noise and feeds this noise into a reference channel of the adaptive filter. The primary sensor accepts both the far-field signal and near-field noise with equally sensitivity. The primary sensor feeds into the primary channel of the adaptive filter. The adaptive filter system subtracts the noise in the reference channel from the signal-plus-noise in the primary channel, thus producing an output having a greatly improved signal-to-noise ratio.

Journal ArticleDOI
TL;DR: In this paper, a large number of highly robust and reliable thin film DC SQUIDs have been designed and fabricated which have excellent low frequency noise properties and showed that improvements in the performance of these devices in the white noise region can be obtained without sacrificing the low frequency resolution.
Abstract: A large number of highly robust and reliable thin film DC SQUIDs have been designed and fabricated which have excellent low frequency noise properties. Measurements performed on isolated devices have yielded a limit on the low frequency (1/f) flux noise component which is at least a factor of 60 below the average value reported for devices of this kind. The corresponding energy factor in the white noise region is 770 h at 0.1 Hz. The input coil inductance is 0.7 μH and the coupling efficiency α = 0.9. The substantial reduction of the low frequency noise in these SQUIDs demonstrates that improvements in the performance of these devices in the white noise region can be obtained without sacrificing the low frequency resolution.

Journal ArticleDOI
TL;DR: The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter.
Abstract: The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to increase by 3 to 30 times with a spectrum which rose steeply and peaked below 6 Hz. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 2 kHz. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thruster events.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the FM and AM noise spectra of 1.3 μm InGaAsP DFB lasers in the frequency range from dc to 4 GHz and compared the relaxation resonances appearing in these spectra to the semiclassical theory of laser noise.
Abstract: The FM and AM noise spectra of 1.3 μm InGaAsP DFB lasers are measured in the frequency range from dc to 4 GHz. The relaxation resonances appearing in these spectra are compared to the semiclassical theory of laser noise. All the resonance parameters, i.e., the linewidth enhancement factor α, the resonance frequency f R , and the damping constant γ e , are determined from the FM noise spectra by successful curve fitting. The estimated value of α is 2.2. Field spectra for various bias currents are measured by using optical heterodyne detection. Theoretical lineshapes are obtained by using four noise-parameter values which have been determined from the FM noise and the linewidth measurements. The results are in excellent agreement with the measured spectra. This agreement verifies the estimation that \alpha = 2.2.

Journal ArticleDOI
TL;DR: In this article, the authors provided a correct solution to the dispersion equation for ion beams observed in the magnetotail by numerically solving this equation, and showed that obliquely propagating waves have growth rates that can be an order of magnitude larger than those of parallel propagating wave, in agreement with observations.
Abstract: Spacecraft observations in the earth's magnetotail at distances of 30 to 40 R(E) have revealed the presence of broadband electrostatic waves These waves are generally most intense in the regions just outside of the plasma sheet and are correlated with the observations of relatively cold and energetic ion beams traveling in either the earthward or the tailward direction These waves are observed to propagate obliquely to the geomagnetic field with wave normal angles around 70 deg Because the broadband electrostatic noise is the most intense of the waves observed in the magnetotail, it is important to understand the generation mechanism of these waves The purpose of this study is to provide for the first time a correct solution to the dispersion equation for ion beams observed in the magnetotail By numerically solving this equation, it is shown that obliquely propagating waves have growth rates that can be an order of magnitude larger than those of parallel propagating waves, in agreement with observations In addition, the effect of beam temperature on the ion beam instability is studied, and it is shown that this instability can be a viable generation mechanism only when the ion beam has a relatively small thermal spread

Journal ArticleDOI
TL;DR: In this article, the authors describe the acoustic results from a well-controlled experiment designed to obtain an understanding of the noise generated by a tone-excited jet, with particular emphasis on the mechanism of broadband jet-noise amplification.

Journal ArticleDOI
TL;DR: In this paper, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons.
Abstract: Numerous plasma wave effects were detected by the AMPTE/IRM spacecraft during the artificial comet experiment on December 27, 1984 As the barium ion cloud produced by the explosion expanded over the spacecraft, emissions at the electron plasma frequency and ion plasma frequency provided a determination of the local electron density The electron density in the diamagnetic cavity produced by the ion cloud reached a peak of more than 5 x 10 to the 5th per cu cm, then decayed smoothly as the cloud expanded, varying approximately as t exp-2 As the cloud began to move due to interactions with the solar wind, a region of compressed plasma was encountered on the upstream side of the diamagnetic cavity The peak electron density in the compression region was about 15 x 10 to the 4th per cu cm Later, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region This noise has characteristics very similar to noise observed in the earth's bow shock, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons

Journal ArticleDOI
TL;DR: It is found that for sufficiently high noise intensities a direct transition from the spatially homogeneous state to turbulence via intermittency can be induced.
Abstract: We show experimentally that for the electrohydrodynamic instability in nematic liquid crystals the threshold for the onset of spatial turbulence can be increased by at least a factor of 2 by superimposing noise on the applied voltage. We find that for sufficiently high noise intensities a direct transition from the spatially homogeneous state to turbulence via intermittency can be induced.

Journal ArticleDOI
TL;DR: The theory of the generation of broadband electrostatic noise (BEN) in the magnetotail is extended through numerical solution of the dispersion relation under conditions that exist in the plasma sheet boundary layer.
Abstract: The theory of the generation of broadband electrostatic noise (BEN) in the magnetotail is extended through numerical solution of the dispersion relation under conditions that exist in the plasma sheet boundary layer. It is found that the low-frequency portion of the spectrum has a broad angular spectrum but a fairly sharp peak near 75 deg with respect to the magnetic field, while the high-frequency portion has a narrower angular spectrum that is strongly concentrated along the magnetic field line. These results are in excellent agreement with observations of the broadband wave spectrum and a recent measurement of the propagation direction. The effect of a second cold component of electrons is analyzed, and it is found that it can increase the upper cutoff frequency of BEN to the observed value at about the plasma frequency.

01 Apr 1985
TL;DR: In this article, the authors present an improved atmospheric noise model based on the CCIR report (CCIR Report 322), which was developed from approximately 4 years of measurements from a worldwide network of 16 measurement stations.
Abstract: The determination of radio communication system performance is a matter of proper statistical treatment of both the desired signal and the real-world noise (or interference) processes. System performance is highly dependent on the detailed statistical characteristics of both the signal and the noise as well as the single parameter: signal-to-noise ratio (which is sometimes the only parameter considered). Generally, the computation of the desired signal characteristics over a given path can be made reasonably accurately. This is not the case when it comes to estimating the noise level and other required noise characteristics. Existing noise models consist primarily of the worldwide atmospheric noise maps contained in CCIR Report 322 and estimated man-made noise levels given in CCIR Report 258. In addition, there are numerous other special purpose models. There is a need for an overall, comprehensive usable noise model for application to telecommunication problems. One needed task that has been accomplished toward the goal of obtaining such an overall model is the development of an improved atmospheric noise model. The existing worldwide atmospheric noise model (CCIR Report 322) was developed from approximately 4 years of measurements from a worldwide network of 16 measurement stations. This network made measurements for 5 years (longer in a few cases) past the completion of CCIR Report 322 in 1963. Also, additional data are now available from other locations, primarily many years of data from 10 Soviet measurement stations. All these additional data have been analyzed and an updated worldwide atmospheric noise model has been prepared in both graphical and numerical forms. Results of this analysis show substantial “corrections” (on the order of 20 dB for some locations) to the 1 MHz noise level values given by CCIR Report 322. It is the purpose of this report to

Journal ArticleDOI
TL;DR: In this article, a siting survey for the NORESS small-aperture regional array (NORESS) was carried out, where the seismic noise field for frequencies up to about 50 Hz was studied for various sites in Fennoscandia.
Abstract: As part of a siting survey for the NORESS small-aperture regional array, the seismic noise field for frequencies up to about 50 Hz was studied for various sites in Fennoscandia, with emphasis on the NORSAR siting area. Power spectral bias sources were studied in order to ensure a sufficient resolution and dynamic range. It was found that the 1-Hz noise level at NORSAR usually ranges from 1 to 10 nm 2 /Hz. Above 2 to 3 Hz, the noise power falls off at a rate of about f −5 to levels of about 10 −5 nm 2 /Hz at 10 Hz and 10 −8 nm 2 /Hz at 40 Hz. The slope is much steeper for lower frequencies, where levels between 10 4 and 10 8 nm 2 /Hz were observed at 0.2 to 0.3 Hz. The noise field shows variability both in time and space for frequencies below 2 to 3 Hz, and stability in time for higher frequencies, where essentially only cultural noise sources contribute to the variation. Windgenerated noise is usually negligible around 10 Hz, but contributes 5 to 15 dB at 20 to 30 Hz. Diurnal variations are about 2 dB at 4 Hz and negligible at low frequencies. Only small variations in noise levels are found throughout Fennoscandia, with slightly lower values for Finland and slightly higher for northern Norway, as compared to southeastern Norway. The spatial correlation properties of the noise show variability for frequencies below 2 to 3 Hz and stability for higher frequencies: in the 1- to 3-Hz band, the correlation coefficients drop to zero at interstation distances ranging from 800 to 1500 m, and in the 3- to 5-Hz range from 400 to 500 m. After reaching zero, the correlation values usually approach a level of about −0.2 before increasing again. A frequency dependence was also found for the propagational characteristics, with westerly noise directions dominating for frequencies of 1 Hz and below, and easterly directions in the 2- to 8-Hz range. The degree of randomness in the noise increases with increasing frequency, leaving only a small propagational part at 8 Hz. There is clear evidence for a difference in noise-generating processes below and above 2 to 3 Hz due to differences in spectral slope, in spectral time and space variability, in correlation characteristics, and in propagational characteristics.