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At least 127 records · Page 7

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NASA NTRS1973

Measurements of the distribution of sound source intensities in turbulent jets.

The spatial distribution of sound source intensities in jets is determined from the sound radiated into the acoustic far field by means of a concave mirror-microphone system. The mirror forms an image of the sound sources in a region far enough from the jet so that near field pressure fluctuations can be neglected. The sound intensity in the image is thus closely related to the strength of the actual sound sources in the jet. Results of measurements with jets of Mach numbers 0.7 to 1.9 emanating from circular nozzles and from slot nozzle-flap combinations demonstrate the influence of Mach number and of other parameters upon the sound source distribution.

Grosche, F.-R.↗

NASA NTRS1977

Sound separation probes for flowing duct noise measurements

In order to understand the propagation of broadband sound from a device such as a jet engine, it is necessary to make fluctuating pressure measurements in the ducted airstream. However, in a flowing duct, fluctuating pressure energy can be due to both turbulence and sound travelling in the duct. By using the principal that sound waves and turbulent flow pressure perturbations travel at different velocities, a probe has been developed that provides the data necessary to separate the energy due to sound from that due to turbulence. A mini-computer based FFT analysis of the probe measurements provides the overall level of the broadband sound in the duct as well as the spectral distribution of the sound energy.

Moore, M. T.↗

NASA NTRS1978

Monitoring the state of the human airways by analysis of respiratory sound

A mechanism whereby sound is generated by the motion of vortices in the human lung is described. This mechanism is believed to be responsible for most of the sound which is generated both on inspiration and expiration in normal lungs. Mathematical expressions for the frequencies of sound generated, which depend only upon the axial flow velocity and diameters of the bronchi, are derived. This theory allows the location within the bronchial tree from which particular sounds emanate to be determined. Redistribution of pulmonary blood volume following transition from earth gravity to the weightless state probably alters the caliber of certain airways and doubtless alters sound transmission properties of the lung. We believe that these changes can be monitored effectively and non-invasively by spectral analysis of pulmonary sound.

Hardin, J. C.↗

NASA NTRS1979

Loudness of steady sounds - A new theory

A new mathematical theory for calculating the loudness of steady sounds from power summation and frequency interaction, based on psychoacoustic and physiological information, assuems that loudness is a subjective measure of the electrical energy transmitted along the auditory nerve to the central nervous system. The auditory system consists of the mechanical part modeled by a bandpass filter with a transfer function dependent on the sound pressure, and the electrical part where the signal is transformed into a half-wave reproduction represented by the electrical power in impulsive discharges transmitted along neurons comprising the auditory nerve. In the electrical part the neurons are distributed among artificial parallel channels with frequency bandwidths equal to 'critical bandwidths for loudness', within which loudness is constant for constant sound pressure. The total energy transmitted to the central nervous system is the sum of the energy transmitted in all channels, and the loudness is proportional to the square root of the total filtered sound energy distributed over all channels. The theory explains many psychoacoustic phenomena such as audible beats resulting from closely spaced tones, interaction of sound stimuli which affect the same neurons affecting loudness, and of individually subliminal sounds becoming audible if they lie within the same critical band.

Howes, W. L.↗

NASA NTRS1981

AVE-SEASAME 5: 25-mb sounding data

The rewinsonde sounding program for the AVE-SESAME 5 experiment is described and tubulated data at 25 mb intervals are presented for the 23 National Weather Service stations and 20 special stations participating in the experiment. Soundings were taken at 3-hr intervals beginning at 1200 GMT on May 20, 1979, and ending at 1200 GMT on may 21, 1979 (nine sounding times). A tenth sounding was teken at many special stations between 2100 and 0000 GMT on May 20. The method of processing is discussed, estimates of the rms errors in the data are presented, and an example of contact data is given. Reasons are given for the termination of soundings below 100 mb, and soundings with abnormal characteristics are listed.

Sienkiewicz, M. E.↗

NASA NTRS1980

Applications of the TIROS-N sounding and cloud motion wind enhancement for the FGGE 'special effort'

In January of 1978, a panel of experts recommended that a 'special effort' be made to enhance and edit satellite soundings and cloud tracked winds in data sparse regions. It was felt that these activities would be necessary to obtain maximum benefits from an evaluation of satellite data during the Global Weather Experiment (FGGE). The 'special effort' is being conducted for the two special observing periods of FGGE. More than sixty cases have been selected for enhancement on the basis of meteorological interest. These cases include situations of blocking, cutoff low development, cyclogenesis, and tropical circulations. The sounding data enhancement process consists of supplementing the operational satellite sounding data set with higher resolution soundings in meteorologically active regions, and with new soundings where data voids or soundings of questionable quality exist.

Atlas, R.↗

NASA NTRS1982

AVE/VAS 3: 25-mb sounding data

The rawinsonde sounding program for the AVE/VAS 3 experiment is described. Tabulated data are presented at 25-mb intervals for the 24 National Weather Service stations and 14 special stations participating in the experiment. Soundings were taken at 3-hr intervals, beginning at 1200 GMT on March 27, 1982, and ending at 0600 GMT on March 28, 1982 (7 sounding times). An additional sounding was taken at the National Weather Service stations at 1200 GMT on March 28, 1982, at the normal synoptic observation time. The method of processing soundings is briefly discussed, estimates of the RMS errors in the data are presented, and an example of contact data is given. Termination pressures of soundings taken in the mesos-beta-scale network are tabulated, as are observations of ground temperature at a depth of 2 cm.

Sienkiewicz, M. E.↗

NASA NTRS1983

Generation of sound in turbulent shear flows

An alternative to the Lighthill acoustic analogy for jet noise is discussed. It involves calculating the unsteady flow that produces the sound along with its resulting sound field starting from a prescribed upstream state that, ideally, is specified just ahead of the region where the sound generation takes place. Sound generation by turbulence interacting with solid obstacles is considered. It is shown that the process can be described by linear theory. Sound generated by turbulence interacting with itself is discussed. The processes are nonlinear and the theory is incomplete. Theories of sound generation are compared with experiment and the inadequacies of each are indicated. Additional mechanisms that appear at supersonic speeds are discussed.

Goldstein, M. E.↗

NASA NTRS1986

Spectroscopic aspects of differential method for sounding gas composition of the atmosphere

The problems concerning the dynamics of populations of the sounded atmospheric gas molecule levels taking into account the nonmonochromatic character of radiation, durations of exciting and sounding pulses, rates of relaxation of excited vibration-rotation states population along different channels in a natural multicomponent mixture of gases and air were investigated. The problems of spectroscopic software, completeness and accuracy of the initial spectroscopic information, information on channels and rates of relaxation from the viewpoint of developing specific schemes of sounding are discussed. The values of deviations of vibration-rotation level populations of some atmospheric molecules from their equilibrium value at simultaneous action of double frequency radiation on the sounding path and the corresponding dynamic variation of lidar return amplitude were estimated. The importance of nonlinear spectrosopic effects in the lidar return value variation at sounding radiation frequency equaling the resonance frequency of vibration-rotation transition in the problem on sounding the humidity profiles and concentrations of gaseous pollutants was also estimated.

Zuev, V. V.↗

NASA NTRS1984

An initial approach to the utilization of VAS satellite sounding data

The primary objective is the development of methods to utilize satellite soundings. To achieve that, a more precise understanding of the characteristics of satellite derived soundings is required. The initial approach in the utilization of satellite soundings is to find a way to combine rawinsondes and satellite data into a unified data set. If this can be done in a meaningful way, satellite data could be integrated into existing data and interpretation would be enhanced. In this attempt, both rawinsonde and satellite soundings will be decomposed by the use of the Fourier cosine series. Then, each harmonic will be compared to get a better understanding of the representativeness of the satellite sounding data. Harmonics taken from satellite and rawinsonde soundings will be combined to provide a unified data set that can be used both over data sparse ocean areas as well as over land where rawinsonde data are available.

Shin, Kyung-Sup↗

NASA NTRS1987

Light aircraft sound transmission studies - Noise reduction model

Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

Atwal, Mahabir S.↗

NASA NTRS1994

The discrepancy between stratospheric ozone profiles from balloon soundings and from other techniques: A possible explanation

Regular balloon ozone soundings with electrochemical sondes have been performed at Uccle since 1969. More than 450 ozone soundings between 1985 and 1989 were used to calculate the altitudes Zs from the VIZ radiosonde data and the altitudes Zr deduced from the tracking of the balloon train with a primary wind-finding radar. The values of Zs at fixed times appeared to be systematically too low as compared to Zr. The differences Zr-Zs increase with altitude; at 30 km the annual mean values of Zr-Zs (plus or minus standard deviation) vary between 590 plus or minus 910 m and 1410 plus or minus 1160 m, according to the pressure calibration of different manufacturing series of radiosondes. From these results it is found that around the 30 km level the ozone concentrations calculated from soundings with VIZ sondes are too low by 7.5 to 14 percent, depending upon the manufacturing series of radiosondes. At least part of the discrepancy which has often been found between ozone profiles from balloon soundings and from other techniques such as rocket observations or Umkehr measurements may be explained by this effect. An altitude correction would have important consequences as to the climatology of ozone in the middle stratosphere as adopted at the moment. About half of the day-to-day variability of ozone observed from soundings with VIZ radiosondes above the 30 km level, is induced by the variability of Zr-Zs. The agreement between altitudes calculated from radar data and Vaisala radiosondes is much better; from 34 comparative soundings a mean difference (plus or minus standard deviation) of about -300 plus/minus 180 m was found at 30 km.

Demuer, Dirk↗

NASA NTRS1997

Monaural Sound Localization Revisited

Research reported during the past few decades has revealed the importance for human sound localization of the so-called 'monaural spectral cues.' These cues are the result of the direction-dependent filtering of incoming sound waves accomplished by the pinnae. One point of view about how these cues are extracted places great emphasis on the spectrum of the received sound at each ear individually. This leads to the suggestion that an effective way of studying the influence of these cues is to measure the ability of listeners to localize sounds when one of their ears is plugged. Numerous studies have appeared using this monaural localization paradigm. Three experiments are described here which are intended to clarify the results of the previous monaural localization studies and provide new data on how monaural spectral cues might be processed. Virtual sound sources are used in the experiments in order to manipulate and control the stimuli independently at the two ears. Two of the experiments deal with the consequences of the incomplete monauralization that may have contaminated previous work. The results suggest that even very low sound levels in the occluded ear provide access to interaural localization cues. The presence of these cues complicates the interpretation of the results of nominally monaural localization studies. The third experiment concerns the role of prior knowledge of the source spectrum, which is required if monaural cues are to be useful. The results of this last experiment demonstrate that extraction of monaural spectral cues can be severely disrupted by trial-to-trial fluctuations in the source spectrum. The general conclusion of the experiments is that, while monaural spectral cues are important, the monaural localization paradigm may not be the most appropriate way to study their role.

Wightman, Frederic L.↗

NASA NTRS1999

An Overview of the NASA Sounding Rockets and Balloon Programs

The U.S. National Aeronautics and Space Administration (NASA) Sounding Rockets and Balloon Programs conduct a combined total of approximately fifty to sixty missions per year in support of the NASA scientific community. These missions are provided in support of investigations sponsored by NASA'S Offices of Space Science, Life and Microgravity Sciences & Applications, and Earth Science. The Goddard Space Flight Center has management and implementation responsibility for these programs. The NASA Sounding Rockets Program has continued to su,pport the science community by integrating their experiments into the sounding rocket payload and providing the rocket vehicle and launch operations necessary to provide the altitude/time required obtain the science objectives. The sounding rockets continue to provide a cost-effective way to make in situ observations from 50 to 1500 km in the near-earth environment and to uniquely cover the altitude regime between 50 km and 130 km above the Earth's surface, which is physically inaccessible to either balloons or satellites. A new architecture for providing this support has been introduced this year with the establishment of the NASA Sounding Rockets Contract. The Program has continued to introduce improvements into their operations and ground and flight systems. An overview of the NASA Sounding Rockets Program with special emphasis on the new support contract will be presented. The NASA Balloon Program continues to make advancements and developments in its capabilities for support of the scientific ballooning community. Long duration balloon (LDB) is a prominent aspect of the program with two campaigns scheduled for this calendar year. Two flights are scheduled in the Northern Hemisphere from Fairbanks, Alaska, in June and two flights are scheduled from McMurdo, Antarctica, in the Southern Hemisphere in December. The comprehensive balloon research and development (R&D) effort has continued with advances being made across the spectrum of balloon related disciplines. As a result of these technology advancements a new ultra long duration balloon project (ULDB) for the development of a 100- day duration balloon capability has been initiated. The ULDB will rely upon new balloon materials and designs to accomplish its goals. The Program has also continued to introduce new technology and improvements into flights systems, ground systems and operational techniques. An overview of the various aspects of the NASA Balloon Program will be presented.

Flowers, Bobby J.↗

NASA NTRS1995

Sound For Animation And Virtual Reality

Sound is an integral part of the experience in computer animation and virtual reality. In this course, we will present some of the important technical issues in sound modeling, rendering, and synchronization as well as the "art" and business of sound that are being applied in animations, feature films, and virtual reality. The central theme is to bring leading researchers and practitioners from various disciplines to share their experiences in this interdisciplinary field. The course will give the participants an understanding of the problems and techniques involved in producing and synchronizing sounds, sound effects, dialogue, and music. The problem spans a number of domains including computer animation and virtual reality. Since sound has been an integral part of animations and films much longer than for computer-related domains, we have much to learn from traditional animation and film production. By bringing leading researchers and practitioners from a wide variety of disciplines, the course seeks to give the audience a rich mixture of experiences. It is expected that the audience will be able to apply what they have learned from this course in their research or production.

Hahn, James K.↗

NASA NTRS1996

A Numerical Experiment on the Role of Surface Shear Stress in the Generation of Sound

The sound generated due to a localized flow over an infinite flat surface is considered. It is known that the unsteady surface pressure, while appearing in a formal solution to the Lighthill equation, does not constitute a source of sound but rather represents the effect of image quadrupoles. The question of whether a similar surface shear stress term constitutes a true source of dipole sound is less settled. Some have boldly assumed it is a true source while others have argued that, like the surface pressure, it depends on the sound field (via an acoustic boundary layer) and is therefore not a true source. A numerical experiment based on the viscous, compressible Navier-Stokes equations was undertaken to investigate the issue. A small region of a wall was oscillated tangentially. The directly computed sound field was found to to agree with an acoustic analogy based calculation which regards the surface shear as an acoustically compact dipole source of sound.

Shariff, Karim↗

NASA NTRS2004

Radio Sounding Techniques for the Galilean Icy Moons and their Jovian Magnetospheric Environment

Radio sounding of the Earth's topside ionosphere and magnetosphere is a proven technique from geospace missions such as the International Satellites for Ionospheric Studies (ISIS) and the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE). Application of this technique to Jupiter's icy moons and the surrounding Jovian magnetosphere will provide unique remote sensing observations of the plasma and magnetic field environments and the subsurface conductivities, of Europa, Ganymede, and Callisto. Spatial structures of ionospheric plasma above the surfaces of the moons vary in response to magnetic-field perturbations from (1) magnetospheric plasma flows, (2) ionospheric currents from ionization of sputtered surface material, and (3) induced electric currents in salty subsurface oceans and from the plasma flows and ionospheric currents themselves. Radio sounding from 3 kHz to 10 MHz can provide the global electron densities necessary for the extraction of the oceanic current signals and supplements in-situ plasma and magnetic field measurements. While radio sounding requires high transmitter power for subsurface sounding, little power is needed to probe the electron density and magnetic field intensity near the spacecraft. For subsurface sounding, reflections occur at changes in the dielectric index, e.g., at the interfaces between two different phases of water or between water and soil. Variations in sub-surface conductivity of the icy moons can be investigated by radio sounding in the frequency range from 10 MHz to 50 MHz, allowing the determination of the presence of density and solid-liquid phase boundaries associated with oceans and related structures in overlying ice crusts. The detection of subsurface oceans underneath the icy crusts of the Jovian moons is one of the primary objectives of the Jupiter Icy Moons Orbiter (JIMO) mission. Preliminary modeling results show that return signals are clearly distinguishable be&een an ice crust with a thickness of 7 km on 1) an ocean and 2) a layer of bedrock. Knowledge of the ionospheric contributions to the time delay of the low-frequency subsurface radar is shown to be important in obtaining accurate depth information.

Green, James L.↗

NASA NTRS2005

Atmospheric Soundings from AIRS/AMSU in Partial Cloud Cover

Simultaneous use of AIRS/AMSU-A observations allow for the determination of accurate atmospheric soundings under partial cloud cover conditions. The methodology involves the determination of the radiances AIRS would have seen if the AIRS fields of view were clear, called clear column radiances, and use of these radiances to infer the atmospheric and surface conditions giving rise to these clear column radiances. Susskind et al. demonstrate via simulation that accurate temperature soundings and clear column radiances can be derived from AIRS/AMSU-A observations in cases of up to 80% partial cloud cover, with only a small degradation in accuracy compared to that obtained in clear scenes. Susskind and Atlas show that these findings hold for real AIRS/AMSU-A soundings as well. For data assimilation purposes, this small degradation in accuracy is more than offset by a significant increase in spatial coverage (roughly 50% of global cases were accepted, compared to 3.6% of the global cases being diagnosed as clear), and assimilation of AIRS temperature soundings in partially cloudy conditions resulted in a larger improvement in forecast skill than when AIRS soundings were assimilated only under clear conditions. Alternatively, derived AIRS clear column radiances under partial cloud cover could also be used for data assimilation purposes. Further improvements in AIRS sounding methodology have been made since the results shown in Susskind and Atlas . A new version of the AIRS/AMSU-A retrieval algorithm, Version 4.0, was delivered to the Goddard DAAC in February 2005 for production of AIRS derived products, including clear column radiances. The major improvement in the Version 4.0 retrieval algorithm is with regard to a more flexible, parameter dependent, quality control. Results are shown of the accuracy and spatial distribution of temperature-moisture profiles and clear column radiances derived from AIRS/AMSU-A as a function of fractional cloud cover using the Version 4.0 algorithm. Use of the Version 4.0 AIRS temperature profiles increased the positive forecast impact arising from AIRS retrievals relative to what was shown in Susskind and Atlas .

Susskind, Joel↗