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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

The OSU self-phased array for propagation measurements using the 11.7 GHz CTS beacon

A self phased array was developed for propagation measurements on an earth-space path. The 11.7 GHz CTS beacon was used as the signal source. The self phased array was used to measure angle of arrival as well as attenuation and scintillation statistics. The performance of the array is described, and sample data are presented. The tracking capability of the self phased array was also studied. This technique permits fully electronic, nonmechanical satellite tracking, thus simplifying unmanned operation and eliminating severe weather tracking constraints.

Theobold, D. M.↗
NASA NTRS1978

Effects of the inhomogeneous background on radiation propagating through turbulent planetary atmospheres

Weak scattering, wave optics results are given for the first-order log-amplitude and phase, and for the second-order phase and angle of arrival, of radiation propagating through a turbulent planetary atmosphere. The analytical results include the effects of coupling to the inhomogeneous background upon which the turbulence is superimposed. Such coupling significantly affects signal characteristics in stellar and spacecraft occultation experiments, in contrast to situations involving much shorter paths, as in terrestrial propagation experiments.

Haugstad, B. S.↗
NASA NTRS1978

Operational modes for a wave injection facility aboard spacelab and a sub-satellite

Various modes of operation are described for an orbiting wave injection facility planned to measure the properties of waves propagating in space plasma. Such a facility would cover a wide frequency range including MF and HF. Phase shift and Doppler shift measurements will yield more accurate measurements of echo time delay and the angle of arrival. Because Spacelab will involve some sub-satellites, some consideration is given to propagation between two vehicles both at HF and VHF.

Dyson, P. L.↗
NASA NTRS1980

The relationship of storm severity to directionally resolved radio emissions

Directionally resolved atmospheric radio frequency emission data were acquired from thunderstorms occurring in the central and southwestern United States. In addition, RF sferic tracking data were obtained from hurricanes and tropical depressions occurring in the Gulf of Mexico. The data were acquired using a crossed baseline phase interferometer operating at a frequency of 2.001 MHz. The received atmospherics were tested for phase linearity across the array, and azimuth/elevation angles of arrival were computed in real time. A histogram analysis of sferic burst count versus azimuth provided lines of bearing to centers of intense electrical activity. Analysis indicates a consistent capability of the phase linear direction finder to detect severe meteorological activity to distances of 2000 km from the receiving site. The technique evidences the ability to discriminate severe storms from nonsevere storms coexistent in large regional scale thunderstorm activity.

Johnson, R. O.↗
NASA NTRS1980

CTS/Comstar communications link characterization experiment

Measurements of angle of arrival and amplitude fluctuations on millimeter wavelength Earth-space communication links are described. Measurement of rainfall attenuation and radiometric temperature statistics and the assessment of the performance of a self-phased array as a receive antenna on an Earth-space link are also included.

Hodge, D. B.↗
NASA NTRS1981

The Ion Drift Meter for Dynamics Explorer-B

The Ion Drift Meter on Dynamics Explorer-B measures two mutually perpendicular angles of arrival of thermal ions with respect to the sensor look direction. These measurements are used to derive two components of the ambient thermal ion drift velocity, which together with the third component from the Retarding Potential Analyzer instrument provide the total velocity. The Ion Drift Meter technique yields high temporal resolution measurements essential in the studies of the convection pattern and energy deposition in the ionosphere.

Heelis, R. A.↗
NASA NTRS1982

Neutral winds in the polar thermosphere as measured from Dynamics Explorer

Possibilities for experimental investigations related to the study of the dynamics of the thermosphere have been markedly improved by the new instrumentation deployed on the Dynamics Explorer Satellite (DE). The Fabry-Perot interferometer (FPI) on DE measures altitude profiles of the meridional component of the neutral wind below the spacecraft by remotely sensing the Doppler shift of the thermospheric O(1D). The Wind and Temperature Spectrometer (WATS) measures the in situ zonal component of the neutral wind by measuring the angle of arrival of the beam of neutral atoms entering the aperture to a mass spectrometer. A description is provided of data handling procedures, and the first results obtained by combining the data sets from the two instruments are presented. Acquisition and determination of neutral wind vectors from the remote (FPI) and in-situ (WATS) measurements requires careful handling of the data to ensure that the two components relate to the same volume of space.

Killeen, T. L.↗
NASA NTRS1984

Line-of-sight observations at 86 GHz with a very large and a small antenna

Amplitude variations over a 12.9 km terrestrial line-of-sight path were measured simultaneously on a 1400 lambda and a 29 lambda antenna at 86.16 GHz. Clear atmosphere data from two occasions with considerably different meteorological conditions are presented. Both sets have statistical and spectral parameters in good agreement with turbulence theory. Some of the data taken after a thunderstorm front passage show a slow gain reduction of the large antenna of up to 2 dB and an increase in variance to a level above that of the small antenna. The power spectral density of these data reveals that the excess fluctuation power is in the region of the spectrum which turbulence theory predicts to be flat. It shows an approximate 1/f dependence. It is attributed to refractive bending of up to 0.025 deg. Gain reductions due to turbulence or turbulence induced angle-of-arrival variations were estimated to be negligible.

Vogel, W. J.↗
NASA NTRS1984

Meteorological factors in Earth-Satellite propagation

A 5-meter paraboloidal antenna operated at 28 GHz showed gain changes of 2 dB due to rain. While precise estimation of the corresponding angle of arrival changes is difficult, they appear to have been on the order of 0.02 degrees. The attenuation at 28.6 GHz inferred from radiometry agreed well with that measured simultaneously over a satellite/Earth link at the same frequency. The radiometers so calibrated have been used to add to the available site diversity data base using a 9 km baseline. An improved empirical model of site diversity gain was obtained by applying regression techniques to available published data. A brief review of the literature has led to suggestions for two experimental programs, one dealing with multifrequency radiometry and the other with the effects of the stochastic properties of precipitation on wideband data transmission.

Levis, C. A.↗
NASA NTRS1986

Sound propagation over uneven ground and irregular topography

The development of theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere is discussed. Irregular topography here is understood to imply a ground surface that (1) is not idealizable as being perfectly flat or (2) that is not idealizable as having a constant specific acoustic impedance. The study focuses on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.

Pierce, A. D.↗
NASA NTRS1986

Sound propagation over uneven ground and irregular topography

Theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere was developed. Irregular topography here is understood to imply a ground surface that is not idealized as being perfectly flat or that is not idealized as having a constant specific acoustic impedance. The interest focuses on circumstances where the propagation is similar to what might be expected for noise from low altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.

Kearns, J. A.↗
NASA NTRS1987

Sound propagation over uneven ground and irregular topography

The goal of this research is to develop theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography here is understood to imply a ground surface that is not idealizable as being perfectly flat or that is not idealizable as having a constant specific acoustic impedance. The interest of this study focuses on circumstances where the propagation is similar to what might be expected for noise from low-attitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence. The activities and developments that have resulted during the period, August 1986 through February 1987, are discussed.

Berthelot, Yves H.↗
NASA NTRS1988

Sound propagation over uneven ground and irregular topography

The goal of this research is to develop theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that is not idealizable as being perfectly flat or that is no idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.

Berthelot, Yves H.↗
NASA NTRS1988

Sound propagation over uneven ground and irregular topography

Theoretical, computational, and experimental techniques were developed for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that: (1) is not idealizable as being perfectly flat, or (2) that is not idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.

Berthelot, Yves H.↗
NASA NTRS1988

DSS 14 antenna calibrations for GSSR/VLA Saturn radar experiments

The DSS 14 pointing and gain were calibrated to support X-band bistatic radar observations of Saturn's rings. The observations used the Goldstone Solar System Radar and the National Radio Astronomy Observatory's Very Large Array (VLA) in Socorro, New Mexico. The pointing calibrations were based on conscan offset data collected during Voyager 1 and 2 support passes. The conscan data show angle-of-arrival sensing with no bias and 0.3 mdeg 1-sigma error. Using the calibrations, demonstrated blind pointing performance on Saturn was less than 3 mdeg 1-sigma error. Meteorological observations at the site were used to reduce elevation errors caused by atmospheric refraction. The techniques used corrected about one-third of the error-poorer than expected performance.

Guiar, C. N.↗
NASA NTRS1988

Atmospheric propagation effects relevant to optical communications

A number of atmospheric phenomena affect the propagation of light. The effects of clear air turbulence are reviewed as well as atmospheric turbidity on optical communications. Among the phenomena considered are astronomical and random refraction, scintillation, beam broadening, spatial coherence, angle of arrival, aperture averaging, absorption and scattering, and the effect of opaque clouds. An extensive reference list is also provided for further study. Useful information on the atmospheric propagation of light in relation to optical deep space communications to an earth based receiving station is available, however, further data must be generated before such a link can be designed with committed performance.

Shaik, K. S.↗
NASA NTRS1992

Determination of meteor flux distribution over the celestial sphere

A new method of determination of meteor flux density distribution over the celestial sphere is discussed. The flux density was derived from observations by radar together with measurements of angles of arrival of radio waves reflected from meteor trails. The role of small meteor showers over the sporadic background is shown.

Andreev, V. V.↗
NASA NTRS1999

The Radio Plasma Imager Investigation on the IMAGE Spacecraft

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole. Echoes from the magnetopause, plasmasphere and cusp will be received with three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring programs operating at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density and temperature by using a thermal noise spectroscopy technique.

Reinisch, Bodo W.↗