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At least 1,207 records · Page 67
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NASA NTRS1975

Calculation of the radio emission from EAS

Time-varying features of an electron-photon cascade are considered, particularly those associated with radio emission. The cosmic ray shower is represented as a superposition of collinear 10 GeV electron-photon cascades launched at different heights in the atmosphere. Actual simulations are performed for only 10 cascades at each of 40 heights and the results are scaled to represent the total number of cascades required. The apparent angular motions of the cascade particles as detected by antennas located at various positions up to 300 m from the shower axis are simulated. The radio pulse waveform and the corresponding frequency spectrum are obtained from these motions.

Allan, H. R.↗
NASA NTRS1976

Radio continuum measurements of compact H II regions and other sources

Results are reported for measurements of the flux densities of 33 sources at wavelengths of 13, 4, and 2 cm, which were conducted using the NASA/JPL Deep Space Network 64-m antenna at Goldstone, Calif. Besides compact H II regions, the sources included five Uhuru X-ray sources, several IR sources, an extragalactic radio source, and a H2O maser. The Lyman continuum flux is derived from the measured radio flux and the assumed distance and temperature for 10 possible H II regions; the spectra of previously known sources are extended to higher frequencies, and upper limits are placed on the flux densities for the five X-ray sources. New compact H II regions are found in the bright nebula M78, the nebula K5, and the Ophiuchus dark cloud/IR region.

Matsakis, D. N.↗
NASA NTRS1975

Electron plasma oscillations associated with type III radio emissions and solar electrons

Results of an extensive search for electron plasma oscillations associated with type III radio noise bursts are presented which were obtained by analyzing 87 type III bursts detected in plasma-wave and charged-particle measurements carried out by IMP 6, 7, and 8. Only one case is found for which plasma oscillations were associated with electrons of solar origin; at least eight events are identified in which no plasma oscillations were detected even though electrons from solar flares were clearly evident. The type III emissions are compared with similar radiation coming from upstream of earth's bow shock at the harmonic of the local electron plasma frequency, and quantitative calculations of the rate of conversion from plasma oscillatory energy to electromagnetic radiation are performed. The results show that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU and that neither the type III emissions nor the radiation from upstream of the bow shock can be adequately explained by a current model for the coupling of electron plasma oscillations to electromagnetic radiation. Several possible explanations are considered for this discrepancy between theory and observations.

Gurnett, D. A.↗
NASA NTRS1976

The problem of spiral galaxies and satellite radio sources

Regions 2-deg x 2-deg in area centered on four spiral galaxies were scanned with the Goldstone 64-m antenna in search of satellite radio sources at 2295 MHz. Four control regions of equal area but free of galaxies brighter than 13th magnitude were also scanned. No significant excess in the number density of sources with flux densities greater than 0.10 Jy relative to the control fields was found. A detailed comparison is made between the results of this program and the results of previous investigators. In particular, attention is directed to the potentially important implications of an investigation by Tovmasyan (1968), who searched a large number of spirals and found evidence that a small percentage of them apparently have radio satellites located up to 20 arcmin from the central galaxy. Fifteen sources selected from Tovmasyan's list of 43 satellite sources were measured. The present results confirm his positions and relative flux densities for each of the sources.

Arp, H.↗
NASA NTRS1976

Possibility of detecting magnetospheric radio bursts from Uranus and Neptune

The intensity of magnetospheric radio bursts (MRBs) is scaled to solar-wind input into planetary magnetospheres and the frequency of emission is scaled to polar surface magnetic-field strength in order to estimate the possibility of detecting MRBs from Uranus and Neptune. A scaling law is derived which relates the ratio of power radiated in MRBs to the solar-wind input for earth, Jupiter, and Saturn. Power-flux spectra of MRBs from these three planets are plotted, and it is shown that Jupiter and Saturn may radiate 1% to 5% of the solar-wind energy input into their magnetospheres. The properties of MRBs from Uranus and Neptune are estimated by assuming a conversion efficiency of 1% to 5%, a bandwidth of half the peak frequency, and conformity of Uranus' and Neptune's dipole moments with the magnetic Bode's law. Based on the results, it is suggested that detection of MRBs from these two planets may be a reasonable cruise-mode radio-astronomy objective on future missions to the outer solar system.

Kennel, C. F.↗
NASA NTRS1976

Apparent 'superrelativistic' expansion of the extragalactic radio source 3C 345

The compact extragalactic radio source 3C 345 was observed by very-long-baseline interferometry (wavelength about 3.8 cm) at 12 epochs distributed over the nearly four-year period from February 1971 to October 1974. For one of these epochs, the multibaseline data were sufficient to allow the brightness distribution to be estimated in a model-independent manner; the resultant distribution was clearly dominated by two components. The remaining sets of data were also represented adequately by two-component models. The angular separation of the two components increased during this period from about 1.00 to 1.30 milliarcsec, corresponding to an apparent average speed of expansion of approximately 2.5 c at a fixed position angle of 105 (plus or minus 5) deg. These results, coupled with the fact that contraction has never been observed, seem difficult to reconcile with the so-called Christmas-tree model of the 'superrelativistic' expansion of extragalactic radio sources.

Wittels, J. J.↗
NASA NTRS1976

The use of dispersion to eliminate multipath in planetary radio occultations

Occultation geometry is analyzed with a view toward eliminating all multipath resulting from layer effects. It is assumed that the spacecraft moves behind the planet with a constant velocity perpendicular to the direction from the spacecraft to the earth, and that for radio frequencies of 1 to 2 GHz the angle of refraction of a radio ray passing through the ionosphere is so small as to be imperceptible if drawn to scale. It is shown that if a particular amount of dispersion is inserted into the process at any stage prior to signal detection, the frequency vs time curve will be converted to a frequency vs ray asymptote height curve. Because there can be only one mode from any one ray asymptote height in a layered medium, frequency must be a single-valued function of this parameter. The introduction of an appropriate dispersion will therefore eliminate all multipath insofar as it is caused by spherically symmetric planetary layers. The degree of accuracy to be provided in flight and during postflight analysis is discussed.

Croft, T. A.↗
NASA NTRS1976

Further joint X-ray, infrared, and radio observations of Cygnus X-3

Observations of Cygnus X-3 have been carried out at 2.5-7.5 keV, 2.2 micrometers, 8.1 GHz, and 2.7 GHz over a two week period. The X-ray data show the periodic structure which is typical of Cyg X-3. At times the X-ray and infrared measurements show very similar periodic structure, both in phase and in shape, while at other times the infrared data show no periodic variability. The radio fluxes were unusually low during the period of observation; both the daily average radio flux levels and the spectral index remained nearly constant.

Mason, K. O.↗
NASA NTRS1976

Possible radio emission from Uranus at 0.5 MHz

Radio emission from the direction of Uranus has been detected in data from the Goddard radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn had been observed by IMP-6 at a number of frequencies near 1 MHz and were identified through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics have been found. The events persisted less than 3 minutes and are strongest in intensity near 0.5 MHz. Identification with Uranus is confused by the likely presence of low-level terrestrial and solar emission. Because of the unfavorable angular separation of earth and Uranus, there is a possibility that the bursts are atypical terrestrial magnetospheric phenomena, although the uniqueness of the set of events indicates the probable detection of radiation from Uranus.

Brown, L. W.↗
NASA NTRS1976

An observational program to search for radio signals from extraterrestrial intelligence through the use of existing facilities

It is argued that a substantial portion of the capability for detecting microwave signals from extraterrestrial civilizations lies not in the application of ever larger antenna collecting areas but rather in the application of millions or billions of simultaneous frequency-channel observations combined with rapid and powerful data processing techniques. The application of these methods to existing facilities is discussed in terms of a program of modest expense and duration which will seek to discover certain classes of extraterrestrial signals of intelligent origin while defining boundaries to the search problem throughout the range of interest. This program will investigate radio-astronomical phenomena of interest and simultaneously define the background of environmental radiation in order to determine physical limitations on both the search strategies and the potential for deep-space communications. Signal parameters that must be determined are examined along with the potential of existing radio-astronomical facilities for detecting narrow-band signals. A seven-year program is described which will carry out a search for extraterrestrial intelligence over 80% of the sky and over the entire frequency range from 1 to 25 GHz with a sensitivity limit varying from 10 to the -21st power W/sq cm at the lowest frequencies to 10 to the -19th power W/sq cm at the higher frequencies.

Edelson, R. E.↗
NASA NTRS1976

Radio source positions from very-long-baseline interferometry observations

Accurate positions of compact radio sources have been determined from very-long-baseline interferometry (VLBI) observations based on the bandwidth-synthesis technique. The coordinates for 18 extragalactic sources were obtained from sets of observations spread over the period from April 1972 to January 1975; the scatter among the independent determinations of the source coordinates from the separate sets of observations is about 0.05 arcsec, except for the declinations of near-equatorial sources, where the scatter is about 0.15 arcsec. Comparison of these positions with those determined with the Cambridge 5-km radio interferometer shows the rms scatter about the mean difference to be about 0.04 arcsec in each coordinate (no sources of low declination were in common). A similar comparison of the present results with those obtained by the Jet Propulsion Laboratory from separate VLBI observations yields a slightly larger rms scatter, after exlusion of the declinations of the near-equatorial sources. A position is also obtained for the galactic object Beta Persei (Algol), which agrees well with the position given in the FK 4 catalogue.

Clark, T. A.↗
NASA NTRS1977

Analysis of a discrete spectrum analyzer for the detection of radio frequency interference

As the radio frequency spectrum becomes increasingly overcrowded, interference with mission-critical DSN operations is rising at an alarming rate. To alleviate this problem the DSN is developing a wideband surveillance system for on-site detection and identification of potential sources of radio frequency interference (RFI), which will complement the existing frequency coordination activities. The RFI monitoring system is based on a wideband, multi-look discrete spectrum analyzer operating on fast Fourier transform principles. An extensive general statistical analysis is presented of such spectrum analyzers and derives threshold detection performance formulas for signals of interest. These results are then applied to the design of the RFI spectrum analyzer under development.

Levitt, B. K.↗
NASA NTRS1976

Structure of the atmosphere of Jupiter from Pioneer 10 and 11 radio occultation measurements

A technique for incorporating effects of the oblateness of Jupiter's atmosphere into the data analysis procedure for radio-occultation measurements is described which makes use of a spherical harmonic representation of the gravity field to compute the shape of the planet. With this technique, the center of refraction is located by the radius of curvature and the normal direction at the closest approach point of the ray. The present technique, a subsequent approximation involving the use of a constant center of refraction, and the Abel integral transform inversion method for spherical planets are applied to Pioneer 10 and 11 data. All the intermediate results obtained show a temperature inversion between 10 and 100 mb, with temperatures from 130 to 170 K at 10 mb and from 80 to 120 K at 100 mb. Comparison of the radio-occultation profiles with radiative-convective equilibrium models and the temperature profile based on Pioneer 10 IR radiometer data indicates good agreement between the models and the occultation results.

Kliore, A. J.↗
NASA NTRS1976

The Pioneer 11 radio occultation measurements of the Jovian ionosphere

Radio occultation data obtained with the Pioneer 11 spacecraft are utilized to study Jupiter's ionosphere. The ingress measurements, which were conducted by using a stable earth-based frequency reference for the tracking link, yielded ionospheric data near the morning terminator at about 79 deg south latitude. Data were also taken during egress on the evening side near 20 deg north latitude. The latter measurements were conducted in the one-way mode; i.e., an on-board crystal oscillator was employed as a frequency reference for the downlink (spacecraft-to-earth) signal. These data confirm previous results obtained with Pioneer 10 and show that Jupiter has a multilayered ionosphere extending over an altitude range of more than 3000 km. The topside scale height near 79 deg south latitude was 540 + or - 60 km. Assuming a topside electron, H(+) distribution controlled by diffusion yields a plasma temperature of 850 + or - 100 K in this region. The radio data indicate that the upper atmosphere is either warmer or more dissociated into atomic hydrogen than previously anticipated.

Fjeldbo, G.↗
NASA NTRS1976

Electron plasma oscillations associated with type III radio bursts

Plasma wave electric field measurements with the solar orbiting Helios spacecraft have shown that intense (approximately 10 millivolts per meter) electron plasma oscillations occur in association with type III solar radio bursts. These observations confirm the basic mechanism, proposed in 1958, that type III radio emissions are produced by intense electron plasma oscillations excited in the solar corona by electrons ejected from a solar flare.

Gurnett, D. A.↗
NASA NTRS1978

Automatic radio-transmission monitor

System continuously monitors radio transmissions stored in memory. If spectrum deviates beyond present limits, alarm is tripped and spectrum is transferred to long-term storage for later analysis. Monitor can be useful in ensuring proper power level and spectral quality and in finding cause of failure. It might also be used to monitor radio-frequency interference or power levels of citizen's-band transmitters.

Bernstein, A. J.↗
NASA NTRS1978

Radio-frequency carrier arraying for high-rate telemetry reception

A method for increasing the sensitivity for radio frequency reception is described. Receiving systems or stations are arrayed in such a manner as to provide signal to noise ratio improvement relative to a single receiving system or station. Radio frequency carrier arraying for high rate telemetry that provides signal to noise ratio improvement for RF carrier reception and demodulation is discussed.

Brockman, M. H.↗