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At least 1,459 records · Page 81
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NASA NTRS1981

Radio emission of sea surface at centimeter wavelengths and is fluctuations

The eigen thermal radio emission of the sea was examined as well as the agitated surface of the sea when the reflection (scattering) is similar in nature to diffused scattering. The contribution of this emission to the total emission of the sea is practically constant in time, and the time fluctuations of the radio emissions of the sea are basically determined only by a change in the eigen emission of the sea, connected with the agitation.

Tseytlin, N. M.↗
NASA NTRS1981

Radio astronomy

The activities of the Deep Space Network in support of Radio Astronomy Operations during April and May 1981 are reported. Work in progres in support of an experiment selected for use of the DSN by the Radio Astronomy Experiment Selection Panel, Twin Quasi-Stellar Object VLBI, is reported.

Wolken, P. R.↗
NASA NTRS1978

Decameter-wave radio observations of Jupiter during the 1977 apparition

A catalog of observations of Jupiter's sporadic decameter wavelength radio emissions obtained with the Goddard Space Flight Center Jupiter Monitor Network between June 1977 and May 1978 is presented. Data were collected using the Goddard Space Flight Center station in Greenbelt, MD. and at facilities installed at Orroral Valley (Canberra), Australia and the Nancay Radio Observatory in France. Observations were obtained daily at frequencies of 16.7 and 22.2 MHz using five-element Yagi antennas at each end of a two-element interferometer. Plots of the two dimensional emission occurrence probability distribution are given.

Alexander, J. K.↗
NASA NTRS1979

Radio spectrum surveillance station

The paper presents a general and functional description of a low-cost surveillance station designed as the first phase of NASA's program to develop a radio spectrum surveillance capability for deep space stations for identifying radio frequency interference sources. The station described has identified several particular interferences and is yielding spectral signature data which, after cataloging, will serve as a library for rapid identification of frequently observed interference. Findings from the use of the station are discussed.

Hersey, D. R.↗
NASA NTRS1980

Correlated observations of a spatially resolved type III solar radio burst group and the associated hard X-ray emission

The first measurements of the spatial structure of a group of type III solar radio bursts associated with an impulsive hard X-ray burst are presented. At 169 MHz the radio source has been found to consist of two principal regions separated by about 300,000 km. The two regions together produced a total of four component bursts in good time correlation with spikes in the hard X-ray emission. The observations indicate that electron acceleration/injection occurs over a region which covers a wide range of magnetic field lines.

Kane, S. R.↗
NASA NTRS1980

Vertical structure of the atmosphere of Venus from Pioneer Venus orbiter radio occultations

Between December 1978 and February 1979 the Pioneer Venus orbiter spacecraft returned some 140 S band and X band radio occultation measurements of the Venus atmosphere. Results from 13 measurements, covering diverse latitudes from near equatorial to polar, are presented in this paper in the form of vertical profiles of temperature. The temperature profiles show a pronounced inversion at the tropopause for latitudes higher than about 50 deg, with the deepest inversions occurring between the latitudes of 60 deg and 70 deg, the latitudes at which the cold collar cloud feature was observed by the Pioneer Venus Vortex instrument. A comparison of the temperature profiles derived from radio occultation measurements with the stratospheric infrared temperature soundings of the Vortex instrument and the in situ measurements of tropospheric temperature and pressure by the North, Sounder, and Day probes indicates excellent agreement.

Kliore, A. J.↗
NASA NTRS1981

Radio science investigations of the Saturn system with Voyager 1 - Preliminary results

Analyses of Voyager 1 radio occultation measurements of the Saturn atmosphere near 75 deg south latitude and of the Titan equatorial atmosphere are presented. Molecular nitrogen appears to be the primary atmospheric constituent of Titan, whose clouds are probably methane ice. Solar abundance considerations of the data suggest large quantities of surface methane near its triple-point temperature, so that the three phases of methane could play a role on Titan analogous to that of water on earth. Ionospheric electron concentration and plasma scale height for the Saturn polar cap and monochromatic attenuation of the Saturn rings are also considered, along with radio tracking figures for the masses of two moons, Rhea and Titan.

Tyler, G. L.↗
NASA NTRS1981

VLBI observations of the nucleus of the radio galaxy Cygnus A

The central component of the radio galaxy Cygnus A has been observed in several (very long baseline interferometry) experiments between 1975 and 1979, and the results have been combined to derive a model for the brightness distribution. Some 65% of the nuclear emission appears to come from a compact core. The remaining flux density comes from a more extended region (or regions) up to 4 or 5 mas away lying along a position angle near 100 deg, which is close to that of the extended lobes. Evidence that compact central components reflect the collimation and transport of energy to the outer lobes of radio galaxies is discussed, and several interpretations of the observed asymmetries are considered.

Kellermann, K. I.↗
NASA NTRS1981

Observations of the giant radio lobes region of Centaurus A with SAS 3

Observations of the X-ray flux from the extended radio lobes of the galaxy Centaurus A obtained with the SAS 3 observatory are reported. The 15 x 15 deg region that includes the lobes was mapped by superposing data from raster scans with the horizontal tubular collimator detectors, which have a 1.7 deg FWHM circular field of view. Data obtained is consistent with the presence of superposed emission from the point sources NGC 5128 and MX 1312-42, a previously unreported source detected by the Einstein Observatory IPC. Fluxes of 4.63 + or - 0.14 x 10 to the -10th and 4.6 + or - 0.6 x 10 to the -11th ergs/sq cm per sec were measured for NGC 5128 and MX 1312-42, respectively, with best fit power law spectra of indices 0.83 + or - 0.04 and 0.62 + or - 0.10 and hydrogen column densities of 1.23 + or - 0.10 x 10 to the 23rd and 9.7 + or - 15.0 x 10 to the 21st atoms/sq cm. Results imply an upper limit of 2.9 x 10 to the 11th for the X-ray emission from the extended radio lobes of Cen A between 2 and 10 keV, which indicates a lower limit to the magnetic field in the lobes of 1.6 x 10 to the -6th gauss.

Marshall, F. J.↗
NASA NTRS1981

Low-frequency radio observations of poor clusters of galaxies

Observations have been made at the Clark Lake Radio Observatory of 16 poor clusters of galaxies at 34.3 MHz. Four of the poor clusters were detected at flux densities greater than 20 Jy. The spectra of the four detected clusters are all rather steep. Two of the detected clusters, AWM 4 and AWM 5, are also known to be X-ray sources. The possibility that the X-ray-emitting gas is heated by Coulomb interactions with the relativistic electrons responsible for the radio emission is investigated, and it is found that the observed X-ray luminosities can be accounted for if the electron energy spectrum extends to very low energies (gamma approximately 1-10). Collective plasma effects may increase the heating efficiency and eliminate the need to extrapolate the electron energy spectrum to such low values.

Hanisch, R. J.↗
NASA NTRS1981

Impulsive radio discharges near Saturn

Nonthermal radio emissions from the Saturn system were first detected by the Voyager planetary radio astronomy (PRA) experiment on board Voyager 1 in January 1980. Since then emission between 100 kHz and 1 MHz from the planet, termed Saturn kilometric radiation (SKR), has been received almost continuously. A description is presented of eight characteristics which have been fairly well defined by the Voyager 1 encounter. These include a very flat broadband frequency spectrum, a period of approximately 10 h 10 min, a change in the envelope shape of episodes between pre and postencounter, an intensity population structure typical of plural populations, and an episodic structure of a width of approximately 180 deg. It was found that postencounter episodes continue for about three times as long as preencounter ones, and that postencounter bursts are left-circularly polarized at high frequencies. At least one episode shows the onset of high frequency events some time before that of lower frequency ones.

Evans, D. R.↗
NASA NTRS1981

Saturn's radio emissions - Rotational modulation

Observational data provided by Pioneer 11 and Voyager 1 have revealed that the Saturnian ring system has important effects on the structures of the planetary ionosphere as well as the magnetospheric environment, such as the unexpected rotational modulation of the Saturn kilometric radiation (SKR) and the Saturn electrostatic discharge (SED) as discovered by the Voyager planetary radio astronomy experiment. The challenge arises to devise a mechanism which can produce electrodynamic coupling between the ring system and the planetary ionosphere and/or magnetosphere in which the associated SKR and SED radio emissions are subject to longitudinal control. One candidate is the establishment of field-aligned current systems, connecting the rings and the ionosphere with longitudinal variation. Local acceleration processes in the vicinity of the rings are also needed. The interplay between the ring-current systems and the geometry of the dipole field and the rings is discussed, and a description is presented of some of the basic ingredients in the longitudinal modulations of SKR and SED.

Goertz, C. K.↗
NASA NTRS1981

Possibility of a new approach to processing space pulse radio signals

A approach to the processing of space pulse radio signals, which makes it possible to achieve a high level of time resolution is proposed. The approach is based on the utilization of the Fourier transform of a radio pulse envelope in the interstellar medium effect. The conditions of applicability of the proposed method and the requirements for recording equipment are substantiated. Also indicated is the possibility of obtaining superresolution with the utilization of the given method of signal processing.

Bocharov, A. A.↗
NASA NTRS1982

Analysis, prediction and control of radio frequency interference with respect to DSN

Susceptibility modeling, prediction of radio frequency interference from satellites, operational radio frequency interference control, and international regulations are considered. The existing satellite interference prediction program DSIP2 is emphasized. A summary status evaluation and recommendations for future work are given.

Degroot, N. F.↗
NASA NTRS1982

Goldstone radio spectrum signal identification, March 1980 - March 1982

The signal identification process is described. The Goldstone radio spectrum environment contains signals that are a potential source of electromagnetic interference to the Goldstone tracking receivers. The identification of these signals is accomplished by the use of signal parameters and environment parameters. Statistical data on the Goldstone radio spectrum environment from 2285 to 2305 MHz are provided.

Gaudian, B. A.↗
NASA NTRS1981

HEAO A-2 observations of non-Abell Zwicky clusters containing extended radio sources

Burns and Owen's sample of 25 4C radio sources which coincide with Zwicky clusters of galaxies has been searched for X-ray emission using the HEAO 1 A-2 experiment. X-ray emission was detected from five sources at the 3sigma level, two of which exceeded 5sigma. Positions and 90% X-ray error boxes are given for each of the five sources detected. The clusters surveyed are non-Abell clusters which would generally not be expected to be detectable with the A-2 experiment. The search for X-ray emission was prompted by the knowledge of the existence of extended radio sources in the clusters. The relaxed structure of these sources implies the presence of a relatively dense intracluster medium which is expected to produce thermal bremsstrahlung X-ray emission.

Holman, G. D.↗
NASA NTRS1981

Radio wave scattering observations of the solar corona First-order measurements of expansion velocity and turbulence spectrum using Viking and Mariner 10 spacecraft

Radio wave scattering data were collected at 3.6 and 13 cm wavelengths by means of the radio link between the Viking orbiters and the earth during the Nov. 25, 1976 solar conjunction of Mars, which occurred near the beginning of solar cycle 21; Mariner 10 solar activity observations during 1974 are also used. It is found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma, and the spectral index of electron density turbulence is obtained. The measurements of solar wind velocity and spectral index cover 78 days for Viking and 49 days for Mariner 10 and show the combined effects of changing heliocentric distance, solar latitude, and solar longitude as well as solar activity. It is concluded that the observational velocity profile differs significantly from the theoretical profiles in two ways: (1) the theoretical profile does not show the abrupt change in velocity at about 15 solar radii, and (2) the observational profile shows acceleration at larger radial distances than the model profiles. The observational profiles indicate velocities of less than about 150 km/sec out to 15 solar radii.

Tyler, G. L.↗