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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

ATS-6 - Radio Beacon Experiment: The first years

The Radio Beacon Experiment aboard Applications Technology Satellite-6 (ATS-6) is designed to measure the total electron content and the ionospheric electron content between the satellite and ground. The spaceborne beacon transmits signals on frequencies of 40, 140, and 360 MHz with amplitude modulations of 1 MHz and/or 0.1 MHz for the measurement of modulation phase, Faraday rotation, and amplitude. The modulation phase delays are calibrated in the satellite and in the ground equipment, and the polarization of the emitted signals are predetermined by standard antenna range techniques. The design of the ATS-6 receiver in Boulder, Colorado, is discussed. The antennae are of the short backfire type described by Ehrenspeck (1967), with nominal gains of 13, 19, and 22 dB at 40, 140, and 360 MHz, respectively. Data recording and overall supervision of the receiver is carried out by a 16-bit minicomputer with 8 k of memory. Overall performance of the system is satisfactory. Sample data on the monthly median hourly values of the total electron content, plasmospheric content, and shape factor show distinct seasonal and diurnal variations.

Davies, K.↗
NASA NTRS1976

Aeronomy report no. 73: Analysis of sounding rocket data from Punta Chilca, Peru

A technique is described for measuring electron concentrations in the lower portion of the ionosphere above Punta Chilca. A radio-propagation experiment for measuring Faraday rotation is combined with a dc/Langmuir probe experiment for measuring electron current. The results obtained from the analysis of radio and probe data from Nike Apache 14.532, which was launched at 20:26 UT on May 28, 1975, at a solar zenith angle of 60 deg are presented. A comparison of the profiles of electron concentration indicates that the value of the maximum ionization in the D region under quiet conditions is proportional to the square of the cosine of the solar zenith angle.

Fillinger, R. W., Jr.↗
NASA NTRS1977

Solar plasma: Viking 1975 interplanetary spacecraft dual-frequency Doppler data

Viking 1975 interplanetary S- and X-band Doppler data are surveyed. These data show consistency with differenced range versus integrated Doppler (DRVID) data when there is solar plasma and with Faraday rotation data otherwise. An increase of solar plasma effects with decreasing sun-earth-probe (SEP) angle (approaching Mars orbit insertion) is demonstrated. The 2-way/3-way data indicate a homogeneous solar plasma structure over a 8,000-km spread. Occasional cycle slips in the data are pinpointed and tabulated.

Wu, S. C.↗
NASA NTRS1977

Mariner Venus Mercury 1973 S/X-band experiment

The S/X-band experiment on the Mariner Venus/Mercury 1973 spacecraft constituted a unique opportunity to demonstrate the capability of an X-band downlink coherent with the normal S-band downlink. This was both a technological and scientific experiment, and the results indicated that it was successful in both cases. Analysis of the tracking data shows that the new S/X data type was capable of reducing the miss distance at the planet Mercury by 80% (post-processed data). The use of S/X electron content was demonstrated by comparison with Faraday rotation data. An X-band turnaround telemetry experiment showed the feasibility of a planetary X-band link. In the science area, the model atmospheric environment of Venus was refined. The ionosphere of the planet was measured to a higher accuracy than before, and the value of the dual-frequency link for measuring the scale size of turbulence was demonstrated. The estimate of the scale size was increased from 100 m to above 5 km.

Levy, G. S.↗
NASA NTRS1977

Helios mission support

Activities of the Deep Space Network in support of the Helios project from 15 April through 15 June 1977 are reported. Information concerning Helios-2's superior conjunction period, Faraday rotation experimentation during solar conjunction, updated Mark III data system status, and other mission oriented activities is included.

Goodwin, P. S.↗
NASA NTRS1976

Observations of Jupiter's radio emission at 327 MHz and 1410 MHz during the Pioneer 11 fly-by

During the 1974 fly-by of Jupiter by the Pioneer 11 spacecraft, radio observations were carried out daily at 327 and 1410 MHz for a period of 60 days centered on December 3, 1974, the day of closest approach to Jupiter. The 1410-MHz data reveal two significant short-term variations in the Jovian radio emission; the largest one is probably present also at 327 MHz although Faraday rotation in earth's ionosphere could have affected the data. The two radio bursts appear to be correlated with two long-duration electron bursts observed in the energy ranges from 2 to 7 and 6 to 30 MeV.

Kundu, M. R.↗
NASA NTRS1977

Transfer of polarized radiation in self-absorbed synchrotron sources. I - Results for a homogeneous source

The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.

Jones, T. W.↗
NASA NTRS1977

Transfer of polarized radiation in self-absorbed synchrotron sources. II - Treatment of inhomogeneous media and calculation of emergent polarization

As an extension of previous treatments of polarized radiation transfer in homogeneous synchrotron sources, a transfer procedure is derived, based on the coupled-wave formulation, which allows consideration of inhomogeneous sources. It is shown that plasma characteristic wave eccentricities in a source must be fairly large unless Faraday rotation per absorption depth is very large, and that coupling between characteristic waves can be strong in inhomogeneous self-absorbed sources. Calculations are made of the polarized radiation emergent from a source with a boundary of finite thickness. It is found that neglect of propagation effects in the source boundary introduces no significant errors at optically thin frequencies, but that below the self-absorption turnover the emergent polarization may depend significantly upon such effects. In particular, the sign of the circular polarization and the linear polarization position angle depend upon the absorption depth in the boundary region.

Jones, T. W.↗
NASA NTRS1977

Polarization loss of a satellite - Data collection sensor link

It is noted that the stringent economy of data-collection systems consisting of several widely dispersed satellite-monitored sensor platforms can be partially achieved by using an inexpensive linearly polarized antenna on each platform and that due to Faraday rotation of the ionosphere, the satellite antenna must be circularly polarized to avoid a prohibitive polarization loss. The cumulative probability distribution of polarization loss between a linearly polarized platform antenna and an elliptically polarized satellite antenna is computed for satellite-antenna axial ratios of 3 and 4 dB. The results indicate that a polarization loss of 4.5 dB must be expected for a reliability of 85% and an axial ratio of 3 dB. It is suggested that the conventional assignment of a 3-dB polarization loss to the communication link considered may not insure the required link reliability.

Estep, H.↗
NASA NTRS1977

Maps of Jovian radio emission

Observations were made of Jupiter with the Westerbork telescope at all three frequencies available: 610 MHz, 1415 MHz, and 4995 MHz. The raw measurements were corrected for position errors, atmospheric extinction, Faraday rotation, clock, frequency, and baseline errors, and errors due to a shadowing effect. The data was then converted into brightness distribution of the sky by Fourier transformation. Maps of both thermal and nonthermal radiation were developed. Results indicate that the thermal disk of Jupiter measured at a wavelength of 6 cm has a temperature of 236 + or - 15 K. The radiation belts have an overall structure governed by the trapping of electrons in the dipolar field of the planet with significant beaming of the synchrotron radiation into the plane of the magnetic equator.

Depater, I.↗
NASA NTRS1978

Equatorial irregularity belt and its movement during a magnetic storm

Evidence for an equatorial irregularity belt and its movement during a magnetic storm has been obtained from Faraday rotation measurements at a chain of 140-MHz radio beacons receiving from the ATS-6 satellite. The stations covered a latitude region from the magnetic equator to the 45 deg N dip on the Indian subcontinent. An irregularity belt extending from the magnetic equator to about 27 deg N latitude was observed during the main phase of the magnetic storm of 10 January, 1976.

Vats, H. O.↗
NASA NTRS1978

Helios mission support

Deep Space Network support of Helios mission operations is discussed. Included is information on the Helios 1, 7th aphelion, Helios 2, 5th aphelion, science experiments, 22-bit error polynomial code (EPC) testing, and other mission-related activities. Mission operations and status are summarized and specific correction commands are described. Special activities and experiments include Faraday rotation data collection and a solar wind tracks experiment.

Goodwin, P. S.↗
NASA NTRS1978

A numerical model for low-latitude ionospheric TEC

A numerical model of total electron content (TEC) at low latitudes has been constructed from the Faraday rotation data recorded at a number of locations in India during the period Oct. 1975-July 1976 when the geostationary satellite ATS-6 was located at 35 deg E. In all, 36 coefficients for each season are required to represent the model. The model can be used for satellite tracking systems in estimating quickly the range, range rate and angular refraction errors. The present model is an improvement over the previously constructed model based on orbiting satellite data.

Sethia, G.↗
NASA NTRS1979

Equatorial electrojet control on the low latitude ionospheric total electron content

Faraday rotation measurements at 140 MHz were made at a number of locations (covering dip latitudes 3 deg N to 27 deg N) in India, during the period October 1975 to July 1976, when the geosynchronous satellite ATS-6 was positioned at 35 deg E. The ionospheric total electron content (TEC) derived from these measurements shows a semi-annual variation with maxima in equinoxes at all the stations. It is observed that the mean peak electron content is more in April than in October, for the stations situated to the north (poleward) of the crest of the equatorial anomaly whereas for the stations situated to the south (equatorward) of the crest of the equatorial anomaly, a peak larger in October than in April is observed. The equatorial electrojet in this period is found to be stronger in April than in October and can be considered as contributing to this asymmetry in the semi-annual variation of the ionospheric TEC.

Sethia, G.↗
NASA NTRS1981

SMMR data set development for GARP

The NIMBUS 7 Scanning Multichannel Microwave Radiometer (SMMR) data are analyzed. The impact of cross polarization and Faraday rotation on SMMR derived brightness temperatures is evaluated. The algorithms used to retrieve the geophysical parameters are tested, refined, and compared with values derived by other techniques. The technical approach taken is described and the results presented.

Kogut, J.↗
NASA NTRS1981

Ionospheric propagation correction modeling for satellite altimeters

The theoretical basis and avaliable accuracy verifications were reviewed and compared for ionospheric correction procedures based on a global ionsopheric model driven by solar flux, and a technique in which measured electron content (using Faraday rotation measurements) for one path is mapped into corrections for a hemisphere. For these two techniques, RMS errors for correcting satellite altimeters data (at 14 GHz) are estimated to be 12 cm and 3 cm, respectively. On the basis of global accuracy and reliability after implementation, the solar flux model is recommended.

Nesterczuk, G.↗
NASA NTRS1982

Helios Mission support

Ongoing Deep Space Network support of the Helios 1 spacecraft is described. In addition, planning for a Solar Corona Faraday Rotation Experiment during the December 1981 14th Helios 1 perihelion and subsequent solar conjunction phase is detailed.

Berman, A. L.↗
NASA NTRS1982

Ionospheric correction for Seasat altimeter height measurement

Descriptions are given of the Faraday rotation technique used by Seasat to measure the ionosphere and the scheme employed in mapping the measurements to the spacecraft location, exploiting the fact that the effect of the ionosphere on signal speed, and therefore on Seasat radar altimeter measurements, is directly proportional to the columnar electron content of the ionosphere. The altimeter ionosphere correction is evaluated through comparison with independent methods, and it is demonstrated that the correction, whose total value can be on the order of 20 cm, is accurate to the 3-5 cm level.

Lorell, J.↗