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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Radio wave heating of the corona and electron precipitation during flares

Electron-cyclotron masers, excited while energy release is occurring in a flaring magnetic loop, are likely to generate extremely intense radiation at decimeter wavelengths. The energy in the radiation can be comparable with that in the electrons associated with hard X-ray bursts, i.e., a significant fraction of the total energy in the flare. Essentially all of the radio energy is likely to be reabsorbed by gyroresonance absorption, either near the emitting region or at some distance away in neighboring loops. Enhanced diffusion of fast electrons caused by the maser can lead to precipitation at the maximum possible rate, and hence account for hard X-ray emission from the footpoints of the magnetic loops.

Melrose, D. B.↗
NASA NTRS1972

Partial reflections of radio waves from the lower ionosphere

The addition of phase difference measurements to partial reflection experiments is discussed, and some advantages of measuring electron density this way are pointed out. The additional information obtained reduces the requirement for an accurate predetermination of collision frequency. Calculations are also made to estimate the errors expected in partial-reflection experiments due to the assumption of Fresnel reflection and to the neglect of coupling between modes. In both cases, the errors are found to be of the same order as known errors in the measurements due to current instrumental limitations.

Connolly, D. J.↗
NASA NTRS1972

Propagation of radio waves through the lower atmosphere of Venus

A simplified model of the Venus atmosphere is developed providing the loss factor profile of the atmosphere. With this profile the atmospheric attenuation as it depends upon the incidence angle is calculated for wavelengths between 2 cm and 20 cm. It is shown that the signal-to-noise ratios for a real aperture radar, a synthetic aperture radar, and communication links between a satellite and a landing probe achieve maximum values by the proper choice of the wavelengths. Furthermore, it turns out that the wavelength dependence is less crucial for the synthetic aperture radar compared to the other cases.

Richter, K. R.↗
NASA NTRS1971

Differential phase shift of partially reflected radio waves.

The addition of phase difference measurements to differential absorption experiments is shown to be both feasible and desirable. The phase information can provide a more sensitive measurement of electron density above about 75 km. The differential phase shift is only weakly dependent on collision frequency in this range, and so an accurate collision frequency profile is not a prerequisite. The differential phase shift and differential absorption measurements taken together can provide both electron density and collision frequency data from about 70 to 90 km.

Connolly, D. J.↗
NASA NTRS1974

A novel method for measuring the polarization angle of satellite radio waves

One of the most important parameters for the study of the physics of the ionosphere is the columnar electron content. This can be obtained indirectly by measuring the Faraday rotation of signals emitted from satellites. Many different types of polarimeters have been developed for this purpose. Efforts to develop a new type of polarimeter, suitable for extensive network operation, led to a novel technique for measuring the polarization angle.

Antoniadis, D. A.↗
NASA NTRS1972

Delay time measurements of the propagation of radio waves in the atmosphere

The characteristics and operation of the Geodetic Secor System are described. The precision of the ionospheric radiation measurements was determined by a collocation experiment. The EGRS-13 satellite, which was used in the experiment, is discussed. The geodetic network is shown in a diagram form. Conclusions resulting from the experiments are reported.

Rohde, F.↗
NASA NTRS1976

Some new results on the statistics of radio wave scintillation. I - Empirical evidence for Gaussian statistics

This paper presents an analysis of ionospheric scintillation data which shows that the underlying statistical structure of the signal can be accurately modeled by the additive complex Gaussian perturbation predicted by the Born approximation in conjunction with an application of the central limit theorem. By making use of this fact, it is possible to estimate the in-phase, phase quadrature, and cophased scattered power by curve fitting to measured intensity histograms. By using this procedure, it is found that typically more than 80% of the scattered power is in phase quadrature with the undeviated signal component. Thus, the signal is modeled by a Gaussian, but highly non-Rician process. From simultaneous UHF and VHF data, only a weak dependence of this statistical structure on changes in the Fresnel radius is deduced. The signal variance is found to have a nonquadratic wavelength dependence. It is hypothesized that this latter effect is a subtle manifestation of locally homogeneous irregularity structures, a mathematical model proposed by Kolmogorov (1941) in his early studies of incompressible fluid turbulence.

Rino, C. L.↗
NASA NTRS1976

Pre-flare association of magnetic fields and millimeter-wave radio emission

Observations of radio emission at 3.3 mm wavelength associated with magnetic fields in active regions are reported. Results of more than 200 regions during the years 1967-1968 show a strong correlation between peak enhanced millimeter emission, total flux of the longitudinal component of photospheric magnetic fields and the number of flares produced during transit of active regions. For magnetic flux greater than (10 to the 21st power) maxwells flares will occur and for flux of (10 to the 23rd power) maxwells the sum of the H-alpha flare importance numbers is about 40. The peak millimeter enhancement increases with magnetic flux for regions which subsequently flared. Estimates of the magnetic energy available and the correlation with flare production indicate that the photospheric fields and probably chromospheric currents are responsible for the observed pre-flare heating and provide the energy of flares.

Mayfield, E. B.↗
NASA NTRS1977

Reflection of radio waves by sporadic-E layers

A full-wave analysis of the reflection coefficient is developed and applied to electron-density profiles of midlatitude sporadic-E layers observed by rocket-borne probes. It is shown that partial reflection from the large electron-density gradients at the upper and lower boundaries of sporadic-E layers does not account for the partial transparency observed by ionosondes.

Miller, K. L.↗