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Gordon, W. E.

Publications and source records attributed to Gordon, W. E..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

HF sideband generation in the ionosphere

The temporal development of sidebands excited near sunrise by two strong HF waves separated by a few hertz is presented. Sidebands are not observed before sunrise when the ionospheric critical frequency is less than the heater frequency. As the ionospheric density increases following sunrise and overdense conditions are established, strong sidebands emerge. Even though these results favor a mechanism which phase modulates the reflected HF wave over one which first downconverts the HF power to ULF before exciting sidebands, it is possible that either mechanism could at times contribute to sideband production.

Noble, S. T.↗
NASA NTRS1987

Multiple frequency radar observations of high-latitude E region irregularities in the HF modified ionosphere

This paper discusses the results of the September 1983 observations of artificial field-aligned irregularities (AFAIs) in the Tromso, Norway region, made by backscatter radars operating at 46.9, 143.8, 21.4, and 140.0 MHz. Four classes of resonant instability processes at work in the E and F regions are examined in detail: (1) the coupling of parametric decay instability waves across geomagnetic field lines, (2) thermal parametric instability, (3) four-wave interaction thermal parametric instability, and (4) the resonance instability. The characteristics of the AFAI scatter are described, with special attention given to the growth and decay time constants, functional dependence on the heater power and polarization, and the scattering cross sections of the irregularities.

Noble, S. T.↗
NASA NTRS1985

Observations of E region irregularities generated at auroral latitudes by a high-power radio wave

The initial results of a series of observations made with the high-power HF heating facility near Tromso, Norway are reported. During these experiments, attention was focused on the production of artificial geomagnetic field-aligned irregularities (AFAIs) in the auroral E region by HF waves. A mobile 46.9-MHz radar was used to diagnose the formation of AFAIs having spatial scales of 3.2 across geomagnetic field lines. The dynamic characteristics of the AFAIs are discussed within the context of current theoretical work dealing with the natural production of AFAIs in the ionosphere.

Djuth, F. T.↗
NASA NTRS1985

The temporal evolution of 3-m striations in the modified ionosphere

Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3-m field-aligned striations produced in the ionosphere by powerful high-frequency (HF) radio waves. The results of this investigation are now summarized. First, the striations' rise times are dependent on the HF electric field. The E region data suggest that this dependence is nonlinear. Second, the threshold value of the HF electric field required to produce detectable striations was experimentally determined. At threshold the component of the HF electric field perpendicular to the geomagnetic field is calculated to be 0.09 V/m in the F region and 0.37 V/m in the E region. Third, both the E and the F region data verify theoretical predictions that the striations' decay times are directly proportional to the electron diffusion across B. Finally, a one-to-one correspondence between the growth of the 3-m striations and the decline of the HF-enhanced plasma line during overshoot is sometimes observed.

Coster, A. J.↗
NASA NTRS1982

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

Frey, A.↗
NASA NTRS1982

Phase perturbation measurements through a heated ionosphere

High frequency radiowaves incident on an overdense (i.e., HF-frequency penetration frequency) ionosphere produce electron density irregularities. The effect of such ionospheric irregularities on the phase of UHF-radiowaves was determined. For that purpose the phase of radiowaves originating from celestial radio sources was observed with two antennas. The radiosources were chosen such that the line of sight to at least one of the antennas (usually both) passed through the modified volume of the ionosphere. Observations at 430 MHz and at 2380 MHz indicate that natural irregularities have a much stronger effect on the UHF phase fluctuations than the HF-induced irregularities for presently achieved HF-power densities of 20-80 uW/sq m. It is not clear whether some of the effects observed are the result of HF-modification of the ionosphere. Upper limits on the phase perturbations produced by HF-modification are 10 deg at 2380 MHz and 80 deg at 430 MHz.

Frey, A.↗
NASA NTRS1980

Ionospheric power beam studies

A power density level of 23 mW/sq cm is presented as a design specification based on theoretical calculations of a threshold for microwave ionosphere nonlinear interaction (thermal runaway). For comparable power densities, enhanced electron heating is observed to change the electron temperature by a factor of two or three, but not by an order of magnitude.

Duncan, L. M.↗
NASA NTRS1978

Ionosphere/microwave beam interaction study

The microwave beam of the Solar Power Satellite (SPS) is predicted to interact with the ionosphere producing thermal runaway up to an altitude of about 100 kilometers at a power density threshold of 12 mW/cm sq (within a factor of two). The operation of the SPS at two frequencies, 2450 and 5800 MHz, is compared. The ionosphere interaction is less at the higher frequency, but the tropospheric problem scattering from heavy rain and hail is worse at the higher frequency. Microwave signals from communication satellites were observed to scintillate, but there is some concern that the uplink pilot signal may be distorted by the SPS heated ionosphere. The microwave scintillations are only observed in the tropics in the early evenings near the equinoxes. Results indicate that large phase errors in the uplink pilot signal can be reduced.

Gordon, W. E.↗
NASA NTRS1977

Ionosphere/microwave beam interaction study

A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results.

Duncan, L. M.↗
NASA NTRS1976

The excitation of plasma lines in blanketing sporadic E

Enhanced plasma lines in blanketing sporadic E have been excited by a powerful HF radio wave illuminating the E region over the Arecibo Observatory. The plasma lines are observed by the incoherent scatter radar at the observatory. They originate in the sporadic E layer when the blanketing frequency exceeds the exciting frequency, a result which confirms that the plasma is overdense for the exciting frequency. Around the time when the blanketing frequency falls through the exciting frequency, large fluctuations in the plasma line intensities are observed, and thus the possibility of overdense patches drifting through the sampled volume is suggested.

Gordon, W. E.↗
NASA NTRS1971

Ionospheric heating at Arecibo - First tests.

Ionospheric F-region heating by a high-frequency transmitter (100 kW at 5.62 MHz fed into a 1000-ft dish producing a beam with an angular half-width of 10 deg) was observed with a 430-MHz incoherent scatter radar, an ionosonde, and several photometers. The electron temperature of the ionosphere was increased by as much as 30% at and just below the height where the local plasma frequency was equal to the frequency of the heating transmitter. Calculations show time constants of 40 sec for electron heating and less than 10 sec for the cooling at 308 km when the heating transmitter was operated in a pulsed mode.

Gordon, W. E.↗