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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Impact of Ionospheric Scintillation on Spaceborne SAR Observations Studied Using GNSS

A survey of artifacts seen in JAXA's Phase Array type L-band synthetic aperture radar (PALSAR) data over South America during a low solar activity year is reported in this paper. A significant impact on the radar data is revealed: about 14% of the surveyed PALSAR images (totally 2779) are affected by the artifacts during a month and the artifacts occur on 74.2% of the surveyed days. The characteristics of the artifacts have led to a consideration that the artifacts are the effects of ionospheric scintillation. This raises not only a concern about scintillation effects on radar but also a question about active scintillation conditions during a low solar activity year. To assess and verify the scintillation conditions, GPS data collected from the constellation of FORMOSAT-3/COSMIC satellites and three ground-based GPS networks are processed and analyzed. The GPS data provides a global context and regional dense converge, respectively, of ionospheric irregularity and scintillation measurements. It is concluded tat even during a low solar activity year, L-band scintillation at low latitudes can occur frequently and affect L-band SAR significantly.

remote sensing↗
NASA NTRS2017

Subnanosecond Scintillation Detector

A scintillation detector, including a scintillator that emits scintillation; a semiconductor photodetector having a surface area for receiving the scintillation, wherein the surface area has a passivation layer configured to provide a peak quantum efficiency greater than 40% for a first component of the scintillation, and the semiconductor photodetector has built in gain through avalanche multiplication; a coating on the surface area, wherein the coating acts as a bandpass filter that transmits light within a range of wavelengths corresponding to the first component of the scintillation and suppresses transmission of light with wavelengths outside said range of wavelengths; and wherein the surface area, the passivation layer, and the coating are controlled to increase the temporal resolution of the semiconductor photodetector.

Hoenk, Michael↗
NASA NTRS1969

Recent development in organic scintillators

Discussion on recent developments of organic scintillators includes studies of organic compounds that form glass-like masses which scintillate and are stable at room temperature, correlations between molecular structure of organic scintillators and self-quenching, recently developed fast scintillators, and applications of liquid-scintillation counters.

Horrocks, D. L.↗
NASA NTRS1971

High latitude scintillation effects on very high frequency /vhf/ and S-band satellite transmissions.

A scintillation study was conducted with the purpose to define the extent of scintillation activity in the S-band region, and to determine if such activities at higher frequencies are caused by ionospheric irregularities similar to those causing scintillations at vhf and lower frequencies. Simultaneous transmissions at 137 and 1695 MHz from polar orbiting satellites were used in this study. Scintillations were found to be present at S-band frequencies in the polar regions; it is concluded that they are caused by ionospheric characteristics similar to those causing scintillations at lower frequencies.

Pope, J. H.↗
NASA NTRS1973

Research Investigation on Dense Scintillation Glass for Use in Total Absorption Nuclear Cascade Detectors

Three approaches to the development of a high density scintillation glass were investigated: They include the increase of density of glass systems containing cerium - the only systems which were known to show scintillation, the testing of a novel silicate glass system containing significant concentrations of silver produced by ion exchange and never tested previously, and the hot pressing of a diphasic compact of low density scintillation glass with high density passive glass. In first two cases, while ultraviolet excited fluorescence was maintained in the glasses showing high density, scintillation response to high energy particles was not retained in the case of the cerium containing glasses or developed in the case of the silver containing glasses. In the case of the compacts, the extremely long path length caused by the multiple internal reflections which occur in such a body resulted in attenuation even with glasses of high specific transmission. It is not clear why the scintillation efficiency is not maintained in the higher density cerium containing glasses.

Hensler, J. R.↗
NASA NTRS1974

Ionospheric irregularities causing scintillation of GHz frequency radio signals

Consideration of the recently observed phenomenon of scintillation of satellite signals at GHz frequency range. Based on the scintillation data and results from in situ measurements, several ionospheric irregularity models with different power spectra are studied. Scintillation index is computed for the various models and compared with observed results. Both magnitude and frequency dependence of the scintillation index are investigated. It is found that a thick irregularity slab of the order of 200 km with an electron density fluctuation of about 20 per cent of its background value and with a nonmonotonic power spectrum may account for the maximum observed values of the scintillation index as well as its frequency dependence. Some future observations and measurements are suggested.

Wernik, A. W.↗
NASA NTRS1974

Interstellar scattering of pulsar radiation. 1: Scintillation

An investigation of the intensity fluctuations of 28 pulsars near 0.4 GHz indicates that scintillation spectra have a Gaussian shape, scintillation indices are near unity, and the scintillation bandwidth depends linearly on dispersion measure. Observations near 2.5 GHz suggest a strong dependence of the frequency at which scintillation indices fall below unity on dispersion measure. Multistation measurements of scintillation provide values or limits for the scale size of the scattering diffraction pattern. The dependences of scattering parameters on dispersion measure is discussed in terms of the current models. It is suggested that any line of sight through the galaxy encounters increasingly rare, increasingly large deviations of thermal electron density on the scale of 10 to the 11th power cm.

Backer, D. C.↗
NASA NTRS1978

Ionospheric scintillations associated with equatorial E-region

Amplitude scintillations at 40, 140, and 360 MHz recorded at an equatorial station Ootacamund (dip 4 deg N) during the ATS-6 phase II and the ionograms at a nearby station Kodaikanal (dip 3.5 deg N) are examined for the scintillation activity. Various sporadic E events, but not the Es-q, are associated with intense daytime scintillations. There are no scintillations at times of normal E-layer or cusp type of Es. Scintillations are also present at times of night Es.

Chandra, H.↗
NASA NTRS1981

Equatorial scintillations - A review

Scintillation observations of equatorial irregularities by techniques such as in situ, radar backscatter, airglow, and total electron content are reviewed, with an emphasis on GHz measurements. New aspects of the spread-F analysis from ionograms are mentioned, followed by a discussion of scintillation morphology, and the longitudinal control of the equatorial scintillations is emphasized. A coordinated multitechnique observation of the equatorial irregularities is described in detail, the study being divided into two parts: (1) an examination of the large field-aligned irregularity structures and their association with discrete patches of scintillation activity, and (2) an investigation of the coexistence of km-scale-irregularities with meter scales and a description of the evolution of the irregularity and scintillation spectra during the various phases of irregularity generation and decay. Unsolved problems are also reviewed, e.g., it is stated that the effects of steep spatial gradients in the electron density structures and their subsequent erosion on both CW and pulse propagation need to be evaluated both from the point of view of theory and experiments.

Basu, S.↗
NASA NTRS1989

High pressure gas scintillation drift chambers with wave shifter fiber readout. I

The authors present results from a prototype xenon-gas scintillation drift chamber. It was operated at pressures up to 20 atm, and the scintillation light yield was measured at various pressures and reduced fields. Scintillation-reduced fields ranged from 1.3 to 3 kV/cm/atm in a 5.4-mm scintillation gap. Drift fields ranged from 45 to 100 V/cm/atm in an 8-cm drift region. The chamber was exposed to an 241Am source in a port either 2.7 or 5.4 cm from the secondary scintillation region. The authors also describe the high-voltage problems encountered during operation at high pressures. Further tests with the wave shifter fiber readout showed that the problem of gas contamination by the fibers is manageable but that the interaction between the optical fibers and the high-pressure xenon gas can lead to fiber damage. A solution to this problem is described.

Parsons, A.↗
NASA NTRS1993

Results from a study of scintillation behavior at 12, 20, and 30 GHz using the results from the Virginia Tech Olympus receivers

Tropospheric scintillations are rapid fluctuations of signal caused by multiple scattering from the small scale turbulent refractive index inhomogeneities in the troposphere. They can strongly impair satellite communications links operating at frequency above 10 GHz. The VA Tech OLYMPUS propagation experiment which includes 12, 20, and 30 GHz beacon receivers at an elevation angle of 14 degrees provides us with valuable multifrequency scintillation data. A long term analysis of tropospheric scintillation results from the VA Tech OLYMPUS experiment is presented. It includes statistics of both the scintillation intensity and the attenuation relative to clear air as well as seasonal, diurnal and meteorological trends. A comparison with the Consultative Committee for International Radio (CCIR) predictive model for scintillation fading is presented.

Pratt, Timothy↗
NASA NTRS2008

Silicon Photo-Multiplier Readouts for Scintillators in High-Energy Astronomy

New scintillator materials have recently been shown to hold great potential for low-cost, reliable gamma-ray detectors in high-energy astronomy. New devices for the detection of scintillation light promise to make scintillator-based instruments even more attractive by reducing mass and power requirements,in particular, silicon photo-multipliers (SiPMs) are starting to become commercially available that offer gains and quantum efficiencies similar to those of photo-multiplier tubes (PMTs), but with greatly reduced mass, high ruggedness, low voltage requirements, and no sensitivity to magnetic fields. We have conducted laboratory tests of a sample of commercially available SiPMs coupled to LaBr3;Ce, a scintillator of relevance to to future high-energy astrophysics missions. We present results for gamma-ray spectroscopy. compare the SiPM performance to that of a PMT, and discuss the extent to which SiPMs offer significant advantages for scintillator-based space missions.

Bloser, Peter F.↗
NASA NTRS2004

Tests of Multibeam Scintillation Mitigation on Laser Uplinks

A report presents additional details about parts of the program of research and development that is the topic of the immediately preceding article. The report emphasizes those aspects of the program that pertain to the use of multiple uplink laser beams in a ground-to-spacecraft optical communication system to reduce (relative to the case of a single uplink laser beam) the depth and frequency of occurrence of fades in the uplink signal received at the spacecraft. The underlying multibeam scintillation-mitigation concept was described in "Multiple-Beam Transmission for Optical Communication" (NPO-20384), NASA Tech Briefs, Vol. 22, No. 11 (November 1998), page 56. The report discusses the need for mitigating uplink scintillation; briefly describes the Optical Communications Telescope Laboratory and its role as the ground station in the research; summarizes prior experiments in uplink scintillation and multibeam mitigation of scintillation in ground-to-spacecraft laser communications; and describes key experiments planned to be performed in the next five years. The report then elaborates somewhat on the initial experiments, which are to be dedicated to understanding and perfecting the multibeam scintillation-mitigation strategy.

Wilson, Keith↗
NASA NTRS1972

Radio wave scintillations at equatorial regions

Radio waves, passing through the atmosphere, experience amplitude and phase fluctuations know as scintillations. A characterization of equatorial scintillation, which has resulted from studies of data recorded primarily in South America and equatorial Africa, is presented. Equatorial scintillation phenomena are complex because they appear to vary with time of day (pre-and postmidnight), season (equinoxes), and magnetic activity. A wider and more systematic geographical coverage is needed for both scientific and engineering purposes; therefore, it is recommended that more observations should be made at earth stations (at low-geomagnetic latitudes) to record equatorial scintillation phenomena.

Poularikas, A. D.↗
NASA NTRS1974

Scintillation spectra of stars and planets and dependence of their characteristics on meteorological conditions

Scintillation spectra of stars and planets were obtained at Goloseyevo. The dependence was studied of the scintillation spectral density and of the amplitude and frequency characteristics on zenith distances and aerological parameters. The differences in the scintillation spectra amplitude characteristics for white and red stars were found. The increase in the limiting frequency of the planet scintillation spectrum (as the wind becomes stronger) was studied along with the dependence of spectral characteristics on wind and star azimuth differences.

Filippov, Y. K.↗
NASA NTRS1975

Entopistic scintillators

Trajectories of cosmic rays through a balloon-borne experiment will be determined by pulse height analyzing the signals from each of the two or more phototubes coupled to each scintillator. Thin or tapered scintillators produce sufficiently strong gradients of phototube signal with respect to scintillation position that position uncertainties of about 1 cm can be achieved over 1-sq-m areas. Calculations and some test results for entopistic, or position determining, scintillators are presented.

Arens, J. F.↗
NASA NTRS1976

Angular sensitivities of scintillator slab configurations for location of gamma ray bursts

Thin flat scintillator slabs are a useful means of measuring the angular location of gamma ray fluxes of astronomical interest. A statistical estimate of position error was made of two scintillator systems suitable for gamma ray burst location from a balloon or satellite platform. A single rotating scintillator with associated flux monitor is compared with a pair of stationary orthogonal scintillators. Position error for a strong burst is of the order of a few arcmin if systematic errors are ignored.

Gregory, J. C.↗
NASA NTRS1977

Measuring solar wind velocity with spacecraft phase scintillations

The measurement of spacecraft phase scintillations with a coherent dual-frequency radio system permits solar-wind velocity measurements based on multiple-station phase scintillations. Advantages of measuring solar-wind velocity on the basis of multiple-station phase scintillations are discussed with respect to amplitude scintillations. These advantages include the ability to carry out observations closer to the sun, a much wider range of possible baselines, a lower S/N ratio for long-baseline phase measurements, and a wider range of antenna sizes and receiver noise temperatures. NASA antennas particularly suitable for these measurements are identified, and observations with the coherent S/X radio system aboard various NASA spacecraft intended for deep-space missions are proposed.

Woo, R.↗