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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 73 records · Page 4
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NASA NTRS1972

Degree and direction of polarization of multiple scattered light. II - Earth's atmosphere with aerosols.

The radiance, polarization, and direction of polarization of the radiation reflected and transmitted through the atmosphere are calculated by a Monte Carlo method on the basis of a realistic model of the atmosphere. The calculated polarization is shown to depend on the aerosol amount and to have normally a value intermediate between that for pure Rayleigh and pure aerosol scattering. The polarization for multiple scattered photons is usually less than the value calculated for single scattering, but may be larger in low-polarization regions near other regions of high polarization. The direction of polarization shows little variation with either the aerosol amount or the value of the surface albedo.

Plass, G. N.↗
NASA NTRS1986

Evaluation studies on carbon supported catalysts for oxygen reduction in alkaline medium

This paper describes tests designed to predict the performance of fuel cell electrodes, as applied to an alkaline oxygen-fuel cell having specially fabricated porous-carbon electrodes with various amounts of dispersed platinum or gold as active catalysts. The tests are based on information obtained from the techniques of cyclic voltammetry and polarization. The parameters obtained from cyclic voltammetry were of limited use in predicting fuel cell performance of the cathode. On the other hand, half-cell polarization measurements offered close simulation of the oxygen electrode, although a predictor of the electrode life is still lacking. The very low polarization of the Au-10 percent Pt catalytic electrode suggests that single-phase catalysts should be considered.

Srinivasan, Vakula S.↗
NASA NTRS1985

Implications of the 1400 MHz flare emission from AD Leo for the emission mechanism and flare environment

High brightness temperature spikes have been observed during a radio flare on the M-dwarf flare star AD Leo (Lang et al., 1983). Their high brightness temperature (greater than 10 to the 13th K) and circular polarization indicate that a coherent radiation mechanism must be responsible for the spike emission. The underlying flare emission, which is identified with a low polarization, gradual component, was found not to be spiky to within the 200 ms time resolution of the observations. This note is concerned primarily with this nonspiky emission.

Holman, G. D.↗
NASA NTRS1991

Observations of the Earth in polarized light from the US Space Shuttle

During the four American Space Shuttle missions of year 1985, the crewmembers took pictures of the Earth in polarized light. Different problems were encountered in the quantitative use of the data: induced polarization by the shuttle window, lack of calibration correction of the window polarization and enveloped in flight calibration methods. The analysis of the selected data first confirmed the previous observation over snow and sand. A low polarization on these surfaces was observed. On the other hand, the measurements show the potentiability of the polarization for agricultural inventory. Contamination of the atmosphere is well characterized.

Roger, Jean-Claude↗
NASA NTRS1972

Observations of charged particle precipitation over the auroral zone during a magnetic substorm

An array of sensitive electrostatic analyzers was launched on the satellite INJUN 5 into a nearly polar, low altitude orbit. A series of three traversals of the northern auroral zone in the local evening sector on 3 December 1968 has provided high energy- and time-resolution observations of low-energy proton and electron intensities within the energy range 50 smaller than E smaller than 15,000 eV before, during and after a polar magnetic substorm. The region of high intensities of plasma-sheet electrons expanded dramatically during the substorm, extending 3.5 deg farther poleward and approximately 4.5 deg farther equatorward relative to that of the preceding pass.

Ackerson, K. L.↗
NASA NTRSDate not supplied

CLARREO Pathfinder as a SI-traceable Reference for Satellite Intercalibration

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder (CPF) consists of an Earthviewing reflected solar (RS) spectrometer that will measure the Earth-reflected solar radiation from International Space Station with an SI-traceable radiometric uncertainty of 0.3% (1-sigma). The high-accuracy CPF measurements will provide an in-orbit reference for intercalibrating other spaceflight RS instruments. The CPF intercalibration team has been tasked to develop a state-of-the-art approach to calibrate the shortwave channel (300-5000 nm) of the Clouds and the Earth’s Radiant Energy System (CERES) instrument and the reflective solar bands (RSB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, both onboard the NOAA-20 satellite, against the CPF benchmark measurements. The aimed intercalibration methodology uncertainty for both the target instruments is also 0.3%. To meet this stringent intercalibration accuracy, the CPF team has developed methods for mitigating the impacts of spatial, spectral, and angular differences between the intercalibration footprints from the CPF and target instruments. To further alleviate uncertainty, the CPF team will employ Polarization Distribution Models (PDMs) to characterize the polarization state of the Earth-reflected radiance as a function of the intercalibration footprint scene type, solar and viewing geometry, and wavelength. The PDMs will assist in identifying low-polarized scene radiances for meticulously intercalibrating the polarization sensitive VIIRS instrument against the significantly-less polarization-sensitive CPF instrument. This paper will highlight the CPF mission overview, the details of the CPF intercalibration approach, and additional outcomes of the CPF intercalibration studies that may benefit the broader remote sensing community.community.

Hyperspectral↗
NASA NTRS2019

Assessment of VIIRS on-orbit polarization sensitivity and its impact on CLARREO pathfinder inter-calibration

The primary objective of the CLARREO Pathfinder (CPF) mission is to demonstrate essential measurement technologies to enable highly accurate decadal change observations traceable on-orbit to SI standards. Another important objective of the CPF is to demonstrate inter-calibration with the VIIRS sensor and to show that such high-accuracy reference inter-calibration is achievable. To satisfy this requirement, it is important to understand and quantify uncertainties in VIIRS sensor measurements. Based on prelaunch test results, the reflective solar bands of both SNPP and NOAA-20 VIIRS have exhibited polarization sensitivities in the shortest wavelength bands, with an unexpectedly larger sensitivity observed for NOAA-20 VIIRS, particularly in bands M1 to M4. In this study, we use VIIRS Level-1B reflectance data collected over the Pseudo-Invariant Calibration Sites over North African desert region to examine the polarization associated uncertainty for these four bands. Impact due to BRDF on the reflectance data is considered by comparing baseline results obtained from the same viewing and solar zenith angles under relatively low polarization sensitivity. Impact due to detector relative difference in polarization sensitivity is examined by normalizing reflectances by the value of the middle detector. Results of this study provide useful information on VIIRS uncertainty contribution due to polarization when conducting CPF and VIIRS inter-calibration.

VIIRS↗
NASA NTRS1979

Wavelength dependence of polarization. XXXV - Vertical structure of scattering layers above the visible Venus clouds

Results of multiple-scattering computations based on whole-disk and Digicon polarization observations are presented which indicate vertical inhomogeneity in the upper atmosphere of Venus. It is shown that the whole-disk observations support a thin upper haze layer of 0.18-micron particles and that the low polarization observed near the limb and terminator requires a haze of slightly larger particles. The Digicon polar regions are found to exhibit increased polarization, which is compatible with CO2 absorption measurements and is explained by increased molecular scattering above the clouds. The decrease in cloud-top height for latitudes greater than 45 deg is estimated to be approximately 1.4 km.

Lane, W. A.↗
NASA NTRS1985

Trends in measurement of solar vector magnetic fields using the Zeeman effect

Trends in spectropolarimetry as applied to the problem of Zeeman effect measurement are discussed. The use of detector arrays to improve observing efficiency is obtained. Which required new polarization modulation schemes that match the time required to read detector arrays. Another significant trend is narrowband filters, to improve angular and temporal coverage, and to Fourier transform spectrometers, to improve spectral coverage and precision. Low-polarization designs and improved methods for compensating instrumental polarization were developed. A requirement for high angular resolution suggests using adaptive optical devices to subdue the effects of bad seeing. The ultimate strategy to beat the seeing is to loft the telescope above the atmosphere such as is planned with a 30-cm telescope in 1985 and a 1250-cm telescope in 1990.

Harvey, J. W.↗
NASA NTRS1985

The ultraviolet excess of quasars 3: The highly polarized quasars PKS 0736+017 and PKS 1510-089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736+017 and PKS 1510-089 is analyzed. A blazar continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510-089, and at least three-quarters of that in 0736+017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510-089, and weakly detected in 0736+017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

Malkan, M. A.↗
NASA NTRS1986

The ultraviolet excess of quasars. III - The highly polarized quasars PKS 0736 + 017 and PKS 1510 - 089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736 + 047 and PKS 1510 089 is analyzed. A blazer continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510 - 089, and at least three-quarters of that in 0736 + 017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510 - 089, and weakly detected in 0736 + 017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

Malkan, M. A.↗
NASA NTRS1990

Polarization in the Lagoon nebula

A V-band polarimetric survey of stars associated with the Lagoon nebula was conducted. The data were combined with existing photometric and spectroscopic observations in order to investigate the alignment of magnetic field lines with identifiable symmetry axes and to evaluate the nature of dust in the immediate vicinity. Although stars are not in general highly polarized, electric vectors align with the minor axis of the Lagoon nebula, perpendicular to the major axis of the spatial distribution of massive stars. The observations indicate that the collapse of the molecular cloud progenitor was inhibited along directions perpendicular to magnetic field lines. Considering the low polarization efficiency and the high ratio of total to selective extinction, smaller grains of intranebular dust appear to have been destroyed.

Mccall, Marshall L.↗
NASA NTRS1988

Stratospheric NO2 over Antarctica as measured by the Solar Mesosphere Explorer during austral spring, 1986

This paper presents the results of polar NO2 measurements carried out by the SME satellite during the fall and spring of 1985 and 1986 and compares the results with observations at the north pole and the results of model calculations. During the austral spring, a polar low was observed in stratospheric NO2 densities measured between 24 and 40 km, consistent with the predictions of standard photochemical theory. The geographic extent of the area of low NO2 densities was found to decrease as the hours of sunlight increased, in marked contrast to the behavior of the Antarctic ozone hole during the same period. A comparison of measurements with model calculations for NO2 imply that much of the odd nitrogen is converted to HNO3 during the polar night. Data also suggest no evidence that changes in high-altitude odd nitrogen are influencing the ozone below, or that the 'ozone hole' penetrates above 24 km to affect odd nitrogen there.

Thomas, Ronald J.↗
NASA NTRS1990

Granularity in the magnetic field structure of M83

Researchers recently reported Very Large Array (VLA) 20 cm continuum polarization observations of the bright, nearly face-on southern spiral galaxy M83 (NGC 5236) at a spatial resolution of 2 kpc (Sukumar and Allen 1989). The strongest linearly-polarized emission is found in two giant arcs, with typical lengths of about 30 kpc, which are situated roughly opposite each other in the dark outer regions of the galaxy at a radius of 12 kpc from the center. These regions of high polarized intensity (and hence highly-uniform magnetic field) do not coincide with any prominent spiral-arm tracers, in contrast to the expectations of simple models for the large-scale compression of magnetic field in density-wave shock fronts. From a comparison of the data with previous results at 6 cm, the authors concluded that the low polarization in the central regions of the galaxy is a result of disorder in the interstellar magnetic field. The most likely cause of this disorder is the greater star formation activity observed in the inner parts of the galaxy. The intrinsic direction of the magnetic field in the outer parts of the galaxy has also recently been determined on a length scale of 6.5 kpc from a comparison of the VLA 20 cm results with 6.3 cm observations obtained earlier with the Effelsberg telescope (Sukumar et al. 1989). There is very little Faraday rotation in the regions of the highly-polarized arcs of emission. The magnetic field in these polarized arcs is parallel to the general spiral arm structure seen in the usual optical tracers (dust, HII regions) in the bright inner parts of the galaxy disk. The maximum observed polarization at 2 kpc resolution is about 50 percent.

Allen, R. J.↗
NASA NTRS2023

A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375

Accreting X-ray pulsars (XRPs) are presumed to be ideal targets for polarization measurements, as their high magnetic field strength is expected to polarize the emission up to a polarization degree of ∼80%. However, such expectations are being challenged by recent observations of XRPs with the Imaging X-ray Polarimeter Explorer (IXPE). Here, we report on the results of yet another XRP, namely, EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT and SRG/ART-XC. In line with recent results obtained with IXPE for similar sources, an analysis of the EXO 2030+375 data returns a low polarization degree of 0%–3% in the phase-averaged study and a variation in the range of 2%–7% in the phase-resolved study. Using the rotating vector model, we constrained the geometry of the system and obtained a value of ∼60° for the magnetic obliquity. When considering the estimated pulsar inclination of ∼130°, this also indicates that the magnetic axis swings close to the observer’s line of sight. Our joint polarimetric, spectral, and timing analyses hint toward a complex accreting geometry, whereby magnetic multipoles with an asymmetric topology and gravitational light bending significantly affect the behavior of the observed source.

EXO 2030+375↗
NASA NTRS1992

On the use of satellites in Molniya orbit for meteorological and oceanographic observations of the high latitudes

Two types of orbits are currently used for meteorological satellites: geostationary orbit and low earth orbit. Neither orbit serves the high latitudes well. The Soviet Molniya satellites fly in a highly elliptic orbit inclined 63.4 deg to the equator. For approximately 8 h of its 12-h orbit, a satellite in Molniya orbit is synchronized with the earth such that it is nearly geostationary in the high latitudes. A meteorological/oceanographic satellite in Molniya orbit would bring nearly the same frequent imaging capability to the high latitudes which the tropics and mid-latitudes now enjoy. The uses of such a satellite include Arctic forecasting, study of polar lows, high latitude precipitation estimation, Antarctic studies, sea ice monitoring, and ozone measurements.

Kidder, Stanley Q.↗
NASA NTRS1967

Study made of dielectric properties of promising materials for cryogenic capacitors

Experimental investigations were conducted to determine dielectric properties of promising materials for cryogenic capacitors to be used in energy storage and pulse applications. The three classes of materials investigated were inorganic bonded ferroelectric materials, anodic coatings on metal foils, and polar low temperature liquids.

Mathes, K. N.↗
NASA NTRS1974

Simulation of a lunar gradiometer mission

A lunar gradiometer mission involves the mounting of a gradiometer on a satellite which is in a low, polar, and circular lunar orbit. The results of a numerical simulation of the mission is presented. It is shown that if the satellite is in a 50 km orbit, 1 deg and 2 deg gravity anomalies may be estimated with accuracies of 12 mgal and 1 mgal respectively. At a 100 km altitude, 2 deg gravity anomalies can be estimated with an accuracy of 12 mgal. These results assume a rotating type gradiometer with a .1E accuracy. The results can be readily scaled to reflect another level.

Argentiero, P. D.↗