SEARCH · Engineering Papers

Results for “Radiative properties”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24

All sources NASA NTRS DOE OSTI

NASA NTRS1979

Collective plasma effects associated with the continuous injection model of solar flare particle streams

A modified continuous injection model for impulsive solar flares that includes self-consistent plasma nonlinearities based on the concept of marginal stability is presented. A quasi-stationary state is established, composed of a hot truncated electron Maxwellian distribution confined by acoustic turbulence on the top of the loop and energetic electron beams precipitating in the chromosphere. It is shown that the radiation properties of the model are in accordance with observations.

Vlahos, L.↗

NASA NTRS1980

Thermal radiation in Arctic stratus clouds

Infrared radiative properties of Arctic stratus clouds in the 10.1-12.7 micron wavelength region are determined from a series of aircraft measurements. The average emissivity of the clouds when scattering is neglected is unity for cloud depths greater than 350 m. Under the assumption that the cloud layers are homogeneous the cloud droplet volume absorption coefficient is estimated as 17 + or - 5 per km. Several mass absorption coefficients are estimated for several assumed liquid water distributions. It is also concluded that the cloud reflectance is not larger than 2 (+ or - 5%).

Herman, G. F.↗

NASA NTRS1981

Infrared experiments for spaceborne planetary atmospheres research. Full report

The role of infrared sensing in atmospheric science is discussed and existing infrared measurement techniques are reviewed. Proposed techniques for measuring planetary atmospheres are criticized and recommended instrument developments for spaceborne investigations are summarized for the following phenomena: global and local radiative budget; radiative flux profiles; winds; temperature; pressure; transient and marginal atmospheres; planetary rotation and global atmospheric activity; abundances of stable constituents; vertical, lateral, and temporal distribution of abundances; composition of clouds and aerosols; radiative properties of clouds and aerosols; cloud microstructure; cloud macrostructure; and non-LTE phenomena.

Source record↗

NASA NTRS1983

Space and planetary environment criteria guidelines for use in space vehicle development. Volume 1: 1982 revision

Guidelines on space and planetary environment criteria for use in space vehicle development are provided. Information is incorporated in the disciplinary areas of atmospheric and ionospheric properties, radiation, geomagnetic field, astrodynamic constants, and meteoroids for the Earth's atmosphere above 90 km, interplanetary space, and the atmosphere and surfaces (when available) of the Moon and the planets (other than Earth) of this solar system. The Sun, Terrestrial Space, the Moon, Mercury, Venus, and Mars are covered.

Smith, R. E.↗

NASA NTRS1983

Computations of Emissions Using a 3-D Combustor Program

A general 3-D combustor performance program developed by Garrett was extended to predict soot and NOx emissions. The soot formation and oxidation rates were computed by quasi-global models, taking into account the influence of turbulence. Radiation heat transfer was computed by the six-flux radiation mode. The radiation properties include the influence of CO2 and H2O in addition to soot. NOx emissions were computed from a global four-step hydrocarbon oxidation scheme and a set of rate-controlled reactions involving radicals and nitrogen oxides.

Srivatsa, S. K.↗

NASA NTRS1984

Antarctic sea ice microwave signatures and their correlation with in situ ice observations

The general characteristics and microwave radiative properties of sea ice in the Weddell Sea region during the onset of spring are studied by using the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and other satellite sensors, in conjunction with in situ observations from the Mikhail Somov. The position of the ice edge, the gradient of ice concentration, and the width of the Marginal Ice Zone are inferred from the microwave data, and are found to be consistent with ship observations, especially at 18 GHz. The sensitivities of the various SMMR frequencies to surface and other effects are investigated by using multispectral cluster analysis. The results show considerable variability in emissivity, especially at 37 GHz, likely associated with varying degrees of surface wetness. Ice concentrations are derived by using two methods: one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed. Using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations.

Comiso, J. C.↗

NASA NTRS1983

Numerical models for cometary dust environments

The development of a numerical model for the dust environment near a comet is described. The major components of the model are a simple treatment of the acceleration of the dust by the gas outflow from an isothermal icy nucleus, a detailed treatment of the dust particle trajectories controlled by solar gravity and radiation pressure, including the formation of the dust envelope and tail, and a simple treatment of the radiation from the dust in the visible and thermal infrared. The results of recent comet observations are used to estimate parameter values for the model, including dust-to-gas ratios by light and by mass, the distribution of dust and gas emission on the nuclear surface, the distributions of dust particle size, density, mass, and radiative properties, and other quantities. Gas and dust production rates as functions of time are derived from observed light curves using the simple photometric theory. Sample results are presented for the dust concentration, flux and fluence along the trajectory of a spacecraft which flies by Comet P/Halley in 1986.

Divine, N.↗

NASA NTRS1984

Diurnal variability of regional cloud and clear-sky radiative parameters derived from GOES data. I - Analysis method. II - November 1978 cloud distributions. III - November 1978 radiative parameters

Cloud cover is one of the most important variables affecting the earth radiation budget (ERB) and, ultimately, the global climate. The present investigation is concerned with several aspects of the effects of extended cloudiness, taking into account hourly visible and infrared data from the Geostationary Operational Environmental Satelite (GOES). A methodology called the hybrid bispectral threshold method is developed to extract regional cloud amounts at three levels in the atmosphere, effective cloud-top temperatures, clear-sky temperature and cloud and clear-sky visible reflectance characteristics from GOES data. The diurnal variations are examined in low, middle, high, and total cloudiness determined with this methodology for November 1978. The bulk, broadband radiative properties of the resultant cloud and clear-sky data are estimated to determine the possible effect of the diurnal variability of regional cloudiness on the interpretation of ERB measurements.

Minnis, P.↗

NASA NTRS1985

Vapor deposited emittance/catalysis coatings for superalloys in heatshield applications

Statically oxidized Inconel 617 and MA 956 superalloys were prepared with vapor deposited aluminosilicate layers and exposed to temperatures which simulated reentry conditions. The aluminosilicate layers were 1-2 microns thick. The trials consisted of exposures to 1500-2300 F heat while surface temperatures were monitored with pyrometers. Analyses were then performed of the catalytic activity, oxidation phenomena, and radiative properties after thermal cycling the specimens for 8 hr. Both alloys were found to be catalytic to the recombination processes of dissociated species in the reentry environment. The coatings reduced the catalytic activity by 40 percent for both alloys but did not change the emittance. An enhanced Cr depletion zone was detected in the Inconel samples, implying that the coating did not prevent diffusion loss of Cr. The coated MA 956, on the other hand, gained weight over the course of the trials.

Clark, R. K.↗

NASA NTRS1984

Stratocumulus cloud field reflected fluxes - The effect of cloud shape

The reflected fluxes of stratocumulus cloud fields are calculated as a function of sky cover aspect ratio and cloud shape. In order to obtain a better fit with general circulation models (GCMs), cloud liquid water volume values were kept invariant relative to cloud shape. On the basis of the required accuracy of the Earth Radiation Budget Experiment (ERBE), an order of magnitude value of 10 W per sq m was used to estimate the difference between plane-parallel and broken cloudiness reflected fluxes. An empirical relationship for effective cloud cover at a solar zenith angle of 60 deg is derived. The relationship allows for the accurate computation of broken cloud field reflected fluxes using plane-parallel calculations. It is predicted that more accurate estimates of broken cloud field radiative properties may be possible in the future.

Welch, R. M.↗

NASA NTRS1986

The lower atmosphere of solar flares; Proceedings of the Solar Maximum Mission Symposium, Sunspot, NM, Aug. 20-24, 1985

The topics discussed by the present conference encompass the chromospheric flare phenomenon, white light flares, UV emission and the flare transition region, the flare corona and high energy emissions, stellar flares, and flare energy release and transport. Attention is given to radiative shocks and condensation in flares, impulsive brightening of H-alpha flare points, the structure and response of the chromosphere to radiation backwarming during solar flares, the interpretation of continuum emissions in white light flares, and the radiation properties of solar plasmas. Also discussed are EUV images of a solar flare and C III intensity, an active region survey in H-alpha and X-rays, dynamic thermal plasma conditions in large flares, the evolution of the flare mechanism in dwarf stars, the evidence concerning electron beams in solar flares, the energetics of the nonlinear tearing mode, macroscopic electric fields during two-ribbon flares, and the low temperature signatures of energetic particles.

Neidig, Donald F.↗

NASA NTRS1988

Electrochromic Variable-Emissivity Surfaces

Temperature controlled by altering infrared radiative properties. Infrared emissivity of electrochromically active layer changed by applying voltage to insert or remove Li atoms electrochemically. Change reversible and continuously variable between specified limits of layered structure.

Rauh, R. David↗

NASA NTRS1988

Effects of cirrus composition on atmospheric radiation budgets

A radiative transfer model that can be used to determine the change in solar and infrared fluxes caused by variations in the composition of cirrus clouds was used to investigate the importance of particle size and shape on the radiation budget of the Earth-atmosphere system. Even though the cloud optical thickness dominates the radiative properties of ice clouds, the particle size and nonsphericity of ice crystals are also important in calculations of the transfer of near-IR solar wavelengths. Results show that, for a given optical thickness, ice clouds composed of larger particles would produce larger greenhouse effects than those composed of smaller particles. Moreover, spherical particles with equivalent surface areas, frequently used for ice crystal clouds, would lead to an overestimation of the greenhouse effect.

Kinne, Stefan↗

NASA NTRS1989

Dielectrics for long term space exposure and spacecraft charging: A briefing

Charging of dielectrics is a bulk, not a surface property. Radiation driven charge stops within the bulk and is not quickly conducted to the surface. Very large electric fields develop in the bulk due to this stopped charge. At space radiation levels, it typically requires hours or days for the internal electric fields to reach steady state. The resulting electric fields are large enough to produce electrical failure within the insulator. This type failure is thought to produce nearly all electric discharge anomalies. Radiation also induces bond breakage, creates reactive radicals, displaces atoms and, in general, severely changes the chemistry of the solid state material. Electric fields can alter this process by reacting with charged species, driving them through the solid. Irradiated polymers often lose as much as a percent of their mass, or more, at exposures typical in space. Very different aging or contaminant emission can be induced by the stopped charge electric fields. These radiation effects are detailed.

Frederickson, A. R.↗

NASA NTRS1989

Contamination

Contamination of spacecraft in the aerospace environment is examined. The optical systems, thermal control systems and solar power systems were deemed to be most vulnerable to particle damage. It was decided that all orbits should be considered. Specific issues concern whether there are changes in transmittance of optics and the radiative properties of protective coatings.

Maag, Carl R.↗

NASA NTRS1989

The tapered slot antenna - A new integrated element for millimeter-wave applications

Tapered slot antennas (TSAs) with a number of potential applications as single elements and focal-plane arrays are discussed. TSAs are fabricated with photolithographic techniques and integrated in either hybrid or MMIC circuits with receiver or transmitter components. They offer considerably narrower beams than other integrated antenna elements and have high aperture efficiency and packing density as array elements. Both the circuit and radiation properties of TSAs are reviewed. Topics covered include: antenna beamwidth, directivity, and gain of single-element TSAs; their beam shape and the effect of different taper shapes; and the input impedance and the effects of using thick dielectrics. These characteristics are also given for TSA arrays, as are the circuit properties of the array elements. Different array structures and their applications are also described.

Yngvesson, K. Sigfrid↗

NASA NTRS1989

MISR - A multiangle imaging spectroradiometer for geophysical and climatological research from EOS

The scientific objectives, instrument concept, and data plan for the multiangle imaging spectroradiometer (MISR), an experiment proposed for the EOS (Earth Observing System) mission, are described. MISR is a pushbroom imaging system designed to obtain continuous imagery of the sunlit Earth at four different view angles (25.8, 45.6, 60.0, and 72.5 deg relative to the vertical at the earth's surface), in both the forward and aftward directions relative to nadir, using eight separate cameras. Observations will be acquired in four spectral bands, centered at 440, 550, 670, and 860 nm. Data analysis algorithms will be applied to MISR imagery to retrieve the optical, geometric, and radiative properties of complex, three-dimensional scenes, such as aerosol-laden atmospheres above a heterogeneously reflecting surface, nonstratified cloud systems, and vegetation canopies. The MISR investigation will address a number of scientific questions concerning the climatic and ecological consequences of many natural and anthropogenic processes, and will furnish aerosol information necessary for atmospheric corrections of surface images.

Diner, David J.↗

NASA NTRS1990

Observations of anthropogenic cloud condensation nuclei

Cloud Condensation Nuclei (CCN) concentrations and spectral measurements obtained with the DRI instantaneous CCN spectrometer (Hudson, 1989) over the last few years are presented. The climatic importance of cloud microphysics has been pointed out. The particles which affect cloud microphysics are cloud condensation nuclei (CCN). The commonly-observed order of magnitude difference in cloud droplet concentrations between maritime and continental air masses (i.e., Squires, 1958) was determined to be caused by systematic differences in the concentrations of CCN between continental and maritime air masses (e.g., Twomey and Wojciechowski, 1969). Twomey (1977) first pointed out that cloud microphysics also affects the radiative properties of clouds. Thus continental and anthropogenic CCN could affect global temperature. Resolution of this Twomey effect requires answers to two questions - whether antropogenic CCN are a significant contribution to atmospheric CCN, and whether they are actually affecting cloud microphysics to an extent which is of climatic importance. The reasons for the contrast between continental and maritime CCN concentration are not understood. The question of the relative importance of anthropogenic CCN is addressed. These observations should shed light on this complex question although further research is being conducted in order to produce more quantitative answers. Accompanying CN measurements made with a TSI 3020 condensation nucleus (CN) counter are also presented.

Hudson, James G.↗