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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Formation of spectral lines in a planetary atmosphere. II - Spectroscopic evidence for the structure of the visible Venus clouds.

We demonstrate in this article that there is spectroscopic evidence for the structure of the visible Venus cloud layers. From physically realistic models of the lower Venus atmosphere, we have shown that only observations of the phase variations of the CO2 bands in the Venus spectrum can provide the information for a unique identification of the structure of the cloud layers. It is proved that Venus cannot have a single dense cloud layer, but must have two scattering layers; a thin aerosol layer situated in the lower stratosphere, overlying a dense cloud deck. The aerosol plays an important role in the scattering of radiation, so that its identification provides an explanation of the reflecting layer-scattering model controversy for the interpretation of spectra formed in a cloudy planetary atmosphere.

Hunt, G. E.↗
NASA NTRS1973

Digital enhancement of multispectral MSS data for maximum image visibility

A systematic approach to the enhancement of images has been developed. This approach exploits two principal features involved in the observation of images: the properties of human vision and the statistics of the images being observed. The rationale of the enhancement procedure is as follows: in the observation of some features of interest in an image, the range of objective luminance-chrominance values being displayed is generally limited and does not use the whole perceptual range of vision of the observer. The purpose of the enhancement technique is to expand and distort in a systematic way the grey scale values of each of the multispectral bands making up a color composite, to enhance the average visibility of the features being observed.

Algazi, V. R.↗
NASA NTRS1973

Visible and near-infra-red transmission and reflectance measurements of the Luna 20 soil.

Visible and near-infrared spectra of chemically analyzed grains of glass and minerals from the Luna 20 sample were compared with diffuse reflectance spectra of the bulk soil. As in the spectra of soil samples from other localities on the moon, pyroxene contributes two broad absorption features near 1 and 2 microns. The soil has a high integral reflectance (or albedo) arising from plagioclase, which appears to be the dominant mineral in the lunar highlands. The Luna 20 soil curve is most similar to the reflectance curves of the non-rayed soils at Apollo 16, in agreement with the generally similar mineralogy of these samples. The average pyroxene composition in the Luna 20 soil, as determined from the absorption bands in the diffuse reflectance spectra, and analyses of single crystals, is more calcic than in the lithic fragments. Thus, the soil appears to have a few per cent of admixed material derived from mare basalts. Comparison of the soil spectrum with telescopic curves of nearby areas reveals a close similarity.

Adams, J. B.↗
NASA NTRS1973

The visible-airglow experiment on Atmosphere Explorer.

The visible-airglow experiment is an airglow photometer designed to measure various thermospheric emission features during the day and night both at low latitudes and in auroras. The photometer has two distinct optical channels, a high-sensitivity channel with a large field of view and a low-sensitivity channel with a narrow field of view to resolve small features. The system is protected by a combination attenuator and cathode back-biasing scheme which allows measurements of maximum sensitivity within a fraction of a second of viewing the sun. This experiment will be a part of the scientific payload on all three Atmosphere Explorer missions.

Hays, P. B.↗
NASA NTRS1974

On a suspected ring external to the visible rings of Saturn

The reexamination of a photograph of Saturn taken on 15 November 1966 when the earth was nearly in the ring plane is investigated which indicates that ring material does exist outside the visible rings, extending to more than 6 Saturnian radii. The observed brightness in blue light was estimated per linear arc second, implying a normal optical thickness, for ice-covered particles.

Feibelman, W. A.↗
NASA NTRS1973

Venus - Composition and structure of the visible clouds

It is proposed that the visible cloud deck on Venus is composed of droplets of sulfuric acid. These are formed by the very rapid photooxidation of carbonyl sulfide in the upper atmosphere. The clouds are best described as an extensive haze since the predicted particulate scale height probably exceeds the gas scale height within the layer. The predicted mixing ratio for water is .000001 (lower limit), and for both carbonyl sulfide and sulfur dioxide it is .0000001 (upper limit); these are in good agreement with observations. Gaps in the layer are not possible unless the planetary scale dynamics produce cloud turnover times of less than a few days. Under these conditions, the water mixing ratio could approach .0001, and the formation of a thin hydrochloric acid haze at high altitude above the main cloud is possible.

Prinn, R. G.↗
NASA NTRS1974

Structure of the visible Jovian clouds

A study of the hydrogen quadrupole line intensities at the center of the planetary disk was conducted during the 1972 apparition of Jupiter. The study involved the observation of the S(1) lines of the H2 (3-0) and (4-0) quadrupole bands. The observations show that the abundance of hydrogen detected at these frequencies is extremely variable because of rapid changes in the structure of the visible clouds.

Hunt, G. E.↗
NASA NTRS1974

Venus - Vertical transport rates in the visible atmosphere

The cloud particles on Venus are sufficiently small for their vertical distribution to be strongly affected by atmospheric turbulence. Reasonably firm estimates of the vertical distribution of cloud particles can be made from current interpretations of refraction, polarization, and absorption band data. These enable very firm upper limits to be placed on average vertical mass diffusion coefficients in the visible atmosphere. These upper limits are independent of the cloud particle composition or mode of formation, and of changes in the particle size distribution with altitude.

Prinn, R. G.↗
NASA NTRS1975

Chemical-ionization visible and ultraviolet gas lasers: A concept

Charge-transfer reactions or Penning ionization reactions are used to produce population inversions between electronic states of molecular ions which should result in stimulated emission in ultraviolet and visible regions. Such lasers could be used in study of short-lived reaction intermediates, crystal structure and scattering, and photolysis.

Laudenslager, J. B.↗
NASA NTRS1974

Experiment S-191 visible and infrared spectrometer

The design, development, fabrication test, and utilization of the visible and infrared spectrometer portion of the S-191 experiment, part of the Earth Resources Experiment Package, on board Skylab is discussed. The S-191 program is described, as well as conclusions and recommendations for improvement of this type of instrument for future applications. Design requirements, instrument design approaches, and the test verification program are presented along with test results, including flight hardware calibration data. A brief discussion of operation during the Skylab mission is included. Documentation associated with the program is listed.

Linnell, E. R.↗
NASA NTRS1975

Semiconductor diode laser material and devices with emission in visible region of the spectrum

Two alloy systems, (AlGa)As and (InGa)P, were studied for their properties relevant to obtaining laser diode operation in the visible region of the spectrum. (AlGa)As was prepared by liquid-phase epitaxy (LPE) and (InGa)P was prepared both by vapor-phase epitaxy and by liquid-phase epitaxy. Various schemes for LPE growth were applied to (InGa)P, one of which was found to be capable of producing device material. All the InGaP device work was done using vapor-phase epitaxy. The most successful devices were fabricated in (AlGa)As using heterojunction structures. At room temperature, the large optical cavity design yielded devices lasing in the red (7000 A). Because of the relatively high threshold due to the basic band structure limitation in this alloy, practical laser diode operation is presently limited to about 7300 A. At liquid-nitrogen temperature, practical continuous-wave operation was obtained at a wavelength of 6500 to 6600 A, with power emission in excess of 50 mW. The lowest pulsed lasing wavelength is 6280 A. At 223 K, lasing was obtained at 6770 A, but with high threshold currents. The work dealing with CW operation at room temperature was successful with practical operation having been achieved to about 7800 A.

Ladany, I.↗
NASA NTRS1975

Experiments in pilot decision-making during simulated low visibility approaches

A simulation task is reported which incorporates both kinds of variables, informational and psychological, to successfully study pilot decision making behavior in the laboratory. Preliminary experiments in the measurement of decisions and the inducement of stress in simulated low visibility approaches are described.

Curry, R. E.↗
NASA NTRS1975

On a suspected ring external to the visible rings of Saturn

Reexamination of a photograph of Saturn taken on Nov. 15, 1966, when the earth was nearly in the ring plane, indicates that ring material may exist outside the visible rings, extending to more than 6 Saturnian radii. Although the suspected feature on the photograph appears to be real, the possibility of its being a developed pressure mark or a chance alignment of grains cannot be ruled out. The observed brightness in the blue light was estimated to be 19.5 plus or minus 0.5 per linear arcsecond, implying a normal optical thickness, .0000001 for ice-covered particles. For spacecraft passing through this region, the hazards are found to be minimal.

Smith, B. A.↗
NASA NTRS1975

Airborne Visible Laser Optical Communications Program (AVLOC)

The design, development, and operation of airborne and ground-based laser communications and laser radar hardware is described in support of the Airborne Visible Laser Optical Communication program. The major emphasis is placed on the development of a highly flexible test bed for the evaluation of laser communications systems techniques and components in an operational environment.

Ward, J. H.↗
NASA NTRS1975

Ultraviolet, visible, and infrared rays

Sources of infrared, visible and ultraviolet radiation are discussed, and important associated biological and psychophysiological effects are described. The problem of protection from excessively high or low levels of radiant energy in these spectral regions is considered and optimal levels are suggested.

Taylor, J. H.↗
NASA NTRS1976

Predicted favorable visibility conditions for anomalous tails of comets

Visibility conditions are used to list the comets that have displayed a sunward dust tail during the time of earth's passage through the orbital plane of the comet. A computer program describing the conditions for this type of antitail observability was applied to the Catalogue of Cometary Orbits (Marsden, 1975), starting with the comets of 1737. It is shown that only about 20-30% of the nearly parabolic comets that should have displayed an antitail at the node were actually observed to do so. There appears to be a general absence of antitails among the short period comets.

Sekanina, Z.↗