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At least 1,027 records · Page 57
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NASA NTRS1985

The eight-color asteroid survey - Results for 589 minor planets

Results are presented from reflection spectrophotometry of 589 minor planets in a photometric system using eight filter passbands ranging from 0.34- to 1.04-micron wavelength. The sampling completeness approaches or exceeds 50 percent of the numbered asteroids for the near-earth objects, the Hungarias, the Nysa family, the Cybeles, the Hildas, and the Trojans. The general evolution of predominant compositional type from S to C to D with increasing heliocentric distance is evident, as is the spectral homogeneity of the Eos, Koronis, Nysa, and Themis families.

Zellner, B.↗
NASA NTRS1985

Analog FM/FM versus digital color TV transmission aboard space station

Langley Research Center is developing an integrated fault tolerant network to support data, voice, and video communications aboard Space Station. The question of transmitting the video data via dedicated analog channels or converting it to the digital domain for consistancy with the test of the data is addressed. The recommendations in this paper are based on a comparison in the signal-to-noise ratio (SNR), the type of video processing required aboard Space Station, the applicability to Space Station, and how they integrate into the network.

Hart, M. M.↗
NASA NTRS1986

A New Method for Laminar Boundary Layer Transition Visualization in Flight: Color Changes in Liquid Crystal Coatings

The visualization of laminar to turbulent boundary layer transition plays an important role in flight and wind tunnel aerodynamic testing of aircraft wing and body surfaces. Visualization can help provide a more complete understanding of both transition location as well as transition modes; without visualization, the transition process can be very difficult to understand. In the past, the most valuable transition visualization methods for fight applications included sublimating chemicals and oil flows. Each method has advantages and limitations. In particular, sublimating chemicals are impractical to use in subsonic applications much above 20,000 feet because of the greatly reduced rates of sublimation at lower temperatures (less than -4 degrees Fahrenheit). Both oil flow and sublimating chemicals have the disadvantage of providing only one good data point per flight. Thus, for many important flight conditions, transition visualization has not been readily available. This paper discusses a new method for visualizing transition in fight by the use of liquid crystals. The new method overcomes the limitations of past techniques, and provides transition visualization capability throughout almost the entire altitude and speed ranges of virtually all subsonic aircraft flight envelopes. The method also has wide applicability for supersonic transition visualization in flight and for general use in wind tunnel research over wide subsonic and supersonic speed ranges.

Holmes, Bruce J.↗
NASA NTRS1986

Colors of reflection nebulae. III - Ultraviolet scattering by small particles in reflection nebulae associated with 17, 20, and 23 Tauri

New surface brightness measurements in the reflection nebulae associated with the Pleiades stars 17, 20, and 23 Tau have been carried out with the IUE satellite. Each nebula was observed at two angular offsets south of the respective illuminating star. At the larger offsets (40, 40, and 60 arcsec respectively) each nebula exhibits a flux distribution which rises much more steeply with decreasing wavelengths than the corresponding stellar spectrum. At the smaller offsets (20 arcsec) the nebular spectra are more similar to those of the stars and fail to show the steep rise at wavelengths less than 2200 A. Independent observations of interstellar absorption lines as well as theoretical arguments by several previous authors lead to a model wherein the reflection nebulosity near the Pleiades stars is caused by a thin sheet of interstellar matter in front of the stars, at an approximate distance of a few x 10 to the -2nd pc. In the context of such a model the nebular spectra obtained near 17, 20, and 23 Tau can be understood only if the phase-function asymmetry of scattering declines with decreasing wavelengths throughout the spectral range. This result indicates that the role of scattering in the UV by particles in the 10 to the -6th cm size range appears more important than is generally recognized by current models.

Witt, A. N.↗
NASA NTRS1986

Diffuse interstellar bands in low color excess stars. III

Measurements of the equivalent widths of the diffuse interstellar bands at 6284 A and 6613 A in the spectra of 23 stars with E(B-V) less than 0.1 mag are reported. The band strengths do not correlate with interstellar H2 column density. They are probably produced by molecular mantles on grains or very stable molecules such as the polycyclic aromatic hydrocarbons.

Kumar, C. K.↗
NASA NTRS1987

Implications of Viking color data for evolution of the Amenthes Region, Mars

In the Eastern Hemisphere of Mars, where the hemispheric dichotomy is not overlain by relatively recent flows from the Tharsis volcanoes, the Mars cratered terrain boundary (CTB) now exists as highly fractured terrain juxtaposed with the smooth plains of the Northern Hemisphere. Based on Mariner 9 photography, the southern cratered terrain in the Amenthes region (0 to 30 deg N, 225 to 270 deg W) is approximately 3 to 4 km above the northern plains, and the transition zone is marked by both broad plateaus and knobby terrain. In the Amenthes Southest quadrangle, in particular, the continuum between large detached plateaus, smaller smooth topped plateaus and knobby hills can be seen. To define the previous position and evolution of the boundary, the distribution of cratered terrain, characteristic landforms (knobby terrain and detached plateaus) have been mapped, as well as structural features across the boundary. Structural mapping indicates that geological formations parallel the boundary in the Eastern Hemisphere with the conclusion that CTB evolution involved normal faulting through extension perpendicular to the boundary.

Maxwell, Ted A.↗
NASA NTRS1987

Single-color laser ranging with a cube-corner-retroreflector array

Lidar cross section of some typical types of cube-corner retroreflectors (CCRs) having a three corner mirror system is investigated for the case that the CCR is tilted from the normal illumination axis. Analytic expressions for the effective aperture area for the two typical window types (circular and hexagonal) of CCRs are obtained for the case that the CCR is tilted. The range of incidence angle in which only the total reflection occurs at all three uncoated corner mirrors has been found to vary considerably with the orientation of CCR and the refractive index of the CCR prism. The analytical expression for the far-field diffraction pattern of a tilted CCR is obtained by taking different polarization transformation of the six sectors of the effective reflecting aperture into account. This expression is essential when evaluating the lidar cross section of a moving CCR which is tilted in general. Formulas for the angles defining the six sectors have also been obtained.

Song, G. Hugh↗
NASA NTRS1986

Effect of intervening galaxies on quasar counts and colors

Ostriker and Heisler (1984) suggested that optically thick dust in galaxies could reduce the number of high-redshift quasars without reddening the observed quasars, because the only observed quasars would be those seen through no intervening galaxies. However, Ostriker and Heisler assumed that galaxies were hard-edged uniform disks, and the fuzzy edges of real galaxies significantly change this conclusion. The quasar distribution observed through more realistic galaxy models is calculated, and it is found that dust cannot significantly reduce the high-redshift quasar counts without also reddening the observed sample. But this reddening could be consistent with past studies of quasar reddening; improved studies of quasar reddening using new UV and IR data are needed.

Wright, Edward L.↗
NASA NTRS1987

Color graphics, interactive processing, and the supercomputer

The development of a common graphics environment for the NASA Langley Research Center user community and the integration of a supercomputer into this environment is examined. The initial computer hardware, the software graphics packages, and their configurations are described. The addition of improved computer graphics capability to the supercomputer, and the utilization of the graphic software and hardware are discussed. Consideration is given to the interactive processing system which supports the computer in an interactive debugging, processing, and graphics environment.

Smith-Taylor, Rudeen↗
NASA NTRS1986

An historical perspective - Brown is not a color

Major shifts in theoretical understanding of the star formation process and the possible components of the local mass density are reviewed. Those aspects of brown dwarf structure and evolution that are still not well enough understood are outlined, and the types of observations that might force the modification of current theories to accommodate the existence of brown dwarfs are suggested. The appropriateness of the name 'brown dwarf' is defended.

Tarter, J. C.↗
NASA NTRS1987

Satellite color observations of spring blooming in Bering Sea shelf waters during the ice edge retreat in 1980

The temporal and spatial development of the ice-edge bloom and the spring open-water bloom on the eastern Bering Sea shelf was studied using CZCS images of the eastern Bering Sea between April 27 and July 22, 1980. Images of the Norton Sound area taken during the period of ice breakup show that the influence of ice melt on phytoplankton growth is particularly significant where the ice is actively melting. Significant levels (5-30 mg/cu m) of chlorophyll could be seen trailing the ice pack as it melted and moved northward and westward in late April and early May. In the ice-free eastern Bering Sea midsummer image, a northwesterly oriented band of high pigment concentration was seen in the area of the outer domain, suggesting periodic offshore movements of shelf waters.

Maynard, Nancy G.↗
NASA NTRS1985

Ocean color imaging

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NASA NTRS1988

Common but unappreciated sources of error in one, two, and multiple-color pyrometry

The most common sources of error in optical pyrometry are examined. They can be classified as either noise and uncertainty errors, stray radiation errors, or speed-of-response errors. Through judicious choice of detectors and optical wavelengths the effect of noise errors can be minimized, but one should strive to determine as many of the system properties as possible. Careful consideration of the optical-collection system can minimize stray radiation errors. Careful consideration must also be given to the slowest elements in a pyrometer when measuring rapid phenomena.

Spjut, R. Erik↗
NASA NTRS1987

Coloration and darkening of methane clathrate and other ices by charged particle irradiation - Applications to the outer solar system

The results of laboratory experiments simulating the irradiation of hydrocarbon-H2O or hydrocarbon-H2O/NH3 clathrates by charged particles in the outer solar system are reported. Ices produced by condensing and boiling liquid CH4 on an H2O frost surface at 100 K or by cocondensing frosts from gaseous mixtures were exposed to coronal-discharge electron irradiation at 77 K, and the spectral properties of the irradiated surfaces were determined. Significant darkening of the initially white ices was observed at doses of 1 Gerg/sq cm, corresponding to 8-500 yrs of irradiation by Uranian magnetospheric electrons on the surfaces of the principal Uranian satellites, or to total destruction of CH4 in the upper 1 mm of the satellite surfaces after 0.05-3.0 Myr. It is estimated that 10 m or more of icy satellite or comet surfaces would be radiation-hardened to a CH4-free ice-tholin mixture over 4 Gyr.

Thompson, W. Reid↗
NASA NTRS1988

Exact Rayleigh scattering calculations for use with the Nimbus-7 Coastal Zone Color Scanner

The radiance reflected from a plane-parallel atmosphere and flat sea surface in the absence of aerosols has been determined with an exact multiple scattering code to improve the analysis of Nimbus-7 CZCS imagery. It is shown that the single scattering approximation normally used to compute this radiance can result in errors of up to 5 percent for small and moderate solar zenith angles. A scheme to include the effect of variations in the surface pressure in the exact computation of the Rayleigh radiance is discussed. The results of an application of these computations to CZCS imagery suggest that accurate atmospheric corrections can be obtained for solar zenith angles at least as large as 65 deg.

Gordon, Howard R.↗
NASA NTRS1988

Time evolution of surface chlorophyll patterns from cross-spectrum analysis of satellite color images

The rate of decorrelation of surface chlorophyll patterns as a function of the time separation between pairs of images was determined from two sequences of CZCS images of the Pacific Ocean area adjacent to Vancouver Island, Canada; cloud-free subareas were selected that were common to several images separated in time by 1-17 days. Image pairs were subjected to two-dimensional autospectrum and cross-spectrum analysis in an array processor, and squared coherence estimates found for several wave bands were plotted against time separation, in analogy with a time-lagged cross correlation function. It was found that, for wavelengths of 50-150 km, significant coherence was lost after 7-10 days, while for wavelengths of 25-50 km, significant coherence was lost after only 5-7 days. In both cases, offshore regions maintained coherence longer than coastal regions.

Denman, Kenneth L.↗