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Mccord, T. B.

Publications and source records attributed to Mccord, T. B..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

High-spectral-resolution imagery of Saturn

High-spectral-resolution images of Saturn over the wavelengths of the 6196.8-A feature of CH4 were obtained and used to extract line profiles for the observed feature over the disk of Saturn and to determine the spatial variation of the equivalent width at the time of the observations. The result of the observations is consistent only with a single class of models for the vertical structure of the atmosphere of Saturn, namely, the homogeneous scattering models. Reflecting-layer or two-layer models are at a striking variance with the observations. With these data, the requirements for new observations to determine the finer details of the vertical structure of Saturn's atmosphere can be specified.

Smith, W. H.↗
NASA NTRS1981

Spectrophotometric remote sensing of planets and satellites

The most recent comprehensive results on spectrophotometric remote sensing of planets and satellites are reviewed. The moon and terrestrial planets are considered in terms of individual surface elements, reflectance spectra being analyzed to show the composition of the soils of these bodies. For more distant, unresolved objects, including the asteroids, the Galilean satellites, the small satellites of Jupiter, the rings and satellites of Saturn and Uranus, as well as Triton and Pluto, the global or hemispheric averages of surface composition are the objects of study. The absorptions due to methane gas and frost are indicated.

Mccord, T. B.↗
NASA NTRS1980

Visible spectral reflectance measurements /0.33-1.1 microns/ of the Galilean satellites at many orbital phase angles

One hundred eighty-seven reflectance spectra (0.33-1.10 microns) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6 deg. Solar phase angle coefficients beyond 0.55 micron are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 micron observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambiguously attribute this particular decrease in reflectance to a change in Io's surface composition.

Mcfadden, L. A.↗
NASA NTRS1980

Interference filter photometry of periodic comet Ashbrook-Jackson

P/Ashbrook-Jackson has a period of 7.43 years and comes to perihelion at 2.284 AU. It is a low inclination object (12.5 deg) of moderate eccentricity (0.400). In 1963, it made the best possible apparition, coming to perihelion and opposition virtually simultaneously, but no one made physical observations of faint periodic comets in 1963. In 1978 Ashbrook-Jackson came to opposition on Sept. 28, just 40 days after perihelion. It will be just over 100 years before an equally favorable apparition recurs. P/Ashbrook-Jackson was recovered by Pereyra at Cordoba Observatory on April 28, 1977, more than a year and a quarter before perilhelion and already showing a diffuse coma with central condensation. Its helio-centric distance was then 3.7 AU. An extensive program was planned, but equipment problems and weather ultimately limited it to the two nights of data reported here.

Newburn, R. L., Jr.↗
NASA NTRS1980

The rings of Saturn - New near-infrared reflectance measurements and a 0.326-4.08 micron summary

A new high-photometric-precision reflectance spectrum of Saturn's rings covering the spectral region 0.65 to 2.5 microns is presented and three previously unreported absorption features at 1.25, 0.85, and probably 1.04 microns are identified. The 1.25- and 1.04 micron absorptions are due to water ice. The 0.85 microns feature may be due to a combination of 0.81- and 0.90 micron ice absorptions but this feature appears too strong relative to the 1.04 micron band to be completely explained by water ice. Another possibility is that the 0.85 micron band is due to Fe(3+)-bearing minerals in an ice-mineral mixture. This explanation could also account for the drop in the visible and ultraviolet reflectance and the rise in reflectance around 3.6 microns. Finally, a composite spectrum from 0.325 to 4.08 is presented which will be useful for future analysis and laboratory studies.

Clark, R. N.↗
NASA NTRS1980

Late high-titanium basalts of the western maria - Geology of the Flamsteed region of Oceanus Procellarum

The evolution, geology, geochemistry and topology of the Flamsteed region of Oceanus Procellarum are examined, considering remote sensing data including multispectral images and spectral reflectance measurements along with crater degradation studies and radar backscatter. Seven spectrally distinct basaltic units ranging in age from 2.5 plus or minus 0.5 to 3.5 plus or minus 0.5 billion years have been identified. The earliest units of the mapped area are composed of highlands material and include partially flooded impact craters, and the oldest surface exposed mare basalts are very low Ti basalts of the Telemann formation.

Pieters, C. M.↗
NASA NTRS1980

The Galilean satellites - New near-infrared spectral reflectance measurements /0.65-2.5 microns/ and a 0.325-5 micron summary

New near-infrared (0.65-2.5 microns) reflectance spectra of the Galilean satellites are presented. These spectra more precisely define the water ice absorption features previously identified on Europa, Ganymede, and Callisto at 1.55 and 2.0 microns. In addition, previously unreported spectral features due to water ice are seen at 1.25, 1.06, 0.90, and 0.81 microns on Europa, and at 1.25, 1.04, and possibly 0.71 microns on Ganymede. Unreported absorption features in Callisto's spectrum occur at 1.2 microns, probably due to H2O, and a weak, broad band extending from 0.75 to 0.95 microns due possibly to other minerals. The spectrum of Io has only weak absorption features at 1.15 microns and between 0.8 and 1.0 microns. No water absorptions are positively identified in the Io spectra, indicating an upper limit of areal water frost coverage of 2% (leading and trailing sides). It is found for Callisto, Ganymede, and Europa that the water ice absorption features are due to free water and not to water bound or absorbed onto minerals. The areal coverage of water frost is approximately 100% on Europa (trailing side), approximately 65% on Ganymede (leading side), and 20-30% on Callisto (leading side). An upper limit of approximately 5% bound water (in addition to the 20-30% ice) may be present on Callisto, based on the strong 3-micron band seen by other investigators. A summary of spectra of the satellites from 0.325 to about 5 microns to aid in laboratory and interpretation studies is also presented.

Clark, R. N.↗
NASA NTRS1979

Mars surface composition from reflectance spectroscopy - A summary

Visible and near-infrared reflectance spectra and multispectral maps of the Martian surface are discussed, and implications of the data for the composition of the Martian surface are considered. Spacecraft and earth-based telescopic observations have confirmed the generally bimodal albedo distribution of the planet, dividing the surface into bright and dark regions. Mars spectra are characterized by the presence of strong Fe(+3) absorption, which is attributed to various ferric oxide minerals. Interpretations of the spectra from the dark regions indicate a basaltic or ultramafic source rock. Evidence for water ice or a highly desiccated metal hydrate has been obtained, along with evidence for CO2-ice only in the south polar cap. Mariner 9 observations of Martian dust suggest the presence of rather acidic rock or mineral particles, or a montmorillonite-type clay. Prospects for the future study of Martian surface composition include continuing earth-based spectrophotometric studies, and high-spectral-resolution mapping of a significant portion of the surface by the Galileo spacecraft and the next Mars mission.

Singer, R. B.↗
NASA NTRS1979

Jupiter and Saturn - Near-infrared spectral albedos

The near-infrared (0.65-2.5 micron) spectral albedo of Jupiter and Saturn with 1.5% spectral resolution is presented for the center of disk and for the limb. There is a distinct difference in the continuum slope between Jupiter and Saturn which may be attributed to a difference in the dust content or composition of the two atmospheres. There is an indication of limb brightening in the deepest CH4 bands on Saturn. No limb brightening is found for Jupiter.

Clark, R. N.↗
NASA NTRS1979

Preliminary design and development of a reflectance spectrometer instrument

An improved design for the reflectance spectrometer is described to be used on various terrestrial body missions. These improvements were made on the original Lunar Polar Orbiter design. These include a larger entrance mirror, rectangular aperture, multiple optical beams, spatial resolution, and a bandwidth extension to 5 microns. In addition, detailed electronic designs were produced for a charge amplifier and an amplifier/demodulator/integrator. Design of a microprocessor driven test system was begun. Laboratory tests were performed on a tuning fork chopper.

Mccord, T. B.↗
NASA NTRS1979

Lunar multispectral maps - Part II of the lunar nearside

Images of the lunar surface are being obtained at several wavelengths using a silicon vidicon imaging system and ground-based telescopes. These images are recorded and processed in digital form so that quantitative information is preserved; their photometric precision has been shown to be 1% or better. Ratio images, calculated by dividing those obtained at two wavelengths (0.40/0.56 and 0.95/0.56 micron), were presented in an earlier article, and more are presented here for a total coverage of about 60% of the lunar frontside. Spatial resolution is about 2 km at the subearth point. A complex of distinct units is evident in the images. Earlier work with the reflectance spectrum of lunar materials indicates that for the most part these units are compositionally distinct. These digital images are being used by lunar geologists to interpret the history of the lunar surface.

Mccord, T. B.↗