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At least 217 records · Page 12

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NASA NTRS1984

4.6 micron absorption features due to solid phase CO and cyano group molecules toward compact infrared sources

Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Lacy, J. H.↗

NASA NTRS1984

Morphology and movements of polarization features on Venus as seen in the Pioneer Orbiter Cloud Photopolarimeter data

The regional structure of Venus seen in polarization data acquired during the first 600 orbits of the Orbiter Cloud Polarimeter are described. Local organized features are seen whose morphology is similar to that of the ultraviolet clouds. No obvious correlation between the observed amount of polarization and the relative brightness is found, suggesting that the polarization features are not due to variations in the unpolarized intensity alone. Substantial variations in the structure and visibility of the polarization features suggest that the amount of haze in and above the main cloud layer is not constant. These features show movements similar to those of the ultraviolet clouds in both direction and speed.

Limaye, S. S.↗

NASA NTRS1984

The Unidentified Emission Features: a Study of the Orion Bar and Planetary Nebulae

The unidentified emission features which are a group of broad emission bands found between 3.3 and 11.3 micro m in many objects which emit UV radiation and are associated with dust were studied. The features emit a substantial fraction of the energy in this wavelength range, and must therefore be an important constituent of the material around these objects. A two phase approach to the problem to better define the factors affecting the features was undertaken. The number of objects with good spectra between 3 and 13 micro m to look for correlations of the features with each other and with chemical and physical conditions were expanded and several positions in a single region, the Orion Bar, where the chemical composition was homogeneous, but the physical conditions varied are examined.

Bregman, J.↗

NASA NTRS1985

Seasonal and Secular Variation of the Solis Lacus Albedo Feature: Relation to the Martian Dust-transport Cycle

As documented over the course of thirty-six Martian years, dramatic seasonal and secular variations occur in albedo features in the Solis Planum region of Mars. The most striking of these is the classical dark albedo features, Solis Lacus. Solis Lacus is generally most distinct during southern spring and summer. Mariner 9 and Viking Orbiter images reveal that Solis Lacus contains and is surrounded by a conspicuous pattern of bright and dark wind streaks. A seasonal dust-transport cycle is proposed to explain these observations. During later southern spring or early summer, dust is eroded from the surface and transported from the region by local dust storms which may become a global dust storm. Removal of dust over a wide area results in the dark Solis Lacus feature. During the cessation stage of global dust-storm activity (typically mid- to late-southern summer), enhanced deposition in the lee of obstacles forms the prominent patterns of bright streaks observed within and around Solis Lacus. As the year progresses (southern fall and winter), sedimentation from the atmospheric dust load occurs over the entire region, decreasing the contrast of the albedo features to their surroundings. Dust-storm activity the following year renews the cycle by again removing dust from the region.

Lee, S. W.↗

NASA NTRS1984

Absorption features in the 5-8 micron spectra of protostars

High signal-to-noise ratio spectra in the range of 5-8 microns of four sources embedded in molecular clouds are examined using low-temperature laboratory measurements of the 5-8-micron spectra of simple molecules and their mixtures. The absorption, apparent in all four sources, is characterized by highly distinct features ranging from two relatively narrow bands at 6.0 and 6.8 microns in W33A to a broad, shallow, and partially structured feature extending from 5.2 to 7.8 microns in Mon R2-IRS2, BN, and NGC2264. The first feature (W33A) is explained by the OH bending mode in H2O and the CH deformation modes in saturated hydrocarbons; while the second feature (Mon R2-IRS2-type) is explained by the presence of a mixture of saturated and unsaturated hydrocarbons possibly containing strongly electronegative groups.

Tielens, A. G. G. M.↗

NASA NTRS1985

Ion and electron energy dispersion features detected by ISEE 1

An energy dispersion feature observed by the ISEE 1 medium energy particle instrument is reported. This feature is characterized by enhancements in both electron and ion fluxes which occur in the 20-200 keV energy range and at radial distances from 5 to 13.5 earth radii. There is a strong energy dependence in the onset times of the enhancements. The time period between the first appearance of an enhancement at high energy to its eventual disappearance in the 20 keV channel can be as much as an hour. The duration of the enhancement in a given energy channel decreases with increasing energy. The species and pitch angle of particles in which the feature is most marked depend on local time. It is shown that the feature is a new manifestation of an old phenomenon, the drift dispersion that frequently produces signatures in particle data from geosynchronous satellites.

Greenspan, M. E.↗

NASA NTRS1986

The solar maximum satellite capture cell: Impact features and orbital debris and micrometeoritic projectile materials

The physical properties of impact features observed in the Solar Max main electronics box (MEB) thermal blanket generally suggest an origin by hypervelocity impact. The chemistry of micrometeorite material suggests that a wide variety of projectile materials have survived impact with retention of varying degrees of pristinity. Impact features that contain only spacecraft paint particles are on average smaller than impact features caused by micrometeorite impacts. In case both types of materials co-occur, it is belevied that the impact feature, generally a penetration hole, was caused by a micrometeorite projectile. The typically smaller paint particles were able to penetrate though the hole in the first layer and deposit in the spray pattern on the second layer. It is suggested that paint particles have arrived with a wide range of velocities relative to the Solar Max satellite. Orbiting paint particles are an important fraction of materials in the near-Earth environment. In general, the data from the Solar Max studies are a good calibration for the design of capture cells to be flown in space and on board Space Station. The data also suggest that development of multiple layer capture cells in which the projectile may retain a large degree of pristinity is a feasible goal.

Mckay, D. S.↗

NASA NTRS1985

A spectral haze diagnostic feature for normalizing Landsat Thematic Mapper data

The effects of atmospheric haze on Thematic Mapper data, transformed to TM Tasseled Cap features, are illustrated by means of simulation. A spectral feature by which the amount of atmospheric haze may be inferred is derived and described for both simulated and actual TM data. Results presented for two actual TM scenes illustrate the diagnostic feature's sensitivity to changes in haze level as well as its insensitivity to scene-class-related variability. The method by which such a diagnostic feature might be incorporated into a haze normalization procedure is also discussed.

Crist, E. P.↗

NASA NTRS1986

More interstellar emission features at 3.3-3.6 micrometers!

The present data set consists of 3.20 to 3.55 micron spectra of HD44179, NGC 7027, BD+30 3639, and Elias 1 obtained with a cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility. Emission features and details of the emission feature profiles are presented for high resolution spectra. Greater complexity is shown than might be expected. It is significant that the 3.29 micron feature has an invariant central wavelength, even at high resolution, and this strongly supports the case for a very specific substance or mixture of substances which is giving rise to this feature.

Tokunaga, A. T.↗

NASA NTRS1986

Resolution of the 7.7 micrometers emission feature in NGC 7027

The unidentified infrared (UIR) features are a group of emission bands observed in a variety of objects, which can be characterized as having moderate density gas (densities from 1000 to 1,000,000/cu.cm.) and a nearby ultraviolet source. The origin of the features is still uncertain, but the current evidence points to Polycyclic Aromatic Hydrocarbons (PAHs) as the source of the UIR features. Problems with identifying PAHs as the source of the UIR features are discussed.

Bregman, J. D.↗

NASA NTRS1986

Elysium region, Mars - Tests of lithospheric loading models for the formation of tectonic features

The hypothesis that the tectonic features in the Elysium region are the product of stress produced by loading of the Martian lithosphere is tested. The lithospheric loading models for the formation of tectonic features in the Elysium region are evaluated under local loading, regional loading of the lithosphere from above and below, and quasi-global loading by Tharsis. The physiographic features in the Elysium region are described. The stress fields predicted by volcanic loading and uplift of the Martian lithosphere are compared with the tectonic features in the Elysium region. It is noted that the comparison suggests the succession of stress fields operating at different times in the region and supports the hypothesis.

Hall, J. Lynn↗

NASA NTRS1986

Lava flows on Mars - Analysis of small surface features and comparisons with terrestrial analogs

High-resolution images of south and west Arsia Mons, eastern Tharsis, and Memnonia Fossae on Mars are analyzed. Lava flows with different types of features, such as pressure ridges, tumuli, festoon ridges, and ring ridges, are observed. The effects of these small features on the type of eruption, mode of flow emplacement, and characteristics of the terrain over which the lavas flow are examined. The development of terrestrial pressure ridges, festoon, and ring structures is discussed and they are compared to the observed Martian features. The interior viscosity of the features are calculated using the Fink and Fletcher (1978) and Fink (1980a) models; the interior viscosity was estimated as 100 MPa sec in flow margins, ponded areas, and across flow lobes. The data reveal that south of Arsia Mons, flows containing pressure ridges are emplaced as multiple flow units from sporadic low-effusion rate eruptions, and the flows at the other three areas are large sheet flows that represent basaltic flood-type volcanism.

Theilig, E.↗

NASA NTRS1987

Causes of spurious features in spectral reflectance data

Several techniques are becoming common in the analysis of imaging spectrometer data that can lead to spurious absorption features or to changes in the position, width, and shape of actual absorption features. It is a common practice to calibrate AIS or other imaging spectrometer data by averaging each pixel along the flight line. The average is used to calibrate the spectral data by dividing the spectrum at each pixel by the average. If some pixels in the data set contain an absorption, then the average will also show an absorption. Some AIS data has had problems with wavelength stability from one scan line to the next which can produce spurious features with some analysis methods. If a pixel has a spectrum with an absorption having a different position or width than the spectrum used in a ratio, then the ratio can produce a spurious absorption at a different position and width than the true absorption feature. An average spectrum ratioed to each pixel will produce band shifts, and changes in width or shape. If continuum removal is performed by substraction rather than division, band positions can also be shifted.

Clark, Roger N.↗

NASA NTRS1988

SiH and the unidentified 4.6 micron feature

Results from experimental studies of the irradiation of SiH4-H2O and Fe(CO)5-SiH4-H2O ice mixtures at 15 K using 1 MeV protons have revealed the synthesis of a very stable infrared spectral feature at 4.6 microns which is characteristic of the SiH functional group. This feature persists through warmup of the ice, exposure to air at 300 K, and vacuum annealing to at least 400 K. Because of the high cosmic abundance of both silicon and hydrogen and the unexpected stability of the SiH feature in our experiments, it is suggested that SiH might be responsible for the 4.6 micron absorption feature observed in W33A.

Nuth, Joseph A.↗

NASA NTRS1988

On the carbon abundance in Comet Halley derived from the 3 micron feature: Comparison with interstellar dust

In spite of some similarities with the infrared features observed in the interstellar medium, the 3 micron signature observed in comet Halley's spectrum shows two distinct differences: (1) the 3.28 micron and 3.37 micron cometary features are both in emission, while the 3.37 micron interstellar feature is most often observed in absorption; and (2) there is no associated emission feature beyond 6 micron in the cometary spectrum. These two facts can be simply explained if it is assumed that the excitation mechanism is resonance fluorescence by the solar IR radiation field. With this assumption, it is found that hydrocarbons are present in roughly equal quantities in both the saturated forms, with a total carbon abundance of about 30 percent of H2O. This carbon abundance can be compared with the abundances derived for the interstellar dust when all condensed (or condensable) components are considered.

Encrenaz, Therese↗

NASA NTRS1988

Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

Loper, D. E.↗

NASA NTRS1988

Automated extraction of absorption features from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Geophysical and Environmental Research Imaging Spectrometer (GERIS) data

Automated techniques were developed for the extraction and characterization of absorption features from reflectance spectra. The absorption feature extraction algorithms were successfully tested on laboratory, field, and aircraft imaging spectrometer data. A suite of laboratory spectra of the most common minerals was analyzed and absorption band characteristics tabulated. A prototype expert system was designed, implemented, and successfully tested to allow identification of minerals based on the extracted absorption band characteristics. AVIRIS spectra for a site in the northern Grapevine Mountains, Nevada, have been characterized and the minerals sericite (fine grained muscovite) and dolomite were identified. The minerals kaolinite, alunite, and buddingtonite were identified and mapped for a site at Cuprite, Nevada, using the feature extraction algorithms on the new Geophysical and Environmental Research 64 channel imaging spectrometer (GERIS) data. The feature extraction routines (written in FORTRAN and C) were interfaced to the expert system (written in PROLOG) to allow both efficient processing of numerical data and logical spectrum analysis.

Kruse, Fred A.↗

NASA NTRS1989

Features and characterization needs of rubber composite structures

Some of the major unique features of rubber composite structures are outlined. The features covered are those related to the material properties, but the analytical features are also briefly discussed. It is essential to recognize these features at the planning stage of any long-range analytical, experimental, or application program. The development of a general and comprehensive program which fully accounts for all the important characteristics of tires, under all the relevant modes of operation, may present a prohibitively expensive and impractical task at the near future. There is therefore a need to develop application methodologies which can utilize the less general models, beyond their theoretical limitations and yet with reasonable reliability, by proper mix of analytical, experimental, and testing activities.

Tabaddor, Farhad↗