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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Spectral Irradiance Calibration in the Infrared: New Composite Spectra, Comparison with Model Atmospheres, and Far-Infrared Extrapolations - Part 7

We present five new absolutely calibrated continuous stellar spectra constructed as far as possible from spectral fragments observed from the ground, the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer. These stars-alpha Boo, gamma Dra, alpha Cet, gamma Cru, and mu UMa-augment our six, published, absolutely calibrated spectra of K and early-M giants. All spectra have a common calibration pedigree. A revised composite for alpha Boo has been constructed from higher quality spectral fragments than our previously published one. The spectrum of gamma Dra was created in direct response to the needs of instruments aboard the Infrared Space Observatory (ISO); this star's location near the north ecliptic pole renders it highly visible throughout the mission. We compare all our low-resolution composite spectra with Kurucz model atmospheres and find good agreement in shape, with the obvious exception of the SiO fundamental, still lacking in current grids of model atmospheres. The CO fundamental seems slightly too deep in these models, but this could reflect our use of generic models with solar metal abundances rather than models specific to the metallicities of the individual stars. Angular diameters derived from these spectra and models are in excellent agreement with the best observed diameters. The ratio of our adopted Sirius and Vega models is vindicated by spectral observations. We compare IRAS fluxes predicted from our cool stellar spectra with those observed and conclude that, at 12 and 25 microns, flux densities measured by IRAS should be revised downwards by about 4.1% and 5.7%, respectively, for consistency with our absolute calibration. We have provided extrapolated continuum versions of these spectra to 300 microns, in direct support of ISO (PHT and LWS instruments). These spectra are consistent with IRAS flux densities at 60 and 100 microns.

Cohen, Martin↗
NASA NTRS1971

Vibrational spectra and structure of dimethylaminodichlorophosphine.

Evaluation of the infrared spectra of dimethylaminodichlorophosphine and dimethylaminodichlorophosphine-d sub 6 recorded from 4000 to 33 per cm in the gas and solid phases. The Raman spectra of the liquid and solid phases for both compounds were also recorded. The spectra were consistent with the presence of only one isomer over the range of phases and temperatures studied. Available experimental data were discussed in connection with the spectra, and it is concluded that the molecule exists in the gauche conformer with the PNC2 portion of the molecule planar. A vibrational assignment is proposed for the molecule.

Durig, J. R.↗
NASA NTRS1994

Spatial variability in the seasonal south polar cap of Mars

The first comprehensive discussion of the south seasonal polar cap spectra obtained by the Mariner 7 infrared spectrometer in the short-wavelength region (2-4 microns) is presented. The infrared spectra is correlated with images acquired by the wide-angle camera. Significant spectral variation is noted in the cap interior and regions of varying water frost abundance, CO2 ice/frost cover, and CO2-ice path length can be distinguished. Many of these spectral variations correlate with heterogeneity noted in the camera images, but certain significant infrared spectral variations are not discernible in the visible. Simple reflectance models are used to classify the observed spectral variations into four regions. Region I is at the cap edge, where there is enhanced absorption beyond 3 microns inferred to be caused by an increased abundance of water frost. The increase in water abundance over that in the interior is on the level of a few parts per thousand or less. Region II is the typical cap interior characterized by spectral features of CO2 ice at grain sizes of several millimeters to centimeters. These spectra also indicate the presence of water frost at the parts per thousand level. A third, unusual region (III), is defined by three spectra in which weak CO2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the CO2. Such large paths are inconsistent with the high reflectance in the visible and at 2.2 microns and suggest layered structures or deposition conditions that are not accounted for in current reflectance models. The final region (IV) is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap. These spectra are a combination of CO2 and ground signatures.

Calvin, Wendy M.↗
DOE OSTI2021

Optical vibrational spectra and proposed crystal structure of ε-UO 3

ε-UO 3 is an exotic polymorph in the uranium trioxide system with an undetermined crystal structure and limited optical vibrational spectroscopic data. To improve understanding of this compound, we synthesize and investigate the crystal structure and optical vibrational spectra of ε-UO 3 . Infrared spectra collected for ε-UO 3 are in good agreement with previously published results, and our studies extend the available data into the low-energy (600–100 cm –1 ) regime. For the first time, Raman spectra are presented for ε-UO 3 using both 785 and 532 nm excitation wavelengths. Previous reports suggest an impurity phase may be present in ε-UO 3 produced by calcination of U 3 O 8 ; however, spectral center-of-mass calculations, principal component analyses, and Raman spectroscopic mapping employed to investigate this possibility indicate that the product of U 3 O 8 calcined in O 3 (g) in this work is likely phase-pure. A possible novel structure solution for ε-UO 3 is determined via Rietveld refinement of powder X-ray diffraction data and is triclinic, P-1, with a = 4.01 Å, b = 3.85 Å, c = 4.18 Å, and α = 98.26°, β = 90.41°, γ = 120.46° (R wp = 8.30%). The asymmetric unit of ε-UO 3 consists of U(VI) in hexagonal bipyramidal coordination with displaced equatorial oxygen. Further analysis reveals that the structure of ε-UO3 is best described by a 2 × 1 × 2 supercell structure in P-1 with a = 8.03 Å, b = 3.86 Å, c = 8.37 Å with α = 98.26°, β = 90.41°, and γ = 120.46°, although a higher-symmetry structure is possible. Optical vibrational spectroscopic and structural measurements of ε-UO 3 presented here furthers our understanding of this complex uranium oxide and clarifies the origin of reported structural similarity to U 3 O 8 .

-UO3↗
NASA NTRS2022

EMIRS Observations of the Aphelion-Season Mars Atmosphere

Thermal infrared spectra taken by the Emirates Mars Infrared Spectrometer (EMIRS) on-board the Emirates Mars Mission (EMM) spacecraft are well suited for the retrieval of surface temperatures, the atmospheric temperature profile from the surface to ∼40 km, and the column abundance of dust aerosols, water ice clouds, and water vapor. A constrained linear inversion retrieval routine that includes multiple scattering has been developed and optimized for this purpose. Here, we present a brief overview of the retrieval algorithm and first atmospheric science results from observations taken by EMIRS over the first Earth year of EMM Science Phase operations. These retrievals show extensive water ice clouds, typical for the aphelion season of these observations, and the expected north polar summer maximum and subsequent equatorward transport of water vapor is well documented. An unusually strong and early regional dust storm and its associated thermal response were also observed.

Michael D. Smith↗
NASA NTRS2000

Spectral Anomalies in the 11 and 12 micron Region From the Mariner Mars 7 Infrared Spectrometer

Two hundred-forty infrared spectra acquired by the 1969 Mariner Mars 7 Infrared Spectrometer (IRS), spanning the wavelength region 1.8-14.4 micron (5550-690/cm), have recently been recovered and calibrated in both wavelength and intensity. An examination of these IRS spectra has revealed absorptions at 11.25 and 12.5 micron that have not previously been reported for Mars. A search of the literature and spectral data bases shows that materials that exhibit a doublet at 11.25 and 12.5 micron are rare. In this paper we examine potential causes for these features and include a detailed discussion of carbonates, goethite, CO2 ice, and water ice. CO2 ice and water ice measured in transmission do not exhibit bands that match those recorded at 11.25 and 12.5 micron for Mars, which indicates that CO2 or water ice clouds are not the source of these features. Since these bands show no clear correlation with atmospheric path length, they are most likely caused by a surface material. In the IRS database they appear to be exceptionally intense in the western part of the Hellas basin. Goethite exhibits bands that are a good spectral match, but confirming whether goethite causes the features will require additional studies of the 20-50 micron region. These studies will require laboratory measurements of weathering coatings and an examination of spectra recorded of Mars by the 1971 Mariner Mars Infrared Interferometer Spectrometer (IRIS; 5-50 micron 2000200/cm) and the 1996 Thermal Emission Spectrometer (TES; 6-50 micron 1667-200/cm).

Kirkland, Laurel E.↗
NASA NTRS1987

Compositional information for the Moon: Some characteristics of current near-IR spectra (telescopic and laboratory)

For the last decade telescopic near infrared spectra have been obtained for small lunar areas. Such spectra, with the ground truth foundation from lunar samples, have been used extensively to address a multitude of problems in lunar science. Much of the near infrared spectral reflectance data from both laboratory and telescopic measurements have recently been compiled in comparable formats and an initial comparative assessment of the available data using selected spectral parameters has been made. The objective is to develop a framework for the systematics of lunar near-IR spectra in order to better interpret spectra of unknown materials in terms of useful compositional information. Each spectrum was first classified according to its general character then a variety of parameters sensitive to mineralogy and alteration products were measured for each spectrum: band width, band strength, absorption band center near 1 micron, band symmetry, continuum slope, etc. The telescopic and laboratory data sets are briefly described. The comparative analysis shows that a few well known lunar spectral properties are evident in both sets, such as the systematic variation in pyroxene composition between the highlands and the mare. However, an additional gabbroic component can be detected in many highland craters.

Pieters, Carle M.↗
NASA NTRS1995

High Resolution Wavenumber Standards for the Infrared. (IUPAC Recommendations 1995)

The calibration of high resolution infrared spectra is generally more precise than accurate. This is the case even when they are recorded with Fourier transform interferometers. This presentation aims at improving the accuracy of wavenumber measurements in the infrared by recommending a selection of spectral lines as wavenumber standards for absolute calibration.

Interferometers Infrared Spectra Wavenumbers Fouri↗
DOE OSTI2021

Chemical Compositions of Red Giant Stars from Habitable Zone Planet Finder Spectroscopy

We have used the Habitable Zone Planet Finder (HPF) to gather high-resolution, high signal-to-noise near-infrared spectra of 13 field red horizontal branch (RHB) stars, one open cluster giant, and one very metal-poor halo red giant. The HPF spectra cover the 0.81–1.28 μm wavelength range of the zyJ bands, partially filling the gap between the optical (0.4–1.0 μm) and infrared (1.5–2.4 μm) spectra already available for the program stars. We derive abundances of 17 species from LTE-based computations involving equivalent widths and spectrum syntheses, and estimate abundance corrections for the species that are most affected by departures from LTE in RHB stars. Generally good agreement is found between HPF-based metallicities and abundance ratios and those from the optical and infrared spectral regions. Light element transitions dominate the HPF spectra of these red giants, and HPF data can be used to derive abundances from species with poor or no representation in optical spectra (e.g., C i, P i, S i, K i). Attention is drawn to the HPF abundances in two field solar-metallicity RHB stars of special interest: one with an extreme carbon isotope ratio, and one with a rare, very large lithium content. The latter star is unique in our sample in exhibiting very strong He i 10830 Å absorption. The abundances of the open cluster giant concur with those derived from other wavelength regions. Detections of C i and S i in HD 122563 are reported, yielding the lowest metallicity determination of [S/Fe] from more than one multiplet.

47 OTHER INSTRUMENTATION↗
NASA NTRS1978

Measurements of constituents of interest in the photochemistry of the ozone layer using infrared techniques

Infrared solar spectra and infrared atmospheric emission spectra were obtained from the ground, from aircraft and from balloons. The initial detection of most stratospheric molecules was achieved by the solar spectral technique because better resolution helps remove interference from other molecules. Because the sun is an intense source of radiation, the resolution which can be obtained with good signal-to-noise, is greater than with atmospheric emission spectroscopy. Data are generally taken using a method that enhances the number of molecules in the optical path i.e. at large solar zenith angles for solar spectra and at low elevation angles for atmospheric emission spectra. The search for molecules which are predicted to be present but which, the detection of a molecule known to be present from other measurement techniques but observed for the first time in infrared solar spectra, and some further data on the variability of HNO3 are discussed.

Murcray, D. G.↗
NASA NTRS2010

Saturn's Atmospheric Composition from Observations by the Cassini/Composite Infrared Spectrometer

Thermal emission infrared observation of Saturn s atmosphere are being made by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft since its insertion in Saturn s orbit on July 2nd, 2004. The measurements made in both limb and nadir modes of observations consist of infrared spectra in the 10-1400/cm region with a variable spectral resolution of 0.53/cm and 2.8/cm, and exhibit rotational and vibrational spectral features that may be analyzed for retrieval of the thermal structure and constituent distribution of Saturn s atmosphere. In this paper, we present a comprehensive analysis of the CIRS infrared observed spectra for retrieval of Saturn s atmospheric composition focusing on the distributions of some selected hydrocarbons, phosphine, ammonia, and possible determination of the isotopic ratios of some species with sufficiently strong isolated spectral features. A comparison of the retrieved constituent distributions with the available data in the literature will be made.

Abbas, M. M.↗
NASA NTRS1989

An infrared survey of Galactic supernova remnants

A survey of Galactic supernova remnants (SNRs) in the infrared has been completed. Flux densities or upper limits on the flux densities have been measured for 157 objects in each of the four broad bands surveyed by the Infrared Astronomical Satellite (IRAS). Nearly one-third of the known SNRs exhibit some evidence of infrared emission. Confusion with other Galactic sources is a serious problem. Contour maps and halftone images are presented for 51 SNRs which are probable infrared sources. Initial analysis indicates that both the infrared spectra or colors and the ratio of infrared to radio brightnesses can discriminate between the youngest SNRs and older SNRs. In general, however, SNRs cannot be distinguished from other Galactic sources solely on the basis of their infrared colors. No apparent relation is found between the infrared surface brightnesses and the diameters of SNRs.

Arendt, Richard G.↗
NASA NTRSDate not supplied

Compositional Analysis of Titan’s Atmosphere Using Spitzer Infrared Spectrograph Data

We present, for the first time, infrared spectra from the Spitzer Space Telescope’s Infrared Spectrograph (IRS) (2004-2008) of Titan in both the short wavelength-low resolution(SL, R=60~127,5.13-14.29 μm) and short wavelength-high resolution channels (SH, R=600, 9.89-19.51 μm) showing the emissions of CH4, C2H4, C2H2, C2H6, HCN, CO2, HC3N, C3H4, C4H2, and C3H8. Spitzer IRS data has been used to measure atmospheric composition of various Solar System bodies, including Neptune [1] and Uranus [2],[3]. Although Spitzer took multiple dedicated observations of Titan, none of the results have been modeled before. We conduct our own investigation of these datasets and search for new results. We retrieve temperature and gas composition profiles and compare the results obtained for Titan to those of the Cassini Composite Infrared Spectrometer (CIRS) and the Infrared Space Observatory Short Wavelength Spectrometer [4], and comment on the effect of spectral resolution on retrieved information content. We conclude by recommending gaps in current spectroscopic knowledge of molecular bands that could be addressed by theoretical and laboratory study to aid future astronomical studies of Titan, for example the James Webb Space Telescope (JWST) and the Stratospheric Observatory for Infrared Astronomy (SOFIA) Acknowledgments: Data analyzed in this project is public available online on the Spitzer Heritage Archive (sha.ipac.caltech.edu). This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.

Titan↗