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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

Time-resolved observations of brown dwarfs' rotational modulations provide powerful insights into the properties of condensate clouds in ultra-cool atmospheres. Multi-wavelength light curves reveal cloud vertical structures, condensate particle sizes, and cloud morphology, which directly constrain condensate cloud and atmospheric circulation models. We report results from Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared G141 taken in six consecutive orbits observations of HNPeg B, an L/T transition brown dwarf companion to a G0V type star. The best-fit sine wave to the 1.1 to 1.7 micron broadband light curve has the amplitude of and period of hour. The modulation amplitude has no detectable wavelength dependence except in the 1.4 micron water absorption band, indicating that the characteristic condensate particle sizes are large (greater than 1 micron). We detect significantly (4.4 sigma) lower modulation amplitude in the 1.4 micron water absorption band, and find that HN Peg B's spectral modulation resembles those of early T type brown dwarfs. We also describe a new empirical interpolation method to remove spectral contamination from the bright host star. This method may be applied in other high-contrast time-resolved observations with WFC3.

brown dwarf↗
NASA NTRS1993

Nongray gas analyses for reflecting walls utilizing a flux technique

A flux formulation for a planar slab of molecular gas radiation bounded by diffuse reflecting walls is developed. While this formulation is limited to the planar geometry, it is useful for studying approximations necessary in modeling nongray radiative heat transfer. The governing equations are derived by considering the history of multiple reflections between the walls. Accurate solutions are obtained by explicitly accounting for a finite number of reflections and approximating the spectral effects of the remaining reflections. Four approximate methods are presented and compared using a single absorption band of H2O. All four methods reduce to an identical zeroth-order formulation, which accounts for all reflections approximately but does handle nonreflected radiation correctly. A single absorption band of CO2 is also considered using the best-behaved approximation for higher orders. A zeroth-order formulation is sufficient to predict the radiative transfer accurately for many cases considered. For highly reflecting walls, higher order solutions are necessary for better accuracy. Including all the important bands of H2O, the radiative source distributions are also obtained for two different temperature and concentration profiles.

Menart, J. A.↗
NASA NTRS1976

The infrared optical constants of sulfuric acid at 250 K

Results are presented for measurements of the IR spectral reflectance at near-normal incidence of aqueous solutions of sulfuric acid with acid concentrations of 75% and 95.6% by weight. Kramers-Kronig analyses of the reflectance data are employed to obtain values of the optical constants n(nu) and k(nu) in the spectral range from 400 to 6000 cm to the -1 power. The optical constants of these solutions at 250 K and 300 K are compared. It is found that in spectral regions remote from strong absorption bands, the values of the n(nu) indices obtained at 250 K agree with the values given by Lorentz-Lorenz correction of the same indices at 300 K. All absorption bands observed at 300 K are found to be present at 250 K with slight shifts in frequency and with significant differences in the k(nu) indices at the band maxima. Based on these results, it is concluded that the clouds of Venus probably consist of droplets of aqueous solutions of sulfuric acid with acid concentrations of about 75% by weight.

Pinkley, L. W.↗
NASA NTRS1992

Separation of cirrus cloud from clear surface from AVIRIS data using the 1.38 micron water vapor band

Cirrus clouds play an important role in climate systems because of their large area coverage, persistence, and radiative effects. Thin cirrus clouds are difficult to detect in visible images and infrared images in the 10-12 micron atmospheric window region, particularly over land, because these clouds are partially transparent. Ackerman recently developed a method for detecting cirrus clouds using three narrow channels centered near 8, 11, and 12 microns, respectively, based on the analysis of IR emission spectra measured with a high spectral resolution interferometer. Barton also described a method for estimating cirrus cloud height and amount from measurements with two narrow channel radiometers of the Selective Chopper Radiometer on Nimbus 5. Both channels are located within the strong 2.7 micron water vapor band absorption region. One of the channels includes additional carbon dioxide absorption. A differential absorption technique with sets of empirical coefficients was used in the estimation of cirrus cloud heights and amounts. A technique using narrow channels in the strong 1.38 micron water vapor band absorption region for detecting cirrus clouds from spectral imaging data acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) on 5 Dec. 1991 during the FIRE (The First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment) Phase 2 Field Experiment is described.

Gao, Bo-Cai↗
NASA NTRS1975

Evidence for frost on Rhea's surface

We have observed Rhea (S5) at 1.6 and 2.2 microns at Mt. Wilson using the Caltech photometer on the 1.52 m and 2.54 m telescopes. The infrared spectral reflectances relative to 0.55 micron are 0.8 at 1.65 micron and 0.6 at 2.2 microns. Such absorption bands in the near infrared are not consistent with spectra of most rocks or minerals; even carbonaceous chondritic materials have nearly flat reflectances over this spectral region. Frosts, however, have strong absorption bands in the 1-3 microns region. In particular, the broadband infrared reflectances of Rhea are similar to those of the Galilean satellites Europa (J2) and Ganymede (J3) and also the rings of Saturn. Rhea's low density, high albedo and relatively flat reflectance from 0.3 to 1.1 micron as well as the low infrared reflectances reported here are consistent with the presence of water ice on Rhea's surface.

Johnson, T. V.↗
NASA NTRS1978

An infrared radiation routine for use in numerical atmospheric models

Previous methods for calculating radiative fluxes due to water vapor and CO2 absorption bands are extended to take into consideration the entire water vapor and CO2 bands, including e-type absorption in the window region and the overlapping of different absorptions. Cooling rate profiles in the water vapor bands for a tropical atmosphere were computed by a detailed line-by-line method and by a far-wing approximation method, and the error of both methods is less than 0.2 C/day. Cooling rate profiles in the 15 micron band including overlapping of CO2 absorption with water vapor were calculated by a method in which flux transmittance is computed by means of a linear expansion and the multiplication rule, and maximum errors of 0.3 C/day were found in comparison with the exact line-by-line method.

Chow, M.-D.↗
NASA NTRS1984

The dependence of reflectance spectra of Mercury on surface terrain

Reflectance spectra of Mercury covering the spectral range of 0.3-1.1 micron, obtained during 1963-1976, were examined for any correlations with surface terrain. Mercury's 6.1385-deg/day rotational rate, the phases of the planet around maximum elongations, and bidirectional-reflectance-spectroscopy theory were used to identify the surface area associated with each spectrum. Data from 1974-1975, rereduced with improved standard-star-flux ratios, show a weak absorption band in the near infrared not seen in earlier analyses. Older spectra suggest that the western longitudes of the unimaged side of Mercury are similar to the rest of the planet. Spectra of the intercrater plains in the 0-90-deg quadrant suggest a possible absorption band. Spectra of areas dominated by Caloris Basin with the encompassing smooth plains may show Fe(2+) abundances in the soil comparable to lunar-highlands soil. No striking differences between spectra of intercrater plains and smooth plains are found. The absorption features seen in spectra of Mercury are generally weaker than features seen in lunar spectra.

Vilas, F.↗
NASA NTRS2005

Experimental Near Infrared Spectroscopy of Polycyclic Aromatic Hydrocarbons Between 0.7 to 2.5 microns

The near infrared (NIR) spectra and absolute band strengths of 27 polycyclic aromatic hydrocarbon (PAH) cations and anions ranging in size from C14H10 to C50H22, are reported. The spectra from 0.7 to 2.5 microns (14,000 to 4000/cm) are presented for the fifteen PAHs ranging in size from C40H18 to C50H22 whereas the spectra of the remaining twelve span the narrower range from 0.7 to 1.1 microns (14,000 to 9000/cm). The spectra of all the ionized PAHs we have studied to date have strong, broad absorption bands in the NIR arising from electronic transitions. This work shows that ionized PAHs have significant absorption bands at longer wavelengths than predicted by the current astronomical models which consider PAHs in their treatment of the radiation balance of the interstellar medium. Two implications are 1)-ionized interstellar PAHs should add weak, broad band structure to the NIR portion of the interstellar extinction curve and 2)- UV poor radiation fields can pump the PAH emission bands provided ionized PAHs are present.

Mattioda, A. L.↗
NASA NTRS2021

Widely Distributed Exogenic Materials of Varying Compositions and Morphologies on Asteroid (101955) Bennu

Using the multiband imager MapCam on board the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft, we identified 77 instances of proposed exogenic materials distributed globally on the surface of the B-type asteroid (101955) Bennu. We identified materials as exogenic on the basis of an absorption near 1 μm that is indicative of anhydrous silicates. The exogenic materials are spatially resolved by the telescopic camera PolyCam. All such materials are brighter than their surroundings, and they are expressed in a variety of morphologies: homogeneous, breccia-like, inclusion-like, and others. Inclusion-like features are the most common. Visible spectrophotometry was obtained for 46 of the 77 locations from MapCam images. Principal component analysis indicates at least two trends: (i) mixing of Bennu's average spectrum with a strong 1-μm band absorption, possibly from pyroxene-rich material, and (ii) mixing with a weak 1-μm band absorption. The end member with a strong 1-μm feature is consistent with Howardite-Eucrite-Diogenite (HED) meteorites, whereas the one showing a weak 1-μm feature may be consistent with HEDs, ordinary chondrites, or carbonaceous chondrites. The variation in the few available near-infrared reflectance spectra strongly suggests varying compositions among the exogenic materials. Thus, Bennu might record the remnants of multiple impacts with different compositions to its parent body, which could have happened in the very early history of the Solar system. Moreover, at least one of the exogenic objects is compositionally different from the exogenic materials found on the similar asteroid (162173) Ryugu, and they suggest different impact tracks.

minor planets↗
NASA NTRS1992

On the correlated k-distribution method for radiative transfer in nonhomogeneous atmospheres

The paper discusses the correlated k(absorption coefficient)-distribution (CKD) method for radiative transfer in nonhomogeneous atmospheres, in terms of the physical and mathematical conditions under which this method is valid. The CKD approach is theoretically formulated, and the mathematical and physical conditions under which this method is valid are identified. The parameterization for incorporating pressure and temperature effects in the k distribution is presented. The errors of CKD for absorption bands in the solar and thermal infrared spectra are examined, and the errors due to both the CKD method and the use of the optimum number of quadrature points are identified. Finally, an overall treatment for various absorption bands is developed, which will provide high efficiency and accuracy.

Fu, Qiang↗
NASA NTRS1994

Detection of the SO2 atmosphere on Io with the Hubble Space Telescope

Observations of the trailing hemisphere of Io made with the Faint Object Spectrograph of the Hubble Space Telescope (HST) in March 1992 have resulted in the first detection of atmospheric SO2 absorption bands in the ultraviolet. These observations represent only the third positive means of detection of what is widely believed to be Io's primary atmospheric constituent. Below approximately 2130 A the geometric albedo of the satellite is dominated by SO2 gas absorption band signatures, which have been analyzed using models that include the effects of optical thickness, temperature, and spatial distribution. The disk-intergrated HST data cannot resolve the spatial distribution, but it is possible to define basic properties and set constraints on the atmosphere at the time of the observations. Hemispheric atmospheres with average column density N = 6 - 10 x 10(exp 15)/sq sm and T(gas) = 110 - 500 K fit the data, with preference for temperatures of approximately 200 - 250 K. Better fits are found as the atmosphere is spatially confined, with a limit of approximately 8% hemispheric areal coverage and N approximately equal to 3 x 10(exp 17)/sq cm with colder 110 - 250 K temepratures. A dense (N greater than or equal to 10(exp 16)/sq cm), localized component of SO2 gas, such as that possibly associated with active volcanoes, can generate the observed spectral constrast only when the atmosphere is cold (110 K) and an extended component such as Pele is included. The combination of a dense, localized atmosphere with a tenuous component (N less than 10(exp 16)/sq cm, either patchy or extended) also fits the data. In all cases the best fit models imply a disk-averaged column density larger than exospheric but approximately 10 - 30 times less than the previous upper limit from near-UV observations.

Ballester, G. E.↗
DOE OSTI2023

One dimensional temperature measurements by resonantly ionized photoemission thermometry of molecular nitrogen

This paper presents an extensive parameter study of a non-intrusive and non-seeded laser diagnostic method for measuring one dimensional (1D) rotational temperature of molecular nitrogen (N 2 ) at 165 - 450 K. Compared to previous efforts using molecular oxygen, here resonantly ionized and photoelectron induced fluorescence of molecular nitrogen for thermometry (N 2 RIPT) was demonstrated. The RIPT signal is generated by directly probing various rotational levels within the rovibrational absorption band of N 2 , corresponding to the 3-photon transition of N 2 ( X 1 Σ g + , v =0→ b 1 Π u , v ′ =6) near 285 nm, without involving collisional effects of molecular oxygen and nitrogen. The photoionized N 2 produces strong first negative band of N 2 + ( B 2 Σ u + − X 2 Σ g + ) near 390 nm, 420 nm, and 425 nm. Boltzmann analyses of various discrete fluorescence emission lines yield rotational temperatures of molecular nitrogen. By empirically choosing multiple rotational levels within the absorption band, non-scanning thermometry can be accurately achieved for molecular nitrogen. It is demonstrated that the N 2 RIPT technique can measure 1D temperature profile up to ∼5 cm in length within a pure N 2 environment. Multiple wavelengths are thoroughly analyzed and listed that are accurate for RIPT for various temperature ranges.

McCord, Walker (ORCID:0000000179747550)↗
NASA NTRS1972

Spectrophotometry /0.3 to 1.1 micron/ of visited and proposed Apollo lunar landing sites.

The study uses information gained by analysis of the spectral properties of lunar samples in the laboratory, and telescope spectra of over 100 lunar areas, to provide information regarding the composition and mineralogy of each proposed lunar landing site. Attention is given to (1) the presence of pyroxenes which cause an absorption band near 0.95 micron in the lunar reflection spectrum, (2) the proportion of crystalline to glassy material present in the soil which is derived from the slope of the reflectivity curve between 0.4 and 0.7 micron and the strength of the 0.95 micron absorption band, and (3) the presence of Ti(3+) ions in the glasses on the lunar surface, which affects the reflection spectrum at blue and ultraviolet wavelengths.

Mccord, T. B.↗
NASA NTRS1991

The composition of Phobos: Meteorite analogs based on KRFM and VSK spectral data from the Phobos 2 spacecraft

In 1989 the Phobos 2 spacecraft obtained 8-channel 0.3 to 0.6 mm KRFM spectra and two-channel wide-angel TV VSK images in bandpasses of 0.40 to 0.56 mm and 0.78 to 1.10 mm. The TV data were used to map four color ratio units on disk-resolved images of Phobos, and were combined with the KRFM spectra to analyze possible meteorite analogs for the mapped units. A total of 58 spectra of 39 meteorites were studied for similarities with Phobos data in spectral shape, absorption features, and visible near-IR color ratio. Analysis of the spectral data show that, among the meteorites studied, there are no unique spectral analogs for Phobos surface material. Currently, the closest spectral analogs are the optically altered black chondrite meteorites Gorlovka and Pervomaisky. The weak UV absorption bands in some KRFM spectra and the red slope in VSK color-ratio data indicate that carbonaceous chondrite-like material may also be a component of Phobos surface material. However, the lack of close carbonaceous chondrite spectral analogs and the existence of apparent absorption bands in KRFM spectra that are not seen in meteorite spectra suggest that there are processes and/or materials on the surface of Phobos that are not represented in the meteorite collections. The similarities between KRFM spectra of Phobos and the spectra of black chondrites suggest that optically altered mafic silicates may constitute a component of the surface material of Phobos, and that optical alteration and mixing by regolith processes may be an important factor in the evolution of Phobos surface material.

Britt, D. T.↗
NASA NTRS1974

Spectral reflectance of 72275 from Boulder 1, Station 2, Apollo 17

Spectral reflectance measurements were made of samples 72275,103 (chip) and 72275,98 (saw cuttings). Both the chips and the cuttings consist mainly of friable feldspathic breccia. Sample 72275,103, a chip taken from eastend piece 72275,27, is rich in gray polymict breccia. The saw cuttings were derived from the entire rock, but they are probably strongly biased toward the friable feldspathic matrix material that has been preferentially disaggregated. The spectra of both samples show two prominent absorption bands arising from Fe2(+) in pyroxene. The depths of these bands are large enough to preclude the presence of much glass or opaque material in the samples. From the spectral properties alone, it is clear that the samples are not soil breccias nor vitric breccias, as, of course, has been verified by petrography. The wavelengths of the principal absorption bands plot on the pyroxene trend, indicating that orthopyroxene is spectrally dominant.

Adams, J. B.↗
NASA NTRS1994

Quantitative reflectance spectroscopy of buddingtonite from the Cuprite mining district, Nevada

Buddingtonite, an ammonium-bearing feldspar diagnostic of volcanic-hosted alteration, can be identified and, in some cases, quantitatively measured using short-wave infrared (SWIR) reflectance spectroscopy. In this study over 200 samples from Cuprite, Nevada, were evaluated by X ray diffraction, chemical analysis, scanning electron microscopy, and SWIR reflectance spectroscopy with the objective of developing a quantitative remote-sensing technique for rapid determination of the amount of ammonium or buddingtonite present, and its distribution across the site. Based upon the Hapke theory of radiative transfer from particulate surfaces, spectra from quantitative, physical mixtures were compared with computed mixture spectra. We hypothesized that the concentration of ammonium in each sample is related to the size and shape of the ammonium absorption bands and tested this hypothesis for samples of relatively pure buddingtonite. We found that the band depth of the 2.12-micron NH4 feature is linearly related to the NH4 concentration for the Cuprite buddingtonite, and that the relationship is approximately exponential for a larger range of NH4 concentrations. Associated minerals such as smectite and jarosite suppress the depth of the 2.12-micron NH4 absorption band. Quantitative reflectance spectroscopy is possible when the effects of these associated minerals are also considered.

Felzer, Benjamin↗
NASA NTRS2011

Spectral Kernel Approach to Study Radiative Response of Climate Variables and Interannual Variability of Reflected Solar Spectrum

The radiative kernel approach provides a simple way to separate the radiative response to different climate parameters and to decompose the feedback into radiative and climate response components. Using CERES/MODIS/Geostationary data, we calculated and analyzed the solar spectral reflectance kernels for various climate parameters on zonal, regional, and global spatial scales. The kernel linearity is tested. Errors in the kernel due to nonlinearity can vary strongly depending on climate parameter, wavelength, surface, and solar elevation; they are large in some absorption bands for some parameters but are negligible in most conditions. The spectral kernels are used to calculate the radiative responses to different climate parameter changes in different latitudes. The results show that the radiative response in high latitudes is sensitive to the coverage of snow and sea ice. The radiative response in low latitudes is contributed mainly by cloud property changes, especially cloud fraction and optical depth. The large cloud height effect is confined to absorption bands, while the cloud particle size effect is found mainly in the near infrared. The kernel approach, which is based on calculations using CERES retrievals, is then tested by direct comparison with spectral measurements from Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) (a different instrument on a different spacecraft). The monthly mean interannual variability of spectral reflectance based on the kernel technique is consistent with satellite observations over the ocean, but not over land, where both model and data have large uncertainty. RMS errors in kernel ]derived monthly global mean reflectance over the ocean compared to observations are about 0.001, and the sampling error is likely a major component.

Jin, Zhonghai↗
NASA NTRS1986

Quantitative photoabsorption and fluorescence study of HCl in vacuum ultraviolet

The photoabsorption and fluorescence cross sections of HCl were measured in the 106-185 nm region. Sharp absorption bands appear at wavelengths shorter than 135 nm, and fluorescence occurs at several excited states. The fluorescence cross sections are generally quite small, indicating that the excited states are strongly predissociative. The molecular processes for producing the VUV and UV fluorescences are investigated, and the Rydberg characteristics of the strong absorption bands are discussed.

Nee, J. B.↗