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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The effects of soil moisture, surface roughness, and vegetation on L-band emission and backscatter

Measurements performed with SIR-B at 1.28 GHz and an airborne multiple-beam push-broom radiometer at 1.4 GHz over agricultural fields near Fresno, California are examined. A theoretical model (Kirchhoff approximation) was used to assess the effects of surface roughness and vegetation (alfalfa and lettuce) with respect to the responses of microwave emission and backscatter to soil-moisture variations. It is found that the surface roughness plays a dominant role compared to the vegetation cover in the microwave backscatter.

Wang, James R.↗
NASA NTRS2003

Wavelength Shifts of the 7.7 Micron Emission Band in Reflection Nebulae

Using spatial-spectral data cubes of reflection nebulae obtained by ISOCAM, we have observed a shift in the central wavelength of the 7.7 micron band within several reflection nebulae. The band shifts progressively from approx. 7.8 microns near the edge of the nebulae to approx. 7.6 microns towards the center of the nebulae. The ratio of the 11.3/7.7 micron bands also changes with distance from the central star, first rising from the center towards the edge of the nebula, then falling at the largest distances from the star, consistent with the 11.3/7.7 micron band ratio being controlled by the PAH ionization state. The behavior of the 7.7 micron band center can be explained either by assuming that anions are the origin of the 7.85 micron band and cations the 7.65 micron band, or that the band center wavelength depends on the chemical nature of the PAHs.

Bregman, Jesse↗
NASA NTRS2022

SNPP and N20 VIIRS Thermal Emissive Bands Calibration Comparison Using the GEO-LEO Double Difference Method

The VIIRS instruments onboard the SNPP and NOAA-20 satellites have identical spatial resolutions and the same spectral bands. Similar prelaunch tests and identical on-orbit calibration algorithms established the foundation for their consistent Earth measurements. Calibration assessment and consistency comparisons are useful to maintain their performance and measurement accuracy. Simultaneous nadir overpasses (SNO) between two satellites are commonly used for a direct calibration comparison between sensors. However, there are no SNO between SNPP and NOAA20. Hence, a reference sensor or Earth measurements are normally used to bridge the comparison. As a reference, we focus on the Advanced Baseline Imager (ABI) onboard the GOES-R series spacecraft and its application to the SNPP and NOAA-20 VIIRS comparison. GOES16 and GOES17are the first two satellites of the GOES-R series and were launched on November 19, 2016, and March 12, 2018, respectively. Their operational positions are on the equator with longitudes of 75.2° West over land and 137.2° West over ocean, respectively. The ABI is the primary imaging instrument of these spacecrafts for the Earth’s weather, oceans, and environment, with observations (every 10 minutes) that provide vast data for GEO-Low Earth orbit (LEO)and LEO-LEO comparisons utilizing it as an intermediate reference sensor. VIIRS and ABI have spectrally matched bands and can have simultaneous measurements over any selected site every day. The simultaneous measurements over the same site also have various scan angles. These features provide advantages for a VIIRS-to-ABI comparison. The spectral response function difference between instruments, sites selected, and view angles will have effects on the instrument measurements. Their impacts on the calibration comparison, including the use of double differences, will be discussed. By collecting VIIRS measurements over a large range of view angles, the view angle effect will also be investigated. The collection of an ample amount of data provides an advantage for statistical analyses and potential big data applications to sensor calibration assessments. This method can also be applied to other sensor calibration comparison and performance assessments, such as GOES16 and GOES17 ABI, and Terra and Aqua MODIS.

Tiejun Chang↗
DOE OSTI2025

Novel white light-emitting CdSe:Mn 2+ synthesized by photo-assisted chemical bath deposition

Nowadays, white light-emitting materials have attracted extensive research due to their potential applications in lighting devices and displaying images. Several semiconductor nanoparticles have been explored to achieve efficient white light emission. In this work, we report on novel white light-emitting CdSe:Mn 2+ thin films synthesized by photo-assisted chemical bath deposition. The effect of varying the Mn 2+ ion concentrations on the thin film structure, morphology, and optical properties was investigated. X-ray powder diffraction results indicated that all the films annealed at 250 degrees C possessed a cubic structure, with crystallite sizes in the range of 1-130 nm. Scanning electron microscopy demonstrated spherical nanoparticles with no significant changes with varying Mn 2+ doping concentrations. Energy dispersive X-ray spectroscopy confirmed the presence of the anticipated elements. The atomic force microscope revealed that the surface roughness has decreased with an increase in Mn 2+ ion concentrations but decreased for 0.7 %Mn 2+ . The UV-Vis absorption spectra showed absorption edges around 600-650 nm. Photoluminescence emission spectra excited at 3.8 eV (325 nm) showed emission bands at around 1.75 eV (709 nm), and 1.88 eV (659 nm), which were attributed to the band-to-band emission, and 4 T 1 ( 4 G)-> 6 A 1 ( 6 S) transitions of Mn 2+ ions, respectively, while emission bands at 2.35 eV (528 nm), and prominent at 3.17 eV (391 nm) were due to the glass substrate. The temperature-dependent luminescence showed a decrease in relative emission intensity with the increase in the operating temperature. The chromaticity colour coordinates showed white light-emitting thin films. These present findings open a new door to developing white light using CdSe thin films.

36 MATERIALS SCIENCE↗
NASA NTRS1976

High resolution spectral analysis of the Jovian decametric radiation. II - The band-like emissions

Analysis of the bandlike Jovian decametric emission is presented. A model for the active region that accounts for the observed radiation characteristics is described using the measured parameters of the bandlike emission and a model of the Jovian magnetic field. The active region is characterized not only by the fact that an upward-flowing electron stream is caused to radiate in this region, but the stream itself is broken into radiating electron bunches within the active region. Observed undulations of the emission band on the time-frequency plane are interpreted as motions of the active region along a flux tube. The instantaneous location of the active region along the flux tube shows a dependence on the density of the stream entering the active region. The mechanism responsible for density modulation of the stream appears to be common to both the bandlike and simple-S-burst emission types.

Flagg, R. S.↗
NASA NTRS1986

3 micron spectroscopy of comet Halley (1982i)

Near-infrared spectroscopy and photometry was obtained of comet Halley in December 1985 when its heliocentric distance was 1.19 AU. No water ice absorption or molecular band emission were observed. The interstellar 3.3-micron emission band was also not observed. The 3-micron spectrum of comet Halley consisted of scattered sunlight at wavelengths less than 3.1 microns and of thermal emission by dust at longer wavelengths.

Tokunaga, A. T.↗
NASA NTRS1981

Frequency band broadening of magnetospheric VLF emissions near the equator

The broadening of the whistler mode VLF emission band has frequently been observed by the equatorially orbiting S3-A (Explorer 45) satellite outside the midnight sector of the plasmasphere, during periods of geomagnetic disturbance. Prior to the broadening, the band of this emission is narrow with a sharp gap at the half electron gyrofrequency. The gradual broadening of the emission band on the low-frequency side is associated with the simultaneously observed spreading of the anisotropy of the ring current electrons to higher and wider energy ranges. Using the modeled distribution function, the linear growth rates of the cyclotron instability are calculated numerically. The results suggest that broadening of the VLF emission band near the plasmasphere can be caused by spreading of the ring current electron anisotropy toward higher energies.

Maeda, K.↗
NASA NTRS1991

3.3 micron emission from ultraviolet excitation of some aromatic molecules

Infrared emissions are observed from photoexcitation of benzene, naphthalene, phenanthrene, anthracene, pyrene, and their methyl derivatives in the gas phase at 193 nm using an ArF laser as a light source. An emission band with peak at 3.3 microns is observed from all the molecules studied. This band is attributed to the aromatic C-H stretching vibrational modes. In addition to the 3.3-microns band, an emission band at 3.4-3.6 microns is observed from photoexcitation of the methyl derivatives, which is attributed to the C-H stretching vibrational modes of the CH3 group. The observed spectra are compared with the IR emission bands observed in many astronomical objects. The current laboratory data lend support to a model in which PAH molecules are responsible for the 'unidentified' interstellar IR emissions. IR emissions from the 193-nm excitation of several interstellar molecules other than PAHs are also observed, but they are quite different from the interstellar IR bands.

Shan, Jun↗
NASA NTRS2002

C-H Hot Bands in the Near-IR Emission Spectra of Leonids

The reported infrared (IR) emission spectra from 1999 Leonid fireballs show a 3.4 micron C-H emission band and unidentified bands at longer wavelengths. Upon atmospheric entry, the Leonid meteorites were flash-heated to temperatures around 2400K, which would destroy any organics on the surface of the meteorite grains. We propose that the nu(sub )CH emission band in the Leonid emission spectra arises from matrix-embedded C(sub n)-H-O entities that are protected from instant pyrolysis. Our model is based on IR absorption nu(sub )CH bands, which we observed in laboratory-grown MgO and natural olivine single crystals, where they arise from C(sub n)-H-O units imbedded in the mineral matrix, indicative of aliphatic -CH2- and -CH3 organics. Instead of being pyrolyzed, the C(sub n)-H-O entities in the Leonid trails become vibrationally excited to higher levels n = 1, 2, 3 etc. During de-excitation they emit at 3.4 microns, due to the (0 => 1) transition, and at longer wavelengths, due to hot bands. As a first step toward verifying this hypothesis we measured the C-H vibrational manifold of hexane (C6H14). The calculated positions of the (2 => l ) , (3 => 2), and possibly (4 => 3) hot bands agree with the Leonid emission bands at 3.5, 3.8 and 4.l microns.

Freund, F. T.↗
DOE OSTI2022

Triple Emission of 5'-( para -R-Phenylene)vinylene-2-(2'-hydroxyphenyl)benzoxazole (PVHBO). Part I: Dual Emission from the Neutral Species

The effects of 5'-(para-R-phenylene)vinylene (PV) substituents on the emission properties of 2-(2'-hydroxyphenyl)benzoxazole (HBO) are analyzed using steady-state and time-resolved absorption and emission spectroscopies in addition to quantum chemical calculations. All members in the series of PVHBOs are capable of excited-state intramolecular proton transfer (ESIPT) with a solvent sensitivity that is typical of a HBO derivative to produce a normal (aka enol) emission and an excited-state tautomer (aka keto) emission. These two emission bands of the neutral dyes are discussed in the current paper. The intermolecular proton transfer, i.e., the deprotonation, of a PVHBO results in the third band of the triple emission, which is described in the succeeding paper. The placement of an electron-withdrawing substituent R on the PVHBO scaffold increases the intensity of the keto emission relative to the enol emission in hydrogen-bonding solvents. The R substituents do not significantly alter the wavelengths of the enol and keto emission bands, which are located in the blue and green regions, respectively, of the visible spectrum. The ultrafast time-resolved spectroscopies and quantum chemical calculations offer explanations on how the R group and the solvent affect the enol and keto emission properties (i.e., wavelength, lifetime, fluorescence quantum yield, and relative ratio of their emissions). Here, the key findings include the following: (1) the emission energies of both enol and keto forms are not sensitively dependent on the R substituent and (2) the solvent-engaged enol excited state is quenched more efficiently as the R substituent becomes more electron-withdrawing. A PVHBO acts as a fusion of HBO and stilbenoid that intersect at the hydroxyphenyl moiety. Depending on the solvent and other environmental conditions, PVHBOs may exhibit the ESIPT property of HBO or the substituent-dependent emission of stilbenoid. This paper and the succeeding article provide a photophysical model of PVHBOs to explain the wavelengths and relative abundances of the three emission bands (enol, keto, and anion) that these compounds are able to produce. Judicial selection of the environmental factors may drive the emission of a PVHBO into the spectral regions of blue, green, and, in a couple of cases, orange or red.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2006

An Overview of Inter-comparison Methodologies for Terra and Aqua MODIS Calibration

With increasing efforts on data fusion and long-term climate data records (CDR) using observations made by multiple sensors, on the same or different platforms, their cross-calibration and validation work has become more and more important. The uncertainties of the climate models and data records depend not only on the calibration quality of individual sensors but also on their calibration consistency. This paper provides an overview of methodologies used by the MODIS Characterization Support Team (MCST) at NASA GSFC for the inter-comparison studies of Terra and Aqua MODIS on-orbit calibration. Each MODIS was built with a set of onboard calibrators (OBC) that include a blackbody (BB), a solar diffuser (SD), and a solar diffuser stability monitor (SDSM). The BB is primarily used for the thermal emissive bands (TEB) calibration and the SD/SDSM system for the reflective solar bands (RSB) calibration. Although the-instrument design and calibration approach are nearly identical for both Terra and Aqua MODIS and they all went through an extensive and similar pre-launch calibration and characterization process, still their on-orbit calibration consistency needs to be carefully examined and validated as many science products have been generated from observations made by both instruments. Methodologies discussed in this paper include inter-comparison studies using the Moon, a third sensor, and ground targets. Our results show that Terra and Aqua reflective solar bands and thermal emissive bands have been calibrated consistently with excellent long-term stabilities. For the 11 and 12 micrometers sea surface temperature (SST) bands, the calibration difference of Terra and Aqua MODIS is less than 0.2K.

Xiong, X.↗
NASA NTRS2024

Morphology and Luminescence Properties of Transition Metal Doped Zinc Selenide Crystals

Zinc selenide is an excellent matrix material to dope with rare-earth and transition metal to achieve mid-infrared luminescence to develop high power lasers. The luminescence, morphology and refractive index is significantly affected by the doping and defects generated due to size and valency of dopants, concentration, growth process and convection during the growth. The aim of the study is to investigate effect of point and line defects generated due to low doping of iron and chromium on the emission and morphology of the zinc selenide. Luminescence and morphological properties of large iron and chromium doped zinc selenide single crystals were studied to evaluate the effect of extremely low residual impurities and defects associated with the doping process. The emission properties following both short wavelength (i.e., ultraviolet; 350 – 370 nm) excitation and longer wavelength (i.e., near infrared; 850 – 870 nm) excitation were characterized. Luminescence emission bands were identified in both doped crystals. In addition to the primary emission bands, satellite peaks and intra-center transitions were also observed. Due to local population defects associated with the residual impurities (ppm to ppb) in the Fe-ZnSe and Cr-ZnSe crystals, peak emission wavelengths were observed to shift. Raman studies using 266 and 532 – nm excitation revealed different positions of longitudinal and transverse peaks for Fe-ZnSe and Cr-ZnSe crystals, associated with different levels of defects due to the different ion sizes. The emission bands were found to decrease in intensity due to recombination of residual impurity co-dopants and complex defects generated during growth and fabrication. Cryogenic temperature analyses revealed a very clean emission band due to freezing of some of the point and line defects. An emission band observed at 980 nm for both crystals at room temperature as well as cryogenic temperatures indicates a vibronic peak in ZnSe. The scanning electron microscopy (SEM) images of the local morphology support the conclusion that small crystallites in doped crystals are also present.

Zinc selenide↗
DOE OSTI2025

Demonstrating the impact of ro-vibrationally excited H 2 on divertor detachment via population modelling

EDGE2D-EIRENE profiles characteristic for low recycling, high recycling and detached plasmas are postprocessed applying a vibrationally resolved collisional radiative (CR) model based on the Yacora solver to predict excited state densities and thus the molecular Lyman-, Werner- and Fulcher band emission intensities. These emission intensities are compared to predictions from the AMJUEL database standardly used in EIRENE. Lower Fulcher band and higher Lyman- and Werner band emission is predicted by the Yacora model in comparison to AMJUEL suggesting that inconsistent results from model based evaluation of measured spectra are expected depending on which model and molecular emission band is considered. The implications on detachment rate predictions are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗