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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Intense radio outburst from the supermassive star Eta Carinae

On five occasions between 1992 June 29 and 1994 May 3, we have used the Australia Telescope Compact Array (ATCA) to image Eta Carinae at a wavelength of 3 cm and a resolution of 1 arcsec. These observations have revealed remarkable activity. Since 1992 June, the total flux density has increase from 0.8 to 2.2 Jy, and the original single compact source has grown to a complex of sources spread over an area of about 16 sq arcsec. Strong hydrogen recombination-line spectral emission has appeared at the site of the strongest of these new sources. This recombination emission has the largest spectral width ever observed from a star, +/- 250 km/s, and reveals gas with turbulent velocities as great as 250 km/s approaching us at an average velocity of about 200 km/s. We believe that this radio outburst has been caused by a more than threefold increase of ultraviolet luminosity, and consequent ionization of previously neutral gas clouds.

Duncan, R. A.↗
NASA NTRS2011

Improved Surface and Tropospheric Temperatures Determined Using Only Shortwave Channels: The AIRS Science Team Version-6 Retrieval Algorithm

The Goddard DISC has generated products derived from AIRS/AMSU-A observations, starting from September 2002 when the AIRS instrument became stable, using the AIRS Science Team Version-5 retrieval algorithm. The AIRS Science Team Version-6 retrieval algorithm will be finalized in September 2011. This paper describes some of the significant improvements contained in the Version-6 retrieval algorithm, compared to that used in Version-5, with an emphasis on the improvement of atmospheric temperature profiles, ocean and land surface skin temperatures, and ocean and land surface spectral emissivities. AIRS contains 2378 spectral channels covering portions of the spectral region 650 cm(sup -1) (15.38 micrometers) - 2665 cm(sup -1) (3.752 micrometers). These spectral regions contain significant absorption features from two CO2 absorption bands, the 15 micrometers (longwave) CO2 band, and the 4.3 micrometers (shortwave) CO2 absorption band. There are also two atmospheric window regions, the 12 micrometer - 8 micrometer (longwave) window, and the 4.17 micrometer - 3.75 micrometer (shortwave) window. Historically, determination of surface and atmospheric temperatures from satellite observations was performed using primarily observations in the longwave window and CO2 absorption regions. According to cloud clearing theory, more accurate soundings of both surface skin and atmospheric temperatures can be obtained under partial cloud cover conditions if one uses observations in longwave channels to determine coefficients which generate cloud cleared radiances R(sup ^)(sub i) for all channels, and uses R(sup ^)(sub i) only from shortwave channels in the determination of surface and atmospheric temperatures. This procedure is now being used in the AIRS Version-6 Retrieval Algorithm. Results are presented for both daytime and nighttime conditions showing improved Version-6 surface and atmospheric soundings under partial cloud cover.

Susskind, Joel↗
DOE OSTI2020

Self-radiography of imploded shells on OMEGA based on additive-free multi-monochromatic continuum spectral analysis

Radiographs of pure-DT cryogenic imploding shells provide critical validation of progress toward ignition-scalable performance of inertial confinement fusion implosions. Cryogenic implosions on the OMEGA Laser System can be self-radiographed by their own core spectral emission near ≈2 keV. Utilizing the distinct spectral dependences of continuum emissivity and opacity, the projected optical-thickness distribution of imploded shells, i.e., the shell radiograph, can be distinguished from the structure of the core emission distribution in images.Importantly, this can be done without relying on spectral additives (shell dopants), as in previous applications of implosion self-radiography. Furthermore, demonstrations with simulated data show that this technique is remarkably well-suited to cryogenic implosions and can also be applied to self-radiography of imploded room-temperature CH shells at higher spectral energy (hv ≈ 3–5 keV) based on the very similar continuum spectrum of carbon. Experimental demonstration of additive-free self-radiography with warm CH shell implosions on OMEGA will provide an important proof of principle for future applications to cryogenic DT implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2010

Hyperspectrally-Resolved Surface Emissivity Derived Under Optically Thin Clouds

Surface spectral emissivity derived from current and future satellites can and will reveal critical information about the Earth s ecosystem and land surface type properties, which can be utilized as a means of long-term monitoring of global environment and climate change. Hyperspectrally-resolved surface emissivities are derived with an algorithm utilizes a combined fast radiative transfer model (RTM) with a molecular RTM and a cloud RTM accounting for both atmospheric absorption and cloud absorption/scattering. Clouds are automatically detected and cloud microphysical parameters are retrieved; and emissivity is retrieved under clear and optically thin cloud conditions. This technique separates surface emissivity from skin temperature by representing the emissivity spectrum with eigenvectors derived from a laboratory measured emissivity database; in other words, using the constraint as a means for the emissivity to vary smoothly across atmospheric absorption lines. Here we present the emissivity derived under optically thin clouds in comparison with that under clear conditions.

Zhou, Daniel K.↗
NASA NTRS1989

Infrared spectroscopy (2.3-20 microns) for the geological interpretation of remotely-sensed multispectral thermal infrared data

The spectral radiance and spectral reflectance of natural weathered surfaces of common sedimentary and igneous rocks is determined from in situ and in the laboratory measurements. In situ spectral radiance measurements (5-14 microns) were made with a portable spectral radiometer and were used to derive the spectral emissivity of the rocks. The spectral reflectance measurements (2.3-20 microns) were made in a laboratory with a Fourier transform IR spectrometer with a diffuse reflectance accessory. Good agreement is found between the two techniques. The field portable spectrometer has a larger field of view and the in situ data provide more accurate measurements of the intensity of spectral features related to temperature and atmospheric effects.

Bartholomew, Mary Jane↗
NASA NTRS1997

Feasibility Investigation for Performing Fireball Temperature Tests

NASA Johnson Space Center White Sands Test Facility (WSTF) was requested by the Launch Abort Subpanel and the Power Systems Subpanel of the Interagency Nuclear Safety Review Panel to investigate the feasibility of using spectroscopic techniques to measure propellant fireball gas temperatures. This report outlines the modeling and experimental approaches and results of this investigation. Descriptions of the theoretical particle temperature and mass effusion models are presented along with the results of the survivability of small plutonium dioxide (less than or equal to 1000 microns diameter) particles entrained in various propellant fireball scenarios. The experimental test systems used to measure the hydroxide radical, water, and particle graybody spectral emissions and absorptions are discussed. Spectral results along with temperatures extracted by analyzing the spectral features are presented for the flames investigated in the laboratory environment. Methods of implementing spectroscopic measurements for future testing using the WSTF Large-scale Hydrogen/Oxygen Explosion Facility are discussed, and the accuracy expected for these measurements is estimated from laboratory measurements.

Tapphorn, Ralph M.↗
NASA NTRS2012

Deriving Plasma Densities and Elemental Abundances from SERTS Differential Emission Measure Analysis

We use high-resolution spectral emission line data obtained by the SERTS instrument during three rocket flights to demonstrate a new approach for constraining electron densities of solar active region plasma.We apply differential emission measure (DEM) forward-fitting techniques to characterize the multithermal solar plasma producing the observed EUV spectra, with constraints on the high-temperature plasma from the Yohkoh Soft X-ray Telescope. In this iterative process, we compare line intensities predicted by an input source distribution to observed line intensities for multiple iron ion species, and search a broad range of densities to optimize chi-square simultaneously for the many available density-sensitive lines. This produces a density weighted by the DEM, which appears to be useful for characterizing the bulk of the emitting plasma over a significant range of temperature. This "DEM-weighted density" technique is complementary to the use of density-sensitive line ratios and less affected by uncertainties in atomic data and ionization fraction for any specific line. Once the DEM shape and the DEM-weighted density have been established from the iron lines, the relative elemental abundances can be determined for other lines in the spectrum. We have also identified spectral lines in the SERTS wavelength range that may be problematic

corona↗
NASA NTRS1963

BLACK RADIATION DETECTOR

Efficiency of conical calorimeter for detecting black body radiation, based on spectral emissivity and reflectance measurements

SPECTRAL EMISSION↗
NASA NTRS1972

Emission polarization study on quartz and calcite.

Calculation of the spectral emission polarization of quartz and calcite polished plates for observation angles of 20 and 70 deg by the substitution of complex index of refraction values for each mineral into Fresnel's equations. The emission polarization is shown to be quite wavelength-dependent, demonstrating that selected narrow or medium-width spectral bands exhibit a significantly higher percentage of polarization than a broad spectral band for these two minerals. Field measurements with a broadband infrared radiometer yield polarizations on the order of 2% for a coarse-grained granite rock and beach sand (both quartz-rich). This implies that a more sensitive detector with a selected medium-width filter may be capable of measuring emission polarization accurately enough to make this parameter useful as a remote sensing tool for discrimination among rocks on the basis of texture.

Vincent, R. K.↗
NASA NTRS2012

Monitoring Surface Climate With its Emissivity Derived From Satellite Measurements

Satellite thermal infrared (IR) spectral emissivity data have been shown to be significant for atmospheric research and monitoring the Earth fs environment. Long-term and large-scale observations needed for global monitoring and research can be supplied by satellite-based remote sensing. Presented here is the global surface IR emissivity data retrieved from the last 5 years of Infrared Atmospheric Sounding Interferometer (IASI) measurements observed from the MetOp-A satellite. Monthly mean surface properties (i.e., skin temperature T(sub s) and emissivity spectra epsilon(sub v) with a spatial resolution of 0.5x0.5-degrees latitude-longitude are produced to monitor seasonal and inter-annual variations. We demonstrate that surface epsilon(sub v) and T(sub s) retrieved with IASI measurements can be used to assist in monitoring surface weather and surface climate change. Surface epsilon(sub v) together with T(sub s) from current and future operational satellites can be utilized as a means of long-term and large-scale monitoring of Earth 's surface weather environment and associated changes.

Zhou, Daniel K.↗
DOE OSTI2022

Establishing temperature from radiance of dynamically compressed metals

Precise temperature determination is a significant challenge in extreme environments of dynamic compression studies. How can radiance measurements taken in high-pressure shock experiments constrain temperature in a meaningful and physically consistent way? Experiments maintaining sample compression against a transparent window can be tailored to present a uniform measurement area with uncertain spectral emissivity. We compare several methods to analyze radiance collected at multiple wavelengths, applying statistical methods and physical principles to improve temperature inference. With proper radiance collection and analysis, dynamic temperature uncertainties become comparable to thermomechanical ambiguities of the emitting surface.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Surface plasmon dispersion analysis in the metal-oxide-metal tunnel diode

A detailed model of surface plasmon dispersion in the metal-oxide-metal tunnel diode is presented in order to clarify the spectral emission from this diode. The model predicts the location of the spectral peaks and the emission between the peaks by considering the effects of retardation on the surface plasmon. A nonradiative mode is found to play a major role in the transition from the visible to UV peaks in the diode spectra.

Donohue, J. F.↗