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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Visible and infrared polarization ratio spectroreflectometer

The instrument assists in determining the refractive index and absorption index, at different spectral frequencies, of a solid sample by illuminating the sample at various angles in incidence and measuring the corresponding reflected intensities at various spectral frequencies and polarization angles. The ratio of the intensity of the reflected light for parallel polarized light to that for perpendicular polarized light at two different angles of incidence can be used to determine the optical constants of the sample. The invention involves an apparatus for facilitating the utilization of a wide variety of angles of incidence. The light source and polarizing element are positioned on an outer platform; the sample is positioned on an inner platform. The two platforms rotate about a common axis and cooperate in their rotation such that the sample is rotated one degree for every two degrees of rotation of the light source. This maintains the impingement of the reflected light upon the detector for any angle of incidence without moving or adjusting the detector which allows a continuous change in the angle of incidence.

Batten, C. E.↗
NASA NTRS1979

Determination of the ground albedo and the index of absorption of atmospheric particulates by remote sensing. I - Theory

A statistical technique is developed for inferring the optimum values of the ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates. The procedure compares measurements of the ratio of the hemispheric diffuse to directly transmitted solar flux density at the earth's surface with radiative transfer computations of the same as suggested by Herman et al. (1975). A detailed study is presented which shows the extent to which the ratio of diffuse to direct solar radiation is sensitive to many of the radiative transfer parameters. Results indicate that the optical depth and size distribution of atmospheric aerosol particles are the two parameters which uniquely specify the radiation field to the point where ground albedo and index of absorption can be inferred. Varying the real part of the complex refractive index of atmospheric particulates as well as their vertical distribution is found to have a negligible effect on the diffuse-direct ratio. The statistical procedure utilizes a semi-analytic gradient search method from least-squares theory and includes a detailed error analysis.

King, M. D.↗
NASA NTRS1979

Determination of the ground albedo and the index of absorption of atmospheric particulates by remote sensing. II - Application

A hemispherical radiometer has been used to obtain spectrally narrow-band measurements of the downward hemispheric diffuse and total (global) flux densities at varying solar zenith angles on 14 days over Tucson. Data are presented which illustrate the effects of temporally varying atmospheric conditions as well as clear stable conditions on the ratio of the diffuse to direct solar radiation at the earth's surface. The ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates are derived from the diffuse-direct ratio measurements on seven clear stable days at two wavelengths using the statistical procedure described by King and Herman (1979). Results indicate that the downwelling diffuse radiation field in the midvisible region in Tucson can be adequately described by Mie scattering theory if the ground albedo is 0.279 + or - 0.100 and the index of absorption is 0.0306 + or - 0.0082.

King, M. D.↗
NASA NTRS1977

Complex refractive index of Martian dust - Wavelength dependence and composition

The size distribution and complex refractive index of Martian dust-cloud particles observed in 1971 with the Mariner 9 UV spectrometer are determined by matching the observed single-scattering albedo and phase function with Mie-scattering calculations for size distributions of spheres. Values of phase function times single-scattering albedo are presented for 12 wavelength intervals in the range from 190 to 350 nm, and best-fit values are obtained for the absorption index. It is found that the absorption index of the dust particles increases with decreasing wavelength from 350 to about 210 nm and then drops off shortward of 210 nm, with a structural shoulder occurring in the absorption spectrum between 240 and 250 nm. A search for a candidate material that can explain the strong UV absorption yields TiO2, whose anatase polymorph has an absorption spectrum matching that of the Martian dust. The TiO2 content of the dust particles is estimated to be a few percent or less.

Pang, K.↗
NASA NTRS1987

Investigation of PTFE transfer films by infrared emission spectroscopy and phase-locked ellipsometry

When a PTFE sheet was rubbed unidirectionally over a smooth surface of stainless steel an essentially monomolecular transfer film was formed. By ellipsometric and emission infrared spectroscopic techniques it was shown that the film was 10 to 15 A thick and birefringent. From the intensity differences of infrared bands obtained with a polarizer passing radiation polarized in mutually perpendicular planes, it was possible to deduce transfer film orientation with the direction of rubbing. After standing in air for several weeks the transfer films apparently increased in thickness by as much as threefold. At the same time both the index of refraction and the absorption index decreased. Examination of the surfaces by optical and electron microscopies showed that the films had become porous and flaky. These observations were consistent with previous tribological measurements. The coefficients of friction decreased with the formation of the transfer film but increased again as the film developed breaks. The applicability of the ellipsometric and polarized infrared emission techniques to the identification of monomolecular tribological transfer films of polymers such as PTFE has been demonstrated.

Lauer, James L.↗
NASA NTRS1988

Investigation of PTFE transfer films by infrared emission spectroscopy and phase-locked ellipsometry

When a PTFE sheet was rubbed unidirectionally over a smooth surface of stainless steel an essentially monomolecular transfer film was formed. by ellipsometric and emission infrared spectroscopic techniques it was shown that the film was 10 to 15 A thick and birefringent. From the intensity differences of infrared bands obtained with a polarizer passing radiation polarized in mutually perpendicular planes, it was possible to deduce transfer film orientation with the direction of rubbing. After standing in air for several weeks the transfer films apparently increased in thickness by as much as threefold. At the same time both the index of refraction and the absorption index decreased. Examination of the surfaces by optical and electron microscopies showed that the films had become porous and flaky. These observations were consistent with previous tribological measurements. The coefficients of friction decreased with the formation of the transfer film but increased again as the film developed breaks. The applicability of the ellipsometric and polarized infrared emission techniques to the identification of monomolecular tribological transfer films of polymers such as PTFE has been demonstrated.

Lauer, James L.↗
NASA NTRS1987

Use of calibration targets in the measurement of 2.22-micron mineral absorption features in Thematic Mapper data

A mineral absorption index (MAI) has been developed to separate leaf water and mineral absorption in the 2.22-micron Thematic Mapper band. The MAI uses three baselines to estimate and subtract the absorption attributable to vegetation. Digital number data from calibration targets devoid of vegetation are used to establish the positions of the baselines in Thematic Mapper data.

Elvidge, Christopher D.↗
NASA NTRS2022

Optimizing Landsat Next Shortwave Infrared Bands for Crop Residue Characterization

This study focused on optimizing the placement of shortwave infrared (SWIR) bands for pixel-level estimation of fractional crop residue cover (f R ) for the upcoming Landsat Next mission. We applied an iterative wavelength shift approach to a database of crop residue field spectra collected in Beltsville, Maryland, USA (n = 916) and computed generalized two- and three-band spectral indices for all wavelength combinations between 2000 and 2350 nm, then used these indices to model field-measured f R . A subset of the full dataset with a Normalized Difference Vegetation Index (NDVI) < 0.3 threshold (n = 643) was generated to evaluate green vegetation impacts on f R estimation. For the two-band wavelength shift analyses applied to the NDVI < 0.3 dataset, a generalized normalized difference using 2226 nm and 2263 nm bands produced the top f R estimation performance (R 2 = 0.8222; RMSE = 0.1296). These findings were similar to the established two-band Shortwave Infrared Normalized Difference Residue Index (SINDRI) (R 2 = 0.8145; RMSE = 0.1324). Performance of the two-band generalized normalized difference and SINDRI decreased for the full-NDVI dataset (R 2 = 0.5865 and 0.4144, respectively). For the three-band wavelength shift analyses applied to the NDVI < 0.3 dataset, a generalized ratio-based index with a 2031–2085–2216 nm band combination, closely matching established Cellulose Absorption Index (CAI) bands, was top performing (R 2 = 0.8397; RMSE = 0.1231). Three-band indices with CAI-type wavelengths maintained top f R estimation performance for the full-NDVI dataset with a 2036–2111–2217 nm band combination (R 2 = 0.7581; RMSE = 0.1548). The 2036–2111–2217 nm band combination was also top performing in f R estimation (R 2 = 0.8690; RMSE = 0.0970) for an additional analysis assessing combined green vegetation cover and surface moisture effects. Our results indicate that a three-band configuration with band centers and wavelength tolerances of 2036 nm (±5 nm), 2097 nm (±14 nm), and 2214 (±11 nm) would optimize Landsat Next SWIR bands for f R estimation.

Landsat Next↗
NASA NTRS2021

Evaluation of SWIR Crop Residue Bands for the Landsat Next Mission

This research reports the findings of a Landsat Next expert review panel that evaluated the use of narrow shortwave infrared (SWIR) reflectance bands to measure ligno-cellulose absorption features centered near 2100 and 2300 nm, with the objective of measuring and mapping non-photosynthetic vegetation (NPV), crop residue cover, and the adoption of conservation tillage practices within agricultural landscapes. Results could also apply to detection of NPV in pasture, grazing lands, and non-agricultural settings. Currently, there are no satellite data sources that provide narrowband or hyperspectral SWIR imagery at sufficient volume to map NPV at a regional scale. The Landsat Next mission, currently under design and expected to launch in the late 2020’s, provides the opportunity for achieving increased SWIR sampling and spectral resolution with the adoption of new sensor technology. This study employed hyperspectral data collected from 916 agricultural field locations with varying fractional NPV, fractional green vegetation, and surface moisture contents. These spectra were processed to generate narrow bands with centers at 2040, 2100, 2210, 2260, and 2230 nm, at various bandwidths, that were subsequently used to derive 13 NPV spectral indices from each spectrum. For crop residues with minimal green vegetation cover, two-band indices derived from 2210 and 2260 nm bands were top performers for measuring NPV (R^(2) = 0.81, RMSE = 0.13) using bandwidths of 30 to 50 nm, and the addition of a third band at 2100 nm increased resistance to atmospheric correction residuals and improved mission continuity with Landsat 8 Operational Land Imager Band 7. For prediction of NPV over a full range of green vegetation cover, the Cellulose Absorption Index, derived from 2040, 2100, and 2210 nm bands, was top performer (R^(2) = 0.77, RMSE = 0.17), but required a narrow (≤20 nm) bandwidth at 2040 nm to avoid interference from atmospheric carbon dioxide absorption. In comparison, broadband NPV indices utilizing Landsat 8 bands centered at 1610 and 2200 nm performed poorly in measuring fractional NPV (R^(2) = 0.44), with significantly increased interference from green vegetation

Wells Dean Hively↗
NASA NTRS1977

Optical constants of ammonium sulfate in the infrared

The infrared spectral reflectance at near normal incidence has been measured for 3.2 M, 2.4 M, and 1.6 M solutions of ammonium sulfate, an aerosol abundant in the stratosphere and also present in the troposphere. Kramers-Kronig analysis was used to determine values of the refractive and absorption indices from the measured spectral reflectance. A synthetic spectrum of crystalline ammonium sulfate was obtained by extrapolation of the absorption index obtained for the solution to the absorber number densities of the NH4 and SO4 ions characteristic of the crystal.

Downing, H. D.↗
NASA NTRS1979

Instrument measures many optical properties in visible and IR

Electro-optical system measures reflectance, reflectance ratio, transmission, absorption, refractive index, and absorption coefficient in both visible and infrared (IR) spectral regions. System effectively combining capabilities of ellisometer, reflectometer, and spectrophotometer is expected to find application in environmental and material composition testing fields.

Batten, C. E.↗
NASA NTRS1977

Measurement of wavelength-dependent extinction to distinguish between absorbing and nonabsorbing aerosol particulates

Measurements of spectral transmission factors in smoky optical transmission paths reveal a difference between wavelength exponents of the extinction cross section of high absorption capacity and those of low absorption capacity. A theoretical explanation of this behavior is presented. In certain cases, it is possible to obtain data on the absorption index of aerosol particles in the optical path by measuring the spectral decadic extinction coefficient at, at least, two wavelengths. In this manner it is possible, for instance, to distinguish smoke containing soot from water vapor.

Portscht, R.↗
NASA NTRS1984

Optical properties of NH3 ice from the far infrared to the near ultraviolet

The optical constants (n(r), n(i)) for solid ammonia in the cubic phase from 0.14 to 200 microns are displayed in both graphical and tabular form. The refractive indices n(r) were obtained from previously published spectra of the absorption index n(i) by means of the Kramers-Kronig dispersion relation. Mie scattering parameters in the same spectral range are graphically illustrated for particle sizes from 1 to 100 microns. An application of these results to the atmosphere of the planet Jupiter is also presented.

Martonchik, J. V.↗
NASA NTRS1991

Semiconductor Laser With Multilayer Dielectric Reflector

Multilayer dielectric reflector included in proposed surface-emitting, distributed-feedback, grating semiconductor laser (e.g., a GaAlAs device). Contributes to efficiency and output power of laser by reducing amount of light entering substrate, where wasted by absorption. Index of refraction in reflector sublayers alternates between higher and lower value. Higher value less than effective index of refraction of waveguide layer.

Lang, Robert J.↗
NASA NTRS1991

Catalog of infrared and cryo-optical properties for selected materials

This report will describe the status of an effort to catalog the refractive index, absorption, reflectance and transmittance of selected IR transmitting materials over the wavelength range from 1 to 1000 microns, and at temperatures from 300 to about 2 K. Data are presented for LiF, CaF2, BaF2, KBr, and TlBr, as well as for KRS-5 (TlBr-I) and KRS-6 (TlBr-Cl). A cryooptical measurements facility at NASA-Goddard, which has been used to generate some of the cataloged data, is also described.

Heaney, James B.↗
NASA NTRS2003

Physical properties and sixth graders' acceptance of an extruded ready-to-eat sweetpotato breakfast cereal

Extruded ready-to-eat breakfast cereals (RTEBCs) were made from varying levels of sweetpotato flour (SPF), whole-wheat bran (WWB), and extrusion cooking. Moisture, protein, and ash contents were lower in the 100% SPF than the 100% WWB. Carbohydrate, beta-carotene, and ascorbic acid contents were higher in the 100% SPF. Fat, thiamin, riboflavin contents, bulk densities, and the water absorption index were similar for the cereals. However, the expansion ratio was highest in the 100% SPF cereal. The 100% WWB had the lightest color and most fibrous morphology. Extruded RTEBC containing 100% SPF and 75%/25% SPF/WWB were well-liked and acceptable to sixth graders attending an elementary school in Auburn, Alabama, but the 100% WWB was unacceptable.

NASA Program Advanced Human Support Technology↗
NASA NTRS2010

Simulations of the Aerosol Index and the Absorption Aerosol Optical Depth and Comparisons with OMI Retrievals During ARCTAS-2008 Campaign

We have computed the Aerosol Index (AI) at 354 nm, useful for observing the presence of absorbing aerosols in the atmosphere, from aerosol simulations conducted with the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) module running online the GEOS-5 Atmospheric GCM. The model simulates five aerosol types: dust, sea salt, black carbon, organic carbon and sulfate aerosol and can be run in replay or data assimilation modes. In the assimilation mode, information's provided by the space-based MODIS and MISR sensors constrains the model aerosol state. Aerosol optical properties are then derived from the simulated mass concentration and the Al is determined at the OMI footprint using the radiative transfer code VLIDORT. In parallel, model derived Absorption Aerosol Optical Depth (AAOD) is compared with OMI retrievals. We have focused our study during ARCTAS (June - July 2008), a period with a good sampling of dust and biomass burning events. Our ultimate goal is to use OMI measurements as independent validation for our MODIS/MISR assimilation. Towards this goal we document the limitation of OMI aerosol absorption measurements on a global scale, in particular sensitivity to aerosol vertical profile and cloud contamination effects, deriving the appropriate averaging kernels. More specifically, model simulated (full) column integrated AAOD is compared with model derived Al, this way identifying those regions and conditions under which OMI cannot detect absorbing aerosols. Making use of ATrain cloud measurements from MODIS, C1oudSat and CALIPSO we also investigate the global impact on clouds on OMI derived Al, and the extent to which GEOS-5 clouds can offer a first order representation of these effects.

Source record↗
NASA NTRS1966

Mariner-Mars absorptance experiment.

Absorptivity standard instrument to investigate solar absorptance of four surfaces used for spacecraft temperature control for Mariner IV on Mars mission

TEMPERATURE CONTROL↗