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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Towed Subsurface Optical Communications Buoy

The innovation allows critical, high-bandwidth submarine communications at speed and depth. This reported innovation is a subsurface optical communications buoy, with active neutral buoyancy and streamlined flow surface veins for depth control. This novel subsurface positioning for the towed communications buoy enables substantial reduction in water-absorption and increased optical transmission by eliminating the intervening water absorption and dispersion, as well as by reducing or eliminating the beam spread and the pulse spreading that is associated with submarine-launched optical beams.

Stirbl, Robert C.↗
NASA NTRS1984

Electrical research on solar cells and photovoltaic materials

The flat-plate solar cell array program which increases the service lifetime of the photovoltaic modules used for terrestrial energy applications is discussed. The current-voltage response characteristics of the solar cells encapsulated in the modules degrade with service time and this degradation places a limitation on the useful lifetime of the modules. The most desirable flat-plate array system involves solar cells consisting of highly polarizable materials with similar electrochemical potentials where the cells are encapsulated in polymers in which ionic concentrations and mobilities are negligibly small. Another possible mechanism limiting the service lifetime of the photovoltaic modules is the gradual loss of the electrical insulation characteristics of the polymer pottant due to water absorption or due to polymer degradation from light or heat effects. The mechanical properties of various polymer pottant materials and of electrochemical corrosion mechanisms in solar cell material are as follows: (1) electrical and ionic resistivity; (2) water absorption kinetics and water solubility limits; and (3) corrosion characterization of various metallization systems used in solar cell construction.

Orehotsky, J.↗
NASA NTRS2010

Prospects for Habitable World Detections Using James Webb Space Telescope (JWST)

Doppler and transit surveys are finding extrasolar planets of ever smaller mass and radius, and are now sampling the domain of superEarths. Recent results from the Doppler surveys suggest that discovery of a transiting superEarth in the habitable zone of a lower main sequence star may be possible. We evaluate the prospects for an all-sky transit survey targeted to the brightest stars I that would find the most favorable cases for photometric and spectroscopic characterization using the James Webb Space Telescope. We use the proposed Transiting Exoplanet Survey Satellite (TESS) as representative of an all-sky survey. We couple the simulated TESS yield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. Our sensitivity model includes all currently known and anticipated sources of random and systematic error for these instruments. We focus on the TESS planets with radii between Earth and Neptune. Our simulations consider secondary eclipse filter photometry using JWST/MIRI, comparing the 11- and 15- micron bands to measure carbon dioxide absorption in superEarths, as well as JWST!NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and carbon dioxide absorption at 4.3 microns. We find that JWST will be capable of characterizing dozens of TESS superEarths with temperatures above the habitable range, using both MIRI and NIRspec. We project that TESS will discover about eight nearby habitable transiting superEarths, all orbiting lower main sequence stars. The principal sources of uncertainty in the prospects for JWST characterization of habitable superEarths are superEarth frequency and the nature of superEarth atmospheres. Based on our estimates of these uncertainties, we project that JWST will be able to measure the temperature, and identify molecular absorptions (water, carbon dioxide) in one to four nearby habitable TESS superEarths orbiting lower main sequence stars.

Deming, Drake↗
NASA NTRS1996

Enhanced Water Vapor Absorption within Tropospheric Clouds: A Partial Explanation for Anomalous Absorption

Comparisons between solar flux measurements and predictions obtained from theoretical radiative transfer models indicate that most of these models underestimate the globally averaged solar energy absorbed by cloudy atmospheres by up to 25Wm&sup-2;.The origin of this anomalous absorption has not yet been established, but it has been attributed to a variety of sources including oversimplified or missing physical processes in the existing models, uncertainties in the input data, and even measurement errors. We used a sophisticated atmospheric radiative transfer model to provide improved constraints on the physical processes that contribute to the absorption of solar radiation by Earth's atmosphere. The results are described herein.

solar flux measurement water vapor absorption atmo↗
NASA NTRS1979

Determination of the Telluric Water Vapor Absorption Correction for Astronomical Data Obtained from the Kuiper Airborne Observatory

The amount of telluric water vapor along the line of sight of the Kuiper Airborne Observatory telescope as obtained concommitantly on 23 flights is compared with the NASA-Ames Michelson interferometer and with the NOAA-Boulder radiometer. A strong correlation between the two determinations exists, and a method for computing the atmospheric transmission for a given radiometer reading is established.

Erickson, E. F.↗
NASA NTRS2002

Impact of MIE-Resonances on the Atmospheric Absorption of Water Clouds

Clouds strongly modulate radiative transfer processes in the Earth's atmosphere. Studies, which simulate bulk properties of clouds, such as absorption, require methods that accurately account for multiple scattering among individual cloud particles. Multiple scattering processes are well described by MIE-theory, if interacting particles have a spherical shape. This is a good assumption for water droplets. Thus, simulations for water clouds (especially for interactions with solar radiation) usually apply readily available MIE-codes. The presence of different drop-sizes, however, necessitates repetitive calculations for many sizes. The usual representation by a few sizes is likely to miss contributions from densely distributed, sharp resonances. Despite their usually narrow width, integrated over the entire size-spectrum of a cloud droplet distribution, the impact of missed resonances could add up. The consideration of these resonances tends to increase cloud extinction and cloud absorption. This mechanism for a larger (than by MIE-methods predicted) solar absorption has the potential to explain observational evidence of larger than predicted cloud absorption at solar wavelengths. The presentation will address the absorption impact of added resonances for typical properties of water clouds (e.g. drop size distributions, drop concentrations and cloud geometry). Special attention will be given to scenarios with observational evidence of law than simulated solar absorption; particularly if simultaneous measurements of cloud micro- and macrophysical properties are available.

Wiscombe, W.↗
NASA NTRS1991

Line-shape asymmetry of water vapor absorption lines in the 720-nm wavelength region

Spectral line-shape analyses were performed for water vapor lines broadened by argon, oxygen, and xenon in the 720-nm wavelength region. A line-shape asymmetry was observed, which is attributed to statistical dependence or correlation between velocity- and state-changing collisions. The generalized (asymmetric) Galatry profile, which results from the soft-collision profile and includes correlation between velocity- and state-changing collisions, was fitted to the observed line shapes and was found to compare favorably with the observed data. The most prominent asymmetries were observed with xenon as the buffer gas.

Grossmann, Benoist E.↗
NASA NTRS2002

Analyzing Water's Optical Absorption

A cooperative agreement between World Precision Instruments (WPI), Inc., and Stennis Space Center has led the UltraPath(TM) device, which provides a more efficient method for analyzing the optical absorption of water samples at sea. UltraPath is a unique, high-performance absorbance spectrophotometer with user-selectable light path lengths. It is an ideal tool for any study requiring precise and highly sensitive spectroscopic determination of analytes, either in the laboratory or the field. As a low-cost, rugged, and portable system capable of high- sensitivity measurements in widely divergent waters, UltraPath will help scientists examine the role that coastal ocean environments play in the global carbon cycle. UltraPath(TM) is a trademark of World Precision Instruments, Inc. LWCC(TM) is a trademark of World Precision Instruments, Inc.

Source record↗
NASA NTRS2019

Homogenized Water Vapor Absorption Band Radiances From International Geostationary Satellites

In the past 20+ years, GEO Imagers with infrared 6.5‐μm bands have been observing the Earth's atmosphere, providing useful information of upper tropospheric moisture. Due to the instrumental differences and local viewing angles in GEO satellites, these observations are not consistent for generating climate data records (CDRs). In this study, a methodology has been developed to homogenize the 6.5‐μm radiances from the international GEO satellites, to generate a consistent CDR. Validations with Infrared Atmospheric Sounding Interferometer radiances from Metops for 2015–2017for seven GEO Imager sensors show that the GEO radiances are homogenized well with small standard deviation and biases of the differences (smaller for newer sensors), temporally stable radiometric accuracy, and weak angle dependency (even weaker for sensors with two water vapor bands). The homogenized 20+ years of consistent 6.5‐μm radiance CDR can be used to evaluate reanalysis and climate models, especially the diurnal variation of the model simulation.

Water Vapor↗
NASA NTRS2013

Infrared Transmission Spectroscopy of the Exoplanets HD 209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope

Exoplanetary transmission spectroscopy in the near-infrared using the Hubble Space Telescope (HST) NICMOS (Near Infrared Camera and Multi-Object Spectrometer) is currently ambiguous because different observational groups claim different results from the same data, depending on their analysis methodologies. Spatial scanning with HST/WFC3 (Wide Field Camera-3) provides an opportunity to resolve this ambiguity.We here report WFC3 spectroscopy of the giant planets HD 209458b and XO-1b in transit, using spatial scanning mode for maximum photon-collecting efficiency. We introduce an analysis technique that derives the exoplanetary transmission spectrum without the necessity of explicitly decorrelating instrumental effects, and achieves nearly photon-limited precision even at the high flux levels collected in spatial scan mode. Our errors are within 6 percent (XO-1) and 26 percent (HD 209458b) of the photon-limit at a resolving power of lambda divided by delta times lambda approximating 70, and are better than 0.01 percent per spectral channel. Both planets exhibit water absorption of approximately 200 ppm at the water peak near 1.38 m. Our result for XO-1b contradicts the much larger absorption derived from NICMOS spectroscopy. The weak water absorption we measure for HD209458b is reminiscent of the weakness of sodium absorption in the first transmission spectroscopy of an exoplanet atmosphere by Charbonneau et al. Model atmospheres having uniformly distributed extra opacity of 0.012 square centimeters per gram account approximately for both our water measurement and the sodium absorption. Our results for HD 209458b support the picture advocated by Pont et al. in which weak molecular absorptions are superposed on a transmission spectrum that is dominated by continuous opacity due to haze and or dust. However,the extra opacity needed for HD 209458b is grayer than for HD 189733b, with a weaker Rayleigh component.

planetary systems↗
NASA NTRS2001

Laboratory Measurements of the 940, 1130, and 1370 nm Water Vapor Absorption Band Profiles

We have used the solar spectral flux radiometer (SSFR) flight instrument with the Ames 25 meter base-path White cell to obtain about 20 moderate resolution (8 nm) pure water vapor spectra from 650 to 1650 nm, with absorbing paths from 806 to 1506 meters and pressures up to 14 torr. We also obtained a set at 806 meters with several different air-broadening pressures. Model simulations were made for the 940, 1130, and 1370 nm absorption bands for some of these laboratory conditions using the Rothman, et al HITRAN-2000 linelist. This new compilation of HITRAN includes new intensity measurements for the 940 nm region. We compared simulations for our spectra of this band using HITRAN-2000 with simulations using the prior HITRAN-1996. The simulations of the 1130 nm band show about 10% less absorption than we measured. There is some evidence that the total intensity of this band is about 38% stronger than the sum of the HITRAN line intensities in this region. In our laboratory conditions the absorption depends approximately on the square root of the intensity. Thus, our measurements agree that the band is stronger than tabulated in HITRAN, but by about 20%, substantially less than the published value. Significant differences have been shown between Doppler-limited resolution spectra of the 1370 nm band obtained at the Pacific Northwest National Laboratory and HITRAN simulations. Additional new intensity measurements in this region are continuing to be made. We expect the simulations of our SSFR lab data of this band will show the relative importance of improving the HITRAN line intensities of this band for atmospheric measurements.

Giver, Lawrence P.↗
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 NTRS1998

Removal of Thin Cirrus Path Radiances in the 0.4-1.0 micron Spectral Region Using the 1.375-micron Strong Water Vapor Absorption Channel

Through analysis of spectral imaging data acquired with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) from an ER-2 aircraft at 20 km altitude during several field programs, it was found that narrow channels near the center of the strong 1.38-micron water vapor band are very sensitive in detecting thin cirrus clouds. Based on this observation from AVIRIS data, a channel centered at 1.375 microns with a width of 30 nm was selected for the Moderate Resolution Imaging Spectrometer (MODIS) for remote sensing of cirrus clouds from space. The sensitivity of the 1.375-micron MODIS channel to detect thin cirrus clouds during the day time is expected to be one to two orders of magnitude better than the current infrared emission techniques. As a result, a larger fraction of the satellite data will likely be identified as containing cirrus clouds. In order to make better studies of surface reflectance properties, thin cirrus effects must be removed from satellite images. We have developed an empirical approach for removing/correcting thin cirrus effects in the 0.4 - 1.0 micron region using channels near 1.375 microns. This algorithm will be incorporated into the present MODIS atmospheric correction algorithms for ocean color and land applications and will yield improved MODIS atmospheric aerosol, land surface, and ocean color products.

Gao, Bo-Cai↗
NASA NTRS2009

Multilayer Cloud Detection with the MODIS Near-Infrared Water Vapor Absorption Band

Data Collection 5 processing for the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Earth Observing System EOS Terra and Aqua spacecraft includes an algorithm for detecting multilayered clouds in daytime. The main objective of this algorithm is to detect multilayered cloud scenes, specifically optically thin ice cloud overlying a lower-level water cloud, that presents difficulties for retrieving cloud effective radius using single layer plane-parallel cloud models. The algorithm uses the MODIS 0.94 micron water vapor band along with CO2 bands to obtain two above-cloud precipitable water retrievals, the difference of which, in conjunction with additional tests, provides a map of where multilayered clouds might potentially exist. The presence of a multilayered cloud results in a large difference in retrievals of above-cloud properties between the CO2 and the 0.94 micron methods. In this paper the MODIS multilayered cloud algorithm is described, results of using the algorithm over example scenes are shown, and global statistics for multilayered clouds as observed by MODIS are discussed. A theoretical study of the algorithm behavior for simulated multilayered clouds is also given. Results are compared to two other comparable passive imager methods. A set of standard cloudy atmospheric profiles developed during the course of this investigation is also presented. The results lead to the conclusion that the MODIS multilayer cloud detection algorithm has some skill in identifying multilayered clouds with different thermodynamic phases

Wind, Galina↗
NASA NTRS1975

Water vapor absorption spectra of the upper atmosphere /45-185 per cm/

The far IR nighttime absorption spectrum of the earth's atmosphere above 14 km is determined from observations of the bright moon. The spectra were obtained using a Michelson interferometer attached to a 30-cm telescope aboard a high-altitude jet aircraft. Comparison with a single-layer model atmosphere implies a vertical column of 3.4 plus or minus 0.4 microns of precipitable water on 30 August 1971 and 2.4 plus or minus 0.3 microns of precipitable water on 6 January 1972.-

Augason, G. C.↗