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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Data analysis and interpretation of lunar dust exosphere

The lunar horizon glow observed by Apollo astronauts and recorded during the Surveyor missions is believed to result from the scattering of sunlight off lunar fines suspended in a dust layer above the lunar surface. For scale heights of tens of kilometers, theory and astronaut's observations suggest that the size of the dust particles will be smaller than 0.1 microns in radius and will act as Rayleigh scatters. This means that the dust scattered light will be 100 percent polarized at a 90 degree scattering angle and will depend on wavelength to the inverse fourth power ('bluing'). Believing these signatures to be observable from ground based telescopes, observational data in the form of CCD images has been collected from McDonald Observatory's 36 in. telescope, and the reduction and analysis of this data is the focus of the present report.

Andrews, George A., Jr.↗
NASA NTRS1992

A multi-layer discrete-ordinate method for vector radiative transfer in a vertically-inhomogeneous, emitting and scattering atmosphere. I - Theory. II - Application

A theory is developed for discretizing the vector integro-differential radiative transfer equation including both solar and thermal radiation. A complete solution and boundary equations are obtained using the discrete-ordinate method. An efficient numerical procedure is presented for calculating the phase matrix and achieving computational stability. With natural light used as a beam source, the Stokes parameters from the model proposed here are compared with the analytical solutions of Chandrasekhar (1960) for a Rayleigh scattering atmosphere. The model is then applied to microwave frequencies with a thermal source, and the brightness temperatures are compared with those from Stamnes'(1988) radiative transfer model.

Weng, Fuzhong↗
DOE OSTI2025

Estimating Ice Water Content for Winter Storms from Millimeter-Wavelength Radar Measurements Using a Synthesis of Polarimetric and Dual-Frequency Radar Observations

The potential of millimeter-wavelength radar-based ice water content (IWC) estimation is demonstrated using a Ka-band Scanning Polarimetric Radar (KASPR) for the U.S. northeast coast winter storms. Two IWC relations for Ka-band polarimetric radar measurements are proposed: one that uses a combination of the radar reflectivity Z and the estimated total number concentration of snow particles N t and the other based on the joint use of Z, specific differential phase K DP , and the degree of riming f rim . A key element of the algorithms is to obtain the “Rayleigh-equivalent” value of Z measured at the Ka band, i.e., the corresponding Z at a longer radar wavelength for which Rayleigh scattering takes place. This is achieved via polarimetric retrieval of the mean volume diameter D m and incorporating the relationship between the dual-wavelength ratio DWR S/Ka and D m . Those techniques allow for retrievals from single millimeter-wavelength radar measurements and do not necessarily require the dual-wavelength ratio (DWR) measurements, if the DWR–D m relation and Rayleigh assumption for Ka-band K DP are valid. Comparison between the quasivertical profile product obtained from KASPR and the columnar vertical profile product generated from the nearby WSR-88D S-band radar measurements demonstrates that the DWR S/Ka can be estimated from the two close radars without the need for collocated radar beams and synchronized antenna scanning and can be used for determining the Rayleigh-equivalent value of Z. As a result, the performance of the suggested techniques is evaluated for seven winter storms using surface disdrometer and snow accumulation measurements.

Cloud retrieval↗
NASA NTRS1999

Atmospheric Multiple Scattering Effects on GLAS Altimetry: Calculations of Single Pulse Bias - Part 1

Estimates of the effect of pulse stretching on satellite laser altimetry in particular the Geoscience Laser Altimeter System (GLAS), by cloud multiple scattering were made from an analytical method and from Monte Carlo calculations. The path delay of the return pulse was found to be largest for low-level clouds with particle radii (3-20 microns). The magnitude of the path delay was affected by several factors including cloud height, cloud optical depth, cloud particle size, particle shape, and receiver field of view. Polar aerosol and Rayleigh scattering usually added less than 1 cm to the overall path delay. Path delay estimates for all cloud conditions would be less if a simple Gaussian fit of the return pulse peak were used to measure the pulse's centroid. However, care must be taken in determining the centroid as factors such as pulse width, surface slope and the fitting method used will affect the estimate. A planned application for laser altimetry is high precision monitoring of the height change of polar ice sheets. In the absence of a correction algorithm, the required GLAS altimetry accuracies will not be achieved unless atmospheric channel information is used to remove profiles that are likely to be heavily contaminated by multiple scattering.

Duda, David P.↗
NASA NTRS2009

The OMPS Limb Profiler Instrument: An Alternative Data Analysis and Retrieval Algorithm

The upcoming Ozone Mapper and Profiler Suite (OMPS), which will be launched on the NPOESS Preparatory Project (NPP) platform in early 2011, will continue monitoring the global distribution of the Earth's middle atmosphere ozone and aerosol. OMPS is composed of three instruments, namely the Total Column Mapper (heritage: TOMS, OMI), the Nadir Profiler (heritage: SBUV) and the Limb Profiler (heritage: SOLSE/LORE, OSIRIS, SCIAMACHY, SAGE III). The ultimate goal of the mission is to better understand and quantify the rate of stratospheric ozone recovery. The focus of the paper will be on the Limb Profiler (LP) instrument. The LP instrument will measure the Earth fs limb radiance (which is due to the scattering of solar photons by air molecules, aerosol and Earth surface) in the ultra-violet (UV), visible and near infrared, from 285 to 1000 nm. The LP simultaneously images the whole vertical extent of the Earth's limb through three vertical slits, each covering a vertical tangent height range of 100 km and each horizontally spaced by 250 km in the cross-track direction. The focal plane of the LP spectrometer is a two ]dimensional CCD array comprised of 340 x 740 pixels. Several data analysis tools are presently being constructed and tested to retrieve ozone and aerosol vertical distribution from limb radiance measurements. The primary NASA algorithm is based on earlier algorithms developed for the SOLSE/LORE and SAGE III limb scatter missions. The paper will describe an alternative algorithm which will retrieve ozone density and aerosol extinction directly from radiance data collected on individual CCD pixels. This alternative method uses an optimal estimation approach to retrieve ozone and aerosol in the 10-60 km range from the information contained within an ensemble of about 50000 down-linked pixels. Tangent height registration is performed using the Rayleigh Scattering Attitude Sensor (RSAS) technique applied to columns of pixels in the 340-360 nm range. Cloud height is determined by analyzing the radiance first derivative along pixel columns at longer wavelengths. Wavelength registration is performed using rows of pixels and identifying Fraunhofer solar lines within the measured spectra. Special attention is given to stray-light decontamination and modeling of the measured finite spectral/spatial line shape functions.

Rault, Didier F.↗
NASA NTRS1973

Absolute intensity and polarization of rotational Raman scattering from N2, O2, and CO2

An experimental examination of the absolute intensity, polarization, and relative line intensities of rotational Raman scattering (RRS) from N2, O2, and CO2 is reported. The absolute scattering intensity for N2 is characterized by its differential cross section for backscattering of incident light at 647.1 nm, which is calculated from basic measured values. The ratio of the corresponding cross section for O2 to that for N2 is 2.50 plus or minus 5 percent. The intensity recent for N2, O2, and CO2 are shown to compare favorably to values calculated from recent measurements of the depolarization of Rayleigh scattering plus RRS. Measured depolarizations of various RRS lines agree to within a few percent with the theoretical value of 3/4. Detailed error analyses are presented for intensity and depolarization measurements. Finally, extensive RRS spectra at nominal gas temperatures of 23 C, 75 C, and 125 C are presented and shown to compare favorably to theoretical predictions.

Penney, C. M.↗
NASA NTRSDate not supplied

NASA TROPOMI Aerosol Products: Algorithmic Upgrades and Preliminary Evaluation

This poster presentation describes an expanded NASA TROPOMI (Tropospheric Monitoring Instrument)aerosol algorithm (N-TROPOMAER) that takes advantage of TROPOMI observations in the ultraviolet and visible spectral regions. The availability of the Oxygen B-band observations, and the unprecedentedly high spatial resolution (3.5 km X 5.5 km) for a hyper-spectral sensor are significant improvements for aerosol properties retrieval. The heritage N-TROPOMAER aerosol algorithm uses near-ultraviolet radiances at 354 nm and 388 nm from Sentinel 5 Precursor-TROPOMI for simultaneously retrieving aerosol optical depth (AOD), single-scattering albedo (SSA), aerosol absorption optical depth (AAOD), and above-cloud aerosol optical depth(ACAOD) at 388 nm, along with the qualitative UV aerosol index (UVAI). We have expanded the inversion capability beyond the UV, to retrieve AOD at 466 nm and 680 nm. Surface reflectance effects at466 nm are accounted for using a recently developed geometry-dependent surface Lambertian-equivalent reflectivity (GLER) product, which is derived from the top-of-atmosphere radiance computed with Rayleigh scattering and surface bidirectional reflectance distribution function (BRDF) for the exact viewing geometry at the sensor’s spatial resolution. Aerosol layer height (ALH) and 680 nm AOD are simultaneously derived from observations at 680 nm and at the Oxygen-B band (688 nm). Another important upgrade is the use of time averaged total column carbon monoxide from the NASA GEOS-CF(Global Earth Observing System Composition Forecast) as a tracer of carbonaceous aerosols.

TROPOMI↗
NASA NTRS2019

100-kHz Rate Rayleigh Imaging for Combustion and Flow Diagnostics

Two-dimensional (2D) Rayleigh scattering (RS) imaging at an ultrahigh repetition rate of 100 kHz is demonstrated in non-reacting and reacting flows employing a high-energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed RS images. Additionally, a 2D instantaneous flow velocity field at 100 kHz was obtained through optical-flow-based analysis of the RS images. The technique was also applied to study turbulent flames having a near-constant Rayleigh cross section. The demonstrated high-speed RS technique in conjunction with optical-flow-based analysis provides non-intrusive, simultaneous measurements of the flow mixing and velocity field, extending the measurement capability of the RS technique to high-speed non-reacting and reacting flows.

Jiang, Naibo↗
NASA NTRS1994

Gaseous hydrogen/oxygen injector performance characterization

Results are presented of spontaneous Raman scattering measurements in the combustion chamber of a 110 N thrust class gaseous hydrogen/oxygen rocket. Temperature, oxygen number density, and water number density profiles at the injector exit plane are presented. These measurements are used as input profiles to a full Navier-Stokes computational fluid dynamics (CFD) code. Predictions of this code while using the measured profiles are compared with predictions while using assumed uniform injector profiles. Axial and radial velocity profiles derived from both sets of predictions are compared with Rayleigh scattering measurements in the exit plane of a 33:1 area ratio nozzle. Temperature and number density Raman scattering measurements at the exit plane of a test rocket with a 1:1.36 area ratio nozzle are also compared with results from both sets of predictions.

Degroot, W. A.↗
DOE OSTI2022

Analysis of coherent Thomson scattering from a low temperature plasma

In this work, the spectrum of coherent Thomson scattering (CTS) induced by a periodic ponderomotive perturbation in a low-density low temperature plasma is considered. The analysis is performed for the case when the period of the resulting optical lattice is less than the Debye screening length in the plasma by solving an electron Boltzmann equation, where the total force is the sum of the periodic force due to the optical lattice and the electrostatic force due to self-consistent electric field in the plasma. An analogy between the CTS spectra calculated here and coherent Rayleigh scattering spectra in a neutral gas is established. For relatively low intensity for the optical lattice, the calculated CTS spectra are nearly Gaussian with widths slightly wider than the incoherent Thomson widths. We demonstrate that at higher intensities the line shape narrows and saturates to a width approximately half of that found at low lattice intensities. The proportionality of the spectral width to the square root of the electron temperature allows one to extract the electron temperature from the saturated spectra. Possible application of CTS for remote measuring the electron temperature in plasma is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1973

Aerosol scattering of ultraviolet sunlight in the tropical maritime atmosphere

The effects of atmospheric aerosol scattering on the vertical profile of solar ultraviolet radiation are investigated. Measurements of diffuse and total ultraviolet radiation were made using a rocketborne optical sonde in the marine atmosphere of Antigua. During observations, the sun was at zenith. Vertical profiles of directly transmitted solar radiation were calculated by subtraction of the diffuse component from the total radiance. Using these values of direct downward solar UV-flux, the optical thickness of the atmosphere was derived as a function of altitude. Absorption by ozone was also considered. In the troposphere the values of observed optical thickness were in general equal to or lower than those expected theoretically from Rayleigh scattering alone. The measured radiation profiles were compared with those computed for a multiple scattering model atmosphere. Some computations regarding the interaction of UV-sunlight with maritime aerosols are presented.

Ghazi, A.↗
NASA NTRS1993

An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements

A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

Ross, H. Richard↗
NASA NTRS2019

Evaluation of Brightness Temperature Sensitivity to Snowpack Physical Properties Using Coupled Snow Physics and Microwave Radiative Transfer Models

There are multiple existing microwave radiative transfer models (RTMs) to simulate the brightness temperature (Tb) of snowpacks. It is still challenging to have consistent Tb responses from RTMs due to individual physical formulations of the snowpack scattering process. This article examines three of the widely-used multi-layer RTMs: 1) the microwave emission model of layered snowpacks (MEMLS); 2) the dense media radiative transfer based on the quasi-crystalline approximation (QCA) of Mie scattering of densely packed sticky spheres (DMRTQMS); and 3) the Helsinki University of Technology (HUT) model. Interestingly, these models yield slightly different Tb responses when driven by the same physical snowpack properties. Tb variations, dependent on the choice of RTMs, are then evaluated to improve the understanding of model differences in microwave emission from a snowpack. We first perform a sensitivity study of the Tb predictions from the three RTMs as a function of snow grain sizes, densities, and depths. While Tb from all three RTMs decreases with increasing snow grain sizes, it is found that a scaling factor is required to have the same amount of Tb attenuation for small grain sizes within the Rayleigh scattering regime. For larger grain sizes, however, a scaling coefficient is not enough to match the model outputs due to the different scattering assumptions of the RTMs. For a single snow layer with increasing snow depths and densities, all three RTMs exhibit Tb attenuations arising from the increase in path lengths and optical depths. Further evaluations are conducted by feeding the three RTMs with the output of a snow physics model driven by in situ weather forcing in a coupled simulation. Outputs of this coupled model include snowpack physical properties and Tbs. By using snow stratigraphy observations, another set of Tb simulation is also conducted with RTMs driven by in situ snowpit observations. The snow physics outputs from the coupled case are compared against in situ snow stratigraphy observations.

Do Hyuk Kang↗
DOE OSTI2025

Phonon-Spin Scattering from Unpaired f-electrons in U atoms and It’s Influence on Thermal Transport in Uranium-doped Thorium Dioxide Single Crystals

In this work, impact of low level of uranium (U) atom substitution on thermal conductivity of thorium dioxide (ThO2) is investigated. ThO2 is an electronic insulator with a wide optical band-gap and no unpaired electrons whose thermal transport is governed by phonons. U-substitution introduces unpaired f-electrons resulting in paramagnetic behavior of U-ThO2 at room temperature, which significantly suppresses its thermal conductivity. A single crystal of U-ThO2 with graded composition of U is grown using a hydrothermal synthesis method, and thermal conductivity measurements are performed in regions with uniform composition of U at levels of 0%, 6%, 9% and 16%. Measured thermal conductivity profiles over 77–300 K temperature range are analyzed using an analytical expression for phonon-mediated thermal transport based on Klemens-Callaway model. Temperature dependent thermal conductivity is found to deviate significantly from the Rayleigh scattering trend expected for a simple substitutional point defect with a small perturbation to mass and interatomic forces. With the resonant scattering term, observed large suppression of thermal conductivity at low temperatures can be closely reproduced. Additionally, the extracted phonon-spin coupling constants imply a nonlinear relation of phonon-spin interaction intensity with respect to U doping percentage. Our study reveals how phonon-spin scattering contributed by unpaired f-electrons in U atoms influences thermal transport in the U-ThO2 system.

36 - MATERIALS SCIENCE↗
NASA NTRS2015

IPRT Polarized Radiative Transfer Model Intercomparison Project-Phase A

The polarization state of electromagnetic radiation scattered by atmospheric particles such as aerosols, cloud droplets, or ice crystals contains much more information about the optical and microphysical properties than the total intensity alone. For this reason an increasing number of polarimetric observations are performed from space, from the ground and from aircraft. Polarized radiative transfer models are required to interpret and analyse these measurements and to develop retrieval algorithms exploiting polarimetric observations. In the last years a large number of new codes have been developed, mostly for specific applications. Benchmark results are available for specific cases, but not for more sophisticated scenarios including polarized surface reflection and multi-layer atmospheres. The International Polarized Radiative Transfer (IPRT) working group of the International Radiation Commission (IRC) has initiated a model intercomparison project in order to fill this gap. This paper presents the results of the first phase A of the IPRT project which includes ten test cases, from simple setups with only one layer and Rayleigh scattering to rather sophisticated setups with a cloud embedded in a standard atmosphere above an ocean surface. All scenarios in the first phase A of the intercomparison project are for a one-dimensional plane-parallel model geometry. The commonly established benchmark results are available at the IPRT website

radiative transfer↗
NASA NTRS1995

Interpretation of Dynamics Explorer far UV images of the quiet time thermosphere

A selected set of far ultra violet images of Earth have been analyzed quanitatively to establish their validity for studying thermospheric weather. The set of images chosen for the study was restricted to mostly geomagnetically quiet conditions in order to obtain a baseline understanding of the relationship between the observations and thermospheric phenomenology. The images included low to modrerate solar activity levels. A new model was developed to generate global dayglow images using first principles methods. The mass Spectrometer/incoherent scatter (MSIS-86) model was used to predict the thermospheric concentrations. The analyses of thermospheric images observed in the 123 to 160-nm nominal passband show that the spectral composition for observations on the projected earth disk is dominated by O I 130.4-nm radiation (85-90%), with concentrations from O I 135.6-nm and N2 Lyman-Birge-Hopefield (LBH) bands of about 5-8% each. The synthetic images reproduce the global features of the observed images rather well. Differences between the model and the data are attributed to real atmospheric effects, such as atomic oxygen depletions which are not well reproduced by the MSIS model when geomagnetic activity is elevated. The absoute values recorded were 38-54% higher than predicted. We attribute this discrepancy to low values of the solar extreme ultraviolet irradiances used in the model. Images obtained in the 136 to 165-nm nominal passband are a factor of 2.7 greater than the model. The excess signal observed is most likely due to a long wavelength tail in the instrument sensitivity which allowed Rayleigh scattered sunlight between 180and 250nm to be detected. The understanding of the Dynamics Explorer (DE 1) images gained by this study provides the basis for future work on the global response of the theremosphere to geomagnetic forcing.

Meier, R. R.↗
DOE OSTI2020

Identifications and classifications of human locomotion using Rayleigh-enhanced distributed fiber acoustic sensors with deep neural networks

Abstract This paper reports on the use of machine learning to delineate data harnessed by fiber-optic distributed acoustic sensors (DAS) using fiber with enhanced Rayleigh backscattering to recognize vibration events induced by human locomotion. The DAS used in this work is based on homodyne phase-sensitive optical time-domain reflectometry (φ-OTDR). The signal-to-noise ratio (SNR) of the DAS was enhanced using femtosecond laser-induced artificial Rayleigh scattering centers in single-mode fiber cores. Both supervised and unsupervised machine-learning algorithms were explored to identify people and specific events that produce acoustic signals. Using convolutional deep neural networks, the supervised machine learning scheme achieved over 76.25% accuracy in recognizing human identities. Conversely, the unsupervised machine learning scheme achieved over 77.65% accuracy in recognizing events and human identities through acoustic signals. Through integrated efforts on both sensor device innovation and machine learning data analytics, this paper shows that the DAS technique can be an effective security technology to detect and to identify highly similar acoustic events with high spatial resolution and high accuracies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2002

Flow Visualization of Density in a Cryogenic Wind Tunnel Using Planar Rayleigh and Raman Scattering

Using a pulsed Nd:YAG laser (532 nm) and a gated, intensified charge-coupled device, planar Rayleigh and Raman scattering techniques have been used to visualize the unseeded Mach 0.2 flow density in a 0.3-meter transonic cryogenic wind tunnel. Detection limits are determined for density measurements by using both unseeded Rayleigh and Raman (N2 vibrational) methods. Seeding with CO2 improved the Rayleigh flow visualization at temperatures below 150 K. The seeded Rayleigh version was used to demonstrate the observation of transient flow features in a separated boundary layer region, which was excited with an oscillatory jet. Finally, a significant degradation of the laser light sheet, in this cryogenic facility, is discussed.

Herring, Gregory C.↗