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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Recalculation of the isotropic H functions

The isotropic H functions defined in radiative transfer theory by Chandrasekhar (1960) have been numerically recalculated for a larger number of single scattering albedo (w) values. The obtained H functions should be accurate to five decimal places at least. The H function values become highly nonlinear as w approaches 1, where calculations were performed with many more points than in Chandrasekhar (1960). A simple linear interpolation of Chandrasekhar's H function table could result in as much as 8% error in the H function values and 16% in the H(exp 2) values that appear in multiple scattering terms such as in Hapke (1981). On the other hand, Hapke's approximations (1981, 1993) give H values within 4.1% and 0.8% error, respectively.

Hiroi, Takahiro↗
NASA NTRS2009

Development of a GCR Event-based Risk Model

A goal at NASA is to develop event-based systems biology models of space radiation risks that will replace the current dose-based empirical models. Complex and varied biochemical signaling processes transmit the initial DNA and oxidative damage from space radiation into cellular and tissue responses. Mis-repaired damage or aberrant signals can lead to genomic instability, persistent oxidative stress or inflammation, which are causative of cancer and CNS risks. Protective signaling through adaptive responses or cell repopulation is also possible. We are developing a computational simulation approach to galactic cosmic ray (GCR) effects that is based on biological events rather than average quantities such as dose, fluence, or dose equivalent. The goal of the GCR Event-based Risk Model (GERMcode) is to provide a simulation tool to describe and integrate physical and biological events into stochastic models of space radiation risks. We used the quantum multiple scattering model of heavy ion fragmentation (QMSFRG) and well known energy loss processes to develop a stochastic Monte-Carlo based model of GCR transport in spacecraft shielding and tissue. We validated the accuracy of the model by comparing to physical data from the NASA Space Radiation Laboratory (NSRL). Our simulation approach allows us to time-tag each GCR proton or heavy ion interaction in tissue including correlated secondary ions often of high multiplicity. Conventional space radiation risk assessment employs average quantities, and assumes linearity and additivity of responses over the complete range of GCR charge and energies. To investigate possible deviations from these assumptions, we studied several biological response pathway models of varying induction and relaxation times including the ATM, TGF -Smad, and WNT signaling pathways. We then considered small volumes of interacting cells and the time-dependent biophysical events that the GCR would produce within these tissue volumes to estimate how GCR event rates mapped to biological signaling induction and relaxation times. We considered several hypotheses related to signaling and cancer risk, and then performed simulations for conditions where aberrant or adaptive signaling would occur on long-duration space mission. Our results do not support the conventional assumptions of dose, linearity and additivity. A discussion on how event-based systems biology models, which focus on biological signaling as the mechanism to propagate damage or adaptation, can be further developed for cancer and CNS space radiation risk projections is given.

Cucinotta, Francis A.↗
NASA NTRS1999

Accuracy of the Independent Pixel Approximation at Absorbing Wavelengths

In order to correctly interpret shortwave cloud radiation measured by satellites and ground-based radiometers, or by two aircraft flying above and below clouds, we need to better understand interactions between inhomogeneous clouds and solar radiation. The discrepancies between shortwave absorption inferred from measurements and predicted by models, between cloud optical depths estimated from satellites and ground measurements, between single scattering albedo retrieved from in situ radiation measurements and computed from measured droplet size distribution, among others, are strongly affected by cloud horizontal inhomogeneity. Net horizontal photon transport (i. e., horizontal fluxes) are a direct consequence of the inhomoqeneity in cloud structure. Horizontal fluxes and their effect on the accuracy of the pixel-by-pixel one-dimensional (1 D) radiative transfer calculations has recently undergone close scrutiny for conservative scattering. However, the properties and magnitude of horizontal fluxes in absorbing wavelengths are still poorly understood. As far as we are aware, only Ackerman and Cox and Titov discussed correlations between horizontal fluxes at absorbing wavelengths, though these were far from comprehensive. This paper partly fills this gap. We discuss here of whether the accuracy of the Independent Pixel Approximation (IPA), a 1 D radiative transfer approximation for each pixel, is a better model for multiple scattering at conservative or at absorbing wavelengths. Issues addressed here are: (1) dependence of net horizontal fluxes on single scattering albedo; (2) connection between pixel-by-pixel accuracy of the IPA and horizontal fluxes and (3) radiative smoothing and horizontal fluxes at absorbing wavelengths. In contrast to the traditional understanding of IPA, we study IPA accuracies not only for reflectance but also for transmittance and absorptance at both conservative and absorbing wavelengths. In spite of the apparent similarity between the three processes, dependence of IPA accuracies on single-scattering albedo is completely different. As a result, cloud optical properties retrieved from high resolution satellite images and ground-based measurements using IPA at absorbing channels will have different accuracies.

Marchak, Alexander↗
NASA NTRS2001

Measurements of the Vertical Structure of Aerosols and Clouds Over the Ocean Using Micro-Pulse LIDAR Systems

The determination of the vertical distribution of aerosols and clouds over the ocean is needed for accurate retrievals of ocean color from satellites observations. The presence of absorbing aerosol layers, especially at altitudes above the boundary layer, has been shown to influence the calculation of ocean color. Also, satellite data must be correctly screened for the presence of clouds, particularly cirrus, in order to measure ocean color. One instrument capable of providing this information is a lidar, which uses pulses of laser light to profile the vertical distribution of aerosol and cloud layers in the atmosphere. However, lidar systems prior to the 1990s were large, expensive, and not eye-safe which made them unsuitable for cruise deployments. During the 1990s the first small, autonomous, and eye-safe lidar system became available: the micro-pulse lidar, or MPL. The MPL is a compact and eye-safe lidar system capable of determining the range of aerosols and clouds by firing a short pulse of laser light (523 nm) and measuring the time-of-flight from pulse transmission to reception of a returned signal. The returned signal is a function of time, converted into range using the speed of light, and is proportional to the amount of light backscattered by atmospheric molecules (Rayleigh scattering), aerosols, and clouds. The MPL achieves ANSI eye-safe standards by sending laser pulses at low energy (micro-J) and expanding the beam to 20.32 cm in diameter. A fast pulse-repetition-frequency (2500 Hz) is used to achieve a good signal-to-noise, despite the low output energy. The MPL has a small field-of-view (< 100 micro-rad) and signals received with the instrument do not contain multiple scattering effects. The MPL has been used successfully at a number of long-term sites and also in several field experiments around the world.

Welton, Ellsworth J.↗
NASA NTRS2017

Retrieval of Water Vapor Column Abundance and Aerosol Properties from ChemCam Passive Sky Spectroscopy

We derive water vapor column abundances and aerosol properties from Mars Science Laboratory (MSL) ChemCam passive mode observations of scattered sky light. This paper covers the methodology and initial results for water vapor and also provides preliminary results for aerosols. The data set presented here includes the results of 113 observations spanning from Mars Year 31 L(s) = 291 deg (March 30, 2013) to Mars Year 33 L(s) = 127 deg (March 24, 2016). Each ChemCam passive sky observation acquires spectra at two different elevation angles. We fit these spectra with a discrete-ordinates multiple scattering radiative transfer model, using the correlated-k approximation for gas absorption bands. The retrieval proceeds by first fitting the continuum of the ratio of the two elevation angles to solve for aerosol properties, and then fitting the continuum-removed ratio to solve for gas abundances. The final step of the retrieval makes use of the observed CO 2 absorptions and the known CO 2 abundance to correct the retrieved water vapor abundance for the effects of the vertical distribution of scattering aerosols and to derive an aerosol scale height parameter. Our water vapor results give water vapor column abundance with a precision of +/-0.6 precipitable microns and systematic errors no larger than +/-0.3 precipitable microns, assuming uniform vertical mixing. The ChemCam-retrieved water abundances show, with only a few exceptions, the same seasonal behavior and the same timing of seasonal minima and maxima as the TES, CRISM, and REMS-H data sets that we compare them to. However ChemCam-retrieved water abundances are generally lower than zonal and regional scale from-orbit water vapor data, while at the same time being significantly larger than pre-dawn REMS-H abundances. Pending further analysis of REMS-H volume mixing ratio uncertainties, the differences between ChemCam and REMS-H pre-dawn mixing ratios appear to be much too large to be explained by large scale circulations and thus they tend to support the hypothesis of substantial diurnal interactions of water vapor with the surface. Our preliminary aerosol results, meanwhile, show the expected seasonal pattern in dust particle size but also indicate a surprising interannual increase in water-ice cloud opacities.

Mcconnochie, Timothy H.↗
DOE OSTI2022

Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering off Nuclei

Here, we present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the GIBUU model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2001

Inherent and Apparent Scattering Properties of Coated or Uncoated Spheres Embedded in an Absorbing Host Medium

The conventional Lorenz-Mie formalism is extended to the scattering process associated with a coated sphere embedded in an absorbing medium. It is shown that apparent and inherent scattering cross sections of a scattering particle, which are identical in the case of transparent host medium, are different if the host medium is absorptive. Here the inherent single-scattering properties are derived from the near-field information whereas the corresponding apparent counterparts are derived from the far-field asymptotic form of the scattered wave with scaling of host absorption that is assumed to be in an exponential form. The formality extinction and scattering efficiencies defined in the same manner as in the conventional sense can be unbounded. For a nonabsorptive particle embedded in an absorbing medium, the effect of host absorption on the phase matrix elements associated with polarization is significant. This effect, however, is largely reduced for strongly absorptive particles such as soot. For soot particles coated with water, the impurity can substantially reduce the single-scattering albedo of the particle if the size parameter is small. For water-coating soot and hollow ice spheres, it is shown that the phase matrix elements -P(sub 12)/P(sub 11) and P(sub 33)/P(sub 11) are unique if the shell is thin, as compared with the case for thick shell. Furthermore, the radiative transfer equation regarding a multidisperse particle system in an absorbing medium is discussed. It is illustrated that the conventional computation algorithms can be applied to solve the multiple scattering process if the scaled apparent single-scattering properties are applied.

Yang, P.↗
NASA NTRS1984

Voyager disk resolved photometry of the Saturnian satellites

The scattering properties of the icy satellites of Saturn are studied. Scans of intensity along the photometric equator near opposition are analyzed, and disk-resolved measurements of intensity are fitted to simple photometric functions. Histograms of the albedo distribution across the satellite disks are constructed, and the geometric albedos are determined as a function of wavelength. It is found that, at low phase angles, Rhea and Dione closely follow lunar behavior with almost no limb darkening. Mimas, Tethys, and especially Enceladus show significant limb darkening at low phase angles, which suggest multiple scattering is important for their surfaces. No satellite's surface can be described by Lambert's law. The darker satellites are redder, and the darker areas of each satellite are redder. A longitudinal dark stripe which represents a 15 percent decrease in albedo is situated near the center of the trailing side of Tethys. Mimas and Enceladus both have remarkably flat spectral reflectances into the ultraviolet.

Buratti, B. J.↗
NASA NTRS2003

New Examination of the Raman Lidar Technique for Water Vapor and Aerosols: Evaluating the Temperature Dependent Lidar Equations - Paper 1

The intent of this paper and its companion is to compile together the essential information required for the analysis of Raman lidar water vapor and aerosol data acquired using a single laser wavelength. In this first paper several details concerning the evaluation of the lidar equation when measuring Raman scattering are considered. These details include the influence of the temperature dependence of both pure rotational and vibrational-rotational Raman scattering on the lidar profile. These are evaluated for the first time using a new form of the lidar equation. The results indicate that, for the range of temperatures encountered in the troposphere, the magnitude of the temperature dependent effect can reach 10% or more for narrowband Raman water vapor measurements. Also the calculation of atmospheric transmission is examined carefully including the effects of depolarization. Different formulations of Rayleigh cross section determination commonly used in the lidar field are compared revealing differences up to 5% among the formulations. The influence of multiple scattering on the measurement of aerosol extinction using the Raman lidar technique is considered as are several photon pulse-pileup correction techniques.

Whiteman, David N.↗
NASA NTRS1992

Reflection and emission properties on Venus - Alpha Regio

Procedures developed from Hagfors' (1964) scattering model have been used with success to extract various properties (reflectivity, emissivity, slope, etc.) from both Pioneer Venus and Magellan data. However, under certain circumstances, such as physically rough areas or areas of nonhomogeneous composition, Hagfors' model may lead to serious errors in the interpretation of radar and radiometry data. The Magellan-derived surface properties are examined for some areas of below average emissivity in Alpha Regio and in an area to the east of Alpha, Crater Stuart, in order to determine if Hagfors' model is applicable. Methods of classical multiple scattering theory are also applied to show that enhanced radar backscattering and depressed thermal emission can be expected with a matrix of silicic or mafic rocks embedded in low loss soils.

Tryka, Kimberly A.↗
NASA NTRS1989

Laser light scattering review

Since the development of laser light sources and fast digital electronics for signal processing, the classical discipline of light scattering on liquid systems experienced a strong revival plus an enormous expansion, mainly due to new dynamic light scattering techniques. While a large number of liquid systems can be investigated, ranging from pure liquids to multicomponent microemulsions, this review is largely restricted to applications on Brownian particles, typically in the submicron range. Static light scattering, the careful recording of the angular dependence of scattered light, is a valuable tool for the analysis of particle size and shape, or of their spatial ordering due to mutual interactions. Dynamic techniques, most notably photon correlation spectroscopy, give direct access to particle motion. This may be Brownian motion, which allows the determination of particle size, or some collective motion, e.g., electrophoresis, which yields particle mobility data. Suitable optical systems as well as the necessary data processing schemes are presented in some detail. Special attention is devoted to topics of current interest, like correlation over very large lag time ranges or multiple scattering.

Schaetzel, Klaus↗
DOE OSTI2026

Glauber-Theory Calculations of High-Energy Nuclear Scattering Observables Using Variational Monte Carlo Wave Functions

Experiments using intermediate- to high-energy radioactive nuclear beams present numerous findings. Extracting important properties of physical observables relies on a firm theoretical analysis. Though Glauber theory is believed to work well, no convincing calculation has so far been done. Here, we perform ab initio Glauber theory calculations of both elastic differential cross sections and total reaction cross sections for p+ 12 C, 12 C+ 12 C, and 6 He+ 12 C systems. The wave functions of both 6 He and 12 C are generated by variational Monte Carlo calculations with spatial and spin-isospin correlations induced by realistic two- and three-nucleon potentials. Glauber’s phase-shift function is computed by Monte Carlo integration up to all orders of nucleon-nucleon multiple scatterings. We show an excellent performance of the Glauber description to the selected data on the above systems. We also find that the cumulant expansion of the phase-shift function converges rapidly up to the second order for the above systems. This finding will open up interesting applications for the analysis of high-energy nuclear experiments.

Horiuchi, W. [Osaka Metropolitan University (Japan↗
DOE OSTI2024

Quantification of Dynamic Scattering Effects in Molecular Crystals using Large Angle Rocking Beam Electron Diffraction

Electron crystallography provides a pathway to solve structure of small crystals (< 1um) in size, and thus overcomes difficult synthesis constraints involved in growing large crystals. Generally, electron diffraction data is collected in the form of integrated intensity using continuous rotation or by precession. The measured intensities in 3D are utilized for structure solution. Using this approach, structure solution of difficult crystals, such as small crystals of zeolites, metal-organic frameworks, molecular crystals, and proteins , can be solved by electron diffraction. However, electron structure solutions are regularly reported with higher Rvalues than x-ray or neutron diffraction. While similar structures are found despite the high R-values, the differences in the measure intensity and theory calculated intensity limit information that can be extracted by electron diffraction. Previous work demonstrated that including multiple-scattering effects significantly reduce the R-values . Thus, it is critical to be able to quantify the dynamical diffraction effects in molecular crystals.

Crystallography↗
NASA NTRS2012

Polarization of Directly Imaged Young Giant Planets as a Probe of Mass, Rotation, and Clouds

Young, hot gas giant planets at large separations from their primaries have been directly imaged around several nearby stars. More such planets will likely be detected by ongoing and new imaging surveys with instruments such as the Gemini Planet Imager (GPI). Efforts continue to model the spectra of these planets in order to constrain their masses, effective temperatures, composition, and cloud structure. One potential tool for analyzing these objects, which has received relatively less attention, is polarization. Linear polarization of gas giant exoplanets can arise from the combined influences of light scattering by atmospheric dust and a rotationally distorted shape. The oblateness of gas giant planet increases of course with rotation rate and for fixed rotation also rises with decreasing gravity. Thus young, lower mass gas giant planets with youthful inflated radii could easily have oblateness greater than that of Saturn s 10%. We find that polarizations of over 1% may easily be produced in the near-infrared in such cases. This magnitude of polarization may be measurable by GPI and other instruments. Thus if detected, polarization of a young Jupiter places constraints on the combination of its gravity, rotation rate, and degree of cloudiness. We will present results of our multiple scattering analysis coupled with a self-consistent dusty atmospheric models to demonstrate the range of polarizations that might be expected from resolved exoplanets and the range of parameter space that such observations may inform.

Marley, Mark Scott↗
NASA NTRS1994

Incorporation of multiple cloud layers for ultraviolet radiation modeling studies

Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud layers into a multiple-scattering radiative transfer model. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979-1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1-1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud layer method and a multiple cloud layer method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud layers may be important in accurately determining the biologically effective UV budget at the surface of the Earth.

Charache, Darryl H.↗
NASA NTRS2011

Vertical Distribution of Aersols and Water Vapor Using CRISM Limb Observations

Near-infrared spectra taken in a limb-viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on-board the Mars Reconnaissance Orbiter (MRO) provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb allows the vertical distribution of both dust and ice aerosols to be retrieved. These data serve as an important supplement to the aerosol profiling provided by the MRO/MCS instrument allowing independent validation and giving additional information on particle physical and scattering properties through multi-wavelength studies. A total of at least ten CRISM limb observations have been taken so far covering a full Martian year. Each set of limb observations nominally contains about four dozen scans across the limb giving pole-to-pole coverage for two orbits at roughly 100 and 290 W longitude over the Tharsis and Syrtis/Hellas regions, respectively. At each longitude, limb scans are spaced roughly 10 degrees apart in latitude, with a vertical spatial resolution on the limb of roughly 800 m. Radiative transfer modeling is used to model the observations. We compute synthetic CRISM limb spectra using a discrete-ordinates radiative transfer code that accounts for multiple scattering from aerosols and accounts for spherical geometry of the limb observations by integrating the source functions along curved paths in that coordinate system. Retrieved are 14-point vertical profiles for dust and water ice aerosols with resolution of 0.4 scale heights between one and six scale heights above the surface. After the aerosol retrieval is completed, the abundances of C02 (or surface pressure) and H20 gas are retrieved by matching the depth of absorption bands at 2000 nm for carbon dioxide and at 2600 run for water vapor. In addition to the column abundance of water vapor, limited information on its vertical structure can also be retrieved depending on the signal available from aerosol scattering.

Smith, Michael D.↗
NASA NTRS1983

On obtaining the forward phase functions of Saturn ring features from radio occultation observations

It is noted that the near-forward scattering functions of particles in Saturn ring features are related to 3.6 cm radio occultation power spectra by a Fredholm integral equation of the first kind. The equation reduces to an algebraic system of equation whose solution by usual inversion techniques (that is, least mean squares) is ruled out by the near singularity of the forward transformation matrix. A combination of constrained linear inversion and a filtering algorithm based on eigenvector decomposition of the matrix reduces the instabilities; this yields derived phase functions valid over the range of zero to about 12 mrad. It is noted that these functions represent the collective forward diffraction lobe of particles greater than about 1 m in radius. Since multiple scattering of the signal is a significant effect, the measured phase functions must be adjusted to obtain the singly scattered component. This single-scattering correction is examined for two physical models, namely the monolayer and the classical discrete random slab; in addition, the fraction of opacity in submeter particles for each model for particular ring features is estimated.

Zebker, H. A.↗
NASA NTRS1981

Radiative transfer in cometary dust atmospheres: Critique of recent developments

The gas and dust production rates of comets near the sun are intimately linked to the fate of the solar radiation as it is scattered and partially absorbed by the cometary dust envelope or halo surrounding the comet's nucleus. The radiation of nuclear matter (mostly water ice) and the release of dust particles embedded in the ice which are entrained by the escaping gas and subsequently form a dust atmosphere or halo. On the other hand, the interaction of the dust cloud with the solar radiation is in turn responsible for the amount of radiative energy received by the nucleus and thus determines the evaporation rate. It is shown that recent attempts to formulate this problem quantitatively are in error. The correct formulation is given and it is pointed out that negative extinction (enhancement of the primary radiation received by the nucleus due to multiple scattering) may not be as large as predicted.

Vonroos, O.↗