Linearized Flux Evolution (LiFE): A technique for rapidly adapting fluxes from full-physics radiative transfer models

NASA Astrophysics Data System (ADS)

Robinson, Tyler D.; Crisp, David

2018-05-01

Solar and thermal radiation are critical aspects of planetary climate, with gradients in radiative energy fluxes driving heating and cooling. Climate models require that radiative transfer tools be versatile, computationally efficient, and accurate. Here, we describe a technique that uses an accurate full-physics radiative transfer model to generate a set of atmospheric radiative quantities which can be used to linearly adapt radiative flux profiles to changes in the atmospheric and surface state-the Linearized Flux Evolution (LiFE) approach. These radiative quantities describe how each model layer in a plane-parallel atmosphere reflects and transmits light, as well as how the layer generates diffuse radiation by thermal emission and by scattering light from the direct solar beam. By computing derivatives of these layer radiative properties with respect to dynamic elements of the atmospheric state, we can then efficiently adapt the flux profiles computed by the full-physics model to new atmospheric states. We validate the LiFE approach, and then apply this approach to Mars, Earth, and Venus, demonstrating the information contained in the layer radiative properties and their derivatives, as well as how the LiFE approach can be used to determine the thermal structure of radiative and radiative-convective equilibrium states in one-dimensional atmospheric models.

A modular radiative transfer program for gas filter correlation radiometry

NASA Technical Reports Server (NTRS)

Casas, J. C.; Campbell, S. A.

1977-01-01

The fundamentals of a computer program, simulated monochromatic atmospheric radiative transfer (SMART), which calculates atmospheric path transmission, solar radiation, and thermal radiation in the 4.6 micrometer spectral region, are described. A brief outline of atmospheric absorption properties and line by line transmission calculations is explained in conjunction with an outline of the SMART computational procedures. Program flexibility is demonstrated by simulating the response of a gas filter correlation radiometer as one example of an atmospheric infrared sensor. Program limitations, input data requirements, program listing, and comparison of SMART transmission calculations are presented.

High performance computation of radiative transfer equation using the finite element method

NASA Astrophysics Data System (ADS)

Badri, M. A.; Jolivet, P.; Rousseau, B.; Favennec, Y.

2018-05-01

This article deals with an efficient strategy for numerically simulating radiative transfer phenomena using distributed computing. The finite element method alongside the discrete ordinate method is used for spatio-angular discretization of the monochromatic steady-state radiative transfer equation in an anisotropically scattering media. Two very different methods of parallelization, angular and spatial decomposition methods, are presented. To do so, the finite element method is used in a vectorial way. A detailed comparison of scalability, performance, and efficiency on thousands of processors is established for two- and three-dimensional heterogeneous test cases. Timings show that both algorithms scale well when using proper preconditioners. It is also observed that our angular decomposition scheme outperforms our domain decomposition method. Overall, we perform numerical simulations at scales that were previously unattainable by standard radiative transfer equation solvers.

Validation of radiative transfer computation with Monte Carlo method for ultra-relativistic background flow

NASA Astrophysics Data System (ADS)

Ishii, Ayako; Ohnishi, Naofumi; Nagakura, Hiroki; Ito, Hirotaka; Yamada, Shoichi

2017-11-01

We developed a three-dimensional radiative transfer code for an ultra-relativistic background flow-field by using the Monte Carlo (MC) method in the context of gamma-ray burst (GRB) emission. For obtaining reliable simulation results in the coupled computation of MC radiation transport with relativistic hydrodynamics which can reproduce GRB emission, we validated radiative transfer computation in the ultra-relativistic regime and assessed the appropriate simulation conditions. The radiative transfer code was validated through two test calculations: (1) computing in different inertial frames and (2) computing in flow-fields with discontinuous and smeared shock fronts. The simulation results of the angular distribution and spectrum were compared among three different inertial frames and in good agreement with each other. If the time duration for updating the flow-field was sufficiently small to resolve a mean free path of a photon into ten steps, the results were thoroughly converged. The spectrum computed in the flow-field with a discontinuous shock front obeyed a power-law in frequency whose index was positive in the range from 1 to 10 MeV. The number of photons in the high-energy side decreased with the smeared shock front because the photons were less scattered immediately behind the shock wave due to the small electron number density. The large optical depth near the shock front was needed for obtaining high-energy photons through bulk Compton scattering. Even one-dimensional structure of the shock wave could affect the results of radiation transport computation. Although we examined the effect of the shock structure on the emitted spectrum with a large number of cells, it is hard to employ so many computational cells per dimension in multi-dimensional simulations. Therefore, a further investigation with a smaller number of cells is required for obtaining realistic high-energy photons with multi-dimensional computations.

Multiscale solutions of radiative heat transfer by the discrete unified gas kinetic scheme

NASA Astrophysics Data System (ADS)

Luo, Xiao-Ping; Wang, Cun-Hai; Zhang, Yong; Yi, Hong-Liang; Tan, He-Ping

2018-06-01

The radiative transfer equation (RTE) has two asymptotic regimes characterized by the optical thickness, namely, optically thin and optically thick regimes. In the optically thin regime, a ballistic or kinetic transport is dominant. In the optically thick regime, energy transport is totally dominated by multiple collisions between photons; that is, the photons propagate by means of diffusion. To obtain convergent solutions to the RTE, conventional numerical schemes have a strong dependence on the number of spatial grids, which leads to a serious computational inefficiency in the regime where the diffusion is predominant. In this work, a discrete unified gas kinetic scheme (DUGKS) is developed to predict radiative heat transfer in participating media. Numerical performances of the DUGKS are compared in detail with conventional methods through three cases including one-dimensional transient radiative heat transfer, two-dimensional steady radiative heat transfer, and three-dimensional multiscale radiative heat transfer. Due to the asymptotic preserving property, the present method with relatively coarse grids gives accurate and reliable numerical solutions for large, small, and in-between values of optical thickness, and, especially in the optically thick regime, the DUGKS demonstrates a pronounced computational efficiency advantage over the conventional numerical models. In addition, the DUGKS has a promising potential in the study of multiscale radiative heat transfer inside the participating medium with a transition from optically thin to optically thick regimes.

Cost-effective computational method for radiation heat transfer in semi-crystalline polymers

NASA Astrophysics Data System (ADS)

Boztepe, Sinan; Gilblas, Rémi; de Almeida, Olivier; Le Maoult, Yannick; Schmidt, Fabrice

2018-05-01

This paper introduces a cost-effective numerical model for infrared (IR) heating of semi-crystalline polymers. For the numerical and experimental studies presented here semi-crystalline polyethylene (PE) was used. The optical properties of PE were experimentally analyzed under varying temperature and the obtained results were used as input in the numerical studies. The model was built based on optically homogeneous medium assumption whereas the strong variation in the thermo-optical properties of semi-crystalline PE under heating was taken into account. Thus, the change in the amount radiative energy absorbed by the PE medium was introduced in the model induced by its temperature-dependent thermo-optical properties. The computational study was carried out considering an iterative closed-loop computation, where the absorbed radiation was computed using an in-house developed radiation heat transfer algorithm -RAYHEAT- and the computed results was transferred into the commercial software -COMSOL Multiphysics- for solving transient heat transfer problem to predict temperature field. The predicted temperature field was used to iterate the thermo-optical properties of PE that varies under heating. In order to analyze the accuracy of the numerical model experimental analyses were carried out performing IR-thermographic measurements during the heating of the PE plate. The applicability of the model in terms of computational cost, number of numerical input and accuracy was highlighted.

Ground temperature measurement by PRT-5 for maps experiment

NASA Technical Reports Server (NTRS)

Gupta, S. K.; Tiwari, S. N.

1978-01-01

A simple algorithm and computer program were developed for determining the actual surface temperature from the effective brightness temperature as measured remotely by a radiation thermometer called PRT-5. This procedure allows the computation of atmospheric correction to the effective brightness temperature without performing detailed radiative transfer calculations. Model radiative transfer calculations were performed to compute atmospheric corrections for several values of the surface and atmospheric parameters individually and in combination. Polynomial regressions were performed between the magnitudes or deviations of these parameters and the corresponding computed corrections to establish simple analytical relations between them. Analytical relations were also developed to represent combined correction for simultaneous variation of parameters in terms of their individual corrections.

Implications of a quadratic stream definition in radiative transfer theory.

NASA Technical Reports Server (NTRS)

Whitney, C.

1972-01-01

An explicit definition of the radiation-stream concept is stated and applied to approximate the integro-differential equation of radiative transfer with a set of twelve coupled differential equations. Computational efficiency is enhanced by distributing the corresponding streams in three-dimensional space in a totally symmetric way. Polarization is then incorporated in this model. A computer program based on the model is briefly compared with a Monte Carlo program for simulation of horizon scans of the earth's atmosphere. It is found to be considerably faster.

Radiative gas dynamics of the Fire-II superorbital space vehicle

NASA Astrophysics Data System (ADS)

Surzhikov, S. T.

2016-03-01

The rates of convective and radiative heating of the Fire-II reentry vehicle are calculated, and the results are compared with experimental flight data. The computational model is based on solving a complete set of equations for (i) the radiative gas dynamics of a physically and chemically nonequilibrium viscous heatconducting gas and (ii) radiative transfer in 2D axisymmetric statement. The spectral optical parameters of high-temperature gases are calculated using ab initio quasi-classical and quantum-mechanical methods. The transfer of selective thermal radiation in terms of atomic lines is calculated using the line-by-line method on a specially generated computational grid that is nonuniform in radiation wavelength.

Predicting radiative heat transfer in thermochemical nonequilibrium flow fields. Theory and user's manual for the LORAN code

NASA Technical Reports Server (NTRS)

Chambers, Lin Hartung

1994-01-01

The theory for radiation emission, absorption, and transfer in a thermochemical nonequilibrium flow is presented. The expressions developed reduce correctly to the limit at equilibrium. To implement the theory in a practical computer code, some approximations are used, particularly the smearing of molecular radiation. Details of these approximations are presented and helpful information is included concerning the use of the computer code. This user's manual should benefit both occasional users of the Langley Optimized Radiative Nonequilibrium (LORAN) code and those who wish to use it to experiment with improved models or properties.

Computational Challenges of 3D Radiative Transfer in Atmospheric Models

NASA Astrophysics Data System (ADS)

Jakub, Fabian; Bernhard, Mayer

2017-04-01

The computation of radiative heating and cooling rates is one of the most expensive components in todays atmospheric models. The high computational cost stems not only from the laborious integration over a wide range of the electromagnetic spectrum but also from the fact that solving the integro-differential radiative transfer equation for monochromatic light is already rather involved. This lead to the advent of numerous approximations and parameterizations to reduce the cost of the solver. One of the most prominent one is the so called independent pixel approximations (IPA) where horizontal energy transfer is neglected whatsoever and radiation may only propagate in the vertical direction (1D). Recent studies implicate that the IPA introduces significant errors in high resolution simulations and affects the evolution and development of convective systems. However, using fully 3D solvers such as for example MonteCarlo methods is not even on state of the art supercomputers feasible. The parallelization of atmospheric models is often realized by a horizontal domain decomposition, and hence, horizontal transfer of energy necessitates communication. E.g. a cloud's shadow at a low zenith angle will cast a long shadow and potentially needs to communication through a multitude of processors. Especially light in the solar spectral range may travel long distances through the atmosphere. Concerning highly parallel simulations, it is vital that 3D radiative transfer solvers put a special emphasis on parallel scalability. We will present an introduction to intricacies computing 3D radiative heating and cooling rates as well as report on the parallel performance of the TenStream solver. The TenStream is a 3D radiative transfer solver using the PETSc framework to iteratively solve a set of partial differential equation. We investigate two matrix preconditioners, (a) geometric algebraic multigrid preconditioning(MG+GAMG) and (b) block Jacobi incomplete LU (ILU) factorization. The TenStream solver is tested for up to 4096 cores and shows a parallel scaling efficiency of 80-90% on various supercomputers.

Near-field radiative heat transfer in scanning thermal microscopy computed with the boundary element method

NASA Astrophysics Data System (ADS)

Nguyen, K. L.; Merchiers, O.; Chapuis, P.-O.

2017-11-01

We compute the near-field radiative heat transfer between a hot AFM tip and a cold substrate. This contribution to the tip-sample heat transfer in Scanning Thermal Microscopy is often overlooked, despite its leading role when the tip is out of contact. For dielectrics, we provide power levels exchanged as a function of the tip-sample distance in vacuum and spatial maps of the heat flux deposited into the sample which indicate the near-contact spatial resolution. The results are compared to analytical expressions of the Proximity Flux Approximation. The numerical results are obtained by means of the Boundary Element Method (BEM) implemented in the SCUFF-EM software, and require first a thorough convergence analysis of the progressive implementation of this method to the thermal emission by a sphere, the radiative transfer between two spheres, and the radiative exchange between a sphere and a finite substrate.

Radiative transfer models for retrieval of cloud parameters from EPIC/DSCOVR measurements

NASA Astrophysics Data System (ADS)

Molina García, Víctor; Sasi, Sruthy; Efremenko, Dmitry S.; Doicu, Adrian; Loyola, Diego

2018-07-01

In this paper we analyze the accuracy and efficiency of several radiative transfer models for inferring cloud parameters from radiances measured by the Earth Polychromatic Imaging Camera (EPIC) on board the Deep Space Climate Observatory (DSCOVR). The radiative transfer models are the exact discrete ordinate and matrix operator methods with matrix exponential, and the approximate asymptotic and equivalent Lambertian cloud models. To deal with the computationally expensive radiative transfer calculations, several acceleration techniques such as, for example, the telescoping technique, the method of false discrete ordinate, the correlated k-distribution method and the principal component analysis (PCA) are used. We found that, for the EPIC oxygen A-band absorption channel at 764 nm, the exact models using the correlated k-distribution in conjunction with PCA yield an accuracy better than 1.5% and a computation time of 18 s for radiance calculations at 5 viewing zenith angles.

Applications of the similarity relations in radiative transfer to remote sensing implementation and flux simulation

NASA Astrophysics Data System (ADS)

Yang, P.; Ding, J.; Tang, G.; King, M. D.; Platnick, S. E.; Meyer, K.; Mlawer, E. J.

2017-12-01

Van de Hulst (1974) showed several quasi-invariant quantities in radiative transfer concerning multiple scattering. Recently, we illustrated that the aforesaid quasi-invariant quantities are useful in remote sensing of ice cloud properties from spaceborne radiometric observations (Ding et al. 2017). Specifically, the overall performance of an ice cloud optical property model can be estimated without carrying out detailed retrieval implementation. In this presentation, we will review the radiative transfer similarity relations and some recent results including the study by Ding et al. (2017). Furthermore, we will illustrate an application of the similarity relations to improvement of broadband radiative flux computation. For example, the Rapid Radiative Transfer Model (RRTM, Mlawer et al, 1999) does not consider multiple scattering in the longwave spectral regime (RRTMG-LW) ("G" indicates a version suitable for GCM applications). We show that the similarity relations can be used to effectively improve the accuracy of RRTMG-LW without increasing computational effort.

Radiation transfer in plant canopies - Scattering of solar radiation and canopy reflectance

NASA Technical Reports Server (NTRS)

Verstraete, Michel M.

1988-01-01

The one-dimensional vertical model of radiation transfer in a plant canopy described by Verstraete (1987) is extended to account for the transfer of diffuse radiation. This improved model computes the absorption and scattering of both visible and near-infrared radiation in a multilayer canopy as a function of solar position and leaf orientation distribution. Multiple scattering is allowed, and the spectral reflectance of the vegetation stand is predicted. The results of the model are compared to those of other models and actual observations.

Nonequilibrium radiation and chemistry models for aerocapture vehicle flowfields, volume 3

NASA Technical Reports Server (NTRS)

Carlson, Leland A.

1991-01-01

The computer programs developed to calculate the shock wave precursor and the method of using them are described. This method calculated the precursor flow field in a nitrogen gas including the effects of emission and absorption of radiation on the energy and composition of gas. The radiative transfer is calculated including the effects of absorption and emission through the line as well as the continuum process in the shock layer and through the continuum processes only in the precursor. The effects of local thermodynamic nonequilibrium in the shock layer and precursor regions are also included in the radiative transfer calculations. Three computer programs utilized by this computational scheme to calculate the precursor flow field solution for a given shock layer flow field are discussed.

Radiative Heat Transfer and Turbulence-Radiation Interactions in a Heavy-Duty Diesel Engine

NASA Astrophysics Data System (ADS)

Paul, C.; Sircar, A.; Ferreyro, S.; Imren, A.; Haworth, D. C.; Roy, S.; Ge, W.; Modest, M. F.

2016-11-01

Radiation in piston engines has received relatively little attention to date. Recently, it is being revisited in light of current trends towards higher operating pressures and higher levels of exhaust-gas recirculation, both of which enhance molecular gas radiation. Advanced high-efficiency engines also are expected to function closer to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. Here several different spectral radiation property models and radiative transfer equation (RTE) solvers have been implemented in an OpenFOAM-based engine CFD code, and simulations have been performed for a heavy-duty diesel engine. Differences in computed temperature fields, NO and soot levels, and wall heat transfer rates are shown for different combinations of spectral models and RTE solvers. The relative importance of molecular gas radiation versus soot radiation is examined. And the influence of turbulence-radiation interactions is determined by comparing results obtained using local mean values of composition and temperature to compute radiative emission and absorption with those obtained using a particle-based transported probability density function method. DOE, NSF.

A computer simulation model to compute the radiation transfer of mountainous regions

NASA Astrophysics Data System (ADS)

Li, Yuguang; Zhao, Feng; Song, Rui

2011-11-01

In mountainous regions, the radiometric signal recorded at the sensor depends on a number of factors such as sun angle, atmospheric conditions, surface cover type, and topography. In this paper, a computer simulation model of radiation transfer is designed and evaluated. This model implements the Monte Carlo ray-tracing techniques and is specifically dedicated to the study of light propagation in mountainous regions. The radiative processes between sun light and the objects within the mountainous region are realized by using forward Monte Carlo ray-tracing methods. The performance of the model is evaluated through detailed comparisons with the well-established 3D computer simulation model: RGM (Radiosity-Graphics combined Model) based on the same scenes and identical spectral parameters, which shows good agreements between these two models' results. By using the newly developed computer model, series of typical mountainous scenes are generated to analyze the physical mechanism of mountainous radiation transfer. The results show that the effects of the adjacent slopes are important for deep valleys and they particularly affect shadowed pixels, and the topographic effect needs to be considered in mountainous terrain before accurate inferences from remotely sensed data can be made.

Numerical study of entropy generation due to coupled laminar and turbulent mixed convection and thermal radiation in an enclosure filled with a semitransparent medium.

PubMed

Goodarzi, M; Safaei, M R; Oztop, Hakan F; Karimipour, A; Sadeghinezhad, E; Dahari, M; Kazi, S N; Jomhari, N

2014-01-01

The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k-ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (10⁴) and turbulent flow (10⁸). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible.

Numerical Study of Entropy Generation due to Coupled Laminar and Turbulent Mixed Convection and Thermal Radiation in an Enclosure Filled with a Semitransparent Medium

PubMed Central

Goodarzi, M.; Safaei, M. R.; Oztop, Hakan F.; Karimipour, A.; Sadeghinezhad, E.; Dahari, M.; Kazi, S. N.; Jomhari, N.

2014-01-01

The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k-ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (104) and turbulent flow (108). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible. PMID:24778601

Multiple Scattering Principal Component-based Radiative Transfer Model (PCRTM) from Far IR to UV-Vis

NASA Astrophysics Data System (ADS)

Liu, X.; Wu, W.; Yang, Q.

2017-12-01

Modern satellite hyperspectral satellite remote sensors such as AIRS, CrIS, IASI, CLARREO all require accurate and fast radiative transfer models that can deal with multiple scattering of clouds and aerosols to explore the information contents. However, performing full radiative transfer calculations using multiple stream methods such as discrete ordinate (DISORT), doubling and adding (AD), successive order of scattering order of scattering (SOS) are very time consuming. We have developed a principal component-based radiative transfer model (PCRTM) to reduce the computational burden by orders of magnitudes while maintain high accuracy. By exploring spectral correlations, the PCRTM reduce the number of radiative transfer calculations in frequency domain. It further uses a hybrid stream method to decrease the number of calls to the computational expensive multiple scattering calculations with high stream numbers. Other fast parameterizations have been used in the infrared spectral region reduce the computational time to milliseconds for an AIRS forward simulation (2378 spectral channels). The PCRTM has been development to cover spectral range from far IR to UV-Vis. The PCRTM model have been be used for satellite data inversions, proxy data generation, inter-satellite calibrations, spectral fingerprinting, and climate OSSE. We will show examples of applying the PCRTM to single field of view cloudy retrievals of atmospheric temperature, moisture, traces gases, clouds, and surface parameters. We will also show how the PCRTM are used for the NASA CLARREO project.

Radiative Heat Transfer modelling in a Heavy-Duty Diesel Engine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Chandan; Sircar, Arpan; Ferreyro-Fernandez, Sebastian

Detailed radiation modelling in piston engines has received relatively little attention to date. Recently, it is being revisited in light of current trends towards higher operating pressures and higher levels of exhaust-gas recirculation, both of which enhance molecular gas radiation. Advanced high-efficiency engines also are expected to function closer to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. Here several different spectral radiation property models and radiative transfer equation (RTE) solvers have been implemented in an OpenFOAM-based engine CFD code, and simulations have been performed for amore » heavy-duty diesel engine. Differences in computed temperature fields, NO and soot levels, and wall heat transfer rates are shown for different combinations of spectral models and RTE solvers. The relative importance of molecular gas radiation versus soot radiation is examined. And the influence of turbulence-radiation interactions is determined by comparing results obtained using local mean values of composition and temperature to compute radiative emission and absorption with those obtained using a particle-based transported probability density function method.« less

Computational Model of Heat Transfer on the ISS

NASA Technical Reports Server (NTRS)

Torian, John G.; Rischar, Michael L.

2008-01-01

SCRAM Lite (SCRAM signifies Station Compact Radiator Analysis Model) is a computer program for analyzing convective and radiative heat-transfer and heat-rejection performance of coolant loops and radiators, respectively, in the active thermal-control systems of the International Space Station (ISS). SCRAM Lite is a derivative of prior versions of SCRAM but is more robust. SCRAM Lite computes thermal operating characteristics of active heat-transport and heat-rejection subsystems for the major ISS configurations from Flight 5A through completion of assembly. The program performs integrated analysis of both internal and external coolant loops of the various ISS modules and of an external active thermal control system, which includes radiators and the coolant loops that transfer heat to the radiators. The SCRAM Lite run time is of the order of one minute per day of mission time. The overall objective of the SCRAM Lite simulation is to process input profiles of equipment-rack, crew-metabolic, and other heat loads to determine flow rates, coolant supply temperatures, and available radiator heat-rejection capabilities. Analyses are performed for timelines of activities, orbital parameters, and attitudes for mission times ranging from a few hours to several months.

Hybrid-dual-fourier tomographic algorithm for a fast three-dimensionial optical image reconstruction in turbid media

NASA Technical Reports Server (NTRS)

Alfano, Robert R. (Inventor); Cai, Wei (Inventor)

2007-01-01

A reconstruction technique for reducing computation burden in the 3D image processes, wherein the reconstruction procedure comprises an inverse and a forward model. The inverse model uses a hybrid dual Fourier algorithm that combines a 2D Fourier inversion with a 1D matrix inversion to thereby provide high-speed inverse computations. The inverse algorithm uses a hybrid transfer to provide fast Fourier inversion for data of multiple sources and multiple detectors. The forward model is based on an analytical cumulant solution of a radiative transfer equation. The accurate analytical form of the solution to the radiative transfer equation provides an efficient formalism for fast computation of the forward model.

Transient radiative transfer in a scattering slab considering polarization.

PubMed

Yi, Hongliang; Ben, Xun; Tan, Heping

2013-11-04

The characteristics of the transient and polarization must be considered for a complete and correct description of short-pulse laser transfer in a scattering medium. A Monte Carlo (MC) method combined with a time shift and superposition principle is developed to simulate transient vector (polarized) radiative transfer in a scattering medium. The transient vector radiative transfer matrix (TVRTM) is defined to describe the transient polarization behavior of short-pulse laser propagating in the scattering medium. According to the definition of reflectivity, a new criterion of reflection at Fresnel surface is presented. In order to improve the computational efficiency and accuracy, a time shift and superposition principle is applied to the MC model for transient vector radiative transfer. The results for transient scalar radiative transfer and steady-state vector radiative transfer are compared with those in published literatures, respectively, and an excellent agreement between them is observed, which validates the correctness of the present model. Finally, transient radiative transfer is simulated considering the polarization effect of short-pulse laser in a scattering medium, and the distributions of Stokes vector in angular and temporal space are presented.

A new hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer

NASA Technical Reports Server (NTRS)

Tamma, Kumar K.; Railkar, Sudhir B.

1988-01-01

This paper describes new and recent advances in the development of a hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer problems. The transfinite element methodology, while retaining the modeling versatility of contemporary finite element formulations, is based on application of transform techniques in conjunction with classical Galerkin schemes and is a hybrid approach. The purpose of this paper is to provide a viable hybrid computational methodology for applicability to general transient thermal analysis. Highlights and features of the methodology are described and developed via generalized formulations and applications to several test problems. The proposed transfinite element methodology successfully provides a viable computational approach and numerical test problems validate the proposed developments for conduction/convection/radiation thermal analysis.

Modeling Radiative Heat Transfer and Turbulence-Radiation Interactions in Engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Chandan; Sircar, Arpan; Ferreyro-Fernandez, Sebastian

Detailed radiation modelling in piston engines has received relatively little attention to date. Recently, it is being revisited in light of current trends towards higher operating pressures and higher levels of exhaust-gas recirculation, both of which enhance molecular gas radiation. Advanced high-efficiency engines also are expected to function closer to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. Here several different spectral radiation property models and radiative transfer equation (RTE) solvers have been implemented in an OpenFOAM-based engine CFD code, and simulations have been performed for amore » full-load (peak pressure ~200 bar) heavy-duty diesel engine. Differences in computed temperature fields, NO and soot levels, and wall heat transfer rates are shown for different combinations of spectral models and RTE solvers. The relative importance of molecular gas radiation versus soot radiation is examined. And the influence of turbulence-radiation interactions is determined by comparing results obtained using local mean values of composition and temperature to compute radiative emission and absorption with those obtained using a particle-based transported probability density function method.« less

Light-Cone Effect of Radiation Fields in Cosmological Radiative Transfer Simulations

NASA Astrophysics Data System (ADS)

Ahn, Kyungjin

2015-02-01

We present a novel method to implement time-delayed propagation of radiation fields in cosmo-logical radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative trans-fer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.

Solution of Radiation and Convection Heat-Transfer Problems

NASA Technical Reports Server (NTRS)

Oneill, R. F.

1986-01-01

Computer program P5399B developed to accommodate variety of fin-type heat conduction applications involving radiative or convective boundary conditions with additionally imposed local heat flux. Program also accommodates significant variety of one-dimensional heat-transfer problems not corresponding specifically to fin-type applications. Program easily accommodates all but few specialized one-dimensional heat-transfer analyses as well as many twodimensional analyses.

DirtyGrid I: 3D Dust Radiative Transfer Modeling of Spectral Energy Distributions of Dusty Stellar Populations

NASA Astrophysics Data System (ADS)

Law, Ka-Hei; Gordon, Karl D.; Misselt, Karl A.

2018-06-01

Understanding the properties of stellar populations and interstellar dust has important implications for galaxy evolution. In normal star-forming galaxies, stars and the interstellar medium dominate the radiation from ultraviolet (UV) to infrared (IR). In particular, interstellar dust absorbs and scatters UV and optical light, re-emitting the absorbed energy in the IR. This is a strongly nonlinear process that makes independent studies of the UV-optical and IR susceptible to large uncertainties and degeneracies. Over the years, UV to IR spectral energy distribution (SED) fitting utilizing varying approximations has revealed important results on the stellar and dust properties of galaxies. Yet the approximations limit the fidelity of the derived properties. There is sufficient computer power now available that it is now possible to remove these approximations and map out of landscape of galaxy SEDs using full dust radiative transfer. This improves upon previous work by directly connecting the UV, optical, and IR through dust grain physics. We present the DIRTYGrid, a grid of radiative transfer models of SEDs of dusty stellar populations in galactic environments designed to span the full range of physical parameters of galaxies. Using the stellar and gas radiation input from the stellar population synthesis model PEGASE, our radiative transfer model DIRTY self-consistently computes the UV to far-IR/sub-mm SEDs for each set of parameters in our grid. DIRTY computes the dust absorption, scattering, and emission from the local radiation field and a dust grain model, thereby physically connecting the UV-optical to the IR. We describe the computational method and explain the choices of parameters in DIRTYGrid. The computation took millions of CPU hours on supercomputers, and the SEDs produced are an invaluable tool for fitting multi-wavelength data sets. We provide the complete set of SEDs in an online table.

Laplace Transform Based Radiative Transfer Studies

NASA Astrophysics Data System (ADS)

Hu, Y.; Lin, B.; Ng, T.; Yang, P.; Wiscombe, W.; Herath, J.; Duffy, D.

2006-12-01

Multiple scattering is the major uncertainty for data analysis of space-based lidar measurements. Until now, accurate quantitative lidar data analysis has been limited to very thin objects that are dominated by single scattering, where photons from the laser beam only scatter a single time with particles in the atmosphere before reaching the receiver, and simple linear relationship between physical property and lidar signal exists. In reality, multiple scattering is always a factor in space-based lidar measurement and it dominates space- based lidar returns from clouds, dust aerosols, vegetation canopy and phytoplankton. While multiple scattering are clear signals, the lack of a fast-enough lidar multiple scattering computation tool forces us to treat the signal as unwanted "noise" and use simple multiple scattering correction scheme to remove them. Such multiple scattering treatments waste the multiple scattering signals and may cause orders of magnitude errors in retrieved physical properties. Thus the lack of fast and accurate time-dependent radiative transfer tools significantly limits lidar remote sensing capabilities. Analyzing lidar multiple scattering signals requires fast and accurate time-dependent radiative transfer computations. Currently, multiple scattering is done with Monte Carlo simulations. Monte Carlo simulations take minutes to hours and are too slow for interactive satellite data analysis processes and can only be used to help system / algorithm design and error assessment. We present an innovative physics approach to solve the time-dependent radiative transfer problem. The technique utilizes FPGA based reconfigurable computing hardware. The approach is as following, 1. Physics solution: Perform Laplace transform on the time and spatial dimensions and Fourier transform on the viewing azimuth dimension, and convert the radiative transfer differential equation solving into a fast matrix inversion problem. The majority of the radiative transfer computation goes to matrix inversion processes, FFT and inverse Laplace transforms. 2. Hardware solutions: Perform the well-defined matrix inversion, FFT and Laplace transforms on highly parallel, reconfigurable computing hardware. This physics-based computational tool leads to accurate quantitative analysis of space-based lidar signals and improves data quality of current lidar mission such as CALIPSO. This presentation will introduce the basic idea of this approach, preliminary results based on SRC's FPGA-based Mapstation, and how we may apply it to CALIPSO data analysis.

Computing Radiative Transfer in a 3D Medium

NASA Technical Reports Server (NTRS)

Von Allmen, Paul; Lee, Seungwon

2012-01-01

A package of software computes the time-dependent propagation of a narrow laser beam in an arbitrary three- dimensional (3D) medium with absorption and scattering, using the transient-discrete-ordinates method and a direct integration method. Unlike prior software that utilizes a Monte Carlo method, this software enables simulation at very small signal-to-noise ratios. The ability to simulate propagation of a narrow laser beam in a 3D medium is an improvement over other discrete-ordinate software. Unlike other direct-integration software, this software is not limited to simulation of propagation of thermal radiation with broad angular spread in three dimensions or of a laser pulse with narrow angular spread in two dimensions. Uses for this software include (1) computing scattering of a pulsed laser beam on a material having given elastic scattering and absorption profiles, and (2) evaluating concepts for laser-based instruments for sensing oceanic turbulence and related measurements of oceanic mixed-layer depths. With suitable augmentation, this software could be used to compute radiative transfer in ultrasound imaging in biological tissues, radiative transfer in the upper Earth crust for oil exploration, and propagation of laser pulses in telecommunication applications.

Asymmetric Base-Bleed Effect on Aerospike Plume-Induced Base-Heating Environment

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Droege, Alan; DAgostino, Mark; Lee, Young-Ching; Williams, Robert

2004-01-01

A computational heat transfer design methodology was developed to study the dual-engine linear aerospike plume-induced base-heating environment during one power-pack out, in ascent flight. It includes a three-dimensional, finite volume, viscous, chemically reacting, and pressure-based computational fluid dynamics formulation, a special base-bleed boundary condition, and a three-dimensional, finite volume, and spectral-line-based weighted-sum-of-gray-gases absorption computational radiation heat transfer formulation. A separate radiation model was used for diagnostic purposes. The computational methodology was systematically benchmarked. In this study, near-base radiative heat fluxes were computed, and they compared well with those measured during static linear aerospike engine tests. The base-heating environment of 18 trajectory points selected from three power-pack out scenarios was computed. The computed asymmetric base-heating physics were analyzed. The power-pack out condition has the most impact on convective base heating when it happens early in flight. The source of its impact comes from the asymmetric and reduced base bleed.

Thermal radiation heat transfer in participating media by finite volume discretization using collimated beam incidence

NASA Astrophysics Data System (ADS)

Harijishnu, R.; Jayakumar, J. S.

2017-09-01

The main objective of this paper is to study the heat transfer rate of thermal radiation in participating media. For that, a generated collimated beam has been passed through a two dimensional slab model of flint glass with a refractive index 2. Both Polar and azimuthal angle have been varied to generate such a beam. The Temperature of the slab and Snells law has been validated by Radiation Transfer Equation (RTE) in OpenFOAM (Open Field Operation and Manipulation), a CFD software which is the major computational tool used in Industry and research applications where the source code is modified in which radiation heat transfer equation is added to the case and different radiation heat transfer models are utilized. This work concentrates on the numerical strategies involving both transparent and participating media. Since Radiation Transfer Equation (RTE) is difficult to solve, the purpose of this paper is to use existing solver buoyantSimlpeFoam to solve radiation model in the participating media by compiling the source code to obtain the heat transfer rate inside the slab by varying the Intensity of radiation. The Finite Volume Method (FVM) is applied to solve the Radiation Transfer Equation (RTE) governing the above said physical phenomena.

Accelerated solution of discrete ordinates approximation to the Boltzmann transport equation via model reduction

DOE PAGES

Tencer, John; Carlberg, Kevin; Larsen, Marvin; ...

2017-06-17

Radiation heat transfer is an important phenomenon in many physical systems of practical interest. When participating media is important, the radiative transfer equation (RTE) must be solved for the radiative intensity as a function of location, time, direction, and wavelength. In many heat-transfer applications, a quasi-steady assumption is valid, thereby removing time dependence. The dependence on wavelength is often treated through a weighted sum of gray gases (WSGG) approach. The discrete ordinates method (DOM) is one of the most common methods for approximating the angular (i.e., directional) dependence. The DOM exactly solves for the radiative intensity for a finite numbermore » of discrete ordinate directions and computes approximations to integrals over the angular space using a quadrature rule; the chosen ordinate directions correspond to the nodes of this quadrature rule. This paper applies a projection-based model-reduction approach to make high-order quadrature computationally feasible for the DOM for purely absorbing applications. First, the proposed approach constructs a reduced basis from (high-fidelity) solutions of the radiative intensity computed at a relatively small number of ordinate directions. Then, the method computes inexpensive approximations of the radiative intensity at the (remaining) quadrature points of a high-order quadrature using a reduced-order model constructed from the reduced basis. Finally, this results in a much more accurate solution than might have been achieved using only the ordinate directions used to compute the reduced basis. One- and three-dimensional test problems highlight the efficiency of the proposed method.« less

Accelerated solution of discrete ordinates approximation to the Boltzmann transport equation via model reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tencer, John; Carlberg, Kevin; Larsen, Marvin

Radiation heat transfer is an important phenomenon in many physical systems of practical interest. When participating media is important, the radiative transfer equation (RTE) must be solved for the radiative intensity as a function of location, time, direction, and wavelength. In many heat-transfer applications, a quasi-steady assumption is valid, thereby removing time dependence. The dependence on wavelength is often treated through a weighted sum of gray gases (WSGG) approach. The discrete ordinates method (DOM) is one of the most common methods for approximating the angular (i.e., directional) dependence. The DOM exactly solves for the radiative intensity for a finite numbermore » of discrete ordinate directions and computes approximations to integrals over the angular space using a quadrature rule; the chosen ordinate directions correspond to the nodes of this quadrature rule. This paper applies a projection-based model-reduction approach to make high-order quadrature computationally feasible for the DOM for purely absorbing applications. First, the proposed approach constructs a reduced basis from (high-fidelity) solutions of the radiative intensity computed at a relatively small number of ordinate directions. Then, the method computes inexpensive approximations of the radiative intensity at the (remaining) quadrature points of a high-order quadrature using a reduced-order model constructed from the reduced basis. Finally, this results in a much more accurate solution than might have been achieved using only the ordinate directions used to compute the reduced basis. One- and three-dimensional test problems highlight the efficiency of the proposed method.« less

Frequency-selective near-field radiative heat transfer between photonic crystal slabs: a computational approach for arbitrary geometries and materials.

PubMed

Rodriguez, Alejandro W; Ilic, Ognjen; Bermel, Peter; Celanovic, Ivan; Joannopoulos, John D; Soljačić, Marin; Johnson, Steven G

2011-09-09

We demonstrate the possibility of achieving enhanced frequency-selective near-field radiative heat transfer between patterned (photonic-crystal) slabs at designable frequencies and separations, exploiting a general numerical approach for computing heat transfer in arbitrary geometries and materials based on the finite-difference time-domain method. Our simulations reveal a tradeoff between selectivity and near-field enhancement as the slab-slab separation decreases, with the patterned heat transfer eventually reducing to the unpatterned result multiplied by a fill factor (described by a standard proximity approximation). We also find that heat transfer can be further enhanced at selective frequencies when the slabs are brought into a glide-symmetric configuration, a consequence of the degeneracies associated with the nonsymmorphic symmetry group.

Analysis of Atmospheric Aerosol Data Sets and Application of Radiative Transfer Models to Compute Aerosol Effects

NASA Technical Reports Server (NTRS)

Schmid, Beat; Bergstrom, Robert W.; Redemann, Jens

2002-01-01

This report is the final report for "Analysis of Atmospheric Aerosol Data Sets and Application of Radiative Transfer Models to Compute Aerosol Effects". It is a bibliographic compilation of 29 peer-reviewed publications (published, in press or submitted) produced under this Cooperative Agreement and 30 first-authored conference presentations. The tasks outlined in the various proposals are listed below with a brief comment as to the research performed. Copies of title/abstract pages of peer-reviewed publications are attached.

Cumulative effective radiation dose received by blunt trauma patients arriving to a military level I trauma center from point of injury and interhospital transfers.

PubMed

Van Arnem, Kerri A; Supinski, David P; Tucker, Jonathan E; Varney, Shawn

2016-12-01

Trauma patients sustaining blunt injuries are exposed to multiple radiologic studies. Evidence indicates that the risk of cancer from exposure to ionizing radiation rises in direct proportion to the cumulative effective dose (CED) received. The purpose of this study is to quantify the amount of ionizing radiation accumulated when arriving directly from point of injury to San Antonio Military Medical Center (SAMMC), a level I trauma center, compared with those transferred from other facilities. A retrospective record review was conducted from 1st January 2010 through 31st December 2012. The SAMMC trauma registry, electronic medical records, and the digital radiology imaging system were searched for possible candidates. The medical records were then analyzed for sex, age, mechanism of injury, received directly from point of injury (direct group), transfer from another medical facility (transfer group), computed tomographic scans received, dose-length product, CED of radiation, and injury severity score. A diagnostic imaging physicist then calculated the estimated CED each subject received based on the dose-length product of each computed tomographic scan. A total of 300 patients were analyzed, with 150 patients in the direct group and 150 patients in the transfer group. Both groups were similar in age and sex. Patients in the transfer group received a significantly greater CED of radiation compared with the direct group (mean, 37.6 mSv vs 28 mSv; P=.001). The radiation received in the direct group correlates with a lifetime attributable risk (LAR) of 1 in 357 compared with the transfer group with an increase in LAR to 1 in 266. Patients transferred to our facility received a 34% increase in ionizing radiation compared with patients brought directly from the injury scene. This increased dose of ionizing radiation contributes to the LAR of cancer and needs to be considered before repeating imaging studies. III. Published by Elsevier Inc.

Advanced Computational Methods for Thermal Radiative Heat Transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tencer, John; Carlberg, Kevin Thomas; Larsen, Marvin E.

2016-10-01

Participating media radiation (PMR) in weapon safety calculations for abnormal thermal environments are too costly to do routinely. This cost may be s ubstantially reduced by applying reduced order modeling (ROM) techniques. The application of ROM to PMR is a new and unique approach for this class of problems. This approach was investigated by the authors and shown to provide significant reductions in the computational expense associated with typical PMR simulations. Once this technology is migrated into production heat transfer analysis codes this capability will enable the routine use of PMR heat transfer in higher - fidelity simulations of weaponmore » resp onse in fire environments.« less

Linearized radiative transfer models for retrieval of cloud parameters from EPIC/DSCOVR measurements

NASA Astrophysics Data System (ADS)

Molina García, Víctor; Sasi, Sruthy; Efremenko, Dmitry S.; Doicu, Adrian; Loyola, Diego

2018-07-01

In this paper, we describe several linearized radiative transfer models which can be used for the retrieval of cloud parameters from EPIC (Earth Polychromatic Imaging Camera) measurements. The approaches under examination are (1) the linearized forward approach, represented in this paper by the linearized discrete ordinate and matrix operator methods with matrix exponential, and (2) the forward-adjoint approach based on the discrete ordinate method with matrix exponential. To enhance the performance of the radiative transfer computations, the correlated k-distribution method and the Principal Component Analysis (PCA) technique are used. We provide a compact description of the proposed methods, as well as a numerical analysis of their accuracy and efficiency when simulating EPIC measurements in the oxygen A-band channel at 764 nm. We found that the computation time of the forward-adjoint approach using the correlated k-distribution method in conjunction with PCA is approximately 13 s for simultaneously computing the derivatives with respect to cloud optical thickness and cloud top height.

Green's function solution to radiative heat transfer between longitudinal gray fins

NASA Technical Reports Server (NTRS)

Frankel, J. I.; Silvestri, J. J.

1991-01-01

A demonstration is presented of the applicability and versatility of a pure integral formulation for radiative-conductive heat-transfer problems. Preliminary results have been obtained which indicate that this formulation allows an accurate, fast, and stable computation procedure to be implemented. Attention is given to the accessory problem defining Green's function.

A design tool for direct and non-stochastic calculations of near-field radiative transfer in complex structures: The NF-RT-FDTD algorithm

NASA Astrophysics Data System (ADS)

Didari, Azadeh; Pinar Mengüç, M.

2017-08-01

Advances in nanotechnology and nanophotonics are inextricably linked with the need for reliable computational algorithms to be adapted as design tools for the development of new concepts in energy harvesting, radiative cooling, nanolithography and nano-scale manufacturing, among others. In this paper, we provide an outline for such a computational tool, named NF-RT-FDTD, to determine the near-field radiative transfer between structured surfaces using Finite Difference Time Domain method. NF-RT-FDTD is a direct and non-stochastic algorithm, which accounts for the statistical nature of the thermal radiation and is easily applicable to any arbitrary geometry at thermal equilibrium. We present a review of the fundamental relations for far- and near-field radiative transfer between different geometries with nano-scale surface and volumetric features and gaps, and then we discuss the details of the NF-RT-FDTD formulation, its application to sample geometries and outline its future expansion to more complex geometries. In addition, we briefly discuss some of the recent numerical works for direct and indirect calculations of near-field thermal radiation transfer, including Scattering Matrix method, Finite Difference Time Domain method (FDTD), Wiener Chaos Expansion, Fluctuating Surface Current (FSC), Fluctuating Volume Current (FVC) and Thermal Discrete Dipole Approximations (TDDA).

A second order radiative transfer equation and its solution by meshless method with application to strongly inhomogeneous media

NASA Astrophysics Data System (ADS)

Zhao, J. M.; Tan, J. Y.; Liu, L. H.

2013-01-01

A new second order form of radiative transfer equation (named MSORTE) is proposed, which overcomes the singularity problem of a previously proposed second order radiative transfer equation [J.E. Morel, B.T. Adams, T. Noh, J.M. McGhee, T.M. Evans, T.J. Urbatsch, Spatial discretizations for self-adjoint forms of the radiative transfer equations, J. Comput. Phys. 214 (1) (2006) 12-40 (where it was termed SAAI), J.M. Zhao, L.H. Liu, Second order radiative transfer equation and its properties of numerical solution using finite element method, Numer. Heat Transfer B 51 (2007) 391-409] in dealing with inhomogeneous media where some locations have very small/zero extinction coefficient. The MSORTE contains a naturally introduced diffusion (or second order) term which provides better numerical property than the classic first order radiative transfer equation (RTE). The stability and convergence characteristics of the MSORTE discretized by central difference scheme is analyzed theoretically, and the better numerical stability of the second order form radiative transfer equations than the RTE when discretized by the central difference type method is proved. A collocation meshless method is developed based on the MSORTE to solve radiative transfer in inhomogeneous media. Several critical test cases are taken to verify the performance of the presented method. The collocation meshless method based on the MSORTE is demonstrated to be capable of stably and accurately solve radiative transfer in strongly inhomogeneous media, media with void region and even with discontinuous extinction coefficient.

Assessment of uncertainty in the numerical simulation of solar irradiance over inclined PV panels: New algorithms using measurements and modeling tools

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Yu; Sengupta, Manajit; Dooraghi, Mike

Development of accurate transposition models to simulate plane-of-array (POA) irradiance from horizontal measurements or simulations is a complex process mainly because of the anisotropic distribution of diffuse solar radiation in the atmosphere. The limited availability of reliable POA measurements at large temporal and spatial scales leads to difficulties in the comprehensive evaluation of transposition models. This paper proposes new algorithms to assess the uncertainty of transposition models using both surface-based observations and modeling tools. We reviewed the analytical derivation of POA irradiance and the approximation of isotropic diffuse radiation that simplifies the computation. Two transposition models are evaluated against themore » computation by the rigorous analytical solution. We proposed a new algorithm to evaluate transposition models using the clear-sky measurements at the National Renewable Energy Laboratory's (NREL's) Solar Radiation Research Laboratory (SRRL) and a radiative transfer model that integrates diffuse radiances of various sky-viewing angles. We found that the radiative transfer model and a transposition model based on empirical regressions are superior to the isotropic models when compared to measurements. We further compared the radiative transfer model to the transposition models under an extensive range of idealized conditions. Our results suggest that the empirical transposition model has slightly higher cloudy-sky POA irradiance than the radiative transfer model, but performs better than the isotropic models under clear-sky conditions. Significantly smaller POA irradiances computed by the transposition models are observed when the photovoltaics (PV) panel deviates from the azimuthal direction of the sun. The new algorithms developed in the current study have opened the door to a more comprehensive evaluation of transposition models for various atmospheric conditions and solar and PV orientations.« less

Assessment of uncertainty in the numerical simulation of solar irradiance over inclined PV panels: New algorithms using measurements and modeling tools

DOE PAGES

Xie, Yu; Sengupta, Manajit; Dooraghi, Mike

2018-03-20

Development of accurate transposition models to simulate plane-of-array (POA) irradiance from horizontal measurements or simulations is a complex process mainly because of the anisotropic distribution of diffuse solar radiation in the atmosphere. The limited availability of reliable POA measurements at large temporal and spatial scales leads to difficulties in the comprehensive evaluation of transposition models. This paper proposes new algorithms to assess the uncertainty of transposition models using both surface-based observations and modeling tools. We reviewed the analytical derivation of POA irradiance and the approximation of isotropic diffuse radiation that simplifies the computation. Two transposition models are evaluated against themore » computation by the rigorous analytical solution. We proposed a new algorithm to evaluate transposition models using the clear-sky measurements at the National Renewable Energy Laboratory's (NREL's) Solar Radiation Research Laboratory (SRRL) and a radiative transfer model that integrates diffuse radiances of various sky-viewing angles. We found that the radiative transfer model and a transposition model based on empirical regressions are superior to the isotropic models when compared to measurements. We further compared the radiative transfer model to the transposition models under an extensive range of idealized conditions. Our results suggest that the empirical transposition model has slightly higher cloudy-sky POA irradiance than the radiative transfer model, but performs better than the isotropic models under clear-sky conditions. Significantly smaller POA irradiances computed by the transposition models are observed when the photovoltaics (PV) panel deviates from the azimuthal direction of the sun. The new algorithms developed in the current study have opened the door to a more comprehensive evaluation of transposition models for various atmospheric conditions and solar and PV orientations.« less

Laser radiation in active amplifying media treated as a transport problem - Transfer equation derived and exactly solved

NASA Astrophysics Data System (ADS)

Gupta, S. R. D.; Gupta, Santanu D.

1991-10-01

The flow of laser radiation in a plane-parallel cylindrical slab of active amplifying medium with axial symmetry is treated as a problem in radiative transfer. The appropriate one-dimensional transfer equation describing the transfer of laser radiation has been derived by an appeal to Einstein's A, B coefficients (describing the processes of stimulated line absorption, spontaneous line emission, and stimulated line emission sustained by population inversion in the medium) and considering the 'rate equations' to completely establish the rational of the transfer equation obtained. The equation is then exactly solved and the angular distribution of the emergent laser beam intensity is obtained; its numerically computed values are given in tables and plotted in graphs showing the nature of peaks of the emerging laser beam intensity about the axis of the laser cylinder.

Incorporation of Three-dimensional Radiative Transfer into a Very High Resolution Simulation of Horizontally Inhomogeneous Clouds

NASA Astrophysics Data System (ADS)

Ishida, H.; Ota, Y.; Sekiguchi, M.; Sato, Y.

2016-12-01

A three-dimensional (3D) radiative transfer calculation scheme is developed to estimate horizontal transport of radiation energy in a very high resolution (with the order of 10 m in spatial grid) simulation of cloud evolution, especially for horizontally inhomogeneous clouds such as shallow cumulus and stratocumulus. Horizontal radiative transfer due to inhomogeneous clouds seems to cause local heating/cooling in an atmosphere with a fine spatial scale. It is, however, usually difficult to estimate the 3D effects, because the 3D radiative transfer often needs a large resource for computation compared to a plane-parallel approximation. This study attempts to incorporate a solution scheme that explicitly solves the 3D radiative transfer equation into a numerical simulation, because this scheme has an advantage in calculation for a sequence of time evolution (i.e., the scene at a time is little different from that at the previous time step). This scheme is also appropriate to calculation of radiation with strong absorption, such as the infrared regions. For efficient computation, this scheme utilizes several techniques, e.g., the multigrid method for iteration solution, and a correlated-k distribution method refined for efficient approximation of the wavelength integration. For a case study, the scheme is applied to an infrared broadband radiation calculation in a broken cloud field generated with a large eddy simulation model. The horizontal transport of infrared radiation, which cannot be estimated by the plane-parallel approximation, and its variation in time can be retrieved. The calculation result elucidates that the horizontal divergences and convergences of infrared radiation flux are not negligible, especially at the boundaries of clouds and within optically thin clouds, and the radiative cooling at lateral boundaries of clouds may reduce infrared radiative heating in clouds. In a future work, the 3D effects on radiative heating/cooling will be able to be included into atmospheric numerical models.

Performance tuning Weather Research and Forecasting (WRF) Goddard longwave radiative transfer scheme on Intel Xeon Phi

NASA Astrophysics Data System (ADS)

Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.

2015-10-01

Next-generation mesoscale numerical weather prediction system, the Weather Research and Forecasting (WRF) model, is a designed for dual use for forecasting and research. WRF offers multiple physics options that can be combined in any way. One of the physics options is radiance computation. The major source for energy for the earth's climate is solar radiation. Thus, it is imperative to accurately model horizontal and vertical distribution of the heating. Goddard solar radiative transfer model includes the absorption duo to water vapor,ozone, ozygen, carbon dioxide, clouds and aerosols. The model computes the interactions among the absorption and scattering by clouds, aerosols, molecules and surface. Finally, fluxes are integrated over the entire longwave spectrum.In this paper, we present our results of optimizing the Goddard longwave radiative transfer scheme on Intel Many Integrated Core Architecture (MIC) hardware. The Intel Xeon Phi coprocessor is the first product based on Intel MIC architecture, and it consists of up to 61 cores connected by a high performance on-die bidirectional interconnect. The coprocessor supports all important Intel development tools. Thus, the development environment is familiar one to a vast number of CPU developers. Although, getting a maximum performance out of MICs will require using some novel optimization techniques. Those optimization techniques are discusses in this paper. The optimizations improved the performance of the original Goddard longwave radiative transfer scheme on Xeon Phi 7120P by a factor of 2.2x. Furthermore, the same optimizations improved the performance of the Goddard longwave radiative transfer scheme on a dual socket configuration of eight core Intel Xeon E5-2670 CPUs by a factor of 2.1x compared to the original Goddard longwave radiative transfer scheme code.

Infrared Algorithm Development for Ocean Observations with EOS/MODIS

NASA Technical Reports Server (NTRS)

Brown, Otis B.

1997-01-01

Efforts continue under this contract to develop algorithms for the computation of sea surface temperature (SST) from MODIS infrared measurements. This effort includes radiative transfer modeling, comparison of in situ and satellite observations, development and evaluation of processing and networking methodologies for algorithm computation and data accession, evaluation of surface validation approaches for IR radiances, development of experimental instrumentation, and participation in MODIS (project) related activities. Activities in this contract period have focused on radiative transfer modeling, evaluation of atmospheric correction methodologies, undertake field campaigns, analysis of field data, and participation in MODIS meetings.

Earth Sciences Push Radiative Transfer Theory

NASA Astrophysics Data System (ADS)

Davis, Anthony; Mishchenko, Michael

2009-12-01

2009 International Conference on Advances in Mathematics, Computational Methods, and Reactor Physics; Saratoga Springs, New York, 4-7 May 2009; The theories of radiative transfer and particle—particularly neutron—transport are grounded in distinctive microscale physics that deals with either optics or particle dynamics. However, it is not practical to track every wave or particle in macroscopic systems, nor do all of these details matter. That is why Newton's laws, which describe individual particles, are replaced by those of Euler, Navier-Stokes, Maxwell, Boltzmann, Gibbs, and others, which describe the collective behavior of vast numbers of particles. And that is why the radiative transfer (RT) equation is used to describe the flow of radiation through geophysical-scale systems, leaving to Maxwell's wave equations only the task of providing the optical properties of the medium, be it air, water, snow, ice, or biomass. Interestingly, particle transport is determined by the linear transport equation, which is mathematically identical to the RT equation, so geophysicists and nuclear scientists are interested in the same mathematics and computational techniques.

Discrete diffusion Lyman α radiative transfer

NASA Astrophysics Data System (ADS)

Smith, Aaron; Tsang, Benny T.-H.; Bromm, Volker; Milosavljević, Miloš

2018-06-01

Due to its accuracy and generality, Monte Carlo radiative transfer (MCRT) has emerged as the prevalent method for Lyα radiative transfer in arbitrary geometries. The standard MCRT encounters a significant efficiency barrier in the high optical depth, diffusion regime. Multiple acceleration schemes have been developed to improve the efficiency of MCRT but the noise from photon packet discretization remains a challenge. The discrete diffusion Monte Carlo (DDMC) scheme has been successfully applied in state-of-the-art radiation hydrodynamics (RHD) simulations. Still, the established framework is not optimal for resonant line transfer. Inspired by the DDMC paradigm, we present a novel extension to resonant DDMC (rDDMC) in which diffusion in space and frequency are treated on equal footing. We explore the robustness of our new method and demonstrate a level of performance that justifies incorporating the method into existing Lyα codes. We present computational speedups of ˜102-106 relative to contemporary MCRT implementations with schemes that skip scattering in the core of the line profile. This is because the rDDMC runtime scales with the spatial and frequency resolution rather than the number of scatterings—the latter is typically ∝τ0 for static media, or ∝(aτ0)2/3 with core-skipping. We anticipate new frontiers in which on-the-fly Lyα radiative transfer calculations are feasible in 3D RHD. More generally, rDDMC is transferable to any computationally demanding problem amenable to a Fokker-Planck approximation of frequency redistribution.

Monte Carlo Calculations of Polarized Microwave Radiation Emerging from Cloud Structures

NASA Technical Reports Server (NTRS)

Kummerow, Christian; Roberti, Laura

1998-01-01

The last decade has seen tremendous growth in cloud dynamical and microphysical models that are able to simulate storms and storm systems with very high spatial resolution, typically of the order of a few kilometers. The fairly realistic distributions of cloud and hydrometeor properties that these models generate has in turn led to a renewed interest in the three-dimensional microwave radiative transfer modeling needed to understand the effect of cloud and rainfall inhomogeneities upon microwave observations. Monte Carlo methods, and particularly backwards Monte Carlo methods have shown themselves to be very desirable due to the quick convergence of the solutions. Unfortunately, backwards Monte Carlo methods are not well suited to treat polarized radiation. This study reviews the existing Monte Carlo methods and presents a new polarized Monte Carlo radiative transfer code. The code is based on a forward scheme but uses aliasing techniques to keep the computational requirements equivalent to the backwards solution. Radiative transfer computations have been performed using a microphysical-dynamical cloud model and the results are presented together with the algorithm description.

HO-CHUNK: Radiation Transfer code

NASA Astrophysics Data System (ADS)

Whitney, Barbara A.; Wood, Kenneth; Bjorkman, J. E.; Cohen, Martin; Wolff, Michael J.

2017-11-01

HO-CHUNK calculates radiative equilibrium temperature solution, thermal and PAH/vsg emission, scattering and polarization in protostellar geometries. It is useful for computing spectral energy distributions (SEDs), polarization spectra, and images.

Vectorial finite elements for solving the radiative transfer equation

NASA Astrophysics Data System (ADS)

Badri, M. A.; Jolivet, P.; Rousseau, B.; Le Corre, S.; Digonnet, H.; Favennec, Y.

2018-06-01

The discrete ordinate method coupled with the finite element method is often used for the spatio-angular discretization of the radiative transfer equation. In this paper we attempt to improve upon such a discretization technique. Instead of using standard finite elements, we reformulate the radiative transfer equation using vectorial finite elements. In comparison to standard finite elements, this reformulation yields faster timings for the linear system assemblies, as well as for the solution phase when using scattering media. The proposed vectorial finite element discretization for solving the radiative transfer equation is cross-validated against a benchmark problem available in literature. In addition, we have used the method of manufactured solutions to verify the order of accuracy for our discretization technique within different absorbing, scattering, and emitting media. For solving large problems of radiation on parallel computers, the vectorial finite element method is parallelized using domain decomposition. The proposed domain decomposition method scales on large number of processes, and its performance is unaffected by the changes in optical thickness of the medium. Our parallel solver is used to solve a large scale radiative transfer problem of the Kelvin-cell radiation.

Introductory Tools for Radiative Transfer Models

NASA Astrophysics Data System (ADS)

Feldman, D.; Kuai, L.; Natraj, V.; Yung, Y.

2006-12-01

Satellite data are currently so voluminous that, despite their unprecedented quality and potential for scientific application, only a small fraction is analyzed due to two factors: researchers' computational constraints and a relatively small number of researchers actively utilizing the data. Ultimately it is hoped that the terabytes of unanalyzed data being archived can receive scientific scrutiny but this will require a popularization of the methods associated with the analysis. Since a large portion of complexity is associated with the proper implementation of the radiative transfer model, it is reasonable and appropriate to make the model as accessible as possible to general audiences. Unfortunately, the algorithmic and conceptual details that are necessary for state-of-the-art analysis also tend to frustrate the accessibility for those new to remote sensing. Several efforts have been made to have web- based radiative transfer calculations, and these are useful for limited calculations, but analysis of more than a few spectra requires the utilization of home- or server-based computing resources. We present a system that is designed to allow for easier access to radiative transfer models with implementation on a home computing platform in the hopes that this system can be utilized in and expanded upon in advanced high school and introductory college settings. This learning-by-doing process is aided through the use of several powerful tools. The first is a wikipedia-style introduction to the salient features of radiative transfer that references the seminal works in the field and refers to more complicated calculations and algorithms sparingly5. The second feature is a technical forum, commonly referred to as a tiki-wiki, that addresses technical and conceptual questions through public postings, private messages, and a ranked searching routine. Together, these tools may be able to facilitate greater interest in the field of remote sensing.

Simple Models of the Spatial Distribution of Cloud Radiative Properties for Remote Sensing Studies

NASA Technical Reports Server (NTRS)

2004-01-01

This project aimed to assess the degree to which estimates of three-dimensional cloud structure can be inferred from a time series of profiles obtained at a point. The work was motivated by the desire to understand the extent to which high-frequency profiles of the atmosphere (e.g. ARM data streams) can be used to assess the magnitude of non-plane parallel transfer of radiation in thc atmosphere. We accomplished this by performing an observing system simulation using a large-eddy simulation and a Monte Carlo radiative transfer model. We define the 3D effect as the part of the radiative transfer that isn't captured by one-dimensional radiative transfer calculations. We assess the magnitude of the 3D effect in small cumulus clouds by using a fine-scale cloud model to simulate many hours of cloudiness over a continental site. We then use a Monte Carlo radiative transfer model to compute the broadband shortwave fluxes at the surface twice, once using the complete three-dimensional radiative transfer F(sup 3D), and once using the ICA F (sup ICA); the difference between them is the 3D effect given.

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

NASA Technical Reports Server (NTRS)

Weng, Fuzhong

1992-01-01

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.

Forward Monte Carlo Computations of Polarized Microwave Radiation

NASA Technical Reports Server (NTRS)

Battaglia, A.; Kummerow, C.

2000-01-01

Microwave radiative transfer computations continue to acquire greater importance as the emphasis in remote sensing shifts towards the understanding of microphysical properties of clouds and with these to better understand the non linear relation between rainfall rates and satellite-observed radiance. A first step toward realistic radiative simulations has been the introduction of techniques capable of treating 3-dimensional geometry being generated by ever more sophisticated cloud resolving models. To date, a series of numerical codes have been developed to treat spherical and randomly oriented axisymmetric particles. Backward and backward-forward Monte Carlo methods are, indeed, efficient in this field. These methods, however, cannot deal properly with oriented particles, which seem to play an important role in polarization signatures over stratiform precipitation. Moreover, beyond the polarization channel, the next generation of fully polarimetric radiometers challenges us to better understand the behavior of the last two Stokes parameters as well. In order to solve the vector radiative transfer equation, one-dimensional numerical models have been developed, These codes, unfortunately, consider the atmosphere as horizontally homogeneous with horizontally infinite plane parallel layers. The next development step for microwave radiative transfer codes must be fully polarized 3-D methods. Recently a 3-D polarized radiative transfer model based on the discrete ordinate method was presented. A forward MC code was developed that treats oriented nonspherical hydrometeors, but only for plane-parallel situations.

Laser Radiation in Active Amplifying Media Treated as a Transport Problem - Transfer Equation Derived and Exactly Solved

NASA Astrophysics Data System (ADS)

Das Gupta, Santanu; Das Gupta, S. R.

1991-10-01

The flow of laser radiation in a plane-parallel cylindrical slab of active amplifying medium with axial symmetry is treated as a problem in radiative transfer. The appropriate one-dimensional transfer equation describing the transfer of laser radiation has been derived by an appeal to Einstein'sA, B coefficients (describing the processes of stimulated line absorption, spontaneous line emission, and stimulated line emission sustained by population inversion in the medium) and considering the ‘rate equations’ to completely establish the rational of the transfer equation obtained. The equation is then exactly solved and the angular distribution of the emergent laser beam intensity is obtained; its numerically computed values are given in tables and plotted in graphs showing the nature of peaks of the emerging laser beam intensity about the axis of the laser cylinder.

Algorithms for radiative transfer simulations for aerosol retrieval

NASA Astrophysics Data System (ADS)

Mukai, Sonoyo; Sano, Itaru; Nakata, Makiko

2012-11-01

Aerosol retrieval work from satellite data, i.e. aerosol remote sensing, is divided into three parts as: satellite data analysis, aerosol modeling and multiple light scattering calculation in the atmosphere model which is called radiative transfer simulation. The aerosol model is compiled from the accumulated measurements during more than ten years provided with the world wide aerosol monitoring network (AERONET). The radiative transfer simulations take Rayleigh scattering by molecules and Mie scattering by aerosols in the atmosphere, and reflection by the Earth surface into account. Thus the aerosol properties are estimated by comparing satellite measurements with the numerical values of radiation simulations in the Earth-atmosphere-surface model. It is reasonable to consider that the precise simulation of multiple light-scattering processes is necessary, and needs a long computational time especially in an optically thick atmosphere model. Therefore efficient algorithms for radiative transfer problems are indispensable to retrieve aerosols from space.

A probabilistic approach to radiative energy loss calculations for optically thick atmospheres - Hydrogen lines and continua

NASA Technical Reports Server (NTRS)

Canfield, R. C.; Ricchiazzi, P. J.

1980-01-01

An approximate probabilistic radiative transfer equation and the statistical equilibrium equations are simultaneously solved for a model hydrogen atom consisting of three bound levels and ionization continuum. The transfer equation for L-alpha, L-beta, H-alpha, and the Lyman continuum is explicitly solved assuming complete redistribution. The accuracy of this approach is tested by comparing source functions and radiative loss rates to values obtained with a method that solves the exact transfer equation. Two recent model solar-flare chromospheres are used for this test. It is shown that for the test atmospheres the probabilistic method gives values of the radiative loss rate that are characteristically good to a factor of 2. The advantage of this probabilistic approach is that it retains a description of the dominant physical processes of radiative transfer in the complete redistribution case, yet it achieves a major reduction in computational requirements.

Radiative Transfer Model for Operational Retrieval of Cloud Parameters from DSCOVR-EPIC Measurements

NASA Astrophysics Data System (ADS)

Yang, Y.; Molina Garcia, V.; Doicu, A.; Loyola, D. G.

2016-12-01

The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) measures the radiance in the backscattering region. To make sure that all details in the backward glory are covered, a large number of streams is required by a standard radiative transfer model based on the discrete ordinates method. Even the use of the delta-M scaling and the TMS correction do not substantially reduce the number of streams. The aim of this work is to analyze the capability of a fast radiative transfer model to retrieve operationally cloud parameters from EPIC measurements. The radiative transfer model combines the discrete ordinates method with matrix exponential for the computation of radiances and the matrix operator method for the calculation of the reflection and transmission matrices. Standard acceleration techniques as, for instance, the use of the normalized right and left eigenvectors, telescoping technique, Pade approximation and successive-order-of-scattering approximation are implemented. In addition, the model may compute the reflection matrix of the cloud by means of the asymptotic theory, and may use the equivalent Lambertian cloud model. The various approximations are analyzed from the point of view of efficiency and accuracy.

Using Neural Networks to Improve the Performance of Radiative Transfer Modeling Used for Geometry Dependent LER Calculations

NASA Astrophysics Data System (ADS)

Fasnacht, Z.; Qin, W.; Haffner, D. P.; Loyola, D. G.; Joiner, J.; Krotkov, N. A.; Vasilkov, A. P.; Spurr, R. J. D.

2017-12-01

In order to estimate surface reflectance used in trace gas retrieval algorithms, radiative transfer models (RTM) such as the Vector Linearized Discrete Ordinate Radiative Transfer Model (VLIDORT) can be used to simulate the top of the atmosphere (TOA) radiances with advanced models of surface properties. With large volumes of satellite data, these model simulations can become computationally expensive. Look up table interpolation can improve the computational cost of the calculations, but the non-linear nature of the radiances requires a dense node structure if interpolation errors are to be minimized. In order to reduce our computational effort and improve the performance of look-up tables, neural networks can be trained to predict these radiances. We investigate the impact of using look-up table interpolation versus a neural network trained using the smart sampling technique, and show that neural networks can speed up calculations and reduce errors while using significantly less memory and RTM calls. In future work we will implement a neural network in operational processing to meet growing demands for reflectance modeling in support of high spatial resolution satellite missions.

Computational attributes of the integral form of the equation of transfer

NASA Technical Reports Server (NTRS)

Frankel, J. I.

1991-01-01

Difficulties can arise in radiative and neutron transport calculations when a highly anisotropic scattering phase function is present. In the presence of anisotropy, currently used numerical solutions are based on the integro-differential form of the linearized Boltzmann transport equation. This paper, departs from classical thought and presents an alternative numerical approach based on application of the integral form of the transport equation. Use of the integral formalism facilitates the following steps: a reduction in dimensionality of the system prior to discretization, the use of symbolic manipulation to augment the computational procedure, and the direct determination of key physical quantities which are derivable through the various Legendre moments of the intensity. The approach is developed in the context of radiative heat transfer in a plane-parallel geometry, and results are presented and compared with existing benchmark solutions. Encouraging results are presented to illustrate the potential of the integral formalism for computation. The integral formalism appears to possess several computational attributes which are well-suited to radiative and neutron transport calculations.

Performance Analysis of GFDL's GCM Line-By-Line Radiative Transfer Model on GPU and MIC Architectures

NASA Astrophysics Data System (ADS)

Menzel, R.; Paynter, D.; Jones, A. L.

2017-12-01

Due to their relatively low computational cost, radiative transfer models in global climate models (GCMs) run on traditional CPU architectures generally consist of shortwave and longwave parameterizations over a small number of wavelength bands. With the rise of newer GPU and MIC architectures, however, the performance of high resolution line-by-line radiative transfer models may soon approach those of the physical parameterizations currently employed in GCMs. Here we present an analysis of the current performance of a new line-by-line radiative transfer model currently under development at GFDL. Although originally designed to specifically exploit GPU architectures through the use of CUDA, the radiative transfer model has recently been extended to include OpenMP in an effort to also effectively target MIC architectures such as Intel's Xeon Phi. Using input data provided by the upcoming Radiative Forcing Model Intercomparison Project (RFMIP, as part of CMIP 6), we compare model results and performance data for various model configurations and spectral resolutions run on both GPU and Intel Knights Landing architectures to analogous runs of the standard Oxford Reference Forward Model on traditional CPUs.

Analysis of Material Sample Heated by Impinging Hot Hydrogen Jet in a Non-Nuclear Tester

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Foote, John; Litchford, Ron

2006-01-01

A computational conjugate heat transfer methodology was developed and anchored with data obtained from a hot-hydrogen jet heated, non-nuclear materials tester, as a first step towards developing an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective and thermal radiative, and conjugate heat transfers. Predicted hot hydrogen jet and material surface temperatures were compared with those of measurement. Predicted solid temperatures were compared with those obtained with a standard heat transfer code. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

Effect of element size on the solution accuracies of finite-element heat transfer and thermal stress analyses of space shuttle orbiter

NASA Technical Reports Server (NTRS)

Ko, William L.; Olona, Timothy

1987-01-01

The effect of element size on the solution accuracies of finite-element heat transfer and thermal stress analyses of space shuttle orbiter was investigated. Several structural performance and resizing (SPAR) thermal models and NASA structural analysis (NASTRAN) structural models were set up for the orbiter wing midspan bay 3. The thermal model was found to be the one that determines the limit of finite-element fineness because of the limitation of computational core space required for the radiation view factor calculations. The thermal stresses were found to be extremely sensitive to a slight variation of structural temperature distributions. The minimum degree of element fineness required for the thermal model to yield reasonably accurate solutions was established. The radiation view factor computation time was found to be insignificant compared with the total computer time required for the SPAR transient heat transfer analysis.

Arcmancer: Geodesics and polarized radiative transfer library

NASA Astrophysics Data System (ADS)

Pihajoki, Pauli; Mannerkoski, Matias; Nättilä, Joonas; Johansson, Peter H.

2018-05-01

Arcmancer computes geodesics and performs polarized radiative transfer in user-specified spacetimes. The library supports Riemannian and semi-Riemannian spaces of any dimension and metric; it also supports multiple simultaneous coordinate charts, embedded geometric shapes, local coordinate systems, and automatic parallel propagation. Arcmancer can be used to solve various problems in numerical geometry, such as solving the curve equation of motion using adaptive integration with configurable tolerances and differential equations along precomputed curves. It also provides support for curves with an arbitrary acceleration term and generic tools for generating ray initial conditions and performing parallel computation over the image, among other tools.

Theory of heat transfer and hydraulic resistance of oil radiators

NASA Technical Reports Server (NTRS)

Mariamov, N B

1942-01-01

In the present report the coefficients of heat transfer and hydraulic resistance are theoretically obtained for the case of laminar flow of a heated viscous liquid in a narrow rectangular channel. The results obtained are applied to the computation of oil radiators, which to a first approximation may be considered as made up of a system of such channels. In conclusion, a comparison is given of the theoretical with the experimental results obtained from tests on airplane oil radiators.

RTE: A UNIX library with on-line documentation and sample programs for microwave radiative transfer calculations

NASA Astrophysics Data System (ADS)

Reynolds, J. C.; Schroeder, J. A.

1993-03-01

The FORTRAN library that the NOAA Wave Propagation Laboratory (WPL) developed to perform radiative transfer calculations for an upward-looking microwave radiometer is described. Although the theory and algorithms have been used for many years in WPL radiometer research, the Radiative Transfer Equation (RTE) software has combined them into a toolbox that is portable, readable, application independent, and easy to update. RTE has been optimized for the UNIX environment. However, the FORTRAN source code can be compiled on any platform that provides a Standard FORTRAN 77 compiler. RTE allows a user to do cloud modeling, calibrate radiometers, simulate hypothetical radiometer systems, develop retrieval techniques, and compute weighting functions. The radiative transfer model used is valid for channel frequencies below 1000 GHz in clear conditions and for frequencies below 100 GHz when clouds are present.

A Computational Fluid Dynamic and Heat Transfer Model for Gaseous Core and Gas Cooled Space Power and Propulsion Reactors

NASA Technical Reports Server (NTRS)

Anghaie, S.; Chen, G.

1996-01-01

A computational model based on the axisymmetric, thin-layer Navier-Stokes equations is developed to predict the convective, radiation and conductive heat transfer in high temperature space nuclear reactors. An implicit-explicit, finite volume, MacCormack method in conjunction with the Gauss-Seidel line iteration procedure is utilized to solve the thermal and fluid governing equations. Simulation of coolant and propellant flows in these reactors involves the subsonic and supersonic flows of hydrogen, helium and uranium tetrafluoride under variable boundary conditions. An enthalpy-rebalancing scheme is developed and implemented to enhance and accelerate the rate of convergence when a wall heat flux boundary condition is used. The model also incorporated the Baldwin and Lomax two-layer algebraic turbulence scheme for the calculation of the turbulent kinetic energy and eddy diffusivity of energy. The Rosseland diffusion approximation is used to simulate the radiative energy transfer in the optically thick environment of gas core reactors. The computational model is benchmarked with experimental data on flow separation angle and drag force acting on a suspended sphere in a cylindrical tube. The heat transfer is validated by comparing the computed results with the standard heat transfer correlations predictions. The model is used to simulate flow and heat transfer under a variety of design conditions. The effect of internal heat generation on the heat transfer in the gas core reactors is examined for a variety of power densities, 100 W/cc, 500 W/cc and 1000 W/cc. The maximum temperature, corresponding with the heat generation rates, are 2150 K, 2750 K and 3550 K, respectively. This analysis shows that the maximum temperature is strongly dependent on the value of heat generation rate. It also indicates that a heat generation rate higher than 1000 W/cc is necessary to maintain the gas temperature at about 3500 K, which is typical design temperature required to achieve high efficiency in the gas core reactors. The model is also used to predict the convective and radiation heat fluxes for the gas core reactors. The maximum value of heat flux occurs at the exit of the reactor core. Radiation heat flux increases with higher wall temperature. This behavior is due to the fact that the radiative heat flux is strongly dependent on wall temperature. This study also found that at temperature close to 3500 K the radiative heat flux is comparable with the convective heat flux in a uranium fluoride failed gas core reactor.

Radiative Instabilities in Three-Dimensional Astrophysical Masers

NASA Technical Reports Server (NTRS)

Scappaticci, Gerardo A.; Watson, William D.

1995-01-01

Inherent instabilities in the radiative transfer for astrophysical masers have been recognized and calculated in the linear maser idealization in our previous investigations. The same instabilities are now shown to occur in the more realistic, three-dimensional geometries. Fluctuations in the emergent flux result and may be related to the observed fluctuations in the radiative flux from the 1665 MHz OH masers that have been reported to occur on timescales as short as 1000 s. The time-dependent differential equations of radiative transfer are solved numerically for three-dimensional astrophysical masers. Computations are performed for spherical and elongated (rectangular parallelepiped) geometries.

A comparison of gray and non-gray modeling approaches to radiative transfer in pool fire simulations.

PubMed

Krishnamoorthy, Gautham

2010-10-15

Decoupled radiative heat transfer calculations of 30 cm-diameter toluene and heptane pool fires are performed employing the discrete ordinates method. The composition and temperature fields within the fires are created from detailed experimental measurements of soot volume fractions based on absorption and emission, temperature statistics and correlations found in the literature. The measured temperature variance data is utilized to compute the temperature self-correlation term for modeling turbulence-radiation interactions. In the toluene pool fire, the presence of cold soot near the fuel surface is found to suppress the average radiation feedback to the pool surface by 27%. The performances of four gray and three non-gray radiative property models for the gases are also compared. The average variations in radiative transfer predictions due to differences in the spectroscopic and experimental databases employed in the property model formulations are found to be between 10% and 20%. Clear differences between the gray and non-gray modeling strategies are seen when the mean beam length is computed based on traditionally employed geometric relations. Therefore, a correction to the mean beam length is proposed to improve the agreement between gray and non-gray modeling in simulations of open pool fires. 2010 Elsevier B.V. All rights reserved.

A fast radiative transfer model for visible through shortwave infrared spectral reflectances in clear and cloudy atmospheres

NASA Astrophysics Data System (ADS)

Wang, Chenxi; Yang, Ping; Nasiri, Shaima L.; Platnick, Steven; Baum, Bryan A.; Heidinger, Andrew K.; Liu, Xu

2013-02-01

A computationally efficient radiative transfer model (RTM) for calculating visible (VIS) through shortwave infrared (SWIR) reflectances is developed for use in satellite and airborne cloud property retrievals. The full radiative transfer equation (RTE) for combinations of cloud, aerosol, and molecular layers is solved approximately by using six independent RTEs that assume the plane-parallel approximation along with a single-scattering approximation for Rayleigh scattering. Each of the six RTEs can be solved analytically if the bidirectional reflectance/transmittance distribution functions (BRDF/BTDF) of the cloud/aerosol layers are known. The adding/doubling (AD) algorithm is employed to account for overlapped cloud/aerosol layers and non-Lambertian surfaces. Two approaches are used to mitigate the significant computational burden of the AD algorithm. First, the BRDF and BTDF of single cloud/aerosol layers are pre-computed using the discrete ordinates radiative transfer program (DISORT) implemented with 128 streams, and second, the required integral in the AD algorithm is numerically implemented on a twisted icosahedral mesh. A concise surface BRDF simulator associated with the MODIS land surface product (MCD43) is merged into a fast RTM to accurately account for non-isotropic surface reflectance. The resulting fast RTM is evaluated with respect to its computational accuracy and efficiency. The simulation bias between DISORT and the fast RTM is large (e.g., relative error >5%) only when both the solar zenith angle (SZA) and the viewing zenith angle (VZA) are large (i.e., SZA>45° and VZA>70°). For general situations, i.e., cloud/aerosol layers above a non-Lambertian surface, the fast RTM calculation rate is faster than that of the 128-stream DISORT by approximately two orders of magnitude.

Halo orbit transfer trajectory design using invariant manifold in the Sun-Earth system accounting radiation pressure and oblateness

NASA Astrophysics Data System (ADS)

Srivastava, Vineet K.; Kumar, Jai; Kushvah, Badam Singh

2018-01-01

In this paper, we study the invariant manifold and its application in transfer trajectory problem from a low Earth parking orbit to the Sun-Earth L1 and L2-halo orbits with the inclusion of radiation pressure and oblateness. Invariant manifold of the halo orbit provides a natural entrance to travel the spacecraft in the solar system along some specific paths due to its strong hyperbolic character. In this regard, the halo orbits near both collinear Lagrangian points are computed first. The manifold's approximation near the nominal halo orbit is computed using the eigenvectors of the monodromy matrix. The obtained local approximation provides globalization of the manifold by applying backward time propagation to the governing equations of motion. The desired transfer trajectory well suited for the transfer is explored by looking at a possible intersection between the Earth's parking orbit of the spacecraft and the manifold.

Toward Improved Modeling of Spectral Solar Irradiance for Solar Energy Applications: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Yu; Sengupta, Manajit

This study introduces the National Renewable Energy Laboratory's (NREL's) recent efforts to extend the capability of the Fast All-sky Radiation Model for Solar applications (FARMS) by computing spectral solar irradiances over both horizontal and inclined surfaces. A new model is developed by computing the optical thickness of the atmosphere using a spectral irradiance model for clear-sky conditions, SMARTS2. A comprehensive lookup table (LUT) of cloud bidirectional transmittance distribution functions (BTDFs) is precomputed for 2002 wavelength bands using an atmospheric radiative transfer model, libRadtran. The solar radiation transmitted through the atmosphere is given by considering all possible paths of photon transmissionmore » and the relevent scattering and absorption attenuation. Our results indicate that this new model has an accuracy that is similar to that of state-of-the-art radiative transfer models, but it is significantly more efficient.« less

Analysis of longwave radiation for the Earth-atmosphere system

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Venuru, C. S.; Subramanian, S. V.

1983-01-01

Accurate radiative transfer models are used to determine the upwelling atmospheric radiance and net radiative flux in the entire longwave spectral range. The validity of the quasi-random band model is established by comparing the results of this model with those of line-by-line formulations and with available theoretical and experimental results. Existing radiative transfer models and computer codes are modified to include various surface and atmospheric effects (surface reflection, nonequilibrium radiation, and cloud effects). The program is used to evaluate the radiative flux in clear atmosphere, provide sensitivity analysis of upwelling radiance in the presence of clouds, and determine the effects of various climatological parameters on the upwelling radiation and anisotropic function. Homogeneous and nonhomogeneous gas emissivities can also be evaluated under different conditions.

Development of a GPU Compatible Version of the Fast Radiation Code RRTMG

NASA Astrophysics Data System (ADS)

Iacono, M. J.; Mlawer, E. J.; Berthiaume, D.; Cady-Pereira, K. E.; Suarez, M.; Oreopoulos, L.; Lee, D.

2012-12-01

The absorption of solar radiation and emission/absorption of thermal radiation are crucial components of the physics that drive Earth's climate and weather. Therefore, accurate radiative transfer calculations are necessary for realistic climate and weather simulations. Efficient radiation codes have been developed for this purpose, but their accuracy requirements still necessitate that as much as 30% of the computational time of a GCM is spent computing radiative fluxes and heating rates. The overall computational expense constitutes a limitation on a GCM's predictive ability if it becomes an impediment to adding new physics to or increasing the spatial and/or vertical resolution of the model. The emergence of Graphics Processing Unit (GPU) technology, which will allow the parallel computation of multiple independent radiative calculations in a GCM, will lead to a fundamental change in the competition between accuracy and speed. Processing time previously consumed by radiative transfer will now be available for the modeling of other processes, such as physics parameterizations, without any sacrifice in the accuracy of the radiative transfer. Furthermore, fast radiation calculations can be performed much more frequently and will allow the modeling of radiative effects of rapid changes in the atmosphere. The fast radiation code RRTMG, developed at Atmospheric and Environmental Research (AER), is utilized operationally in many dynamical models throughout the world. We will present the results from the first stage of an effort to create a version of the RRTMG radiation code designed to run efficiently in a GPU environment. This effort will focus on the RRTMG implementation in GEOS-5. RRTMG has an internal pseudo-spectral vector of length of order 100 that, when combined with the much greater length of the global horizontal grid vector from which the radiation code is called in GEOS-5, makes RRTMG/GEOS-5 particularly suited to achieving a significant speed improvement through GPU technology. This large number of independent cases will allow us to take full advantage of the computational power of the latest GPUs, ensuring that all thread cores in the GPU remain active, a key criterion for obtaining significant speedup. The CUDA (Compute Unified Device Architecture) Fortran compiler developed by PGI and Nvidia will allow us to construct this parallel implementation on the GPU while remaining in the Fortran language. This implementation will scale very well across various CUDA-supported GPUs such as the recently released Fermi Nvidia cards. We will present the computational speed improvements of the GPU-compatible code relative to the standard CPU-based RRTMG with respect to a very large and diverse suite of atmospheric profiles. This suite will also be utilized to demonstrate the minimal impact of the code restructuring on the accuracy of radiation calculations. The GPU-compatible version of RRTMG will be directly applicable to future versions of GEOS-5, but it is also likely to provide significant associated benefits for other GCMs that employ RRTMG.

Terrestrial solar spectral modeling. [SOLTRAN, BRITE, and FLASH codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bird, R.E.

The utility of accurate computer codes for calculating the solar spectral irradiance under various atmospheric conditions was recognized. New absorption and extraterrestrial spectral data are introduced. Progress is made in radiative transfer modeling outside of the solar community, especially for space and military applications. Three rigorous radiative transfer codes SOLTRAN, BRITE, and FLASH are employed. The SOLTRAN and BRITE codes are described and results from their use are presented.

A new spherical model for computing the radiation field available for photolysis and heating at twilight

NASA Technical Reports Server (NTRS)

Dahlback, Arne; Stamnes, Knut

1991-01-01

Accurate computation of atmospheric photodissociation and heating rates is needed in photochemical models. These quantities are proportional to the mean intensity of the solar radiation penetrating to various levels in the atmosphere. For large solar zenith angles a solution of the radiative transfer equation valid for a spherical atmosphere is required in order to obtain accurate values of the mean intensity. Such a solution based on a perturbation technique combined with the discrete ordinate method is presented. Mean intensity calculations are carried out for various solar zenith angles. These results are compared with calculations from a plane parallel radiative transfer model in order to assess the importance of using correct geometry around sunrise and sunset. This comparison shows, in agreement with previous investigations, that for solar zenith angles less than 90 deg adequate solutions are obtained for plane parallel geometry as long as spherical geometry is used to compute the direct beam attenuation; but for solar zenith angles greater than 90 deg this pseudospherical plane parallel approximation overstimates the mean intensity.

Quasi-analytical treatment of spatially averaged radiation transfer in complex terrain

NASA Astrophysics Data System (ADS)

Löwe, H.; Helbig, N.

2012-04-01

We provide a new quasi-analytical method to compute the topographic influence on the effective albedo of complex topography as required for meteorological, land-surface or climate models. We investigate radiative transfer in complex terrain via the radiosity equation on isotropic Gaussian random fields. Under controlled approximations we derive expressions for domain averages of direct, diffuse and terrain radiation and the sky view factor. Domain averaged quantities are related to a type of level-crossing probability of the random field which is approximated by longstanding results developed for acoustic scattering at ocean boundaries. This allows us to express all non-local horizon effects in terms of a local terrain parameter, namely the mean squared slope. Emerging integrals are computed numerically and fit formulas are given for practical purposes. As an implication of our approach we provide an expression for the effective albedo of complex terrain in terms of the sun elevation angle, mean squared slope, the area averaged surface albedo, and the direct-to-diffuse ratio of solar radiation. As an application, we compute the effective albedo for the Swiss Alps and discuss possible generalizations of the method.

Single-node orbit analsyis with radiation heat transfer only

NASA Technical Reports Server (NTRS)

Peoples, J. A.

1977-01-01

The steady-state temperature of a single node which dissipates energy by radiation only is discussed for a nontime varying thermal environment. Relationships are developed to illustrate how shields can be utilized to represent a louver system. A computer program is presented which can assess periodic temperature characteristics of a single node in a time varying thermal environment having energy dissipation by radiation only. The computer program performs thermal orbital analysis for five combinations of plate, shields, and louvers.

Integrated simulation of continuous-scale and discrete-scale radiative transfer in metal foams

NASA Astrophysics Data System (ADS)

Xia, Xin-Lin; Li, Yang; Sun, Chuang; Ai, Qing; Tan, He-Ping

2018-06-01

A novel integrated simulation of radiative transfer in metal foams is presented. It integrates the continuous-scale simulation with the direct discrete-scale simulation in a single computational domain. It relies on the coupling of the real discrete-scale foam geometry with the equivalent continuous-scale medium through a specially defined scale-coupled zone. This zone holds continuous but nonhomogeneous volumetric radiative properties. The scale-coupled approach is compared to the traditional continuous-scale approach using volumetric radiative properties in the equivalent participating medium and to the direct discrete-scale approach employing the real 3D foam geometry obtained by computed tomography. All the analyses are based on geometrical optics. The Monte Carlo ray-tracing procedure is used for computations of the absorbed radiative fluxes and the apparent radiative behaviors of metal foams. The results obtained by the three approaches are in tenable agreement. The scale-coupled approach is fully validated in calculating the apparent radiative behaviors of metal foams composed of very absorbing to very reflective struts and that composed of very rough to very smooth struts. This new approach leads to a reduction in computational time by approximately one order of magnitude compared to the direct discrete-scale approach. Meanwhile, it can offer information on the local geometry-dependent feature and at the same time the equivalent feature in an integrated simulation. This new approach is promising to combine the advantages of the continuous-scale approach (rapid calculations) and direct discrete-scale approach (accurate prediction of local radiative quantities).

Fast radiative transfer models for retrieval of cloud properties in the back-scattering region: application to DSCOVR-EPIC sensor

NASA Astrophysics Data System (ADS)

Molina Garcia, Victor; Sasi, Sruthy; Efremenko, Dmitry; Doicu, Adrian; Loyola, Diego

2017-04-01

In this work, the requirements for the retrieval of cloud properties in the back-scattering region are described, and their application to the measurements taken by the Earth Polychromatic Imaging Camera (EPIC) on board the Deep Space Climate Observatory (DSCOVR) is shown. Various radiative transfer models and their linearizations are implemented, and their advantages and issues are analyzed. As radiative transfer calculations in the back-scattering region are computationally time-consuming, several acceleration techniques are also studied. The radiative transfer models analyzed include the exact Discrete Ordinate method with Matrix Exponential (DOME), the Matrix Operator method with Matrix Exponential (MOME), and the approximate asymptotic and equivalent Lambertian cloud models. To reduce the computational cost of the line-by-line (LBL) calculations, the k-distribution method, the Principal Component Analysis (PCA) and a combination of the k-distribution method plus PCA are used. The linearized radiative transfer models for retrieval of cloud properties include the Linearized Discrete Ordinate method with Matrix Exponential (LDOME), the Linearized Matrix Operator method with Matrix Exponential (LMOME) and the Forward-Adjoint Discrete Ordinate method with Matrix Exponential (FADOME). These models were applied to the EPIC oxygen-A band absorption channel at 764 nm. It is shown that the approximate asymptotic and equivalent Lambertian cloud models give inaccurate results, so an offline processor for the retrieval of cloud properties in the back-scattering region requires the use of exact models such as DOME and MOME, which behave similarly. The combination of the k-distribution method plus PCA presents similar accuracy to the LBL calculations, but it is up to 360 times faster, and the relative errors for the computed radiances are less than 1.5% compared to the results when the exact phase function is used. Finally, the linearized models studied show similar behavior, with relative errors less than 1% for the radiance derivatives, but FADOME is 2 times faster than LDOME and 2.5 times faster than LMOME.

Radiative transfer in a polluted urban planetary boundary layer

NASA Technical Reports Server (NTRS)

Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

1977-01-01

Radiative transfer in a polluted urban atmosphere is studied using a dynamic model. The diurnal nature of radiative transfer for summer conditions is simulated for an urban area 40 km in extent and the effects of various parameters arising in the problem are investigated. The results of numerical computations show that air pollution has the potential of playing a major role in the radiative regime of the urban area. Absorption of solar energy by aerosols in realistic models of urban atmosphere are of the same order of magnitude as that due to water vapor. The predicted effect of the air pollution aerosol in the city is to warm the earth-atmosphere system, and the net effect of gaseous pollutant is to warm the surface and cool the planetary boundary layer, particularly near the top.

Computing NLTE Opacities -- Node Level Parallel Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holladay, Daniel

Presentation. The goal: to produce a robust library capable of computing reasonably accurate opacities inline with the assumption of LTE relaxed (non-LTE). Near term: demonstrate acceleration of non-LTE opacity computation. Far term (if funded): connect to application codes with in-line capability and compute opacities. Study science problems. Use efficient algorithms that expose many levels of parallelism and utilize good memory access patterns for use on advanced architectures. Portability to multiple types of hardware including multicore processors, manycore processors such as KNL, GPUs, etc. Easily coupled to radiation hydrodynamics and thermal radiative transfer codes.

The solution of radiative transfer problems in molecular bands without the LTE assumption by accelerated lambda iteration methods

NASA Technical Reports Server (NTRS)

Kutepov, A. A.; Kunze, D.; Hummer, D. G.; Rybicki, G. B.

1991-01-01

An iterative method based on the use of approximate transfer operators, which was designed initially to solve multilevel NLTE line formation problems in stellar atmospheres, is adapted and applied to the solution of the NLTE molecular band radiative transfer in planetary atmospheres. The matrices to be constructed and inverted are much smaller than those used in the traditional Curtis matrix technique, which makes possible the treatment of more realistic problems using relatively small computers. This technique converges much more rapidly than straightforward iteration between the transfer equation and the equations of statistical equilibrium. A test application of this new technique to the solution of NLTE radiative transfer problems for optically thick and thin bands (the 4.3 micron CO2 band in the Venusian atmosphere and the 4.7 and 2.3 micron CO bands in the earth's atmosphere) is described.

Influence of radiant energy exchange on the determination of convective heat transfer rates to Orbiter leeside surfaces during entry

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1982-01-01

Temperatures measured at the aerodynamic surface of the Orbiter's thermal protection system (TPS), and calorimeter measurements, are used to determine heating rates to the TPS surface during atmospheric entry. On the Orbiter leeside, where convective heating rates are low, it is possible that a significant portion of the total energy input may result from solar radiation, and for the wing, cross radiation from the hot (relatively) Orbiter fuselage. In order to account for the potential impact of these sources, values of solar- and cross-radiation heat transfer are computed, based upon vehicle trajectory and attitude information and measured surface temperatures. Leeside heat-transfer data from the STS-2 mission are presented, and the significance of solar radiation and fuselage-to-wing cross-radiation contributions to total energy input to Orbiter leeside surfaces is assessed.

SPRAI: coupling of radiative feedback and primordial chemistry in moving mesh hydrodynamics

NASA Astrophysics Data System (ADS)

Jaura, O.; Glover, S. C. O.; Klessen, R. S.; Paardekooper, J.-P.

2018-04-01

In this paper, we introduce a new radiative transfer code SPRAI (Simplex Photon Radiation in the Arepo Implementation) based on the SIMPLEX radiation transfer method. This method, originally used only for post-processing, is now directly integrated into the AREPO code and takes advantage of its adaptive unstructured mesh. Radiated photons are transferred from the sources through the series of Voronoi gas cells within a specific solid angle. From the photon attenuation, we derive corresponding photon fluxes and ionization rates and feed them to a primordial chemistry module. This gives us a self-consistent method for studying dynamical and chemical processes caused by ionizing sources in primordial gas. Since the computational cost of the SIMPLEX method does not scale directly with the number of sources, it is convenient for studying systems such as primordial star-forming haloes that may form multiple ionizing sources.

Numerical Analysis of Thermo Hydraulic Conditions in Car Fog Lamp

NASA Astrophysics Data System (ADS)

Ramšak, M.; Žunič, Z.; Škerget, L.; Jurejevčič, T.

2009-08-01

In the article a coupled heat transfer in the solid and fluid inside of a car fog lamp is presented using CFD software CFX [1]. All three basic principles of heat transfer are dealt with: conduction, convection and radiation. Two different approaches to radiation modeling are compared. Laminar and turbulent flow modeling are compared since computed Rayleight number indicates transitional flow regime. Results are in good agreement with the measurements.

A Fast Infrared Radiative Transfer Model for Overlapping Clouds

NASA Technical Reports Server (NTRS)

Niu, Jianguo; Yang, Ping; Huang, Huang-Lung; Davies, James E.; Li, Jun; Baum, Bryan A.; Hu, Yong X.

2006-01-01

A fast infrared radiative transfer model (FIRTM2) appropriate for application to both single-layered and overlapping cloud situations is developed for simulating the outgoing infrared spectral radiance at the top of the atmosphere (TOA). In FIRTM2 a pre-computed library of cloud reflectance and transmittance values is employed to account for one or two cloud layers, whereas the background atmospheric optical thickness due to gaseous absorption can be computed from a clear-sky radiative transfer model. FIRTM2 is applicable to three atmospheric conditions: 1) clear-sky, 2) single-layered ice or water cloud, and 3) two simultaneous cloud layers in a column (e.g., ice cloud overlying water cloud). Moreover, FIRTM2 outputs the derivatives (i.e., Jacobians) of the TOA brightness temperature with respect to cloud optical thickness and effective particle size. Sensitivity analyses have been carried out to assess the performance of FIRTM2 for two spectral regions, namely the longwave (LW) band (587.3 - 1179.5/cm) and the short-to-medium wave (SMW) band (1180.1 - 2228.9/cm). The assessment is carried out in terms of brightness temperature differences (BTD) between FIRTM2 and the well-known discrete ordinates radiative transfer model (DISORT), henceforth referred to as BTD (F-D). The BTD (F-D) values for single-layered clouds are generally less than 0.8 K. For the case of two cloud layers (specifically ice cloud over water cloud), the BTD(F-D) values are also generally less than 0.8 K except for the SMW band for the case of a very high altitude (>15 km) cloud comprised of small ice particles. Note that for clear-sky atmospheres, FIRTM2 reduces to the clear-sky radiative transfer model that is incorporated into FIRTM2, and the errors in this case are essentially those of the clear-sky radiative transfer model.

Efficient Radiative Transfer for Dynamically Evolving Stratified Atmospheres

NASA Astrophysics Data System (ADS)

Judge, Philip G.

2017-12-01

We present a fast multi-level and multi-atom non-local thermodynamic equilibrium radiative transfer method for dynamically evolving stratified atmospheres, such as the solar atmosphere. The preconditioning method of Rybicki & Hummer (RH92) is adopted. But, pressed for the need of speed and stability, a “second-order escape probability” scheme is implemented within the framework of the RH92 method, in which frequency- and angle-integrals are carried out analytically. While minimizing the computational work needed, this comes at the expense of numerical accuracy. The iteration scheme is local, the formal solutions for the intensities are the only non-local component. At present the methods have been coded for vertical transport, applicable to atmospheres that are highly stratified. The probabilistic method seems adequately fast, stable, and sufficiently accurate for exploring dynamical interactions between the evolving MHD atmosphere and radiation using current computer hardware. Current 2D and 3D dynamics codes do not include this interaction as consistently as the current method does. The solutions generated may ultimately serve as initial conditions for dynamical calculations including full 3D radiative transfer. The National Center for Atmospheric Research is sponsored by the National Science Foundation.

An efficient and accurate technique to compute the absorption, emission, and transmission of radiation by the Martian atmosphere

NASA Technical Reports Server (NTRS)

Lindner, Bernhard Lee; Ackerman, Thomas P.; Pollack, James B.

1990-01-01

CO2 comprises 95 pct. of the composition of the Martian atmosphere. However, the Martian atmosphere also has a high aerosol content. Dust particles vary from less than 0.2 to greater than 3.0. CO2 is an active absorber and emitter in near IR and IR wavelengths; the near IR absorption bands of CO2 provide significant heating of the atmosphere, and the 15 micron band provides rapid cooling. Including both CO2 and aerosol radiative transfer simultaneously in a model is difficult. Aerosol radiative transfer requires a multiple scattering code, while CO2 radiative transfer must deal with complex wavelength structure. As an alternative to the pure atmosphere treatment in most models which causes inaccuracies, a treatment was developed called the exponential sum or k distribution approximation. The chief advantage of the exponential sum approach is that the integration over k space of f(k) can be computed more quickly than the integration of k sub upsilon over frequency. The exponential sum approach is superior to the photon path distribution and emissivity techniques for dusty conditions. This study was the first application of the exponential sum approach to Martian conditions.

Development of programs for computing characteristics of ultraviolet radiation

NASA Technical Reports Server (NTRS)

Dave, J. V.

1972-01-01

Efficient programs were developed for computing all four characteristics of the radiation scattered by a plane-parallel, turbid, terrestrial atmospheric model. They were developed (FORTRAN 4) and tested on the IBM /360 computers with 2314 direct access storage facility. The storage requirement varies between 200K and 750K bytes depending upon the task. The scattering phase matrix (or function) is expanded in a Fourier series whose number of terms depend upon the zenith angles of the incident and scattered radiations, as well as on the nature of aerosols. A Gauss-Seidel procedure is used for obtaining the numerical solution of the transfer equation.

National Renewable Energy Laboratory Pyrheliometer Comparisons: 24 September - 5 October 2012 (NPC-2012)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoffel, T.; Reda, I.

2013-05-01

The NREL Pyrheliometer Comparisons for 2012 (NPC-2012) were held at the Solar Radiation Research Laboratory in Golden, Colorado, from September 24 through October 5 for the purpose of transferring the World Radiometric Reference (WRR) to participating instrument. Twenty scientists and engineers operated 32 absolute cavity radiometers and 18 conventional thermopile-based pyrheliometers to simultaneously measure clear-sky direct normal irradiance during the comparisons. The transfer standard group of reference radiometers for NPC-2012 consisted of four NREL radiometers with direct traceability to the WRR, having participated in the Eleventh International Pyrheliometer Comparisons (IPC-XI) hosted by the World Radiation Center in the fall ofmore » 2010. As the result of NPC-2012, each participating absolute cavity radiometer was assigned a new WRR transfer factor, computed as the reference irradiance computed by the transfer standard group divided by the observed irradiance from the participating radiometer. The performance of the transfer standard group during NPC-2012 was consistent with previous comparisons, including IPC-XI. The measurement performance of the transfer standard group allowed the transfer of the WRR to each participating radiometer with an estimated uncertainty of +/- 0.33% with respect to the International System of Units.« less

A Fast Vector Radiative Transfer Model for Atmospheric and Oceanic Remote Sensing

NASA Astrophysics Data System (ADS)

Ding, J.; Yang, P.; King, M. D.; Platnick, S. E.; Meyer, K.

2017-12-01

A fast vector radiative transfer model is developed in support of atmospheric and oceanic remote sensing. This model is capable of simulating the Stokes vector observed at the top of the atmosphere (TOA) and the terrestrial surface by considering absorption, scattering, and emission. The gas absorption is parameterized in terms of atmospheric gas concentrations, temperature, and pressure. The parameterization scheme combines a regression method and the correlated-K distribution method, and can easily integrate with multiple scattering computations. The approach is more than four orders of magnitude faster than a line-by-line radiative transfer model with errors less than 0.5% in terms of transmissivity. A two-component approach is utilized to solve the vector radiative transfer equation (VRTE). The VRTE solver separates the phase matrices of aerosol and cloud into forward and diffuse parts and thus the solution is also separated. The forward solution can be expressed by a semi-analytical equation based on the small-angle approximation, and serves as the source of the diffuse part. The diffuse part is solved by the adding-doubling method. The adding-doubling implementation is computationally efficient because the diffuse component needs much fewer spherical function expansion terms. The simulated Stokes vector at both the TOA and the surface have comparable accuracy compared with the counterparts based on numerically rigorous methods.

Radiative heat transfer in 2D Dirac materials

NASA Astrophysics Data System (ADS)

Rodriguez-López, Pablo; Tse, Wang-Kong; Dalvit, Diego A. R.

2015-06-01

We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. Finally, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.

Radiative heat transfer in 2D Dirac materials

DOE PAGES

Rodriguez-López, Pablo; Tse, Wang -Kong; Dalvit, Diego A. R.

2015-05-12

We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. In conclusion, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials.

Numerical simulations of electromagnetic scattering by Solar system objects

NASA Astrophysics Data System (ADS)

Dlugach, Janna M.

2016-11-01

Having been profoundly stimulated by the seminal work of Viktor V. Sobolev, I have been involved in multi-decadal research in the fields of radiative transfer, electromagnetic scattering by morphologically complex particles and particulate media, and planetary remote sensing. Much of this research has been done in close collaboration with other "descendants" of Academician Sobolev. This tutorial paper gives a representative overview of the results of extensive numerical simulations (in the vast majority carried out in collaboration with Michael Mishchenko) used to analyze remote-sensing observations of Solar system objects and based on highly accurate methods of the radiative transfer theory and direct computer solvers of the Maxwell equations. Using the atmosphere of Jupiter as a proving ground and performing T-matrix and radiative-transfer calculations helps demonstrate the strong effect of aerosol-particle shapes on the accuracy of remote-sensing retrievals. I then discuss the application of the T-matrix method, a numerically exact solution of the vector radiative transfer equation, and the theory of coherent backscattering to an analysis of polarimetric radar observations of Saturn's rings. Numerical modeling performed by using the superposition T-matrix method in application to cometary dust in the form of aggregates serves to reproduce the results of polarimetric observations of the distant comet C/2010 S1. On the basis of direct computer solutions of the Maxwell equations, it is demonstrated that all backscattering effects predicted by the low-density theories of radiative transfer and coherent backscattering can also be identified for media with volume packing densities typically encountered in natural and artificial environments. This result implies that spectacular opposition effects observed for some high-albedo atmoshereless Solar system bodies can be attributed to coherent backscattering of sunlight by regolith layers composed of microscopic particles.

Multidimensional Modeling of Atmospheric Effects and Surface Heterogeneities on Remote Sensing

NASA Technical Reports Server (NTRS)

Gerstl, S. A. W.; Simmer, C.; Zardecki, A. (Principal Investigator)

1985-01-01

The overall goal of this project is to establish a modeling capability that allows a quantitative determination of atmospheric effects on remote sensing including the effects of surface heterogeneities. This includes an improved understanding of aerosol and haze effects in connection with structural, angular, and spatial surface heterogeneities. One important objective of the research is the possible identification of intrinsic surface or canopy characteristics that might be invariant to atmospheric perturbations so that they could be used for scene identification. Conversely, an equally important objective is to find a correction algorithm for atmospheric effects in satellite-sensed surface reflectances. The technical approach is centered around a systematic model and code development effort based on existing, highly advanced computer codes that were originally developed for nuclear radiation shielding applications. Computational techniques for the numerical solution of the radiative transfer equation are adapted on the basis of the discrete-ordinates finite-element method which proved highly successful for one and two-dimensional radiative transfer problems with fully resolved angular representation of the radiation field.

Millimeter wave radiative transfer studies for precipitation measurements

NASA Technical Reports Server (NTRS)

Vivekanandan, J.; Evans, Frank

1989-01-01

Scattering calculations using the discrete dipole approximation and vector radiative transfer calculations were performed to model multiparameter radar return and passive microwave emission for a simple model of a winter storm. The issue of dendrite riming was addressed by computing scattering properties of thin ice disks with varying bulk density. It was shown that C-band multiparameter radar contains information about particle density and the number concentration of the ice particles. The radiative transfer modeling indicated that polarized multifrequency passive microwave emission may be used to infer some properties of ice hydrometers. Detailed radar modeling and vector radiative transfer modeling is in progress to enhance the understanding of simultaneous radar and radiometer measurements, as in the case of the proposed TRMM field program. A one-dimensional cloud model will be used to simulate the storm structure in detail and study the microphysics, such as size and density. Multifrequency polarized radiometer measurements from the SSMI satellite instrument will be analyzed in relation to dual-frequency and dual-polarization radar measurements.

Study of radiative heat transfer in Ångström- and nanometre-sized gaps

DOE PAGES

Cui, Longji; Jeong, Wonho; Fernández-Hurtado, Víctor; ...

2017-02-15

Radiative heat transfer in Ångström- and nanometre-sized gaps is of great interest because of both its technological importance and open questions regarding the physics of energy transfer in this regime. Here in this paper we report studies of radiative heat transfer in few Å to 5nm gap sizes, performed under ultrahigh vacuum conditions between a Au-coated probe featuring embedded nanoscale thermocouples and a heated planar Au substrate that were both subjected to various surface-cleaning procedures. By drawing on the apparent tunnelling barrier height as a signature of cleanliness, we found that upon systematically cleaning via a plasma or locally pushingmore » the tip into the substrate by a few nanometres, the observed radiative conductances decreased from unexpectedly large values to extremely small ones—below the detection limit of our probe—as expected from our computational results. Our results show that it is possible to avoid the confounding effects of surface contamination and systematically study thermal radiation in Ångström- and nanometre-sized gaps.« less

Analysis of Aerospike Plume Induced Base-Heating Environment

NASA Technical Reports Server (NTRS)

Wang, Ten-See

1998-01-01

Computational analysis is conducted to study the effect of an aerospike engine plume on X-33 base-heating environment during ascent flight. To properly account for the effect of forebody and aftbody flowfield such as shocks and to allow for potential plume-induced flow-separation, thermo-flowfield of trajectory points is computed. The computational methodology is based on a three-dimensional finite-difference, viscous flow, chemically reacting, pressure-base computational fluid dynamics formulation, and a three-dimensional, finite-volume, spectral-line based weighted-sum-of-gray-gases radiation absorption model computational heat transfer formulation. The predicted convective and radiative base-heat fluxes are presented.

Computing Temperatures in Optically Thick Protoplanetary Disks

NASA Technical Reports Server (NTRS)

Capuder, Lawrence F.. Jr.

2011-01-01

We worked with a Monte Carlo radiative transfer code to simulate the transfer of energy through protoplanetary disks, where planet formation occurs. The code tracks photons from the star into the disk, through scattering, absorption and re-emission, until they escape to infinity. High optical depths in the disk interior dominate the computation time because it takes the photon packet many interactions to get out of the region. High optical depths also receive few photons and therefore do not have well-estimated temperatures. We applied a modified random walk (MRW) approximation for treating high optical depths and to speed up the Monte Carlo calculations. The MRW is implemented by calculating the average number of interactions the photon packet will undergo in diffusing within a single cell of the spatial grid and then updating the packet position, packet frequencies, and local radiation absorption rate appropriately. The MRW approximation was then tested for accuracy and speed compared to the original code. We determined that MRW provides accurate answers to Monte Carlo Radiative transfer simulations. The speed gained from using MRW is shown to be proportional to the disk mass.

GPU-BASED MONTE CARLO DUST RADIATIVE TRANSFER SCHEME APPLIED TO ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heymann, Frank; Siebenmorgen, Ralf, E-mail: fheymann@pa.uky.edu

2012-05-20

A three-dimensional parallel Monte Carlo (MC) dust radiative transfer code is presented. To overcome the huge computing-time requirements of MC treatments, the computational power of vectorized hardware is used, utilizing either multi-core computer power or graphics processing units. The approach is a self-consistent way to solve the radiative transfer equation in arbitrary dust configurations. The code calculates the equilibrium temperatures of two populations of large grains and stochastic heated polycyclic aromatic hydrocarbons. Anisotropic scattering is treated applying the Heney-Greenstein phase function. The spectral energy distribution (SED) of the object is derived at low spatial resolution by a photon counting proceduremore » and at high spatial resolution by a vectorized ray tracer. The latter allows computation of high signal-to-noise images of the objects at any frequencies and arbitrary viewing angles. We test the robustness of our approach against other radiative transfer codes. The SED and dust temperatures of one- and two-dimensional benchmarks are reproduced at high precision. The parallelization capability of various MC algorithms is analyzed and included in our treatment. We utilize the Lucy algorithm for the optical thin case where the Poisson noise is high, the iteration-free Bjorkman and Wood method to reduce the calculation time, and the Fleck and Canfield diffusion approximation for extreme optical thick cells. The code is applied to model the appearance of active galactic nuclei (AGNs) at optical and infrared wavelengths. The AGN torus is clumpy and includes fluffy composite grains of various sizes made up of silicates and carbon. The dependence of the SED on the number of clumps in the torus and the viewing angle is studied. The appearance of the 10 {mu}m silicate features in absorption or emission is discussed. The SED of the radio-loud quasar 3C 249.1 is fit by the AGN model and a cirrus component to account for the far-infrared emission.« less

Earth radiation budget measurements from satellites and their interpretation for climate modeling and studies

NASA Technical Reports Server (NTRS)

Vonderhaar, T. H.; Stephens, G. L.; Campbell, G. G.

1980-01-01

The annual and seasonal averaged Earth atmosphere radiation budgets derived from the most complete set of satellite observations available are presented. The budgets were derived from a composite of 48 monthly mean radiation budget maps. Annually and seasonally averaged radiation budgets are presented as global averages and zonal averages. The geographic distribution of the various radiation budget quantities is described. The annual cycle of the radiation budget was analyzed and the annual variability of net flux was shown to be largely dominated by the regular semi and annual cycles forced by external Earth-Sun geometry variations. Radiative transfer calculations were compared to the observed budget quantities and surface budgets were additionally computed with particular emphasis on discrepancies that exist between the present computations and previous surface budget estimates.

Formal Solutions for Polarized Radiative Transfer. II. High-order Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janett, Gioele; Steiner, Oskar; Belluzzi, Luca, E-mail: gioele.janett@irsol.ch

When integrating the radiative transfer equation for polarized light, the necessity of high-order numerical methods is well known. In fact, well-performing high-order formal solvers enable higher accuracy and the use of coarser spatial grids. Aiming to provide a clear comparison between formal solvers, this work presents different high-order numerical schemes and applies the systematic analysis proposed by Janett et al., emphasizing their advantages and drawbacks in terms of order of accuracy, stability, and computational cost.

Two-Flux and Green's Function Method for Transient Radiative Transfer in a Semi-Transparent Layer

NASA Technical Reports Server (NTRS)

Siegel, Robert

1995-01-01

A method using a Green's function is developed for computing transient temperatures in a semitransparent layer by using the two-flux method coupled with the transient energy equation. Each boundary of the layer is exposed to a hot or cold radiative environment, and is heated or cooled by convection. The layer refractive index is larger than one, and the effect of internal reflections is included with the boundaries assumed diffuse. The analysis accounts for internal emission, absorption, heat conduction, and isotropic scattering. Spectrally dependent radiative properties are included, and transient results are given to illustrate two-band spectral behavior with optically thin and thick bands. Transient results using the present Green's function method are verified for a gray layer by comparison with a finite difference solution of the exact radiative transfer equations; excellent agreement is obtained. The present method requires only moderate computing times and incorporates isotropic scattering without additional complexity. Typical temperature distributions are given to illustrate application of the method by examining the effect of strong radiative heating on one side of a layer with convective cooling on the other side, and the interaction of strong convective heating with radiative cooling from the layer interior.

Computational study of heat transfer in gas fluidization

NASA Astrophysics Data System (ADS)

Hou, Q. F.; Zhou, Z. Y.; Yu, A. B.

2013-06-01

Heat transfer in gas fluidization is investigated at a particle scale by means of a combined discrete element method and computational fluid dynamicsapproach. To develop understanding of heat transfer at various conditions, the effects of a few important material properties such as particle size, the Hamaker constant and particle thermal conductivity are examined through controlled numerical experiments. It is found that the convective heat transfer is dominant, and radiative heat transfer becomes important when the temperature is high. Conductive heat transfer also plays a role depending on the flow regimes and material properties. The heat transfer between a fluidized bed and an immersed surface is enhanced by the increase of particle thermal conductivity while it is little affected by Young's modulus. The findings should be useful for better understanding and predicting the heat transfer in gas fluidization.

The Intercomparison of 3D Radiation Codes (I3RC): Showcasing Mathematical and Computational Physics in a Critical Atmospheric Application

NASA Astrophysics Data System (ADS)

Davis, A. B.; Cahalan, R. F.

2001-05-01

The Intercomparison of 3D Radiation Codes (I3RC) is an on-going initiative involving an international group of over 30 researchers engaged in the numerical modeling of three-dimensional radiative transfer as applied to clouds. Because of their strong variability and extreme opacity, clouds are indeed a major source of uncertainty in the Earth's local radiation budget (at GCM grid scales). Also 3D effects (at satellite pixel scales) invalidate the standard plane-parallel assumption made in the routine of cloud-property remote sensing at NASA and NOAA. Accordingly, the test-cases used in I3RC are based on inputs and outputs which relate to cloud effects in atmospheric heating rates and in real-world remote sensing geometries. The main objectives of I3RC are to (1) enable participants to improve their models, (2) publish results as a community, (3) archive source code, and (4) educate. We will survey the status of I3RC and its plans for the near future with a special emphasis on the mathematical models and computational approaches. We will also describe some of the prime applications of I3RC's efforts in climate models, cloud-resolving models, and remote-sensing observations of clouds, or that of the surface in their presence. In all these application areas, computational efficiency is the main concern and not accuracy. One of I3RC's main goals is to document the performance of as wide a variety as possible of three-dimensional radiative transfer models for a small but representative number of ``cases.'' However, it is dominated by modelers working at the level of linear transport theory (i.e., they solve the radiative transfer equation) and an overwhelming majority of these participants use slow-but-robust Monte Carlo techniques. This means that only a small portion of the efficiency vs. accuracy vs. flexibility domain is currently populated by I3RC participants. To balance this natural clustering the present authors have organized a systematic outreach towards modelers that have used approximate methods in radiation transport. In this context, different, presumably simpler, equations (such as diffusion) are used in order to make a significant gain on the efficiency axis. We will describe in some detail the most promising approaches to approximate 3D radiative transfer in clouds. Somewhat paradoxically, and in spite of its importance in the above-mentioned applications, approximate radiative transfer modeling lags significantly behind its exact counterpart because the required mathematical and computational culture is essentially alien to the native atmospheric radiation community. I3RC is receiving enough funding from NASA/HQ and DOE/ARM for its essential operations out of NASA/GSFC. However, this does not cover the time and effort of any of the participants; so only existing models were entered. At present, none of inherently approximate methods are represented, only severe truncations of some exact methods. We therefore welcome the Math/Geo initiative at NSF which should enable the proper consortia of experts in atmospheric radiation and in applied mathematics to fill an important niche.

Application of the TEMPEST computer code to canister-filling heat transfer problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farnsworth, R.K.; Faletti, D.W.; Budden, M.J.

Pacific Northwest Laboratory (PNL) researchers used the TEMPEST computer code to simulate thermal cooldown behavior of nuclear waste glass after it was poured into steel canisters for long-term storage. The objective of this work was to determine the accuracy and applicability of the TEMPEST code when used to compute canister thermal histories. First, experimental data were obtained to provide the basis for comparing TEMPEST-generated predictions. Five canisters were instrumented with appropriately located radial and axial thermocouples. The canister were filled using the pilot-scale ceramic melter (PSCM) at PNL. Each canister was filled in either a continous or a batch fillingmore » mode. One of the canisters was also filled within a turntable simulant (a group of cylindrical shells with heat transfer resistances similar to those in an actual melter turntable). This was necessary to provide a basis for assessing the ability of the TEMPEST code to also model the transient cooling of canisters in a melter turntable. The continous-fill model, Version M, was found to predict temperatures with more accuracy. The turntable simulant experiment demonstrated that TEMPEST can adequately model the asymmetric temperature field caused by the turntable geometry. Further, TEMPEST can acceptably predict the canister cooling history within a turntable, despite code limitations in computing simultaneous radiation and convection heat transfer between shells, along with uncertainty in stainless-steel surface emissivities. Based on the successful performance of TEMPEST Version M, development was initiated to incorporate 1) full viscous glass convection, 2) a dynamically adaptive grid that automatically follows the glass/air interface throughout the transient, and 3) a full enclosure radiation model to allow radiation heat transfer to non-nearest neighbor cells. 5 refs., 47 figs., 17 tabs.« less

Light scattering by planetary-regolith analog samples: computational results

NASA Astrophysics Data System (ADS)

Väisänen, Timo; Markkanen, Johannes; Hadamcik, Edith; Levasseur-Regourd, Anny-Chantal; Lasue, Jeremie; Blum, Jürgen; Penttilä, Antti; Muinonen, Karri

2017-04-01

We compute light scattering by a planetary-regolith analog surface. The corresponding experimental work is from Hadamcik et al. [1] with the PROGRA2-surf [2] device measuring the polarization of dust particles. The analog samples are low density (volume fraction 0.15 ± 0.03) agglomerates produced by random ballistic deposition of almost equisized silica spheres (refractive index n=1.5 and diameter 1.45 ± 0.06 µm). Computations are carried out with the recently developed codes entitled Radiative Transfer with Reciprocal Transactions (R2T2) and Radiative Transfer Coherent Backscattering with incoherent interactions (RT-CB-ic). Both codes incorporate the so-called incoherent treatment which enhances the applicability of the radiative transfer as shown by Muinonen et al. [3]. As a preliminary result, we have computed scattering from a large spherical medium with the RT-CB-ic using equal-sized particles with diameters of 1.45 microns. The preliminary results have shown that the qualitative characteristics are similar for the computed and measured intensity and polarization curves but that there are still deviations between the characteristics. We plan to remove the deviations by incorporating a size distribution of particles (1.45 ± 0.02 microns) and detailed information about the volume density profile within the analog surface. Acknowledgments: We acknowledge the ERC Advanced Grant no. 320773 entitled Scattering and Absorption of Electromagnetic Waves in Particulate Media (SAEMPL). Computational resources were provided by CSC - IT Centre for Science Ltd, Finland. References: [1] Hadamcik E. et al. (2007), JQSRT, 106, 74-89 [2] Levasseur-Regourd A.C. et al. (2015), Polarimetry of stars and planetary systems, CUP, 61-80 [3] Muinonen K. et al. (2016), extended abstract for EMTS.

TIME-DEPENDENT MULTI-GROUP MULTI-DIMENSIONAL RELATIVISTIC RADIATIVE TRANSFER CODE BASED ON SPHERICAL HARMONIC DISCRETE ORDINATE METHOD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tominaga, Nozomu; Shibata, Sanshiro; Blinnikov, Sergei I., E-mail: tominaga@konan-u.ac.jp, E-mail: sshibata@post.kek.jp, E-mail: Sergei.Blinnikov@itep.ru

We develop a time-dependent, multi-group, multi-dimensional relativistic radiative transfer code, which is required to numerically investigate radiation from relativistic fluids that are involved in, e.g., gamma-ray bursts and active galactic nuclei. The code is based on the spherical harmonic discrete ordinate method (SHDOM) which evaluates a source function including anisotropic scattering in spherical harmonics and implicitly solves the static radiative transfer equation with ray tracing in discrete ordinates. We implement treatments of time dependence, multi-frequency bins, Lorentz transformation, and elastic Thomson and inelastic Compton scattering to the publicly available SHDOM code. Our code adopts a mixed-frame approach; the source functionmore » is evaluated in the comoving frame, whereas the radiative transfer equation is solved in the laboratory frame. This implementation is validated using various test problems and comparisons with the results from a relativistic Monte Carlo code. These validations confirm that the code correctly calculates the intensity and its evolution in the computational domain. The code enables us to obtain an Eddington tensor that relates the first and third moments of intensity (energy density and radiation pressure) and is frequently used as a closure relation in radiation hydrodynamics calculations.« less

Estimation of surface temperature in remote pollution measurement experiments

NASA Technical Reports Server (NTRS)

Gupta, S. K.; Tiwari, S. N.

1978-01-01

A simple algorithm has been developed for estimating the actual surface temperature by applying corrections to the effective brightness temperature measured by radiometers mounted on remote sensing platforms. Corrections to effective brightness temperature are computed using an accurate radiative transfer model for the 'basic atmosphere' and several modifications of this caused by deviations of the various atmospheric and surface parameters from their base model values. Model calculations are employed to establish simple analytical relations between the deviations of these parameters and the additional temperature corrections required to compensate for them. Effects of simultaneous variation of two parameters are also examined. Use of these analytical relations instead of detailed radiative transfer calculations for routine data analysis results in a severalfold reduction in computation costs.

The Skylab concentrated atmospheric radiation project

NASA Technical Reports Server (NTRS)

Kuhn, P. M.; Marlatt, W. E.; Whitehead, V. S. (Principal Investigator)

1975-01-01

The author has identified the following significant results. Comparison of several existing infrared radiative transfer models under somewhat controlled conditions and with atmospheric observations of Skylab's S191 and S192 radiometers illustrated that the models tend to over-compute atmospheric attenuation in the window region of the atmospheric infrared spectra.

Computational Spectrally Correlated Thermal Radiation through Gaseous Mixture

NASA Astrophysics Data System (ADS)

Lakhal, W.; Trabelsi, S.; Sediki, E.; Soufiani, A.; Moussa, M.

2007-09-01

The Treatment of the spectral nature of thermal radiation in absorbing emitting gases at high temperature inside a heated or cooled duct is presented with taking into account the non-gray behavior of gas. Radiative properties of the flowing gases (H2O or CO2) are modeled by using narrow-band and global models. Although the narrow-band models are considered more accurate, global model are more adequate for combined heat transfer study in complex geometry. Thus, accuracy of narrow-band and global models study is provide. In this investigation, we focus our attention on the practical way to use the Correlated-K narrow-band model in radiative transfer, as the asymptotic limit of accuracy of the global model. Results are presented in terms of radiative power fields.

Modeling the Atmosphere of Solar and Other Stars: Radiative Transfer with PHOENIX/3D

NASA Astrophysics Data System (ADS)

Baron, Edward

The chemical composition of stars is an important ingredient in our understanding of the formation, structure, and evolution of both the Galaxy and the Solar System. The composition of the sun itself is an essential reference standard against which the elemental contents of other astronomical objects are compared. Recently, redetermination of the elemental abundances using three-dimensional, time-dependent hydrodynamical models of the solar atmosphere has led to a reduction in the inferred metal abundances, particularly C, N, O, and Ne. However, this reduction in metals reduces the opacity such that models of the Sun no longer agree with the observed results obtained using helioseismology. Three dimensional (3-D) radiative transfer is an important problem in physics, astrophysics, and meteorology. Radiative transfer is extremely computationally complex and it is a natural problem that requires computation on the exascale. We intend to calculate the detailed compositional structure of the Sun and other stars at high resolution with full NLTE, treating the turbulent velocity flows in full detail in order to compare results from hydrodynamics and helioseismology, and understand the nature of the discrepancies found between the two approaches. We propose to perform 3-D high-resolution radiative transfer calculations with the PHOENIX/3D suite of solar and other stars using 3-D hydrodynamic models from different groups. While NLTE radiative transfer has been treated by the groups doing hydrodynamics, they are necessarily limited in their resolution to the consideration of only a few (4-20) frequency bins, whereas we can calculate full NLTE including thousands of wavelength points, resolving the line profiles, and solving the scattering problem with extremely high angular resolution. The code has been used for the analysis of supernova spectra, stellar and planetary spectra, and for time-dependent modeling of transient objects. PHOENIX/3D runs and scales very well on Cray XC-30 and XC-40 machines (tested up to 100,800 CPU cores) and should scale up to several million cores for large simulations. Non-local problems, particularly radiation hydrodynamics problems, are at the forefront of computational astrophysics and we will share our work with the community. Our research program brings a unified modeling strategy to the results of several disparate groups and thus will provide a unifying framework with which to assess the metal abundance of the stars and the chemical evolution of the galaxy. We will bring together 3-D hydrodynamical models, detailed radiative transfer, and astronomical abundance studies. We will also provide results of interest to the atomic physics and plasma physics communities. Our work will use data from NASA telescopes including the Hubble Space Telescope and the James Webb Space telescope. The ability to work with data from the UV to the far IR is crucial from validating our results. Our work will also extend the exascale computational capabilities, which is a national goal.

An Internal Thermal Environment Model of an Aluminized Solid Rocket Motor with Experimental Validation

NASA Technical Reports Server (NTRS)

Martin, Heath T.

2015-01-01

Due to the severity of the internal solid rocket motor (SRM) environment, very few direct measurements of that environment exist; therefore, the appearance of such data provides a unique opportunity to assess current thermal/fluid modeling capabilities. As part of a previous study of SRM internal insulation performance, the internal thermal environment of a laboratory-scale SRM featuring aluminized propellant was characterized with two types of custom heat-flux calorimeters: one that measured the total heat flux to a graphite slab within the SRM chamber and another that measured the thermal radiation flux. Therefore, in the current study, a thermal/fluid model of this lab-scale SRM was constructed using ANSYS Fluent to predict not only the flow field structure within the SRM and the convective heat transfer to the interior walls, but also the resulting dispersion of alumina droplets and the radiative heat transfer to the interior walls. The dispersion of alumina droplets within the SRM chamber was determined by employing the Lagrangian discrete phase model that was fully coupled to the Eulerian gas-phase flow. The P1-approximation was engaged to model the radiative heat transfer through the SRM chamber where the radiative contributions of the gas phase were ignored and the aggregate radiative properties of the alumina dispersion were computed from the radiative properties of its individual constituent droplets, which were sourced from literature. The convective and radiative heat fluxes computed from the thermal/fluid model were then compared with those measured in the lab-scale SRM test firings and the modeling approach evaluated.

AccuRT: A versatile tool for radiative transfer simulations in the coupled atmosphere-ocean system

NASA Astrophysics Data System (ADS)

Hamre, Børge; Stamnes, Snorre; Stamnes, Knut; Stamnes, Jakob

2017-02-01

Reliable, accurate, and efficient modeling of the transport of electromagnetic radiation in turbid media has important applications in the study of the Earth's climate by remote sensing. For example, such modeling is needed to develop forward-inverse methods used to quantify types and concentrations of aerosol and cloud particles in the atmosphere, the dissolved organic and particulate biogeochemical matter in lakes, rivers, coastal, and open-ocean waters. It is also needed to simulate the performance of remote sensing detectors deployed on aircraft, balloons, and satellites as well as radiometric detectors deployed on buoys, gliders and other aquatic observing systems. Accurate radiative transfer modeling is also required to compute irradiances and scalar irradiances that are used to compute warming/cooling and photolysis rates in the atmosphere and primary production and warming/cooling rates in the water column. AccuRT is a radiative transfer model for the coupled atmosphere-water system that is designed to be a versatile tool for researchers in the ocean optics and remote sensing communities. It addresses the needs of researchers interested in analyzing irradiance and radiance measurements in the field and laboratory as well as those interested in making simulations of the top-of-the-atmosphere radiance in support of remote sensing algorithm development.

Effect of polarized radiative transfer on the Hanle magnetic field determination in prominences: Analysis of hydrogen H alpha line observations at Pic-du-Midi

NASA Technical Reports Server (NTRS)

Bommier, V.; Deglinnocenti, E. L.; Leroy, J. L.; Sahal-Brechot, S.

1985-01-01

The linear polarization of the Hydrogen H alpha line of prominences has been computed, taking into account the effect of a magnetic field (Hanle effect), of the radiative transfer in the prominence, and of the depolarization due to collisions with the surrounding electrons and protons. The corresponding formalisms are developed in a forthcoming series of papers. In this paper, the main features of the computation method are summarized. The results of computation have been used for interpretation in terms of magnetic field vector measurements from H alpha polarimetric observations in prominences performed at Pic-du-Midi coronagraph-polarimeter. Simultaneous observations in one optically thin line (He I D(3)) and one optically thick line (H alpha) give an opportunity for solving the ambiguity on the field vector determination.

A Parallel Numerical Algorithm To Solve Linear Systems Of Equations Emerging From 3D Radiative Transfer

NASA Astrophysics Data System (ADS)

Wichert, Viktoria; Arkenberg, Mario; Hauschildt, Peter H.

2016-10-01

Highly resolved state-of-the-art 3D atmosphere simulations will remain computationally extremely expensive for years to come. In addition to the need for more computing power, rethinking coding practices is necessary. We take a dual approach by introducing especially adapted, parallel numerical methods and correspondingly parallelizing critical code passages. In the following, we present our respective work on PHOENIX/3D. With new parallel numerical algorithms, there is a big opportunity for improvement when iteratively solving the system of equations emerging from the operator splitting of the radiative transfer equation J = ΛS. The narrow-banded approximate Λ-operator Λ* , which is used in PHOENIX/3D, occurs in each iteration step. By implementing a numerical algorithm which takes advantage of its characteristic traits, the parallel code's efficiency is further increased and a speed-up in computational time can be achieved.

An Improved Radiative Transfer Model for Climate Calculations

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Mlawer, Eli J.; Sokolik, Irina N.; Clough, Shepard A.; Toon, Owen B.

1998-01-01

This paper presents a radiative transfer model that has been developed to accurately predict the atmospheric radiant flux in both the infrared and the solar spectrum with a minimum of computational effort. The model is designed to be included in numerical climate models To assess the accuracy of the model, the results are compared to other more detailed models for several standard cases in the solar and thermal spectrum. As the thermal spectrum has been treated in other publications, we focus here on the solar part of the spectrum. We perform several example calculations focussing on the question of absorption of solar radiation by gases and aerosols.

A cloud model-radiative model combination for determining microwave TB-rain rate relations

NASA Technical Reports Server (NTRS)

Szejwach, Gerard; Adler, Robert F.; Jobard, Esabelle; Mack, Robert A.

1986-01-01

The development of a cloud model-radiative transfer model combination for computing average brightness temperature, T(B), is discussed. The cloud model and radiative transfer model used in this study are described. The relations between rain rate, cloud and rain water, cloud and precipitation ice, and upwelling radiance are investigated. The effects of the rain rate relations on T(B) under different climatological conditions are examined. The model-derived T(B) results are compared to the 92 and 183 GHz aircraft observations of Hakkarinen and Adler (1984, 1986) and the radar-estimated rain rate of Hakkarinen and Adler (1986); good correlation between the data is detected.

Principal Component-Based Radiative Transfer Model (PCRTM) for Hyperspectral Sensors. Part I; Theoretical Concept

NASA Technical Reports Server (NTRS)

Liu, Xu; Smith, William L.; Zhou, Daniel K.; Larar, Allen

2005-01-01

Modern infrared satellite sensors such as Atmospheric Infrared Sounder (AIRS), Cosmic Ray Isotope Spectrometer (CrIS), Thermal Emission Spectrometer (TES), Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) and Infrared Atmospheric Sounding Interferometer (IASI) are capable of providing high spatial and spectral resolution infrared spectra. To fully exploit the vast amount of spectral information from these instruments, super fast radiative transfer models are needed. This paper presents a novel radiative transfer model based on principal component analysis. Instead of predicting channel radiance or transmittance spectra directly, the Principal Component-based Radiative Transfer Model (PCRTM) predicts the Principal Component (PC) scores of these quantities. This prediction ability leads to significant savings in computational time. The parameterization of the PCRTM model is derived from properties of PC scores and instrument line shape functions. The PCRTM is very accurate and flexible. Due to its high speed and compressed spectral information format, it has great potential for super fast one-dimensional physical retrievals and for Numerical Weather Prediction (NWP) large volume radiance data assimilation applications. The model has been successfully developed for the National Polar-orbiting Operational Environmental Satellite System Airborne Sounder Testbed - Interferometer (NAST-I) and AIRS instruments. The PCRTM model performs monochromatic radiative transfer calculations and is able to include multiple scattering calculations to account for clouds and aerosols.

One-dimensional transient radiative transfer by lattice Boltzmann method.

PubMed

Zhang, Yong; Yi, Hongliang; Tan, Heping

2013-10-21

The lattice Boltzmann method (LBM) is extended to solve transient radiative transfer in one-dimensional slab containing scattering media subjected to a collimated short laser irradiation. By using a fully implicit backward differencing scheme to discretize the transient term in the radiative transfer equation, a new type of lattice structure is devised. The accuracy and computational efficiency of this algorithm are examined firstly. Afterwards, effects of the medium properties such as the extinction coefficient, the scattering albedo and the anisotropy factor, and the shapes of laser pulse on time-resolved signals of transmittance and reflectance are investigated. Results of the present method are found to compare very well with the data from the literature. For an oblique incidence, the LBM results in this paper are compared with those by Monte Carlo method generated by ourselves. In addition, transient radiative transfer in a two-Layer inhomogeneous media subjected to a short square pulse irradiation is investigated. At last, the LBM is further extended to study the transient radiative transfer in homogeneous medium with a refractive index discontinuity irradiated by the short pulse laser. Several trends on the time-resolved signals different from those for refractive index of 1 (i.e. refractive-index-matched boundary) are observed and analysed.

A Radiation Transfer Solver for Athena Using Short Characteristics

NASA Astrophysics Data System (ADS)

Davis, Shane W.; Stone, James M.; Jiang, Yan-Fei

2012-03-01

We describe the implementation of a module for the Athena magnetohydrodynamics (MHD) code that solves the time-independent, multi-frequency radiative transfer (RT) equation on multidimensional Cartesian simulation domains, including scattering and non-local thermodynamic equilibrium (LTE) effects. The module is based on well known and well tested algorithms developed for modeling stellar atmospheres, including the method of short characteristics to solve the RT equation, accelerated Lambda iteration to handle scattering and non-LTE effects, and parallelization via domain decomposition. The module serves several purposes: it can be used to generate spectra and images, to compute a variable Eddington tensor (VET) for full radiation MHD simulations, and to calculate the heating and cooling source terms in the MHD equations in flows where radiation pressure is small compared with gas pressure. For the latter case, the module is combined with the standard MHD integrators using operator splitting: we describe this approach in detail, including a new constraint on the time step for stability due to radiation diffusion modes. Implementation of the VET method for radiation pressure dominated flows is described in a companion paper. We present results from a suite of test problems for both the RT solver itself and for dynamical problems that include radiative heating and cooling. These tests demonstrate that the radiative transfer solution is accurate and confirm that the operator split method is stable, convergent, and efficient for problems of interest. We demonstrate there is no need to adopt ad hoc assumptions of questionable accuracy to solve RT problems in concert with MHD: the computational cost for our general-purpose module for simple (e.g., LTE gray) problems can be comparable to or less than a single time step of Athena's MHD integrators, and only few times more expensive than that for more general (non-LTE) problems.

A demonstration of adjoint methods for multi-dimensional remote sensing of the atmosphere and surface

NASA Astrophysics Data System (ADS)

Martin, William G. K.; Hasekamp, Otto P.

2018-01-01

In previous work, we derived the adjoint method as a computationally efficient path to three-dimensional (3D) retrievals of clouds and aerosols. In this paper we will demonstrate the use of adjoint methods for retrieving two-dimensional (2D) fields of cloud extinction. The demonstration uses a new 2D radiative transfer solver (FSDOM). This radiation code was augmented with adjoint methods to allow efficient derivative calculations needed to retrieve cloud and surface properties from multi-angle reflectance measurements. The code was then used in three synthetic retrieval studies. Our retrieval algorithm adjusts the cloud extinction field and surface albedo to minimize the measurement misfit function with a gradient-based, quasi-Newton approach. At each step we compute the value of the misfit function and its gradient with two calls to the solver FSDOM. First we solve the forward radiative transfer equation to compute the residual misfit with measurements, and second we solve the adjoint radiative transfer equation to compute the gradient of the misfit function with respect to all unknowns. The synthetic retrieval studies verify that adjoint methods are scalable to retrieval problems with many measurements and unknowns. We can retrieve the vertically-integrated optical depth of moderately thick clouds as a function of the horizontal coordinate. It is also possible to retrieve the vertical profile of clouds that are separated by clear regions. The vertical profile retrievals improve for smaller cloud fractions. This leads to the conclusion that cloud edges actually increase the amount of information that is available for retrieving the vertical profile of clouds. However, to exploit this information one must retrieve the horizontally heterogeneous cloud properties with a 2D (or 3D) model. This prototype shows that adjoint methods can efficiently compute the gradient of the misfit function. This work paves the way for the application of similar methods to 3D remote sensing problems.

Gauss-Seidel and Successive Overrelaxation Methods for Radiative Transfer with Partial Frequency Redistribution

NASA Astrophysics Data System (ADS)

Sampoorna, M.; Trujillo Bueno, J.

2010-04-01

The linearly polarized solar limb spectrum that is produced by scattering processes contains a wealth of information on the physical conditions and magnetic fields of the solar outer atmosphere, but the modeling of many of its strongest spectral lines requires solving an involved non-local thermodynamic equilibrium radiative transfer problem accounting for partial redistribution (PRD) effects. Fast radiative transfer methods for the numerical solution of PRD problems are also needed for a proper treatment of hydrogen lines when aiming at realistic time-dependent magnetohydrodynamic simulations of the solar chromosphere. Here we show how the two-level atom PRD problem with and without polarization can be solved accurately and efficiently via the application of highly convergent iterative schemes based on the Gauss-Seidel and successive overrelaxation (SOR) radiative transfer methods that had been previously developed for the complete redistribution case. Of particular interest is the Symmetric SOR method, which allows us to reach the fully converged solution with an order of magnitude of improvement in the total computational time with respect to the Jacobi-based local accelerated lambda iteration method.

Galactic cosmic ray radiation levels in spacecraft on interplanetary missions

NASA Technical Reports Server (NTRS)

Shinn, J. L.; Nealy, J. E.; Townsend, L. W.; Wilson, J. W.; Wood, J.S.

1994-01-01

Using the Langley Research Center Galactic Cosmic Ray (GCR) transport computer code (HZETRN) and the Computerized Anatomical Man (CAM) model, crew radiation levels inside manned spacecraft on interplanetary missions are estimated. These radiation-level estimates include particle fluxes, LET (Linear Energy Transfer) spectra, absorbed dose, and dose equivalent within various organs of interest in GCR protection studies. Changes in these radiation levels resulting from the use of various different types of shield materials are presented.

A study of the thermal and optical characteristics of radiometric channels for Earth radiation budget applications

NASA Technical Reports Server (NTRS)

Mahan, J. R.; Tira, Nour E.

1991-01-01

An improved dynamic electrothermal model for the Earth Radiation Budget Experiment (ERBE) total, nonscanning channels is formulated. This model is then used to accurately simulate two types of dynamic solar observation: the solar calibration and the so-called pitchover maneuver. Using a second model, the nonscanner active cavity radiometer (ACR) thermal noise is studied. This study reveals that radiative emission and scattering by the surrounding parts of the nonscanner cavity are acceptably small. The dynamic electrothermal model is also used to compute ACR instrument transfer function. Accurate in-flight measurement of this transfer function is shown to depend on the energy distribution over the frequency spectrum of the radiation input function. A new array-type field of view limiter, whose geometry controls the input function, is proposed for in-flight calibration of an ACR and other types of radiometers. The point spread function (PSF) of the ERBE and the Clouds and Earth's Radiant Energy System (CERES) scanning radiometers is computed. The PSF is useful in characterizing the channel optics. It also has potential for recovering the distribution of the radiative flux from Earth by deconvolution.

3D-radiative transfer in terrestrial atmosphere: An efficient parallel numerical procedure

NASA Astrophysics Data System (ADS)

Bass, L. P.; Germogenova, T. A.; Nikolaeva, O. V.; Kokhanovsky, A. A.; Kuznetsov, V. S.

2003-04-01

Light propagation and scattering in terrestrial atmosphere is usually studied in the framework of the 1D radiative transfer theory [1]. However, in reality particles (e.g., ice crystals, solid and liquid aerosols, cloud droplets) are randomly distributed in 3D space. In particular, their concentrations vary both in vertical and horizontal directions. Therefore, 3D effects influence modern cloud and aerosol retrieval procedures, which are currently based on the 1D radiative transfer theory. It should be pointed out that the standard radiative transfer equation allows to study these more complex situations as well [2]. In recent year the parallel version of the 2D and 3D RADUGA code has been developed. This version is successfully used in gammas and neutrons transport problems [3]. Applications of this code to radiative transfer in atmosphere problems are contained in [4]. Possibilities of code RADUGA are presented in [5]. The RADUGA code system is an universal solver of radiative transfer problems for complicated models, including 2D and 3D aerosol and cloud fields with arbitrary scattering anisotropy, light absorption, inhomogeneous underlying surface and topography. Both delta type and distributed light sources can be accounted for in the framework of the algorithm developed. The accurate numerical procedure is based on the new discrete ordinate SWDD scheme [6]. The algorithm is specifically designed for parallel supercomputers. The version RADUGA 5.1(P) can run on MBC1000M [7] (768 processors with 10 Gb of hard disc memory for each processor). The peak productivity is equal 1 Tfl. Corresponding scalar version RADUGA 5.1 is working on PC. As a first example of application of the algorithm developed, we have studied the shadowing effects of clouds on neighboring cloudless atmosphere, depending on the cloud optical thickness, surface albedo, and illumination conditions. This is of importance for modern satellite aerosol retrieval algorithms development. [1] Sobolev, V. V., 1972: Light scattering in planetary atmosphere, M.:Nauka. [2] Evans, K. F., 1998: The spherical harmonic discrete ordinate method for three dimensional atmospheric radiative transfer, J. Atmos. Sci., 55, 429 446. [3] L.P. Bass, T.A. Germogenova, V.S. Kuznetsov, O.V. Nikolaeva. RADUGA 5.1 and RADUGA 5.1(P) codes for stationary transport equation solution in 2D and 3D geometries on one and multiprocessors computers. Report on seminar “Algorithms and Codes for neutron physical of nuclear reactor calculations” (Neutronica 2001), Obninsk, Russia, 30 October 2 November 2001. [4] T.A. Germogenova, L.P. Bass, V.S. Kuznetsov, O.V. Nikolaeva. Mathematical modeling on parallel computers solar and laser radiation transport in 3D atmosphere. Report on International Symposium CIS countries “Atmosphere radiation”, 18 21 June 2002, St. Peterburg, Russia, p. 15 16. [5] L.P. Bass, T.A. Germogenova, O.V. Nikolaeva, V.S. Kuznetsov. Radiative Transfer Universal 2D 3D Code RADUGA 5.1(P) for Multiprocessor Computer. Abstract. Poster report on this Meeting. [6] L.P. Bass, O.V. Nikolaeva. Correct calculation of Angular Flux Distribution in Strongly Heterogeneous Media and Voids. Proc. of Joint International Conference on Mathematical Methods and Supercomputing for Nuclear Applications, Saratoga Springs, New York, October 5 9, 1997, p. 995 1004. [7] http://www/jscc.ru

Reflectance Modeling

NASA Technical Reports Server (NTRS)

Smith, J. A. (Principal Investigator)

1985-01-01

The overall goal of this work has been to develop a set of computational tools and media abstractions for the terrain bidirectional reflectance problem. The modeling of soil and vegetation surfaces has been emphasized with a gradual increase in the complexity of the media geometries treated. Pragmatic problems involved in the combined modeling of soil, vegetation, and atmospheric effects have been of interest and one of the objectives has been to describe the canopy reflectance problem in a classical radiative transfer sense permitting easier inclusion of our work by other workers in the radiative transfer field.

Reflection of solar radiation by a cylindrical cloud

NASA Technical Reports Server (NTRS)

Smith, G. L.

1989-01-01

Potential applications of an analytic method for computing the solar radiation reflected by a cylindrical cloud are discussed, including studies of radiative transfer within finite clouds and evaluations of these effects on other clouds and on remote sensing problems involving finite clouds. The pattern of reflected sunlight from a cylindrical cloud as seen at a large distance has been considered and described by the bidirectional function method for finite cloud analysis, as previously studied theoretically for plane-parallel atmospheres by McKee and Cox (1974); Schmetz and Raschke (1981); and Stuhlmann et al. (1985). However, the lack of three-dimensional radiative transfer solutions for anisotropic scattering media have hampered theoretical investigations of bidirectional functions for finite clouds. The present approach permits expression of the directional variation of the radiation field as a spherical harmonic series to any desired degree and order.

Infrared radiative transfer through a regular array of cuboidal clouds

NASA Technical Reports Server (NTRS)

HARSHVARDHAN; Weinman, J. A.

1981-01-01

Infrared radiative transfer through a regular array of cuboidal clouds is studied and the interaction of the sides of the clouds with each other and the ground is considered. The theory is developed for black clouds and is extended to scattering clouds using a variable azimuth two-stream approximation. It is shown that geometrical considerations often dominate over the microphysical aspects of radiative transfer through the clouds. For example, the difference in simulated 10 micron brightness temperature between black isothermal cubic clouds and cubic clouds of optical depth 10, is less than 2 deg for zenith angles less than 50 deg for all cloud fractions when viewed parallel to the array. The results show that serious errors are made in flux and cooling rate computations if broken clouds are modeled as planiform. Radiances computed by the usual practice of area-weighting cloudy and clear sky radiances are in error by 2 to 8 K in brightness temperature for cubic clouds over a wide range of cloud fractions and zenith angles. It is also shown that the lapse rate does not markedly affect the exiting radiances for cuboidal clouds of unit aspect ratio and optical depth 10.

CO2, H2O, and chlorophyll fluorescence retrieved from OCO-2 measurements using a fast radiative transfer model approximating multiple scattering effects

NASA Astrophysics Data System (ADS)

Reuter, Maximilian; Bovensmann, Heinrich; Buchwitz, Michael; Burrows, John P.; Heymann, Jens; Noël, Stefan; Rozanov, Vladimir; Schneising, Oliver

2017-04-01

Carbon dioxide is the most important anthropogenic greenhouse gas. Its global increasing concentration in the Earth's atmosphere is the main driver for global climate change. In spite of its importance, there are still large uncertainties on its global sources and sinks. Satellite measurements have the potential to reduce these surface flux uncertainties. However, the demanding accuracy requirements usually involve the need for precise radiative transfer calculations in a scattering atmosphere. These can be computationally so expensive that hundreds or thousands of CPU cores are need to keep up with the data stream of an instrument like OCO-2. Future instruments will further increase the amount of soundings at least by an order of magnitude. A radiative transfer model has been developed approximating scattering effects by multiple scattering at an optically thin scattering layer reducing the computational costs by several orders of magnitude. The model can be used to simulate the radiance in all three OCO-2 spectral bands allowing the simultaneous retrieval of CO2, H2O, and chlorophyll fluorescence. First retrieval results for OCO-2 data will be presented.

An Algorithm to Compress Line-transition Data for Radiative-transfer Calculations

NASA Astrophysics Data System (ADS)

Cubillos, Patricio E.

2017-11-01

Molecular line-transition lists are an essential ingredient for radiative-transfer calculations. With recent databases now surpassing the billion-line mark, handling them has become computationally prohibitive, due to both the required processing power and memory. Here I present a temperature-dependent algorithm to separate strong from weak line transitions, reformatting the large majority of the weaker lines into a cross-section data file, and retaining the detailed line-by-line information of the fewer strong lines. For any given molecule over the 0.3-30 μm range, this algorithm reduces the number of lines to a few million, enabling faster radiative-transfer computations without a significant loss of information. The final compression rate depends on how densely populated the spectrum is. I validate this algorithm by comparing Exomol’s HCN extinction-coefficient spectra between the complete (65 million line transitions) and compressed (7.7 million) line lists. Over the 0.6-33 μm range, the average difference between extinction-coefficient values is less than 1%. A Python/C implementation of this algorithm is open-source and available at https://github.com/pcubillos/repack. So far, this code handles the Exomol and HITRAN line-transition format.

Multiple Scattering in Planetary Regoliths Using Incoherent Interactions

NASA Astrophysics Data System (ADS)

Muinonen, K.; Markkanen, J.; Vaisanen, T.; Penttilä, A.

2017-12-01

We consider scattering of light by a planetary regolith using novel numerical methods for discrete random media of particles. Understanding the scattering process is of key importance for spectroscopic, photometric, and polarimetric modeling of airless planetary objects, including radar studies. In our modeling, the size of the spherical random medium can range from microscopic to macroscopic sizes, whereas the particles are assumed to be of the order of the wavelength in size. We extend the radiative transfer and coherent backscattering method (RT-CB) to the case of dense packing of particles by adopting the ensemble-averaged first-order incoherent extinction, scattering, and absorption characteristics of a volume element of particles as input. In the radiative transfer part, at each absorption and scattering process, we account for absorption with the help of the single-scattering albedo and peel off the Stokes parameters of radiation emerging from the medium in predefined scattering angles. We then generate a new scattering direction using the joint probability density for the local polar and azimuthal scattering angles. In the coherent backscattering part, we utilize amplitude scattering matrices along the radiative-transfer path and the reciprocal path. Furthermore, we replace the far-field interactions of the RT-CB method with rigorous interactions facilitated by the Superposition T-matrix method (STMM). This gives rise to a new RT-RT method, radiative transfer with reciprocal interactions. For microscopic random media, we then compare the new results to asymptotically exact results computed using the STMM, succeeding in the numerical validation of the new methods.Acknowledgments. Research supported by European Research Council with Advanced Grant No. 320773 SAEMPL, Scattering and Absorption of ElectroMagnetic waves in ParticuLate media. Computational resources provided by CSC - IT Centre for Science Ltd, Finland.

Energy transfer by radiation in non-grey atomic gases in isothermal and non-isothermal slabs

NASA Technical Reports Server (NTRS)

Poon, P. T. Y.

1975-01-01

A multiband model for the absorption coefficient of atomic hydrogen-helium plasmas is constructed which includes continuum and line contributions. Emission from 28 stronger lines of 106 that have been screened is considered, of which 21 are from hydrogen and 7 belong to helium, with reabsorption due to line-line, line-continuum overlap accurately accounted for. The model is utilized in the computation of intensities and fluxes from shock-heated slabs of 85% H2-15% He mixtures for slab thicknesses from 1 to 30 cm, temperature from 10,000 to 20,000 K, and for different densities. In conjunction with the multiband model, simple numerical schemes have been devised which provide a quick and comprehensive way of computing radiative energy transfer in nonisothermal and nongrey gases.

Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun

NASA Astrophysics Data System (ADS)

Dombrovsky, Leonid A.; Reviznikov, Dmitry L.; Kryukov, Alexei P.; Levashov, Vladimir Yu

2017-10-01

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1 kg/m2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere.

FIIDOS--A Computer Code for the Computation of Fallout Inhalation and Ingestion Dose to Organs Computer User’s Guide (Revision 4)

DTIC Science & Technology

2007-05-01

35 5 Actinide product radionuclides... actinides , and fission products in fallout. Doses from low-linear energy transfer (LET) radiation (beta particles and gamma rays) are reported separately...assumptions about the critical parameters used in calculating internal doses – resuspension factor, breathing rate, fractionation, and scenario elements – to

EOSPEC: a complementary toolbox for MODTRAN calculations

NASA Astrophysics Data System (ADS)

Dion, Denis

2016-09-01

For more than a decade, Defence Research and Development Canada (DRDC) has been developing a Library of computer models for the calculations of atmospheric effects on EO-IR sensor performances. The Library, called EOSPEC-LIB (EO-IR Sensor PErformance Computation LIBrary) has been designed as a complement to MODTRAN, the radiative transfer code developed by the Air Force Research Laboratory and Spectral Science Inc. in the USA. The Library comprises modules for the definition of the atmospheric conditions, including aerosols, and provides modules for the calculation of turbulence and fine refraction effects. SMART (Suite for Multi-resolution Atmospheric Radiative Transfer), a key component of EOSPEC, allows one to perform fast computations of transmittances and radiances using MODTRAN through a wide-band correlated-k computational approach. In its most recent version, EOSPEC includes a MODTRAN toolbox whose functions help generate in a format compatible to MODTRAN 5 and 6 atmospheric and aerosol profiles, user-defined refracted optical paths and inputs for configuring the MODTRAN sea radiance (BRDF) model. The paper gives an overall description of the EOSPEC features and capacities. EOSPEC provides augmented capabilities for computations in the lower atmosphere, and for computations in maritime environments.

F--Ray: A new algorithm for efficient transport of ionizing radiation

NASA Astrophysics Data System (ADS)

Mao, Yi; Zhang, J.; Wandelt, B. D.; Shapiro, P. R.; Iliev, I. T.

2014-04-01

We present a new algorithm for the 3D transport of ionizing radiation, called F2-Ray (Fast Fourier Ray-tracing method). The transfer of ionizing radiation with long mean free path in diffuse intergalactic gas poses a special challenge to standard numerical methods which transport the radiation in position space. Standard methods usually trace each individual ray until it is fully absorbed by the intervening gas. If the mean free path is long, the computational cost and memory load are likely to be prohibitive. We have developed an algorithm that overcomes these limitations and is, therefore, significantly more efficient. The method calculates the transfer of radiation collectively, using the Fast Fourier Transform to convert radiation between position and Fourier spaces, so the computational cost will not increase with the number of ionizing sources. The method also automatically combines parallel rays with the same frequency at the same grid cell, thereby minimizing the memory requirement. The method is explicitly photon-conserving, i.e. the depletion of ionizing photons is guaranteed to equal the photoionizations they caused, and explicitly obeys the periodic boundary condition, i.e. the escape of ionizing photons from one side of a simulation volume is guaranteed to be compensated by emitting the same amount of photons into the volume through the opposite side. Together, these features make it possible to numerically simulate the transfer of ionizing photons more efficiently than previous methods. Since ionizing radiation such as the X-ray is responsible for heating the intergalactic gas when first stars and quasars form at high redshifts, our method can be applied to simulate thermal distribution, in addition to cosmic reionization, in three-dimensional inhomogeneous cosmological density field.

Improvement and Application of Atmospheric Radiative Transfer Models for Prediction of the Climatic Effects of Aerosol

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Mlawer, Eli J.; Sokolik, Irina N.; Clough, Shepard A.; Toon, Owen B.

1998-01-01

This paper presents a radiative transfer model that has been developed to accurately predict the atmospheric radiant flux in both the infrared and the solar spectrum with a minimum of computational effort. The model is designed to be included in numerical climate models. To assess the accuracy of the model, the results are compared to other more detailed models for several standard cases in the solar and thermal spectrum. As the thermal spectrum has been treated in other publications, we focus here on the solar part of the spectrum. We perform several example calculations focussing on the question of absorption of solar radiation by gases and aerosols.

Improvement and Application of Atmospheric Radiative Transfer Models for Prediction of the Climatic Effects of Aerosol

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.

1998-01-01

This paper presents a radiative transfer model that has been developed to accurately predict the atmospheric radiant flux in both the infrared and the solar spectrum with a minimum of computational effort. The model is designed to be included in numerical climate models. To assess the accuracy of the model, the results are compared to other more detailed models for several standard cases in the solar and thermal spectrum. As the thermal spectrum has been treated in other publications we focus here on the solar part of the spectrum. We perform several example calculations focussing on the question of absorption of solar radiation by gases and aerosols.

Numerical techniques in radiative heat transfer for general, scattering, plane-parallel media

NASA Technical Reports Server (NTRS)

Sharma, A.; Cogley, A. C.

1982-01-01

The study of radiative heat transfer with scattering usually leads to the solution of singular Fredholm integral equations. The present paper presents an accurate and efficient numerical method to solve certain integral equations that govern radiative equilibrium problems in plane-parallel geometry for both grey and nongrey, anisotropically scattering media. In particular, the nongrey problem is represented by a spectral integral of a system of nonlinear integral equations in space, which has not been solved previously. The numerical technique is constructed to handle this unique nongrey governing equation as well as the difficulties caused by singular kernels. Example problems are solved and the method's accuracy and computational speed are analyzed.

A NUMERICAL SCHEME FOR SPECIAL RELATIVISTIC RADIATION MAGNETOHYDRODYNAMICS BASED ON SOLVING THE TIME-DEPENDENT RADIATIVE TRANSFER EQUATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohsuga, Ken; Takahashi, Hiroyuki R.

2016-02-20

We develop a numerical scheme for solving the equations of fully special relativistic, radiation magnetohydrodynamics (MHDs), in which the frequency-integrated, time-dependent radiation transfer equation is solved to calculate the specific intensity. The radiation energy density, the radiation flux, and the radiation stress tensor are obtained by the angular quadrature of the intensity. In the present method, conservation of total mass, momentum, and energy of the radiation magnetofluids is guaranteed. We treat not only the isotropic scattering but also the Thomson scattering. The numerical method of MHDs is the same as that of our previous work. The advection terms are explicitlymore » solved, and the source terms, which describe the gas–radiation interaction, are implicitly integrated. Our code is suitable for massive parallel computing. We present that our code shows reasonable results in some numerical tests for propagating radiation and radiation hydrodynamics. Particularly, the correct solution is given even in the optically very thin or moderately thin regimes, and the special relativistic effects are nicely reproduced.« less

Turbulent Flow past High Temperature Surfaces

NASA Astrophysics Data System (ADS)

Mehmedagic, Igbal; Thangam, Siva; Carlucci, Pasquale; Buckley, Liam; Carlucci, Donald

2014-11-01

Flow over high-temperature surfaces subject to wall heating is analyzed with applications to projectile design. In this study, computations are performed using an anisotropic Reynolds-stress model to study flow past surfaces that are subject to radiative flux. The model utilizes a phenomenological treatment of the energy spectrum and diffusivities of momentum and heat to include the effects of wall heat transfer and radiative exchange. The radiative transport is modeled using Eddington approximation including the weighted effect of nongrayness of the fluid. The time-averaged equations of motion and energy are solved using the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation with an efficient finite-volume algorithm. The model is applied for available test cases to validate its predictive capabilities for capturing the effects of wall heat transfer. Computational results are compared with experimental data available in the literature. Applications involving the design of projectiles are summarized. Funded in part by U.S. Army, ARDEC.

Quantitative computational infrared imaging of buoyant diffusion flames

NASA Astrophysics Data System (ADS)

Newale, Ashish S.

Studies of infrared radiation from turbulent buoyant diffusion flames impinging on structural elements have applications to the development of fire models. A numerical and experimental study of radiation from buoyant diffusion flames with and without impingement on a flat plate is reported. Quantitative images of the radiation intensity from the flames are acquired using a high speed infrared camera. Large eddy simulations are performed using fire dynamics simulator (FDS version 6). The species concentrations and temperature from the simulations are used in conjunction with a narrow-band radiation model (RADCAL) to solve the radiative transfer equation. The computed infrared radiation intensities rendered in the form of images and compared with the measurements. The measured and computed radiation intensities reveal necking and bulging with a characteristic frequency of 7.1 Hz which is in agreement with previous empirical correlations. The results demonstrate the effects of stagnation point boundary layer on the upstream buoyant shear layer. The coupling between these two shear layers presents a model problem for sub-grid scale modeling necessary for future large eddy simulations.

Evaluation of a continuous-rotation, high-speed scanning protocol for micro-computed tomography.

PubMed

Kerl, Hans Ulrich; Isaza, Cristina T; Boll, Hanne; Schambach, Sebastian J; Nolte, Ingo S; Groden, Christoph; Brockmann, Marc A

2011-01-01

Micro-computed tomography is used frequently in preclinical in vivo research. Limiting factors are radiation dose and long scan times. The purpose of the study was to compare a standard step-and-shoot to a continuous-rotation, high-speed scanning protocol. Micro-computed tomography of a lead grid phantom and a rat femur was performed using a step-and-shoot and a continuous-rotation protocol. Detail discriminability and image quality were assessed by 3 radiologists. The signal-to-noise ratio and the modulation transfer function were calculated, and volumetric analyses of the femur were performed. The radiation dose of the scan protocols was measured using thermoluminescence dosimeters. The 40-second continuous-rotation protocol allowed a detail discriminability comparable to the step-and-shoot protocol at significantly lower radiation doses. No marked differences in volumetric or qualitative analyses were observed. Continuous-rotation micro-computed tomography significantly reduces scanning time and radiation dose without relevantly reducing image quality compared with a normal step-and-shoot protocol.

Bidirectional Reflectance of Flat, Optically Thick Particulate Layers: An Efficient Radiative Transfer Solution and Applications to Snow and Soil Surfaces

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Dlugach, Janna M.; Yanovitsku, Edgard G.; Zakharova, Nadia T.

1999-01-01

We describe a simple and highly efficient and accurate radiative transfer technique for computing bidirectional reflectance of a macroscopically flat scattering layer composed of nonabsorbing or weakly absorbing, arbitrarily shaped, randomly oriented and randomly distributed particles. The layer is assumed to be homogeneous and optically semi-infinite, and the bidirectional reflection function (BRF) is found by a simple iterative solution of the Ambartsumian's nonlinear integral equation. As an exact Solution of the radiative transfer equation, the reflection function thus obtained fully obeys the fundamental physical laws of energy conservation and reciprocity. Since this technique bypasses the computation of the internal radiation field, it is by far the fastest numerical approach available and can be used as an ideal input for Monte Carlo procedures calculating BRFs of scattering layers with macroscopically rough surfaces. Although the effects of packing density and coherent backscattering are currently neglected, they can also be incorporated. The FORTRAN implementation of the technique is available on the World Wide Web at http://ww,,v.giss.nasa.gov/-crmim/brf.html and can be applied to a wide range of remote sensing, engineering, and biophysical problems. We also examine the potential effect of ice crystal shape on the bidirectional reflectance of flat snow surfaces and the applicability of the Henyey-Greenstein phase function and the 6-Eddington approximation in calculations for soil surfaces.

Merced

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hedstrom, Gerald; Beck, Bret; Mattoon, Caleb

2016-10-01

Merced performs a multi-dimensional integral tl generate so-called 'transfer matrices' for use in deterministic radiation transport applications. It produces transfer matrices on the user-defind energy grid. The angular dependence of outgoing products is captured in a Legendre expansion, up to a user-specified maximun Legendre order. Merced calculations can use multi-threading for enhanced performance on a single compute node.

Radiative-Transfer Modeling of Spectra of Densely Packed Particulate Media

NASA Astrophysics Data System (ADS)

Ito, G.; Mishchenko, M. I.; Glotch, T. D.

2017-12-01

Remote sensing measurements over a wide range of wavelengths from both ground- and space-based platforms have provided a wealth of data regarding the surfaces and atmospheres of various solar system bodies. With proper interpretations, important properties, such as composition and particle size, can be inferred. However, proper interpretation of such datasets can often be difficult, especially for densely packed particulate media with particle sizes on the order of wavelength of light being used for remote sensing. Radiative transfer theory has often been applied to the study of densely packed particulate media like planetary regoliths and snow, but with difficulty, and here we continue to investigate radiative transfer modeling of spectra of densely packed media. We use the superposition T-matrix method to compute scattering properties of clusters of particles and capture the near-field effects important for dense packing. Then, the scattering parameters from the T-matrix computations are modified with the static structure factor correction, accounting for the dense packing of the clusters themselves. Using these corrected scattering parameters, reflectance (or emissivity via Kirchhoff's Law) is computed with the method of invariance imbedding solution to the radiative transfer equation. For this work we modeled the emissivity spectrum of the 3.3 µm particle size fraction of enstatite, representing some common mineralogical and particle size components of regoliths, in the mid-infrared wavelengths (5 - 50 µm). The modeled spectrum from the T-matrix method with static structure factor correction using moderate packing densities (filling factors of 0.1 - 0.2) produced better fits to the laboratory measurement of corresponding spectrum than the spectrum modeled by the equivalent method without static structure factor correction. Future work will test the method of the superposition T-matrix and static structure factor correction combination for larger particles sizes and polydispersed clusters in search for the most effective modeling of spectra of densely packed particulate media.

Turbulence radiation coupling in boundary layers of heavy-duty diesel engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sircar, Arpan; Paul, Chandan; Ferreyro-Fernandez, Sebastian

The lack of accurate submodels for in-cylinder radiation and heat transfer has been identified as a key shortcoming in developing truly predictive, physics-based computational fluid dynamics (CFD) models that can be used to develop combustion systems for advanced high-efficiency, low-emissions engines. Recent measurements of wall layers in engines show discrepancies of up to 100% with respect to standard CFD boundary-layer models. And recent analysis of in-cylinder radiation based on the most recent spectral property databases and high-fidelity radiative transfer equation (RTE) solvers has shown that at operating pressures and exhaust-gas recirculation levels typical of modern heavy-duty compression-ignition engines, radiative emissionmore » can be as high as 40% of the wall heat losses, that molecular gas radiation (mainly CO2 and H2O) can be more important than soot radiation, and that a significant fraction of the emitted radiation can be reabsorbed before reaching the walls. That is, radiation not only contributes to heat losses, but also changes the in-cylinder temperature distribution, which in turn affects combustion and emissions. The goal of this research is to develop models that explicitly account for the potentially strong coupling between radiative and turbulent boundary layer heat transfer. For example, for optically thick conditions, a simple diffusion model might be formulated in terms of an absorption-coefficient-dependent turbulent Prandtl number.« less

Quasi-analytical treatment of spatially averaged radiation transfer in complex terrain

NASA Astrophysics Data System (ADS)

LöWe, H.; Helbig, N.

2012-10-01

We provide a new quasi-analytical method to compute the subgrid topographic influences on the shortwave radiation fluxes and the effective albedo in complex terrain as required for large-scale meteorological, land surface, or climate models. We investigate radiative transfer in complex terrain via the radiosity equation on isotropic Gaussian random fields. Under controlled approximations we derive expressions for domain-averaged fluxes of direct, diffuse, and terrain radiation and the sky view factor. Domain-averaged quantities can be related to a type of level-crossing probability of the random field, which is approximated by long-standing results developed for acoustic scattering at ocean boundaries. This allows us to express all nonlocal horizon effects in terms of a local terrain parameter, namely, the mean-square slope. Emerging integrals are computed numerically, and fit formulas are given for practical purposes. As an implication of our approach, we provide an expression for the effective albedo of complex terrain in terms of the Sun elevation angle, mean-square slope, the area-averaged surface albedo, and the ratio of atmospheric direct beam to diffuse radiation. For demonstration we compute the decrease of the effective albedo relative to the area-averaged albedo in Switzerland for idealized snow-covered and clear-sky conditions at noon in winter. We find an average decrease of 5.8% and spatial patterns which originate from characteristics of the underlying relief. Limitations and possible generalizations of the method are discussed.

Effect of atmospheric scattering and surface reflection on upwelling solar radiation

NASA Technical Reports Server (NTRS)

Suttles, J. T.; Barkstrom, B. R.; Tiwari, S. N.

1981-01-01

A study is presented of the solar radiation transfer in the complete earth-atmosphere system, and numerical results are compared with satellite data obtained during the Earth Radiation Budget Experiment on Nimbus 6, in August, 1975. Emphasis is placed on the upwelling radiance distribution at the top of the atmosphere, assumed to be at 50 km. The numerical technique is based on the finite difference method, which includes azimuth and spectral variations for the entire solar wavelength range. Detailed solar properties, atmospheric physical properties, and optical properties are used. However, since the property descriptions are based on a trade-off between accuracy and computational realities, aerosol and cloud optical properties are treated with simple approximations. The radiative transfer model is in good agreement with the satellite radiance observations. The method provides a valuable tool in analyzing satellite- and ground-based radiation budget measurements and in designing instrumentation.

The COBAIN (COntact Binary Atmospheres with INterpolation) Code for Radiative Transfer

NASA Astrophysics Data System (ADS)

Kochoska, Angela; Prša, Andrej; Horvat, Martin

2018-01-01

Standard binary star modeling codes make use of pre-existing solutions of the radiative transfer equation in stellar atmospheres. The various model atmospheres available today are consistently computed for single stars, under different assumptions - plane-parallel or spherical atmosphere approximation, local thermodynamical equilibrium (LTE) or non-LTE (NLTE), etc. However, they are nonetheless being applied to contact binary atmospheres by populating the surface corresponding to each component separately and neglecting any mixing that would typically occur at the contact boundary. In addition, single stellar atmosphere models do not take into account irradiance from a companion star, which can pose a serious problem when modeling close binaries. 1D atmosphere models are also solved under the assumption of an atmosphere in hydrodynamical equilibrium, which is not necessarily the case for contact atmospheres, as the potentially different densities and temperatures can give rise to flows that play a key role in the heat and radiation transfer.To resolve the issue of erroneous modeling of contact binary atmospheres using single star atmosphere tables, we have developed a generalized radiative transfer code for computation of the normal emergent intensity of a stellar surface, given its geometry and internal structure. The code uses a regular mesh of equipotential surfaces in a discrete set of spherical coordinates, which are then used to interpolate the values of the structural quantites (density, temperature, opacity) in any given point inside the mesh. The radiaitive transfer equation is numerically integrated in a set of directions spanning the unit sphere around each point and iterated until the intensity values for all directions and all mesh points converge within a given tolerance. We have found that this approach, albeit computationally expensive, is the only one that can reproduce the intensity distribution of the non-symmetric contact binary atmosphere and can be used with any existing or new model of the structure of contact binaries. We present results on several test objects and future prospects of the implementation in state-of-the-art binary star modeling software.

A simple and fast method for computing the relativistic Compton Scattering Kernel for radiative transfer

NASA Technical Reports Server (NTRS)

Kershaw, David S.; Prasad, Manoj K.; Beason, J. Douglas

1986-01-01

The Klein-Nishina differential cross section averaged over a relativistic Maxwellian electron distribution is analytically reduced to a single integral, which can then be rapidly evaluated in a variety of ways. A particularly fast method for numerically computing this single integral is presented. This is, to the authors' knowledge, the first correct computation of the Compton scattering kernel.

Assessment of the Accuracy of the Conventional Ray-Tracing Technique: Implications in Remote Sensing and Radiative Transfer Involving Ice Clouds.

NASA Technical Reports Server (NTRS)

Bi, Lei; Yang, Ping; Liu, Chao; Yi, Bingqi; Baum, Bryan A.; Van Diedenhoven, Bastiaan; Iwabuchi, Hironobu

2014-01-01

A fundamental problem in remote sensing and radiative transfer simulations involving ice clouds is the ability to compute accurate optical properties for individual ice particles. While relatively simple and intuitively appealing, the conventional geometric-optics method (CGOM) is used frequently for the solution of light scattering by ice crystals. Due to the approximations in the ray-tracing technique, the CGOM accuracy is not well quantified. The result is that the uncertainties are introduced that can impact many applications. Improvements in the Invariant Imbedding T-matrix method (II-TM) and the Improved Geometric-Optics Method (IGOM) provide a mechanism to assess the aforementioned uncertainties. The results computed by the II-TMþIGOM are considered as a benchmark because the IITM solves Maxwell's equations from first principles and is applicable to particle size parameters ranging into the domain at which the IGOM has reasonable accuracy. To assess the uncertainties with the CGOM in remote sensing and radiative transfer simulations, two independent optical property datasets of hexagonal columns are developed for sensitivity studies by using the CGOM and the II-TMþIGOM, respectively. Ice cloud bulk optical properties obtained from the two datasets are compared and subsequently applied to retrieve the optical thickness and effective diameter from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. Additionally, the bulk optical properties are tested in broadband radiative transfer (RT) simulations using the general circulation model (GCM) version of the Rapid Radiative Transfer Model (RRTMG) that is adopted in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM, version 5.1). For MODIS retrievals, the mean bias of uncertainties of applying the CGOM in shortwave bands (0.86 and 2.13 micrometers) can be up to 5% in the optical thickness and as high as 20% in the effective diameter, depending on cloud optical thickness and effective diameter. In the MODIS infrared window bands centered at 8.5, 11, and 12 micrometers biases in the optical thickness and effective diameter are up to 12% and 10%, respectively. The CGOM-based simulation errors in ice cloud radiative forcing calculations are on the order of 10Wm(exp 2).

Validation of a Solid Rocket Motor Internal Environment Model

NASA Technical Reports Server (NTRS)

Martin, Heath T.

2017-01-01

In a prior effort, a thermal/fluid model of the interior of Penn State University's laboratory-scale Insulation Test Motor (ITM) was constructed to predict both the convective and radiative heat transfer to the interior walls of the ITM with a minimum of empiricism. These predictions were then compared to values of total and radiative heat flux measured in a previous series of ITM test firings to assess the capabilities and shortcomings of the chosen modeling approach. Though the calculated fluxes reasonably agreed with those measured during testing, this exercise revealed means of improving the fidelity of the model to, in the case of the thermal radiation, enable direct comparison of the measured and calculated fluxes and, for the total heat flux, compute a value indicative of the average measured condition. By replacing the P1-Approximation with the discrete ordinates (DO) model for the solution of the gray radiative transfer equation, the radiation intensity field in the optically thin region near the radiometer is accurately estimated, allowing the thermal radiation flux to be calculated on the heat-flux sensor itself, which was then compared directly to the measured values. Though the fully coupling the wall thermal response with the flow model was not attempted due to the excessive computational time required, a separate wall thermal response model was used to better estimate the average temperature of the graphite surfaces upstream of the heat flux gauges and improve the accuracy of both the total and radiative heat flux computations. The success of this modeling approach increases confidence in the ability of state-of-the-art thermal and fluid modeling to accurately predict SRM internal environments, offers corrections to older methods, and supplies a tool for further studies of the dynamics of SRM interiors.

Efficient radiative transfer methods for continuum and line transfer in large three-dimensional models

NASA Astrophysics Data System (ADS)

Juvela, Mika J.

The relationship between physical conditions of an interstellar cloud and the observed radiation is defined by the radiative transfer problem. Radiative transfer calculations are needed if, e.g., one wants to disentangle abundance variations from excitation effects or wants to model variations of dust properties inside an interstellar cloud. New observational facilities (e.g., ALMA and Herschel) will bring improved accuracy both in terms of intensity and spatial resolution. This will enable detailed studies of the densest sub-structures of interstellar clouds and star forming regions. Such observations must be interpreted with accurate radiative transfer methods and realistic source models. In many cases this will mean modelling in three dimensions. High optical depths and observed wide range of linear scales are, however, challenging for radiative transfer modelling. A large range of linear scales can be accessed only with hierarchical models. Figure 1 shows an example of the use of a hierarchical grid for radiative transfer calculations when the original model cloud (L=10 pc, =500 cm-3) was based a MHD simulation carried out on a regular grid (Juvela & Padoan, 2005). For computed line intensities an accuracy of 10% was still reached when the number of individual cells (and the run time) was reduced by a factor of ten. This illustrates how, as long as cloud is not extremely optically thick, most of the emission comes from a small sub-volume. It is also worth noting that while errors are ~10% for any given point they are much smaller when compared with intensity variations. In particular, calculations on hierarchical grid recovered the spatial power spectrum of line emission with very good accuracy. Monte Carlo codes are used widely in both continuum and line transfer calculations. Like any lambda iteration schemes these suffer from slow convergence when models are optically thick. In line transfer Accelerated Monte Carlo methods (AMC) present a partial solution to this problem (Juvela & Padoan, 2000; Hogerheijde & van der Tak, 2000). AMC methods can be used similarly in continuum calculations to speed up the computation of dust temperatures (Juvela, 2005). The sampling problems associated with high optical depths can be solved with weighted sampling and the handling of models with τV ~ 1000 is perfectly feasible. Transiently heated small dust grains pose another problem because the calculation of their temperature distribution is very time consuming. However, a 3D model will contain thousands of cells at very similar conditions. If dust temperature distributions are calculated only once for such a set an approximate solution can be found in a much shorter time time. (Juvela & Padoan, 2003; see Figure 2a). MHD simulations with Automatic Mesh Refinement (AMR) techniques present an exciting development for the modelling of interstellar clouds. Cloud models consist of a hierarchy of grids with different grid steps and the ratio between the cloud size and the smallest resolution elements can be 106 or even larger. We are currently working on radiative transfer codes (line and continuum) that could be used efficiently on such grids (see Figure 2b). The radiative transfer problem can be solved relatively independently on each of the sub-grids. This means that the use of convergence acceleration methods can be limited to those sub-grids where they are needed and, on the other hand, parallelization of the code is straightforward.

Validating an operational physical method to compute surface radiation from geostationary satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sengupta, Manajit; Dhere, Neelkanth G.; Wohlgemuth, John H.

We developed models to compute global horizontal irradiance (GHI) and direct normal irradiance (DNI) over the last three decades. These models can be classified as empirical or physical based on the approach. Empirical models relate ground-based observations with satellite measurements and use these relations to compute surface radiation. Physical models consider the physics behind the radiation received at the satellite and create retrievals to estimate surface radiation. Furthermore, while empirical methods have been traditionally used for computing surface radiation for the solar energy industry, the advent of faster computing has made operational physical models viable. The Global Solar Insolation Projectmore » (GSIP) is a physical model that computes DNI and GHI using the visible and infrared channel measurements from a weather satellite. GSIP uses a two-stage scheme that first retrieves cloud properties and uses those properties in a radiative transfer model to calculate GHI and DNI. Developed for polar orbiting satellites, GSIP has been adapted to NOAA's Geostationary Operation Environmental Satellite series and can run operationally at high spatial resolutions. Our method holds the possibility of creating high quality datasets of GHI and DNI for use by the solar energy industry. We present an outline of the methodology and results from running the model as well as a validation study using ground-based instruments.« less

Global Aerosol Radiative Forcing Derived from Sea WiFS-Inferred Aerosol Optical Properties

NASA Technical Reports Server (NTRS)

Chou, Ming-Dah; Chan, Pui-King; Wang, Menghua

1999-01-01

Aerosol optical properties inferred from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) radiance measurements are used to compute the aerosol shortwave radiative forcing using a radiative transfer model. The aerosol optical thickness at the wavelength of 865-nm is taken from the SeaWIFS archive. It is found that the nominal optical thickness over oceans ranges from 0.1 to 0.2. Using a maritime aerosol model and the radiances measured at the various SeaWiFS channels, the Angstrom exponent is determined to be 0.2174, the single-scattering albedo to be 0.995, and the asymmetry factor to be 0.786. The radiative transfer model has eight bands in the visible and ultraviolet spectral regions and three bands in the near infrared. It includes the absorption due to aerosols, water vapor, carbon dioxide, and oxygen, and the scattering due to aerosols and gases (Rayleigh scattering). The radiative forcing is computed over global oceans for four months (January, April, July, and October, 1998) to represent four seasons. It is found that the aerosol radiative forcing is large and changes significantly with seasons near the continents with large-scale forest fires and desert dust. Averaged over oceans and the four months, the aerosol radiative forcing is approximately 7 W/sq m at the top of the atmosphere. This large radiative forcing is expected to have a significant cooling effect on the Earth's climate as implied from simulations of a number of general circulation models.

Theorems on symmetries and flux conservation in radiative transfer using the matrix operator theory.

NASA Technical Reports Server (NTRS)

Kattawar, G. W.

1973-01-01

The matrix operator approach to radiative transfer is shown to be a very powerful technique in establishing symmetry relations for multiple scattering in inhomogeneous atmospheres. Symmetries are derived for the reflection and transmission operators using only the symmetry of the phase function. These results will mean large savings in computer time and storage for performing calculations for realistic planetary atmospheres using this method. The results have also been extended to establish a condition on the reflection matrix of a boundary in order to preserve reciprocity. Finally energy conservation is rigorously proven for conservative scattering in inhomogeneous atmospheres.

Formal Solutions for Polarized Radiative Transfer. I. The DELO Family

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janett, Gioele; Carlin, Edgar S.; Steiner, Oskar

The discussion regarding the numerical integration of the polarized radiative transfer equation is still open and the comparison between the different numerical schemes proposed by different authors in the past is not fully clear. Aiming at facilitating the comprehension of the advantages and drawbacks of the different formal solvers, this work presents a reference paradigm for their characterization based on the concepts of order of accuracy , stability , and computational cost . Special attention is paid to understand the numerical methods belonging to the Diagonal Element Lambda Operator family, in an attempt to highlight their specificities.

A stochastic model for density-dependent microwave Snow- and Graupel scattering coefficients of the NOAA JCSDA community radiative transfer model

NASA Astrophysics Data System (ADS)

Stegmann, Patrick G.; Tang, Guanglin; Yang, Ping; Johnson, Benjamin T.

2018-05-01

A structural model is developed for the single-scattering properties of snow and graupel particles with a strongly heterogeneous morphology and an arbitrary variable mass density. This effort is aimed to provide a mechanism to consider particle mass density variation in the microwave scattering coefficients implemented in the Community Radiative Transfer Model (CRTM). The stochastic model applies a bicontinuous random medium algorithm to a simple base shape and uses the Finite-Difference-Time-Domain (FDTD) method to compute the single-scattering properties of the resulting complex morphology.

Prediction of the 21-cm signal from reionization: comparison between 3D and 1D radiative transfer schemes

NASA Astrophysics Data System (ADS)

Ghara, Raghunath; Mellema, Garrelt; Giri, Sambit K.; Choudhury, T. Roy; Datta, Kanan K.; Majumdar, Suman

2018-05-01

Three-dimensional radiative transfer simulations of the epoch of reionization can produce realistic results, but are computationally expensive. On the other hand, simulations relying on one-dimensional radiative transfer solutions are faster but limited in accuracy due to their more approximate nature. Here, we compare the performance of the reionization simulation codes GRIZZLY and C2-RAY which use 1D and 3D radiative transfer schemes, respectively. The comparison is performed using the same cosmological density fields, halo catalogues, and source properties. We find that the ionization maps, as well as the 21-cm signal maps from these two simulations are very similar even for complex scenarios which include thermal feedback on low-mass haloes. The comparison between the schemes in terms of the statistical quantities such as the power spectrum of the brightness temperature fluctuation agrees with each other within 10 per cent error throughout the entire reionization history. GRIZZLY seems to perform slightly better than the seminumerical approaches considered in Majumdar et al. which are based on the excursion set principle. We argue that GRIZZLY can be efficiently used for exploring parameter space, establishing observations strategies, and estimating parameters from 21-cm observations.

Bayesian modelling of uncertainties of Monte Carlo radiative-transfer simulations

NASA Astrophysics Data System (ADS)

Beaujean, Frederik; Eggers, Hans C.; Kerzendorf, Wolfgang E.

2018-04-01

One of the big challenges in astrophysics is the comparison of complex simulations to observations. As many codes do not directly generate observables (e.g. hydrodynamic simulations), the last step in the modelling process is often a radiative-transfer treatment. For this step, the community relies increasingly on Monte Carlo radiative transfer due to the ease of implementation and scalability with computing power. We show how to estimate the statistical uncertainty given the output of just a single radiative-transfer simulation in which the number of photon packets follows a Poisson distribution and the weight (e.g. energy or luminosity) of a single packet may follow an arbitrary distribution. Our Bayesian approach produces a posterior distribution that is valid for any number of packets in a bin, even zero packets, and is easy to implement in practice. Our analytic results for large number of packets show that we generalise existing methods that are valid only in limiting cases. The statistical problem considered here appears in identical form in a wide range of Monte Carlo simulations including particle physics and importance sampling. It is particularly powerful in extracting information when the available data are sparse or quantities are small.

Bayesian modelling of uncertainties of Monte Carlo radiative-transfer simulations

NASA Astrophysics Data System (ADS)

Beaujean, Frederik; Eggers, Hans C.; Kerzendorf, Wolfgang E.

2018-07-01

One of the big challenges in astrophysics is the comparison of complex simulations to observations. As many codes do not directly generate observables (e.g. hydrodynamic simulations), the last step in the modelling process is often a radiative-transfer treatment. For this step, the community relies increasingly on Monte Carlo radiative transfer due to the ease of implementation and scalability with computing power. We consider simulations in which the number of photon packets is Poisson distributed, while the weight assigned to a single photon packet follows any distribution of choice. We show how to estimate the statistical uncertainty of the sum of weights in each bin from the output of a single radiative-transfer simulation. Our Bayesian approach produces a posterior distribution that is valid for any number of packets in a bin, even zero packets, and is easy to implement in practice. Our analytic results for large number of packets show that we generalize existing methods that are valid only in limiting cases. The statistical problem considered here appears in identical form in a wide range of Monte Carlo simulations including particle physics and importance sampling. It is particularly powerful in extracting information when the available data are sparse or quantities are small.

Effect of thermal radiation and suction on convective heat transfer of nanofluid along a wedge in the presence of heat generation/absorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasmani, Ruhaila Md; Bhuvaneswari, M.; Sivasankaran, S.

2015-10-22

An analysis is presented to find the effects of thermal radiation and heat generation/absorption on convection heat transfer of nanofluid past a wedge in the presence of wall suction. The governing partial differential equations are transformed into a system of ordinary differential equations using similarity transformation. The resulting system is solved numerically using a fourth-order Runge–Kutta method with shooting technique. Numerical computations are carried out for different values of dimensionless parameters to predict the effects of wedge angle, thermophoresis, Brownian motion, heat generation/absorption, thermal radiation and suction. It is found that the temperature increases significantly when the value of themore » heat generation/absorption parameter increases. But the opposite observation is found for the effect of thermal radiation.« less

Contributions of the ARM Program to Radiative Transfer Modeling for Climate and Weather Applications

NASA Technical Reports Server (NTRS)

Mlawer, Eli J.; Iacono, Michael J.; Pincus, Robert; Barker, Howard W.; Oreopoulos, Lazaros; Mitchell, David L.

2016-01-01

Accurate climate and weather simulations must account for all relevant physical processes and their complex interactions. Each of these atmospheric, ocean, and land processes must be considered on an appropriate spatial and temporal scale, which leads these simulations to require a substantial computational burden. One especially critical physical process is the flow of solar and thermal radiant energy through the atmosphere, which controls planetary heating and cooling and drives the large-scale dynamics that moves energy from the tropics toward the poles. Radiation calculations are therefore essential for climate and weather simulations, but are themselves quite complex even without considering the effects of variable and inhomogeneous clouds. Clear-sky radiative transfer calculations have to account for thousands of absorption lines due to water vapor, carbon dioxide, and other gases, which are irregularly distributed across the spectrum and have shapes dependent on pressure and temperature. The line-by-line (LBL) codes that treat these details have a far greater computational cost than can be afforded by global models. Therefore, the crucial requirement for accurate radiation calculations in climate and weather prediction models must be satisfied by fast solar and thermal radiation parameterizations with a high level of accuracy that has been demonstrated through extensive comparisons with LBL codes. See attachment for continuation.

Balancing accuracy, efficiency, and flexibility in a radiative transfer parameterization for dynamical models

NASA Astrophysics Data System (ADS)

Pincus, R.; Mlawer, E. J.

2017-12-01

Radiation is key process in numerical models of the atmosphere. The problem is well-understood and the parameterization of radiation has seen relatively few conceptual advances in the past 15 years. It is nonthelss often the single most expensive component of all physical parameterizations despite being computed less frequently than other terms. This combination of cost and maturity suggests value in a single radiation parameterization that could be shared across models; devoting effort to a single parameterization might allow for fine tuning for efficiency. The challenge lies in the coupling of this parameterization to many disparate representations of clouds and aerosols. This talk will describe RRTMGP, a new radiation parameterization that seeks to balance efficiency and flexibility. This balance is struck by isolating computational tasks in "kernels" that expose as much fine-grained parallelism as possible. These have simple interfaces and are interoperable across programming languages so that they might be repalced by alternative implementations in domain-specific langauges. Coupling to the host model makes use of object-oriented features of Fortran 2003, minimizing branching within the kernels and the amount of data that must be transferred. We will show accuracy and efficiency results for a globally-representative set of atmospheric profiles using a relatively high-resolution spectral discretization.

Introduction of Parallel GPGPU Acceleration Algorithms for the Solution of Radiative Transfer

NASA Technical Reports Server (NTRS)

Godoy, William F.; Liu, Xu

2011-01-01

General-purpose computing on graphics processing units (GPGPU) is a recent technique that allows the parallel graphics processing unit (GPU) to accelerate calculations performed sequentially by the central processing unit (CPU). To introduce GPGPU to radiative transfer, the Gauss-Seidel solution of the well-known expressions for 1-D and 3-D homogeneous, isotropic media is selected as a test case. Different algorithms are introduced to balance memory and GPU-CPU communication, critical aspects of GPGPU. Results show that speed-ups of one to two orders of magnitude are obtained when compared to sequential solutions. The underlying value of GPGPU is its potential extension in radiative solvers (e.g., Monte Carlo, discrete ordinates) at a minimal learning curve.

APC: A New Code for Atmospheric Polarization Computations

NASA Technical Reports Server (NTRS)

Korkin, Sergey V.; Lyapustin, Alexei I.; Rozanov, Vladimir V.

2014-01-01

A new polarized radiative transfer code Atmospheric Polarization Computations (APC) is described. The code is based on separation of the diffuse light field into anisotropic and smooth (regular) parts. The anisotropic part is computed analytically. The smooth regular part is computed numerically using the discrete ordinates method. Vertical stratification of the atmosphere, common types of bidirectional surface reflection and scattering by spherical particles or spheroids are included. A particular consideration is given to computation of the bidirectional polarization distribution function (BPDF) of the waved ocean surface.

Surface temperatures in New York City: Geospatial data enables the accurate prediction of radiative heat transfer.

PubMed

Ghandehari, Masoud; Emig, Thorsten; Aghamohamadnia, Milad

2018-02-02

Despite decades of research seeking to derive the urban energy budget, the dynamics of thermal exchange in the densely constructed environment is not yet well understood. Using New York City as a study site, we present a novel hybrid experimental-computational approach for a better understanding of the radiative heat transfer in complex urban environments. The aim of this work is to contribute to the calculation of the urban energy budget, particularly the stored energy. We will focus our attention on surface thermal radiation. Improved understanding of urban thermodynamics incorporating the interaction of various bodies, particularly in high rise cities, will have implications on energy conservation at the building scale, and for human health and comfort at the urban scale. The platform presented is based on longwave hyperspectral imaging of nearly 100 blocks of Manhattan, in addition to a geospatial radiosity model that describes the collective radiative heat exchange between multiple buildings. Despite assumptions in surface emissivity and thermal conductivity of buildings walls, the close comparison of temperatures derived from measurements and computations is promising. Results imply that the presented geospatial thermodynamic model of urban structures can enable accurate and high resolution analysis of instantaneous urban surface temperatures.

Regression model for estimating inactivation of microbial aerosols by solar radiation.

PubMed

Ben-David, Avishai; Sagripanti, Jose-Luis

2013-01-01

The inactivation of pathogenic aerosols by solar radiation is relevant to public health and biodefense. We investigated whether a relatively simple method to calculate solar diffuse and total irradiances could be developed and used in environmental photobiology estimations instead of complex atmospheric radiative transfer computer programs. The second-order regression model that we developed reproduced 13 radiation quantities calculated for equinoxes and solstices at 35(°) latitude with a computer-intensive and rather complex atmospheric radiative transfer program (MODTRAN) with a mean error <6% (2% for most radiation quantities). Extending the application of the regression model from a reference latitude and date (chosen as 35° latitude for 21 March) to different latitudes and days of the year was accomplished with variable success: usually with a mean error <15% (but as high as 150% for some combination of latitudes and days of year). This accuracy of the methodology proposed here compares favorably to photobiological experiments where the microbial survival is usually measured with an accuracy no better than ±0.5 log10 units. The approach and equations presented in this study should assist in estimating the maximum time during which microbial pathogens remain infectious after accidental or intentional aerosolization in open environments. © Published 2013. This article is a U.S. Government work and is in the public domain in the USA. Photochemistry and Photobiology © 2013 The American Society of Photobiology.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habte, A.; Sengupta, M.; Wilcox, S.

Models to compute Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI) have been in development over the last 3 decades. These models can be classified as empirical or physical, based on the approach. Empirical models relate ground based observations with satellite measurements and use these relations to compute surface radiation. Physical models consider the radiation received from the earth at the satellite and create retrievals to estimate surface radiation. While empirical methods have been traditionally used for computing surface radiation for the solar energy industry the advent of faster computing has made operational physical models viable. The Global Solarmore » Insolation Project (GSIP) is an operational physical model from NOAA that computes GHI using the visible and infrared channel measurements from the GOES satellites. GSIP uses a two-stage scheme that first retrieves cloud properties and uses those properties in a radiative transfer model to calculate surface radiation. NREL, University of Wisconsin and NOAA have recently collaborated to adapt GSIP to create a 4 km GHI and DNI product every 30 minutes. This paper presents an outline of the methodology and a comprehensive validation using high quality ground based solar data from the National Oceanic and Atmospheric Administration (NOAA) Surface Radiation (SURFRAD) (http://www.srrb.noaa.gov/surfrad/sitepage.html) and Integrated Surface Insolation Study (ISIS) http://www.srrb.noaa.gov/isis/isissites.html), the Solar Radiation Research Laboratory (SRRL) at National Renewable Energy Laboratory (NREL), and Sun Spot One (SS1) stations.« less

A comprehensive evaluation of different radiation models in a gas turbine combustor under conditions of oxy-fuel combustion with dry recycle

NASA Astrophysics Data System (ADS)

Kez, V.; Liu, F.; Consalvi, J. L.; Ströhle, J.; Epple, B.

2016-03-01

The oxy-fuel combustion is a promising CO2 capture technology from combustion systems. This process is characterized by much higher CO2 concentrations in the combustion system compared to that of the conventional air-fuel combustion. To accurately predict the enhanced thermal radiation in oxy-fuel combustion, it is essential to take into account the non-gray nature of gas radiation. In this study, radiation heat transfer in a 3D model gas turbine combustor under two test cases at 20 atm total pressure was calculated by various non-gray gas radiation models, including the statistical narrow-band (SNB) model, the statistical narrow-band correlated-k (SNBCK) model, the wide-band correlated-k (WBCK) model, the full spectrum correlated-k (FSCK) model, and several weighted sum of gray gases (WSGG) models. Calculations of SNB, SNBCK, and FSCK were conducted using the updated EM2C SNB model parameters. Results of the SNB model are considered as the benchmark solution to evaluate the accuracy of the other models considered. Results of SNBCK and FSCK are in good agreement with the benchmark solution. The WBCK model is less accurate than SNBCK or FSCK. Considering the three formulations of the WBCK model, the multiple gases formulation is the best choice regarding the accuracy and computational cost. The WSGG model with the parameters of Bordbar et al. (2014) [20] is the most accurate of the three investigated WSGG models. Use of the gray WSSG formulation leads to significant deviations from the benchmark data and should not be applied to predict radiation heat transfer in oxy-fuel combustion systems. A best practice to incorporate the state-of-the-art gas radiation models for high accuracy of radiation heat transfer calculations at minimal increase in computational cost in CFD simulation of oxy-fuel combustion systems for pressure path lengths up to about 10 bar m is suggested.

Explicit validation of a surface shortwave radiation balance model over snow-covered complex terrain

NASA Astrophysics Data System (ADS)

Helbig, N.; Löwe, H.; Mayer, B.; Lehning, M.

2010-09-01

A model that computes the surface radiation balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky radiation is determined from observations of incident global radiation, air temperature, and relative humidity at a single measurement location. Incident radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky radiation for all sky conditions are obtained by decomposing the measured global radiation value. Spatial incident radiation values under all atmospheric conditions are computed by adjusting the spatial radiation values obtained from the parametric model with the radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected radiation. Validations of the shortwave radiation balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual radiation components is performed with high-quality measurements. A new measurement setup was designed to determine terrain reflected radiation. There is good agreement between the measurements and the modeled terrain reflected radiation values as well as with incident radiation values. A comparison of the model with a fully three-dimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled radiation values.

The Poynting-Stokes Tensor And Radiative Transfer In Turbid Media: The Microphysical Paradigm

NASA Astrophysics Data System (ADS)

Mishchenko, M. I.

2010-12-01

This paper solves the long-standing problem of establishing the fundamental physical link between the radiative transfer theory and macroscopic electromagnetics in the case of elastic scattering by a sparse discrete random medium. The radiative transfer equation (RTE) is derived directly from the macroscopic Maxwell equations by computing theoretically the appropriately defined so-called Poynting-Stokes tensor carrying informa-tion on both the direction, magnitude, and polarization characteristics of lo-cal electromagnetic energy flow. Our derivation from first principles shows that to compute the local Poynting vector averaged over a sufficiently long period of time, one can solve the RTE for the direction-dependent specific intensity column vector and then integrate the direction-weighted specific intensity over all directions. Furthermore, we demonstrate that the specific intensity (or specific intensity column vector) can be measured with a well-collimated radiometer (photopolarimeter), which provides the ultimate physical justification for the use of such instruments in radiation-budget and particle-characterization applications. However, the specific intensity cannot be interpreted in phenomenological terms as signifying the amount of elec-tromagnetic energy transported in a given direction per unit area normal to this direction per unit time per unit solid angle. Also, in the case of a densely packed scattering medium the relation of the measurement with a well-collimated radiometer to the time-averaged local Poynting vector re-mains uncertain, and the theoretical modeling of this measurement is likely to require a much more complicated approach than solving an RTE.

Development and application of computational aerothermodynamics flowfield computer codes

NASA Technical Reports Server (NTRS)

Venkatapathy, Ethiraj

1994-01-01

Research was performed in the area of computational modeling and application of hypersonic, high-enthalpy, thermo-chemical nonequilibrium flow (Aerothermodynamics) problems. A number of computational fluid dynamic (CFD) codes were developed and applied to simulate high altitude rocket-plume, the Aeroassist Flight Experiment (AFE), hypersonic base flow for planetary probes, the single expansion ramp model (SERN) connected with the National Aerospace Plane, hypersonic drag devices, hypersonic ramp flows, ballistic range models, shock tunnel facility nozzles, transient and steady flows in the shock tunnel facility, arc-jet flows, thermochemical nonequilibrium flows around simple and complex bodies, axisymmetric ionized flows of interest to re-entry, unsteady shock induced combustion phenomena, high enthalpy pulsed facility simulations, and unsteady shock boundary layer interactions in shock tunnels. Computational modeling involved developing appropriate numerical schemes for the flows on interest and developing, applying, and validating appropriate thermochemical processes. As part of improving the accuracy of the numerical predictions, adaptive grid algorithms were explored, and a user-friendly, self-adaptive code (SAGE) was developed. Aerothermodynamic flows of interest included energy transfer due to strong radiation, and a significant level of effort was spent in developing computational codes for calculating radiation and radiation modeling. In addition, computational tools were developed and applied to predict the radiative heat flux and spectra that reach the model surface.

A Radiation Solver for the National Combustion Code

NASA Technical Reports Server (NTRS)

Sockol, Peter M.

2015-01-01

A methodology is given that converts an existing finite volume radiative transfer method that requires input of local absorption coefficients to one that can treat a mixture of combustion gases and compute the coefficients on the fly from the local mixture properties. The Full-spectrum k-distribution method is used to transform the radiative transfer equation (RTE) to an alternate wave number variable, g . The coefficients in the transformed equation are calculated at discrete temperatures and participating species mole fractions that span the values of the problem for each value of g. These results are stored in a table and interpolation is used to find the coefficients at every cell in the field. Finally, the transformed RTE is solved for each g and Gaussian quadrature is used to find the radiant heat flux throughout the field. The present implementation is in an existing cartesian/cylindrical grid radiative transfer code and the local mixture properties are given by a solution of the National Combustion Code (NCC) on the same grid. Based on this work the intention is to apply this method to an existing unstructured grid radiation code which can then be coupled directly to NCC.

A Discrete Probability Function Method for the Equation of Radiative Transfer

NASA Technical Reports Server (NTRS)

Sivathanu, Y. R.; Gore, J. P.

1993-01-01

A discrete probability function (DPF) method for the equation of radiative transfer is derived. The DPF is defined as the integral of the probability density function (PDF) over a discrete interval. The derivation allows the evaluation of the PDF of intensities leaving desired radiation paths including turbulence-radiation interactions without the use of computer intensive stochastic methods. The DPF method has a distinct advantage over conventional PDF methods since the creation of a partial differential equation from the equation of transfer is avoided. Further, convergence of all moments of intensity is guaranteed at the basic level of simulation unlike the stochastic method where the number of realizations for convergence of higher order moments increases rapidly. The DPF method is described for a representative path with approximately integral-length scale-sized spatial discretization. The results show good agreement with measurements in a propylene/air flame except for the effects of intermittency resulting from highly correlated realizations. The method can be extended to the treatment of spatial correlations as described in the Appendix. However, information regarding spatial correlations in turbulent flames is needed prior to the execution of this extension.

Intercomparison of three microwave/infrared high resolution line-by-line radiative transfer codes

NASA Astrophysics Data System (ADS)

Schreier, Franz; Milz, Mathias; Buehler, Stefan A.; von Clarmann, Thomas

2018-05-01

An intercomparison of three line-by-line (lbl) codes developed independently for atmospheric radiative transfer and remote sensing - ARTS, GARLIC, and KOPRA - has been performed for a thermal infrared nadir sounding application assuming a HIRS-like (High resolution Infrared Radiation Sounder) setup. Radiances for the 19 HIRS infrared channels and a set of 42 atmospheric profiles from the "Garand dataset" have been computed. The mutual differences of the equivalent brightness temperatures are presented and possible causes of disagreement are discussed. In particular, the impact of path integration schemes and atmospheric layer discretization is assessed. When the continuum absorption contribution is ignored because of the different implementations, residuals are generally in the sub-Kelvin range and smaller than 0.1 K for some window channels (and all atmospheric models and lbl codes). None of the three codes turned out to be perfect for all channels and atmospheres. Remaining discrepancies are attributed to different lbl optimization techniques. Lbl codes seem to have reached a maturity in the implementation of radiative transfer that the choice of the underlying physical models (line shape models, continua etc) becomes increasingly relevant.

Computational analysis of Variable Thrust Engine (VTE) performance

NASA Technical Reports Server (NTRS)

Giridharan, M. G.; Krishnan, A.; Przekwas, A. J.

1993-01-01

The Variable Thrust Engine (VTE) of the Orbital Maneuvering Vehicle (OMV) uses a hypergolic propellant combination of Monomethyl Hydrazine (MMH) and Nitrogen Tetroxide (NTO) as fuel and oxidizer, respectively. The performance of the VTE depends on a number of complex interacting phenomena such as atomization, spray dynamics, vaporization, turbulent mixing, convective/radiative heat transfer, and hypergolic combustion. This study involved the development of a comprehensive numerical methodology to facilitate detailed analysis of the VTE. An existing Computational Fluid Dynamics (CFD) code was extensively modified to include the following models: a two-liquid, two-phase Eulerian-Lagrangian spray model; a chemical equilibrium model; and a discrete ordinate radiation heat transfer model. The modified code was used to conduct a series of simulations to assess the effects of various physical phenomena and boundary conditions on the VTE performance. The details of the models and the results of the simulations are presented.

Radiative cooling in shock-heated hydrogen-helium plasmas. [for planetary entry probe heat shields

NASA Technical Reports Server (NTRS)

Poon, P. T. Y.; Stickford, G. H., Jr.

1978-01-01

Axial and off-axis radiative cooling of cylindrical shock-heated hydrogen-helium plasmas is investigated theoretically and experimentally. The coupled fluid dynamic-radiative transfer equations are solved by a combination of approximation techniques aimed at simplifying the computation of the flux divergence term, namely, the quasi-isothermal approximation and the exponential approximation developed for the solid angle integration. The accuracy of the approximation schemes has been assessed and found acceptable for applying the methods to the rapid computation of the radiatively coupled flow problem. Radiative cooling experiments were conducted in a 6-inch annular arc accelerator shock tube (ANAA) for an initial pressure of 1 torr and shock speeds from 35 to 45 Km/sec. The results indicate that the lateral cooling is small compared with the axial cooling, and that better agreement is achieved between the data and the theoretical results by inclusion of the lateral temperature gradient.

Modeling radiative transfer with the doubling and adding approach in a climate GCM setting

NASA Astrophysics Data System (ADS)

Lacis, A. A.

2017-12-01

The nonlinear dependence of multiply scattered radiation on particle size, optical depth, and solar zenith angle, makes accurate treatment of multiple scattering in the climate GCM setting problematic, due primarily to computational cost issues. In regard to the accurate methods of calculating multiple scattering that are available, their computational cost is far too prohibitive for climate GCM applications. Utilization of two-stream-type radiative transfer approximations may be computationally fast enough, but at the cost of reduced accuracy. We describe here a parameterization of the doubling/adding method that is being used in the GISS climate GCM, which is an adaptation of the doubling/adding formalism configured to operate with a look-up table utilizing a single gauss quadrature point with an extra-angle formulation. It is designed to closely reproduce the accuracy of full-angle doubling and adding for the multiple scattering effects of clouds and aerosols in a realistic atmosphere as a function of particle size, optical depth, and solar zenith angle. With an additional inverse look-up table, this single-gauss-point doubling/adding approach can be adapted to model fractional cloud cover for any GCM grid-box in the independent pixel approximation as a function of the fractional cloud particle sizes, optical depths, and solar zenith angle dependence.

Radiative Heat Transfer Modeling in Fibrous Porous Media

NASA Technical Reports Server (NTRS)

Sobhani, Sadaf; Panerai, Francesco; Borner, Arnaud; Ferguson, Joseph C.; Wray, Alan; Mansour, Nagi N.

2017-01-01

Phenolic-Impregnated Carbon Ablator (PICA) was developed at NASA Ames Research Center as a lightweight thermal protection system material for successful atmospheric entries. The objective of the current work is to compute the effective radiative conductivity of fibrous porous media, such as preforms used to make PICA, to enable the efficient design of materials that can meet the thermal performance goals of forthcoming space exploration missions.

SPAMCART: a code for smoothed particle Monte Carlo radiative transfer

NASA Astrophysics Data System (ADS)

Lomax, O.; Whitworth, A. P.

2016-10-01

We present a code for generating synthetic spectral energy distributions and intensity maps from smoothed particle hydrodynamics simulation snapshots. The code is based on the Lucy Monte Carlo radiative transfer method, I.e. it follows discrete luminosity packets as they propagate through a density field, and then uses their trajectories to compute the radiative equilibrium temperature of the ambient dust. The sources can be extended and/or embedded, and discrete and/or diffuse. The density is not mapped on to a grid, and therefore the calculation is performed at exactly the same resolution as the hydrodynamics. We present two example calculations using this method. First, we demonstrate that the code strictly adheres to Kirchhoff's law of radiation. Secondly, we present synthetic intensity maps and spectra of an embedded protostellar multiple system. The algorithm uses data structures that are already constructed for other purposes in modern particle codes. It is therefore relatively simple to implement.

A rapid radiative transfer model for reflection of solar radiation

NASA Technical Reports Server (NTRS)

Xiang, X.; Smith, E. A.; Justus, C. G.

1994-01-01

A rapid analytical radiative transfer model for reflection of solar radiation in plane-parallel atmospheres is developed based on the Sobolev approach and the delta function transformation technique. A distinct advantage of this model over alternative two-stream solutions is that in addition to yielding the irradiance components, which turn out to be mathematically equivalent to the delta-Eddington approximation, the radiance field can also be expanded in a mathematically consistent fashion. Tests with the model against a more precise multistream discrete ordinate model over a wide range of input parameters demonstrate that the new approximate method typically produces average radiance differences of less than 5%, with worst average differences of approximately 10%-15%. By the same token, the computational speed of the new model is some tens to thousands times faster than that of the more precise model when its stream resolution is set to generate precise calculations.

Preliminary analyses of space radiation protection for lunar base surface systems

NASA Technical Reports Server (NTRS)

Nealy, John E.; Wilson, John W.; Townsend, Lawrence W.

1989-01-01

Radiation shielding analyses are performed for candidate lunar base habitation modules. The study primarily addresses potential hazards due to contributions from the galactic cosmic rays. The NASA Langley Research Center's high energy nucleon and heavy ion transport codes are used to compute propagation of radiation through conventional and regolith shield materials. Computed values of linear energy transfer are converted to biological dose-equivalent using quality factors established by the International Commision of Radiological Protection. Special fluxes of heavy charged particles and corresponding dosimetric quantities are computed for a series of thicknesses in various shield media and are used as an input data base for algorithms pertaining to specific shielded geometries. Dosimetric results are presented as isodose contour maps of shielded configuration interiors. The dose predictions indicate that shielding requirements are substantial, and an abbreviated uncertainty analysis shows that better definition of the space radiation environment as well as improvement in nuclear interaction cross-section data can greatly increase the accuracy of shield requirement predictions.

Radiative transfer of X-rays in the solar corona

NASA Technical Reports Server (NTRS)

Acton, L. W.

1978-01-01

The problem of resonance scattering of X-ray emission lines in the solar corona is investigated. For the resonance lines of some helium-like ions, significant optical depths are reached over distances small compared with the size of typical coronal features. A general integral equation for the transfer of resonance-line radiation under solar coronal conditions is derived. This expression is in a form useful for modeling the complex three-dimensional temperature and density structure of coronal active regions. The transfer equation is then cast in a form illustrating the terms which give rise to the attenuation or enhancement of the resonance-line intensity. The source function for helium-like oxygen (O VII) under coronal conditions is computed and discussed in terms of the relative importance of scattering.

A RADIATION TRANSFER SOLVER FOR ATHENA USING SHORT CHARACTERISTICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, Shane W.; Stone, James M.; Jiang Yanfei

2012-03-01

We describe the implementation of a module for the Athena magnetohydrodynamics (MHD) code that solves the time-independent, multi-frequency radiative transfer (RT) equation on multidimensional Cartesian simulation domains, including scattering and non-local thermodynamic equilibrium (LTE) effects. The module is based on well known and well tested algorithms developed for modeling stellar atmospheres, including the method of short characteristics to solve the RT equation, accelerated Lambda iteration to handle scattering and non-LTE effects, and parallelization via domain decomposition. The module serves several purposes: it can be used to generate spectra and images, to compute a variable Eddington tensor (VET) for full radiationmore » MHD simulations, and to calculate the heating and cooling source terms in the MHD equations in flows where radiation pressure is small compared with gas pressure. For the latter case, the module is combined with the standard MHD integrators using operator splitting: we describe this approach in detail, including a new constraint on the time step for stability due to radiation diffusion modes. Implementation of the VET method for radiation pressure dominated flows is described in a companion paper. We present results from a suite of test problems for both the RT solver itself and for dynamical problems that include radiative heating and cooling. These tests demonstrate that the radiative transfer solution is accurate and confirm that the operator split method is stable, convergent, and efficient for problems of interest. We demonstrate there is no need to adopt ad hoc assumptions of questionable accuracy to solve RT problems in concert with MHD: the computational cost for our general-purpose module for simple (e.g., LTE gray) problems can be comparable to or less than a single time step of Athena's MHD integrators, and only few times more expensive than that for more general (non-LTE) problems.« less

Radiative Transfer Modeling of a Large Pool Fire by Discrete Ordinates, Discrete Transfer, Ray Tracing, Monte Carlo and Moment Methods

NASA Technical Reports Server (NTRS)

Jensen, K. A.; Ripoll, J.-F.; Wray, A. A.; Joseph, D.; ElHafi, M.

2004-01-01

Five computational methods for solution of the radiative transfer equation in an absorbing-emitting and non-scattering gray medium were compared on a 2 m JP-8 pool fire. The temperature and absorption coefficient fields were taken from a synthetic fire due to the lack of a complete set of experimental data for fires of this size. These quantities were generated by a code that has been shown to agree well with the limited quantity of relevant data in the literature. Reference solutions to the governing equation were determined using the Monte Carlo method and a ray tracing scheme with high angular resolution. Solutions using the discrete transfer method, the discrete ordinate method (DOM) with both S(sub 4) and LC(sub 11) quadratures, and moment model using the M(sub 1) closure were compared to the reference solutions in both isotropic and anisotropic regions of the computational domain. DOM LC(sub 11) is shown to be the more accurate than the commonly used S(sub 4) quadrature technique, especially in anisotropic regions of the fire domain. This represents the first study where the M(sub 1) method was applied to a combustion problem occurring in a complex three-dimensional geometry. The M(sub 1) results agree well with other solution techniques, which is encouraging for future applications to similar problems since it is computationally the least expensive solution technique. Moreover, M(sub 1) results are comparable to DOM S(sub 4).

The FluxCompensator: Making Radiative Transfer Models of Hydrodynamical Simulations Directly Comparable to Real Observations

NASA Astrophysics Data System (ADS)

Koepferl, Christine M.; Robitaille, Thomas P.

2017-11-01

When modeling astronomical objects throughout the universe, it is important to correctly treat the limitations of the data, for instance finite resolution and sensitivity. In order to simulate these effects, and to make radiative transfer models directly comparable to real observations, we have developed an open-source Python package called the FluxCompensator that enables the post-processing of the output of 3D Monte Carlo radiative transfer codes, such as Hyperion. With the FluxCompensator, realistic synthetic observations can be generated by modeling the effects of convolution with arbitrary point-spread functions, transmission curves, finite pixel resolution, noise, and reddening. Pipelines can be applied to compute synthetic observations that simulate observatories, such as the Spitzer Space Telescope or the Herschel Space Observatory. Additionally, this tool can read in existing observations (e.g., FITS format) and use the same settings for the synthetic observations. In this paper, we describe the package as well as present examples of such synthetic observations.

Time evolution of photon-pulse propagation in scattering and absorbing media: The dynamic radiative transfer system

NASA Astrophysics Data System (ADS)

Georgakopoulos, A.; Politopoulos, K.; Georgiou, E.

2018-03-01

A new dynamic-system approach to the problem of radiative transfer inside scattering and absorbing media is presented, directly based on first-hand physical principles. This method, the Dynamic Radiative Transfer System (DRTS), employs a dynamical system formality using a global sparse matrix, which characterizes the physical, optical and geometrical properties of the material-volume of interest. The new system state is generated by the above time-independent matrix, using simple matrix-vector multiplication for each subsequent time step. DRTS is capable of calculating accurately the time evolution of photon propagation in media of complex structure and shape. The flexibility of DRTS allows the integration of time-dependent sources, boundary conditions, different media and several optical phenomena like reflection and refraction in a unified and consistent way. Various examples of DRTS simulation results are presented for ultra-fast light pulse 3-D propagation, demonstrating greatly reduced computational cost and resource requirements compared to other methods.

The FluxCompensator: Making Radiative Transfer Models of Hydrodynamical Simulations Directly Comparable to Real Observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koepferl, Christine M.; Robitaille, Thomas P., E-mail: koepferl@usm.lmu.de

When modeling astronomical objects throughout the universe, it is important to correctly treat the limitations of the data, for instance finite resolution and sensitivity. In order to simulate these effects, and to make radiative transfer models directly comparable to real observations, we have developed an open-source Python package called the FluxCompensator that enables the post-processing of the output of 3D Monte Carlo radiative transfer codes, such as Hyperion. With the FluxCompensator, realistic synthetic observations can be generated by modeling the effects of convolution with arbitrary point-spread functions, transmission curves, finite pixel resolution, noise, and reddening. Pipelines can be applied tomore » compute synthetic observations that simulate observatories, such as the Spitzer Space Telescope or the Herschel Space Observatory . Additionally, this tool can read in existing observations (e.g., FITS format) and use the same settings for the synthetic observations. In this paper, we describe the package as well as present examples of such synthetic observations.« less

Non-LTE radiative transfer with lambda-acceleration - Convergence properties using exact full and diagonal lambda-operators

NASA Technical Reports Server (NTRS)

Macfarlane, J. J.

1992-01-01

We investigate the convergence properties of Lambda-acceleration methods for non-LTE radiative transfer problems in planar and spherical geometry. Matrix elements of the 'exact' A-operator are used to accelerate convergence to a solution in which both the radiative transfer and atomic rate equations are simultaneously satisfied. Convergence properties of two-level and multilevel atomic systems are investigated for methods using: (1) the complete Lambda-operator, and (2) the diagonal of the Lambda-operator. We find that the convergence properties for the method utilizing the complete Lambda-operator are significantly better than those of the diagonal Lambda-operator method, often reducing the number of iterations needed for convergence by a factor of between two and seven. However, the overall computational time required for large scale calculations - that is, those with many atomic levels and spatial zones - is typically a factor of a few larger for the complete Lambda-operator method, suggesting that the approach should be best applied to problems in which convergence is especially difficult.

Using Neural Networks to Improve the Performance of Radiative Transfer Modeling Used for Geometry Dependent Surface Lambertian-Equivalent Reflectivity Calculations

NASA Technical Reports Server (NTRS)

Fasnacht, Zachary; Qin, Wenhan; Haffner, David P.; Loyola, Diego; Joiner, Joanna; Krotkov, Nickolay; Vasilkov, Alexander; Spurr, Robert

2017-01-01

Surface Lambertian-equivalent reflectivity (LER) is important for trace gas retrievals in the direct calculation of cloud fractions and indirect calculation of the air mass factor. Current trace gas retrievals use climatological surface LER's. Surface properties that impact the bidirectional reflectance distribution function (BRDF) as well as varying satellite viewing geometry can be important for retrieval of trace gases. Geometry Dependent LER (GLER) captures these effects with its calculation of sun normalized radiances (I/F) and can be used in current LER algorithms (Vasilkov et al. 2016). Pixel by pixel radiative transfer calculations are computationally expensive for large datasets. Modern satellite missions such as the Tropospheric Monitoring Instrument (TROPOMI) produce very large datasets as they take measurements at much higher spatial and spectral resolutions. Look up table (LUT) interpolation improves the speed of radiative transfer calculations but complexity increases for non-linear functions. Neural networks perform fast calculations and can accurately predict both non-linear and linear functions with little effort.

A case study of view-factor rectification procedures for diffuse-gray radiation enclosure computations

NASA Technical Reports Server (NTRS)

Taylor, Robert P.; Luck, Rogelio

1995-01-01

The view factors which are used in diffuse-gray radiation enclosure calculations are often computed by approximate numerical integrations. These approximately calculated view factors will usually not satisfy the important physical constraints of reciprocity and closure. In this paper several view-factor rectification algorithms are reviewed and a rectification algorithm based on a least-squares numerical filtering scheme is proposed with both weighted and unweighted classes. A Monte-Carlo investigation is undertaken to study the propagation of view-factor and surface-area uncertainties into the heat transfer results of the diffuse-gray enclosure calculations. It is found that the weighted least-squares algorithm is vastly superior to the other rectification schemes for the reduction of the heat-flux sensitivities to view-factor uncertainties. In a sample problem, which has proven to be very sensitive to uncertainties in view factor, the heat transfer calculations with weighted least-squares rectified view factors are very good with an original view-factor matrix computed to only one-digit accuracy. All of the algorithms had roughly equivalent effects on the reduction in sensitivity to area uncertainty in this case study.

Advanced Doubling Adding Method for Radiative Transfer in Planetary Atmospheres

NASA Astrophysics Data System (ADS)

Liu, Quanhua; Weng, Fuzhong

2006-12-01

The doubling adding method (DA) is one of the most accurate tools for detailed multiple-scattering calculations. The principle of the method goes back to the nineteenth century in a problem dealing with reflection and transmission by glass plates. Since then the doubling adding method has been widely used as a reference tool for other radiative transfer models. The method has never been used in operational applications owing to tremendous demand on computational resources from the model. This study derives an analytical expression replacing the most complicated thermal source terms in the doubling adding method. The new development is called the advanced doubling adding (ADA) method. Thanks also to the efficiency of matrix and vector manipulations in FORTRAN 90/95, the advanced doubling adding method is about 60 times faster than the doubling adding method. The radiance (i.e., forward) computation code of ADA is easily translated into tangent linear and adjoint codes for radiance gradient calculations. The simplicity in forward and Jacobian computation codes is very useful for operational applications and for the consistency between the forward and adjoint calculations in satellite data assimilation.

Ground truth data for test sites (SL-3). [solar radiation and thermal radiation brightness temperature measurements

NASA Technical Reports Server (NTRS)

1974-01-01

Field measurements performed simultaneously with Skylab overpasses in order to provide comparative calibration and performance evaluation measurements for the EREP sensors are presented. The solar radiation region from 400 to 1300 nanometers and the thermal radiation region from 8 to 14 micrometer region were investigated. The measurements of direct solar radiation were analyzed for atmospheric optical depth; the total and reflected solar radiation were analyzed for target reflectivity. These analyses were used in conjunction with a radiative transfer computer program in order to calculate the amount and spectral distribution of solar radiation at the apertures of the EREP sensors. The instrumentation and techniques employed, calibrations and analyses performed, and results obtained are discussed.

Evaluation of the Anisotropic Radiative Conductivity of a Low-Density Carbon Fiber Material from Realistic Microscale Imaging

NASA Technical Reports Server (NTRS)

Nouri, Nima; Panerai, Francesco; Tagavi, Kaveh A.; Mansour, Nagi N.; Martin, Alexandre

2015-01-01

The radiative heat transfer inside a low-density carbon fiber insulator is analyzed using a three-dimensional direct simulation model. A robust procedure is presented for the numerical calculation of the geometric configuration factor to compute the radiative energy exchange processes among the small discretized surface areas of the fibrous material. The methodology is applied to a polygonal mesh of a fibrous insulator obtained from three-dimensional microscale imaging of the real material. The anisotropic values of the radiative conductivity are calculated for that geometry. The results yield both directional and thermal dependence of the radiative conductivity.

On the division of contribution of the atmosphere and ocean in the radiation of the earth for the tasks of remote sensing and climate

NASA Astrophysics Data System (ADS)

Sushkevich, T. A.; Strelkov, S. A.; Maksakova, S. V.

2017-11-01

We are talking about the national achievements of the world level in theory of radiation transfer in the system atmosphere-oceans and about the modern scientific potential developing in Russia, which adequately provides a methodological basis for theoretical and computational studies of radiation processes and radiation fields in the natural environments with the use of supercomputers and massively parallel processing for problems of remote sensing and the climate of Earth. A model of the radiation field in system "clouds cover the atmosphere-ocean" to the separation of the contributions of clouds, atmosphere and ocean.

Solar UV dose patterns in Italy.

PubMed

Meloni, D; Casale, G R; Siani, A M; Palmieri, S; Cappellani, F

2000-06-01

Since 1992 solar ultraviolet (UV) spectral irradiance (290-325 nm) has been measured at two Italian stations of Rome (urban site) and Ispra (semirural site) using Brewer spectrophotometry. The data collected under all sky conditions, are compared with the output of a sophisticated radiative transfer model (System for Transfer of Atmospheric Radiation--STAR model). The STAR multiple scattering scheme is able to cope with all physical processes relevant to the UV transfer through the atmosphere. The experience so far acquired indicates that, in spite of the unavoidable uncertainties in the input parameters (ozone, aerosol, surface albedo, pressure, temperature, relative humidity, cloud cover), measured and computed clear sky iradiances are in reasonable agreement. The STAR model is applied to build up the solar UV geographic patterns in Italy: the daily dose in the range 290-325 nm is computed at about 70 sites where a thorough and homogeneous climatology is available. For each month the concept of an idealized "standard day" is introduced and the surface distribution of solar UV field determined. The map of solar UV patterns for Italy, available for the first time, meets the study requirements in the field of skin and eye epidemiology, as well as in other investigations dealing with the impact of UV on the biosphere. The results are interpreted in terms of atmospheric and meteorological parameters modulating UV radiation reaching the ground.

Assessment of polarization effect on aerosol retrievals from MODIS

NASA Astrophysics Data System (ADS)

Korkin, S.; Lyapustin, A.

2010-12-01

Light polarization affects the total intensity of scattered radiation. In this work, we compare aerosol retrievals performed by code MAIAC [1] with and without taking polarization into account. The MAIAC retrievals are based on the look-up tables (LUT). For this work, MAIAC was run using two different LUTs, the first one generated using the scalar code SHARM [2], and the second one generated with the vector code Modified Vector Discrete Ordinates Method (MVDOM). MVDOM is a new code suitable for computations with highly anisotropic phase functions, including cirrus clouds and snow [3]. To this end, the solution of the vector radiative transfer equation (VRTE) is represented as a sum of anisotropic and regular components. The anisotropic component is evaluated in the Small Angle Modification of the Spherical Harmonics Method (MSH) [4]. The MSH is formulated in the frame of reference of the solar beam where z-axis lies along the solar beam direction. In this case, the MSH solution for anisotropic part is nearly symmetric in azimuth, and is computed analytically. In scalar case, this solution coincides with the Goudsmit-Saunderson small-angle approximation [5]. To correct for an analytical separation of the anisotropic part of the signal, the transfer equation for the regular part contains a correction source function term [6]. Several examples of polarization impact on aerosol retrievals over different surface types will be presented. 1. Lyapustin A., Wang Y., Laszlo I., Kahn R., Korkin S., Remer L., Levy R., and Reid J. S. Multi-Angle Implementation of Atmospheric Correction (MAIAC): Part 2. Aerosol Algorithm. J. Geophys. Res., submitted (2010). 2. Lyapustin A., Muldashev T., Wang Y. Code SHARM: fast and accurate radiative transfer over spatially variable anisotropic surfaces. In: Light Scattering Reviews 5. Chichester: Springer, 205 - 247 (2010). 3. Budak, V.P., Korkin S.V. On the solution of a vectorial radiative transfer equation in an arbitrary three-dimensional turbid medium with anisotropic scattering. JQSRT, 109, 220-234 (2008). 4. Budak V.P., Sarmin S.E. Solution of radiative transfer equation by the method of spherical harmonics in the small angle modification. Atmospheric and Oceanic Optics, 3, 898-903 (1990). 5. Goudsmit S., Saunderson J.L. Multiple scattering of electrons. Phys. Rev., 57, 24-29 (1940). 6. Budak V.P, Klyuykov D.A., Korkin S.V. Convergence acceleration of radiative transfer equation solution at strongly anisotropic scattering. In: Light Scattering Reviews 5. Chichester: Springer, 147 - 204 (2010).

PROM7: 1D modeler of solar filaments or prominences

NASA Astrophysics Data System (ADS)

Gouttebroze, P.

2018-05-01

PROM7 is an update of PROM4 (ascl:1306.004) and computes simple models of solar prominences and filaments using Partial Radiative Distribution (PRD). The models consist of plane-parallel slabs standing vertically above the solar surface. Each model is defined by 5 parameters: temperature, density, geometrical thickness, microturbulent velocity and height above the solar surface. It solves the equations of radiative transfer, statistical equilibrium, ionization and pressure equilibria, and computes electron and hydrogen level population and hydrogen line profiles. Moreover, the code treats calcium atom which is reduced to 3 ionization states (Ca I, Ca II, CA III). Ca II ion has 5 levels which are useful for computing 2 resonance lines (H and K) and infrared triplet (to 8500 A).

Modelling thermal radiation in buoyant turbulent diffusion flames

NASA Astrophysics Data System (ADS)

Consalvi, J. L.; Demarco, R.; Fuentes, A.

2012-10-01

This work focuses on the numerical modelling of radiative heat transfer in laboratory-scale buoyant turbulent diffusion flames. Spectral gas and soot radiation is modelled by using the Full-Spectrum Correlated-k (FSCK) method. Turbulence-Radiation Interactions (TRI) are taken into account by considering the Optically-Thin Fluctuation Approximation (OTFA), the resulting time-averaged Radiative Transfer Equation (RTE) being solved by the Finite Volume Method (FVM). Emission TRIs and the mean absorption coefficient are then closed by using a presumed probability density function (pdf) of the mixture fraction. The mean gas flow field is modelled by the Favre-averaged Navier-Stokes (FANS) equation set closed by a buoyancy-modified k-ɛ model with algebraic stress/flux models (ASM/AFM), the Steady Laminar Flamelet (SLF) model coupled with a presumed pdf approach to account for Turbulence-Chemistry Interactions, and an acetylene-based semi-empirical two-equation soot model. Two sets of experimental pool fire data are used for validation: propane pool fires 0.3 m in diameter with Heat Release Rates (HRR) of 15, 22 and 37 kW and methane pool fires 0.38 m in diameter with HRRs of 34 and 176 kW. Predicted flame structures, radiant fractions, and radiative heat fluxes on surrounding surfaces are found in satisfactory agreement with available experimental data across all the flames. In addition further computations indicate that, for the present flames, the gray approximation can be applied for soot with a minor influence on the results, resulting in a substantial gain in Computer Processing Unit (CPU) time when the FSCK is used to treat gas radiation.

The fourth radiation transfer model intercomparison (RAMI-IV): Proficiency testing of canopy reflectance models with ISO-13528

NASA Astrophysics Data System (ADS)

Widlowski, J.-L.; Pinty, B.; Lopatka, M.; Atzberger, C.; Buzica, D.; Chelle, M.; Disney, M.; Gastellu-Etchegorry, J.-P.; Gerboles, M.; Gobron, N.; Grau, E.; Huang, H.; Kallel, A.; Kobayashi, H.; Lewis, P. E.; Qin, W.; Schlerf, M.; Stuckens, J.; Xie, D.

2013-07-01

The radiation transfer model intercomparison (RAMI) activity aims at assessing the reliability of physics-based radiative transfer (RT) models under controlled experimental conditions. RAMI focuses on computer simulation models that mimic the interactions of radiation with plant canopies. These models are increasingly used in the development of satellite retrieval algorithms for terrestrial essential climate variables (ECVs). Rather than applying ad hoc performance metrics, RAMI-IV makes use of existing ISO standards to enhance the rigor of its protocols evaluating the quality of RT models. ISO-13528 was developed "to determine the performance of individual laboratories for specific tests or measurements." More specifically, it aims to guarantee that measurement results fall within specified tolerance criteria from a known reference. Of particular interest to RAMI is that ISO-13528 provides guidelines for comparisons where the true value of the target quantity is unknown. In those cases, "truth" must be replaced by a reliable "conventional reference value" to enable absolute performance tests. This contribution will show, for the first time, how the ISO-13528 standard developed by the chemical and physical measurement communities can be applied to proficiency testing of computer simulation models. Step by step, the pre-screening of data, the identification of reference solutions, and the choice of proficiency statistics will be discussed and illustrated with simulation results from the RAMI-IV "abstract canopy" scenarios. Detailed performance statistics of the participating RT models will be provided and the role of the accuracy of the reference solutions as well as the choice of the tolerance criteria will be highlighted.

Transport and Chemical Effects on Concurrent and Opposed-flow Flame Spread at Microgravity

NASA Technical Reports Server (NTRS)

Son, Y.; Honda, L. K.; Ronney, P. D.

2001-01-01

Flame spread over flat solid fuel beds is a useful means of understanding more complex two-phase non-premixed spreading flames, such as those that may occur due to accidents in inhabited buildings and orbiting spacecraft. The role of buoyant convection on flame spread is substantial, especially for thermally-thick fuels. The conventional view, as supported by computations and space experiments, is that for quiescent mu-g conditions, the spread rate must be unsteady and decreasing until extinction occurs due to radiative losses. However, this view does not consider that radiative transfer to the fuel surface can enhance flame spread. In this work we suggest that radiative transfer from the flame itself, not just from an external source, can lead to steady flame spread at mu-g over thick fuel beds.

SKIRT: Hybrid parallelization of radiative transfer simulations

NASA Astrophysics Data System (ADS)

Verstocken, S.; Van De Putte, D.; Camps, P.; Baes, M.

2017-07-01

We describe the design, implementation and performance of the new hybrid parallelization scheme in our Monte Carlo radiative transfer code SKIRT, which has been used extensively for modelling the continuum radiation of dusty astrophysical systems including late-type galaxies and dusty tori. The hybrid scheme combines distributed memory parallelization, using the standard Message Passing Interface (MPI) to communicate between processes, and shared memory parallelization, providing multiple execution threads within each process to avoid duplication of data structures. The synchronization between multiple threads is accomplished through atomic operations without high-level locking (also called lock-free programming). This improves the scaling behaviour of the code and substantially simplifies the implementation of the hybrid scheme. The result is an extremely flexible solution that adjusts to the number of available nodes, processors and memory, and consequently performs well on a wide variety of computing architectures.

Multiple scattering in planetary regoliths using first-order incoherent interactions

NASA Astrophysics Data System (ADS)

Muinonen, Karri; Markkanen, Johannes; Väisänen, Timo; Penttilä, Antti

2017-10-01

We consider scattering of light by a planetary regolith modeled using discrete random media of spherical particles. The size of the random medium can range from microscopic sizes of a few wavelengths to macroscopic sizes approaching infinity. The size of the particles is assumed to be of the order of the wavelength. We extend the numerical Monte Carlo method of radiative transfer and coherent backscattering (RT-CB) to the case of dense packing of particles. We adopt the ensemble-averaged first-order incoherent extinction, scattering, and absorption characteristics of a volume element of particles as input for the RT-CB. The volume element must be larger than the wavelength but smaller than the mean free path length of incoherent extinction. In the radiative transfer part, at each absorption and scattering process, we account for absorption with the help of the single-scattering albedo and peel off the Stokes parameters of radiation emerging from the medium in predefined scattering angles. We then generate a new scattering direction using the joint probability density for the local polar and azimuthal scattering angles. In the coherent backscattering part, we utilize amplitude scattering matrices along the radiative-transfer path and the reciprocal path, and utilize the reciprocity of electromagnetic waves to verify the computation. We illustrate the incoherent volume-element scattering characteristics and compare the dense-medium RT-CB to asymptotically exact results computed using the Superposition T-matrix method (STMM). We show that the dense-medium RT-CB compares favorably to the STMM results for the current cases of sparse and dense discrete random media studied. The novel method can be applied in modeling light scattering by the surfaces of asteroids and other airless solar system objects, including UV-Vis-NIR spectroscopy, photometry, polarimetry, and radar scattering problems.Acknowledgments. Research supported by European Research Council with Advanced Grant No. 320773 SAEMPL, Scattering and Absorption of ElectroMagnetic waves in ParticuLate media. Computational resources provided by CSC - IT Centre for Science Ltd, Finland.

Fast and Accurate Radiative Transfer Calculations Using Principal Component Analysis for (Exo-)Planetary Retrieval Models

NASA Astrophysics Data System (ADS)

Kopparla, P.; Natraj, V.; Shia, R. L.; Spurr, R. J. D.; Crisp, D.; Yung, Y. L.

2015-12-01

Radiative transfer (RT) computations form the engine of atmospheric retrieval codes. However, full treatment of RT processes is computationally expensive, prompting usage of two-stream approximations in current exoplanetary atmospheric retrieval codes [Line et al., 2013]. Natraj et al. [2005, 2010] and Spurr and Natraj [2013] demonstrated the ability of a technique using principal component analysis (PCA) to speed up RT computations. In the PCA method for RT performance enhancement, empirical orthogonal functions are developed for binned sets of inherent optical properties that possess some redundancy; costly multiple-scattering RT calculations are only done for those few optical states corresponding to the most important principal components, and correction factors are applied to approximate radiation fields. Kopparla et al. [2015, in preparation] extended the PCA method to a broadband spectral region from the ultraviolet to the shortwave infrared (0.3-3 micron), accounting for major gas absorptions in this region. Here, we apply the PCA method to a some typical (exo-)planetary retrieval problems. Comparisons between the new model, called Universal Principal Component Analysis Radiative Transfer (UPCART) model, two-stream models and line-by-line RT models are performed, for spectral radiances, spectral fluxes and broadband fluxes. Each of these are calculated at the top of the atmosphere for several scenarios with varying aerosol types, extinction and scattering optical depth profiles, and stellar and viewing geometries. We demonstrate that very accurate radiance and flux estimates can be obtained, with better than 1% accuracy in all spectral regions and better than 0.1% in most cases, as compared to a numerically exact line-by-line RT model. The accuracy is enhanced when the results are convolved to typical instrument resolutions. The operational speed and accuracy of UPCART can be further improved by optimizing binning schemes and parallelizing the codes, work on which is under way.

Prediction of the Aerothermodynamic Environment of the Huygens Probe

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Striepe, Scott A.; Wright, Michael J.; Bose, Deepak; Sutton, Kenneth; Takashima, Naruhisa

2005-01-01

An investigation of the aerothermodynamic environment of the Huygens entry probe has been conducted. A Monte Carlo simulation of the trajectory of the probe during entry into Titan's atmosphere was performed to identify a worst-case heating rate trajectory. Flowfield and radiation transport computations were performed at points along this trajectory to obtain convective and radiative heat-transfer distributions on the probe's heat shield. This investigation identified important physical and numerical factors, including atmospheric CH4 concentration, transition to turbulence, numerical diffusion modeling, and radiation modeling, which strongly influenced the aerothermodynamic environment.

Computational fluid dynamics and aerothermodynamics

NASA Technical Reports Server (NTRS)

Carlson, Leland A.

1989-01-01

The primary objective was the development of nonequilibrium radiation and chemistry models suitable for engineering applications associated with the flow fields about aeroassisted orbital transfer vehicles (AOTVs), the aero-assisted flight experiment vehicle (AFE), and other vehicles operating at superorbital velocities and very high attitudes.

UV missile-plume signature model

NASA Astrophysics Data System (ADS)

Roblin, Antoine; Baudoux, Pierre E.; Chervet, Patrick

2002-08-01

A new 3D radiative code is used to solve the radiative transfer equation in the UV spectral domain for a nonequilibrium and axisymmetric media such as a rocket plume composed of hot reactive gases and metallic oxide particles like alumina. Calculations take into account the dominant chemiluminescence radiation mechanism and multiple scattering effects produced by alumina particles. Plume radiative properties are studied by using a simple cylindrical media of finite length, deduced from different aerothermochemical real rocket plume afterburning zones. Assumed a log-normal size distribution of alumina particles, optical properties are calculated by using Mie theory. Due to large uncertainties of particles properties, systematic tests have been performed in order to evaluate the influence of the different input data (refractive index, particle mean geometric radius) upon the radiance field. These computations will help us to define the set of parameters which need to be known accurately in order to compare computations with radiance measurements obtained during field experiments.

The potential influence of multiple scattering on longwave flux and heating rate simulations with clouds

NASA Astrophysics Data System (ADS)

Kuo, C. P.; Yang, P.; Huang, X.; Feldman, D.; Flanner, M.; Kuo, C.; Mlawer, E. J.

2017-12-01

Clouds, which cover approximately 67% of the globe, serve as one of the major modulators in adjusting radiative energy on the Earth. Since rigorous radiative transfer computations including multiple scattering are costly, only absorption is considered in the longwave spectral bands in the radiation sub-models of the general circulation models (GCMs). Quantification of the effect of ignoring longwave scattering for flux and heating rate simulations is performed by using the GCM version of the Longwave Rapid Radiative Transfer Model (RRTMG_LW) with an implementation with the 16-stream Discrete Ordinates Radiative Transfer (DISORT) Program for a Multi-Layered Plane-Parallel Medium in conjunction with the 2010 CCCM products that merge satellite observations from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), the CloudSat, the Clouds and the Earth's Radiant Energy System (CERES) and the Moderate Resolution Imaging Spectrometer (MODIS). One-year global simulations show that neglecting longwave scattering overestimates upward flux at the top of the atmosphere (TOA) and underestimates downward flux at the surface by approximately 2.63 and 1.15 W/m2, respectively. Furthermore, when longwave scattering is included in the simulations, the tropopause is cooled by approximately 0.018 K/day and the surface is heated by approximately 0.028 K/day. As a result, the radiative effects of ignoring longwave scattering and doubling CO2 are comparable in magnitude.

Application of the sequential quadratic programming algorithm for reconstructing the distribution of optical parameters based on the time-domain radiative transfer equation.

PubMed

Qi, Hong; Qiao, Yao-Bin; Ren, Ya-Tao; Shi, Jing-Wen; Zhang, Ze-Yu; Ruan, Li-Ming

2016-10-17

Sequential quadratic programming (SQP) is used as an optimization algorithm to reconstruct the optical parameters based on the time-domain radiative transfer equation (TD-RTE). Numerous time-resolved measurement signals are obtained using the TD-RTE as forward model. For a high computational efficiency, the gradient of objective function is calculated using an adjoint equation technique. SQP algorithm is employed to solve the inverse problem and the regularization term based on the generalized Gaussian Markov random field (GGMRF) model is used to overcome the ill-posed problem. Simulated results show that the proposed reconstruction scheme performs efficiently and accurately.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierra Thermal /Fluid Team

The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASCI fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the coremore » architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.« less

Effect of narrow band nonuniformity on unsteady heat up of water vapor under radiation-conduction combined heat transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okamoto, Tatsuyuki; Tanaka, Tomohiro; Morimune, Atsushi

Effect of narrow band nonuniformity on unsteady heat up process of water vapor under radiation-conduction combined heat transfer is examined by comparing the result of numerical simulations with and without incorporation of narrow band nonuniformity. The authors propose a rational and comprehensive computational approach for incorporating the narrow band nonuniformity into numerical simulations of radiative heat transfer when the considered field is nonisothermal. Results of examination exhibited that the contribution of radiative heat transfer to the heat up rate of water vapor may be almost twice overestimated, if the narrow band nonuniformity effect is neglected. Separate analyses of radiative energymore » attributed to wall emission and gas emission clarified that the absorption of wall emission is overestimated and, on the contrary, the absorption of radiation energy emitted by water vapor itself is underestimated if the narrow band nonuniformity is neglected. The reason why such over- or under-estimation is induced is understood by examining the influence of line overlap parameter on the transmittance averaged within a narrow band. Smaller value of line overlap parameter {gamma}/d means more violent narrow band nonuniformity. The broken lines show the narrow band transmittance for flat incident power spectrum, and the solid lines show that for the radiative emission from the absorbing gas itself. It is also clarified that the disregard of the narrow band nonuniformity give rise to serious error in the estimation of absorption rate of wall and gas emission even in the case where the disregard of narrow band nonuniformity bring little change to the temperature distribution. The results illustrated in this paper suggest that the narrow band nonuniformity should not be neglected.« less

Improved atmospheric 3D BSDF model in earthlike exoplanet using ray-tracing based method

NASA Astrophysics Data System (ADS)

Ryu, Dongok; Kim, Sug-Whan; Seong, Sehyun

2012-10-01

The studies on planetary radiative transfer computation have become important elements to disk-averaged spectral characterization of potential exoplanets. In this paper, we report an improved ray-tracing based atmospheric simulation model as a part of 3-D earth-like planet model with 3 principle sub-components i.e. land, sea and atmosphere. Any changes in ray paths and their characteristics such as radiative power and direction are computed as they experience reflection, refraction, transmission, absorption and scattering. Improved atmospheric BSDF algorithms uses Q.Liu's combined Rayleigh and aerosol Henrey-Greenstein scattering phase function. The input cloud-free atmosphere model consists of 48 layers with vertical absorption profiles and a scattering layer with their input characteristics using the GIOVANNI database. Total Solar Irradiance data are obtained from Solar Radiation and Climate Experiment (SORCE) mission. Using aerosol scattering computation, we first tested the atmospheric scattering effects with imaging simulation with HRIV, EPOXI. Then we examined the computational validity of atmospheric model with the measurements of global, direct and diffuse radiation taken from NREL(National Renewable Energy Laboratory)s pyranometers and pyrheliometers on a ground station for cases of single incident angle and for simultaneous multiple incident angles of the solar beam.

Solution of Radiative Transfer Equation with a Continuous and Stochastic Varying Refractive Index by Legendre Transform Method

PubMed Central

Gantri, M.

2014-01-01

The present paper gives a new computational framework within which radiative transfer in a varying refractive index biological tissue can be studied. In our previous works, Legendre transform was used as an innovative view to handle the angular derivative terms in the case of uniform refractive index spherical medium. In biomedical optics, our analysis can be considered as a forward problem solution in a diffuse optical tomography imaging scheme. We consider a rectangular biological tissue-like domain with spatially varying refractive index submitted to a near infrared continuous light source. Interaction of radiation with the biological material into the medium is handled by a radiative transfer model. In the studied situation, the model displays two angular redistribution terms that are treated with Legendre integral transform. The model is used to study a possible detection of abnormalities in a general biological tissue. The effect of the embedded nonhomogeneous objects on the transmitted signal is studied. Particularly, detection of targets of localized heterogeneous inclusions within the tissue is discussed. Results show that models accounting for variation of refractive index can yield useful predictions about the target and the location of abnormal inclusions within the tissue. PMID:25013454

Fast and Accurate Hybrid Stream PCRTMSOLAR Radiative Transfer Model for Reflected Solar Spectrum Simulation in the Cloudy Atmosphere

NASA Technical Reports Server (NTRS)

Yang, Qiguang; Liu, Xu; Wu, Wan; Kizer, Susan; Baize, Rosemary R.

2016-01-01

A hybrid stream PCRTM-SOLAR model has been proposed for fast and accurate radiative transfer simulation. It calculates the reflected solar (RS) radiances with a fast coarse way and then, with the help of a pre-saved matrix, transforms the results to obtain the desired high accurate RS spectrum. The methodology has been demonstrated with the hybrid stream discrete ordinate (HSDO) radiative transfer (RT) model. The HSDO method calculates the monochromatic radiances using a 4-stream discrete ordinate method, where only a small number of monochromatic radiances are simulated with both 4-stream and a larger N-stream (N = 16) discrete ordinate RT algorithm. The accuracy of the obtained channel radiance is comparable to the result from N-stream moderate resolution atmospheric transmission version 5 (MODTRAN5). The root-mean-square errors are usually less than 5x10(exp -4) mW/sq cm/sr/cm. The computational speed is three to four-orders of magnitude faster than the medium speed correlated-k option MODTRAN5. This method is very efficient to simulate thousands of RS spectra under multi-layer clouds/aerosols and solar radiation conditions for climate change study and numerical weather prediction applications.

Computation of diffuse sky irradiance from multidirectional radiance measurements

NASA Technical Reports Server (NTRS)

Ahmad, Suraiya P.; Middleton, Elizabeth M.; Deering, Donald W.

1987-01-01

Accurate determination of the diffuse solar spectral irradiance directly above the land surface is important in characterizing the reflectance properties of these surfaces, especially vegetation canopies. This determination is also needed to infer the net radiation budget of the earth-atmosphere system above these surfaces. An algorithm is developed here for the computation of hemispheric diffuse irradiance using the measurements from an instrument called PARABOLA, which rapidly measures upwelling and downwelling radiances in three selected wavelength bands. The validity of the algorithm is established from simulations. The standard reference data set of diffuse radiances of Dave (1978), obtained by solving the radiative transfer equation numerically for realistic atmospheric models, is used to simulate PARABOLA radiances. Hemispheric diffuse irradiance is estimated from a subset of simulated radiances by using the algorithm described. The algorithm is validated by comparing the estimated diffuse irradiance with the true diffuse irradiance of the standard data set. The validations include sensitivity studies for two wavelength bands (visible, 0.65-0.67 micron; near infrared, 0.81-0.84 micron), different atmospheric conditions, solar elevations, and surface reflectances. In most cases the hemispheric diffuse irradiance computed from simulated PARABOLA radiances and the true irradiance obtained from radiative transfer calculations agree within 1-2 percent. This technique can be applied to other sampling instruments designed to estimate hemispheric diffuse sky irradiance.

A combined study of heat and mass transfer in an infant incubator with an overhead screen.

PubMed

Ginalski, Maciej K; Nowak, Andrzej J; Wrobel, Luiz C

2007-06-01

The main objective of this study is to investigate the major physical processes taking place inside an infant incubator, before and after modifications have been made to its interior chamber. The modification involves the addition of an overhead screen to decrease radiation heat losses from the infant placed inside the incubator. The present study investigates the effect of these modifications on the convective heat flux from the infant's body to the surrounding environment inside the incubator. A combined analysis of airflow and heat transfer due to conduction, convection, radiation and evaporation has been performed, in order to calculate the temperature and velocity fields inside the incubator before and after the design modification. Due to the geometrical complexity of the model, computer-aided design (CAD) applications were used to generate a computer-based model. All numerical calculations have been performed using the commercial computational fluid dynamics (CFD) package FLUENT, together with in-house routines used for managing purposes and user-defined functions (UDFs) which extend the basic solver capabilities. Numerical calculations have been performed for three different air inlet temperatures: 32, 34 and 36 degrees C. The study shows a decrease of the radiative and convective heat losses when the overhead screen is present. The results obtained were numerically verified as well as compared with results available in the literature from investigations of dry heat losses from infant manikins.

Simulations of recoiling black holes: adaptive mesh refinement and radiative transfer

NASA Astrophysics Data System (ADS)

Meliani, Zakaria; Mizuno, Yosuke; Olivares, Hector; Porth, Oliver; Rezzolla, Luciano; Younsi, Ziri

2017-02-01

Context. In many astrophysical phenomena, and especially in those that involve the high-energy regimes that always accompany the astronomical phenomenology of black holes and neutron stars, physical conditions that are achieved are extreme in terms of speeds, temperatures, and gravitational fields. In such relativistic regimes, numerical calculations are the only tool to accurately model the dynamics of the flows and the transport of radiation in the accreting matter. Aims: We here continue our effort of modelling the behaviour of matter when it orbits or is accreted onto a generic black hole by developing a new numerical code that employs advanced techniques geared towards solving the equations of general-relativistic hydrodynamics. Methods: More specifically, the new code employs a number of high-resolution shock-capturing Riemann solvers and reconstruction algorithms, exploiting the enhanced accuracy and the reduced computational cost of adaptive mesh-refinement (AMR) techniques. In addition, the code makes use of sophisticated ray-tracing libraries that, coupled with general-relativistic radiation-transfer calculations, allow us to accurately compute the electromagnetic emissions from such accretion flows. Results: We validate the new code by presenting an extensive series of stationary accretion flows either in spherical or axial symmetry that are performed either in two or three spatial dimensions. In addition, we consider the highly nonlinear scenario of a recoiling black hole produced in the merger of a supermassive black-hole binary interacting with the surrounding circumbinary disc. In this way, we can present for the first time ray-traced images of the shocked fluid and the light curve resulting from consistent general-relativistic radiation-transport calculations from this process. Conclusions: The work presented here lays the ground for the development of a generic computational infrastructure employing AMR techniques to accurately and self-consistently calculate general-relativistic accretion flows onto compact objects. In addition to the accurate handling of the matter, we provide a self-consistent electromagnetic emission from these scenarios by solving the associated radiative-transfer problem. While magnetic fields are currently excluded from our analysis, the tools presented here can have a number of applications to study accretion flows onto black holes or neutron stars.

The coupling of MATISSE and the SE-WORKBENCH: a new solution for simulating efficiently the atmospheric radiative transfer and the sea surface radiation

NASA Astrophysics Data System (ADS)

Cathala, Thierry; Douchin, Nicolas; Latger, Jean; Caillault, Karine; Fauqueux, Sandrine; Huet, Thierry; Lubarre, Luc; Malherbe, Claire; Rosier, Bernard; Simoneau, Pierre

2009-05-01

The SE-WORKBENCH workshop, also called CHORALE (French acceptation for "simulated Optronic Acoustic Radar battlefield") is used by the French DGA (MoD) and several other Defense organizations and companies all around the World to perform multi-sensors simulations. CHORALE enables the user to create virtual and realistic multi spectral 3D scenes that may contain several types of target, and then generate the physical signal received by a sensor, typically an IR sensor. The SE-WORKBENCH can be used either as a collection of software modules through dedicated GUIs or as an API made of a large number of specialized toolkits. The SE-WORKBENCH is made of several functional block: one for geometrically and physically modeling the terrain and the targets, one for building the simulation scenario and one for rendering the synthetic environment, both in real and non real time. Among the modules that the modeling block is composed of, SE-ATMOSPHERE is used to simulate the atmospheric conditions of a Synthetic Environment and then to integrate the impact of these conditions on a scene. This software product generates an exploitable physical atmosphere by the SE WORKBENCH tools generating spectral images. It relies on several external radiative transfer models such as MODTRAN V4.2 in the current version. MATISSE [4,5] is a background scene generator developed for the computation of natural background spectral radiance images and useful atmospheric radiative quantities (radiance and transmission along a line of sight, local illumination, solar irradiance ...). Backgrounds include atmosphere, low and high altitude clouds, sea and land. A particular characteristic of the code is its ability to take into account atmospheric spatial variability (temperatures, mixing ratio, etc) along each line of sight. An Application Programming Interface (API) is included to facilitate its use in conjunction with external codes. MATISSE is currently considered as a new external radiative transfer model to be integrated in SE-ATMOSPHERE as a complement to MODTRAN. Compared to the latter which is used as a whole MATISSE can be used step by step and modularly as an API: this can avoid to pre compute large atmospheric parameters tables as it is done currently with MODTRAN. The use of MATISSE will also enable a real coupling between the ray tracing process of the SEWORKBENCH and the radiative transfer model of MATISSE. This will lead to the improvement of the link between a general atmospheric model and a specific 3D terrain. The paper will demonstrate the advantages for the SE WORKEBNCH of using MATISSE as a new atmospheric code, but also for computing the radiative properties of the sea surface.

Computing Models of M-type Host Stars and their Panchromatic Spectral Output

NASA Astrophysics Data System (ADS)

Linsky, Jeffrey; Tilipman, Dennis; France, Kevin

2018-06-01

We have begun a program of computing state-of-the-art model atmospheres from the photospheres to the coronae of M stars that are the host stars of known exoplanets. For each model we are computing the emergent radiation at all wavelengths that are critical for assessingphotochemistry and mass-loss from exoplanet atmospheres. In particular, we are computing the stellar extreme ultraviolet radiation that drives hydrodynamic mass loss from exoplanet atmospheres and is essential for determing whether an exoplanet is habitable. The model atmospheres are computed with the SSRPM radiative transfer/statistical equilibrium code developed by Dr. Juan Fontenla. The code solves for the non-LTE statistical equilibrium populations of 18,538 levels of 52 atomic and ion species and computes the radiation from all species (435,986 spectral lines) and about 20,000,000 spectral lines of 20 diatomic species.The first model computed in this program was for the modestly active M1.5 V star GJ 832 by Fontenla et al. (ApJ 830, 152 (2016)). We will report on a preliminary model for the more active M5 V star GJ 876 and compare this model and its emergent spectrum with GJ 832. In the future, we will compute and intercompare semi-empirical models and spectra for all of the stars observed with the HST MUSCLES Treasury Survey, the Mega-MUSCLES Treasury Survey, and additional stars including Proxima Cen and Trappist-1.This multiyear theory program is supported by a grant from the Space Telescope Science Institute.

Action spectra affect variability of the climatology of biologically effective ultraviolet radiation on cloud-free days.

PubMed

Grifoni, D; Zipoli, G; Sabatini, F; Messeri, G; Bacci, L

2013-12-01

Action spectrum (AS) describes the relative effectiveness of ultraviolet (UV) radiation in producing biological effects and allows spectral UV irradiance to be weighted in order to compute biologically effective UV radiation (UVBE). The aim of this research was to study the seasonal and latitudinal distribution over Europe of daily UVBE doses responsible for various biological effects on humans and plants. Clear sky UV radiation spectra were computed at 30-min time intervals for the first day of each month of the year for Rome, Potsdam and Trondheim using a radiative transfer model fed with climatological data. Spectral data were weighted using AS for erythema, vitamin D synthesis, cataract and photokeratitis for humans, while the generalised plant damage and the plant damage AS were used for plants. The daily UVBE doses for the above-mentioned biological processes were computed and are analysed in this study. The patterns of variation due to season (for each location) and latitude (for each date) resulted as being specific for each adopted AS. The biological implications of these results are briefly discussed highlighting the importance of a specific UVBE climatology for each biological process.

Soot and Spectral Radiation Modeling for a High-Pressure Turbulent Spray Flame

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferreryo-Fernandez, Sebastian; Paul, Chandan; Sircar, Arpan

Simulations are performed of a transient high-pressure turbulent n-dodecane spray flame under engine-relevant conditions. An unsteady RANS formulation is used, with detailed chemistry, a semi-empirical two-equation soot model, and a particle-based transported composition probability density function (PDF) method to account for unresolved turbulent fluctuations in composition and temperature. Results from the PDF model are compared with those from a locally well-stirred reactor (WSR) model to quantify the effects of turbulence-chemistry-soot interactions. Computed liquid and vapor penetration versus time, ignition delay, and flame lift-off height are in good agreement with experiment, and relatively small differences are seen between the WSR andmore » PDF models for these global quantities. Computed soot levels and spatial soot distributions from the WSR and PDF models show large differences, with PDF results being in better agreement with experimental measurements. An uncoupled photon Monte Carlo method with line-by-line spectral resolution is used to compute the spectral intensity distribution of the radiation leaving the flame. This provides new insight into the relative importance of molecular gas radiation versus soot radiation, and the importance of turbulent fluctuations on radiative heat transfer.« less

Transmission mode terahertz computed tomography

DOEpatents

Ferguson, Bradley Stuart; Wang, Shaohong; Zhang, Xi-Cheng

2006-10-10

A method of obtaining a series of images of a three-dimensional object by transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a scanning spot. The object is placed within the Rayleigh range of the focused THz beam and a focusing system is used to transfer the imaging plane from adjacent the object to a desired distance away from the object. A related system is also disclosed.

Combined effects of heat and mass transfer to magneto hydrodynamics oscillatory dusty fluid flow in a porous channel

NASA Astrophysics Data System (ADS)

Govindarajan, A.; Vijayalakshmi, R.; Ramamurthy, V.

2018-04-01

The main aim of this article is to study the combined effects of heat and mass transfer to radiative Magneto Hydro Dynamics (MHD) oscillatory optically thin dusty fluid in a saturated porous medium channel. Based on certain assumptions, the momentum, energy, concentration equations are obtained.The governing equations are non-dimensionalised, simplified and solved analytically. The closed analytical form solutions for velocity, temperature, concentration profiles are obtained. Numerical computations are presented graphically to show the salient features of various physical parameters. The shear stress, the rate of heat transfer and the rate of mass transfer are also presented graphically.

On the Formation of Massive Stars

NASA Technical Reports Server (NTRS)

Yorke, Harold W.; Sonnhalter, Cordula

2002-01-01

We calculate numerically the collapse of slowly rotating, nonmagnetic, massive molecular clumps of masses 30,60, and 120 Stellar Mass, which conceivably could lead to the formation of massive stars. Because radiative acceleration on dust grains plays a critical role in the clump's dynamical evolution, we have improved the module for continuum radiation transfer in an existing two-dimensional (axial symmetry assumed) radiation hydrodynamic code. In particular, rather than using "gray" dust opacities and "gray" radiation transfer, we calculate the dust's wavelength-dependent absorption and emission simultaneously with the radiation density at each wavelength and the equilibrium temperatures of three grain components: amorphous carbon particles. silicates, and " dirty ice " -coated silicates. Because our simulations cannot spatially resolve the innermost regions of the molecular clump, however, we cannot distinguish between the formation of a dense central cluster or a single massive object. Furthermore, we cannot exclude significant mass loss from the central object(s) that may interact with the inflow into the central grid cell. Thus, with our basic assumption that all material in the innermost grid cell accretes onto a single object. we are able to provide only an upper limit to the mass of stars that could possibly be formed. We introduce a semianalytical scheme for augmenting existing evolutionary tracks of pre-main-sequence protostars by including the effects of accretion. By considering an open outermost boundary, an arbitrary amount of material could, in principal, be accreted onto this central star. However, for the three cases considered (30, 60, and 120 Stellar Mass originally within the computation grid), radiation acceleration limited the final masses to 3 1.6, 33.6, and 42.9 Stellar Mass, respectively, for wavelength-dependent radiation transfer and to 19.1, 20.1, and 22.9 Stellar Mass. for the corresponding simulations with gray radiation transfer. Our calculations demonstrate that massive stars can in principle be formed via accretion through a disk. The accretion rate onto the central source increases rapidly after one initial free-fall time and decreases monotonically afterward. By enhancing the nonisotropic character of the radiation field, the accretion disk reduces the effects of radiative acceleration in the radial direction - a process we call the "flashlight effect." The flashlight effect is further amplified in our case by including the effects of frequency-dependent radiation transfer. We conclude with the warning that a careful treatment of radiation transfer is a mandatory requirement for realistic simulations of the formation of massive stars.

Coupled atmosphere/canopy model for remote sensing of plant reflectance features

NASA Technical Reports Server (NTRS)

Gerstl, S. A.; Zardecki, A.

1985-01-01

Solar radiative transfer through a coupled system of atmosphere and plant canopy is modeled as a multiple-scattering problem through a layered medium of random scatterers. The radiative transfer equation is solved by the discrete-ordinates finite-element method. Analytic expressions are derived that allow the calculation of scattering and absorption cross sections for any plant canopy layer form measurable biophysical parameters such as the leaf area index, leaf angle distribution, and individual leaf reflectance and transmittance data. An expression for a canopy scattering phase function is also given. Computational results are in good agreement with spectral reflectance measurements directly above a soybean canopy, and the concept of greenness- and brightness-transforms of Landsat MSS data is reconfirmed with the computed results. A sensitivity analysis with the coupled atmosphere/canopy model quantifies how satellite-sensed spectral radiances are affected by increased atmospheric aerosols, by varying leaf area index, by anisotropic leaf scattering, and by non-Lambertian soil boundary conditions. Possible extensions to a 2-D model are also discussed.

A vector radiative transfer model for coupled atmosphere and ocean systems based on successive order of scattering method.

PubMed

Zhai, Peng-Wang; Hu, Yongxiang; Trepte, Charles R; Lucker, Patricia L

2009-02-16

A vector radiative transfer model has been developed for coupled atmosphere and ocean systems based on the Successive Order of Scattering (SOS) Method. The emphasis of this study is to make the model easy-to-use and computationally efficient. This model provides the full Stokes vector at arbitrary locations which can be conveniently specified by users. The model is capable of tracking and labeling different sources of the photons that are measured, e.g. water leaving radiances and reflected sky lights. This model also has the capability to separate florescence from multi-scattered sunlight. The delta - fit technique has been adopted to reduce computational time associated with the strongly forward-peaked scattering phase matrices. The exponential - linear approximation has been used to reduce the number of discretized vertical layers while maintaining the accuracy. This model is developed to serve the remote sensing community in harvesting physical parameters from multi-platform, multi-sensor measurements that target different components of the atmosphere-oceanic system.

ENGINEERING APPLICATIONS OF ANALOG COMPUTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryant, L.T.; Janicke, M.J.; Just, L.C.

1961-02-01

Six examples are given of the application of analog computers in the fields of reactor engineering, heat transfer, and dynamics: deceleration of a reactor control rod by dashpot, pressure variations through a packed bed, reactor kinetics over many decades with thermal feedback (simulation of a TREAT transient), vibrating system with two degrees of freedom, temperature distribution in a radiating fin, and temperature distribution in an irfinite slab with variable thermal properties. (D.L.C.)

Radiative transfer modeling applied to sea water constituent determination. [Gulf of Mexico

NASA Technical Reports Server (NTRS)

Faller, K. H.

1979-01-01

Optical radiation from the sea is influenced by pigments dissolved in the water and contained in discrete organisms suspended in the sea, and by pigmented and unpigmented inorganic and organic particles. The problem of extracting the information concerning these pigments and particulates from the optical properties of the sea is addressed and the properties which determine characteristics of the radiation that a remote sensor will detect and measure are considered. The results of the application of the volume scattering function model to the data collected in the Gulf of Mexico and its environs indicate that the size distribution of the concentrations of particles found in the sea can be predicted from measurements of the volume scattering function. Furthermore, with the volume scattering function model and knowledge of the absorption spectra of dissolved pigments, the radiative transfer model can compute a distribution of particle sizes and indices of refraction and concentration of dissolved pigments that give an upwelling light spectrum that closely matches measurements of that spectrum at sea.

Computational manipulation of a radiative MHD flow with Hall current and chemical reaction in the presence of rotating fluid

NASA Astrophysics Data System (ADS)

Alias Suba, Subbu; Muthucumaraswamy, R.

2018-04-01

A numerical analysis of transient radiative MHD(MagnetoHydroDynamic) natural convective flow of a viscous, incompressible, electrically conducting and rotating fluid along a semi-infinite isothermal vertical plate is carried out taking into consideration Hall current, rotation and first order chemical reaction.The coupled non-linear partial differential equations are expressed in difference form using implicit finite difference scheme. The difference equations are then reduced to a system of linear algebraic equations with a tri-diagonal structure which is solved by Thomas Algorithm. The primary and secondary velocity profiles, temperature profile, concentration profile, skin friction, Nusselt number and Sherwood Number are depicted graphically for a range of values of rotation parameter, Hall parameter,magnetic parameter, chemical reaction parameter, radiation parameter, Prandtl number and Schmidt number.It is recognized that rate of heat transfer and rate of mass transfer decrease with increase in time but they increase with increasing values of radiation parameter and Schmidt number respectively.

Using RADMC-3D to model the radiative transfer of spectral lines in protoplanetary disks and envelopes

NASA Astrophysics Data System (ADS)

DeVries, John; Terebey, Susan

2018-06-01

Protoplanetary disks are the birthplaces of planets in our universe. Observations of these disks with radio telescopes like the Atacama Large Millimeter Array (ALMA) offer great insight into the star and planet formation process. Comparing theories of formation with observations requires tracing the energy transfer via electromagnetic radiation, known as radiative transfer. To determine the temperature distribution of circumstellar material, a Monte Carlo code (Whitney et al. [1]) was used to to perform the radiative transfer through dust. The goal of this research is to utilize RADMC-3D [2] to handle the spectral line radiative transfer computations. An existing model of a rotating ring was expanded to include emission from the C18O isotopologue of carbon monoxide using data from the Leiden Atomic and Molecular Database (LAMDA). This feature of our model compliments ALMA's ability to measure C18O line emission, a proxy for disk rotation. In addition to modeling gas in the protoplanetary disk, dust also plays an important role. The generic description of absorption and scattering for dust provided by RADMC-3D was changed in favor of a more physically-realistic description with OH5 grains. This description is more appropriate in high-density regions of the envelope around a protostar. Further improvements, such as consideration for the finite resolution of observations, have been implemented. The task at present is to compare our model with observations of protoplanetary systems like L1527. Some results of these comparisons will be presented.[1] Whitney et al. 2013, ApJS, 207:30[2] RADMC-3D: http://www.ita.uni-heidelberg.de/~dullemond/software/radmc-3d/

Active and Passive 3D Vector Radiative Transfer with Preferentially-Aligned Ice Particles

NASA Astrophysics Data System (ADS)

Adams, I. S.; Munchak, S. J.; Pelissier, C.; Kuo, K. S.; Heymsfield, G. M.

2017-12-01

To support the observation of clouds and precipitation using combinations of radars and radiometers, a forward model capable of representing diverse sensing geometries for active and passive instruments is necessary for correctly interpreting and consistently combining multi-sensor measurements from ground-based, airborne, and spaceborne platforms. As such, the Atmospheric Radiative Transfer Simulator (ARTS) uses Monte Carlo integration to produce radar reflectivities and radiometric brightness temperatures for three-dimensional cloud and precipitation input fields. This radiative transfer framework is capable of efficiently sampling Gaussian antenna beams and fully accounting for multiple scattering. By relying on common ray-tracing tools, gaseous absorption models, and scattering properties, the model reproduces accurate and consistent radar and radiometer observables. While such a framework is an important component for simulating remote sensing observables, the key driver for self-consistent radiative transfer calculations of clouds and precipitation is scattering data. Research over the past decade has demonstrated that spheroidal models of frozen hydrometeors cannot accurately reproduce all necessary scattering properties at all desired frequencies. The discrete dipole approximation offers flexibility in calculating scattering for arbitrary particle geometries, but at great computational expense. When considering scattering for certain pristine ice particles, the Extended Boundary Condition Method, or T-Matrix, is much more computationally efficient; however, convergence for T-Matrix calculations fails at large size parameters and high aspect ratios. To address these deficiencies, we implemented the Invariant Imbedding T-Matrix Method (IITM). A brief overview of ARTS and IITM will be given, including details for handling preferentially-aligned hydrometeors. Examples highlighting the performance of the model for simulating space-based and airborne measurements will be offered, and some case studies showing the response to particle type and orientation will be presented. Simulations of polarized radar (Z, LDR, ZDR) and radiometer (Stokes I and Q) quantities will be used to demonstrate the capabilities of the model.

Pediatric Trauma Transfer Imaging Inefficiencies-Opportunities for Improvement with Cloud Technology.

PubMed

Puckett, Yana; To, Alvin

2016-01-01

This study examines the inefficiencies of radiologic imaging transfers from one hospital to the other during pediatric trauma transfers in an era of cloud based information sharing. Retrospective review of all patients transferred to a pediatric trauma center from 2008-2014 was performed. Imaging was reviewed for whether imaging accompanied the patient, whether imaging was able to be uploaded onto computer for records, whether imaging had to be repeated, and whether imaging obtained at outside hospitals (OSH) was done per universal pediatric trauma guidelines. Of the 1761 patients retrospectively reviewed, 559 met our inclusion criteria. Imaging was sent with the patient 87.7% of the time. Imaging was unable to be uploaded 31.9% of the time. CT imaging had to be repeated 1.8% of the time. CT scan was not done per universal pediatric trauma guidelines 1.2% of the time. Our study demonstrated that current imaging transfer is inefficient, leads to excess ionizing radiation, and increased healthcare costs. Universal implementation of cloud based radiology has the potential to eliminate excess ionizing radiation to children, improve patient care, and save cost to healthcare system.

Dynamical and Radiative Modeling of Sagittarius A*

NASA Astrophysics Data System (ADS)

Shcherbakov, Roman V.

2011-09-01

Sgr A* in our Galactic Center is the closest supermassive black hole (SMBH) with the largest event horizon angular size. Most other SMBHs are likely in the same dormant low-luminosity accretion state as Sgr A*. Thus, the important physical effects in lives of BHs can be best observed and studied in our Galactic Center. One of these effects is electron heat conduction. Conduction may be the main reason why Sgr A* is so dramatically underluminous: it transfers heat outwards from the inner flow and unbinds the outer flow, quenching the accretion. In Chapter 3 I build a realistic model of accretion with conduction, which incorporates feeding by stellar winds. In a model with accretion rate < 1% of the naive Bondi estimate I achieve agreement of the X-ray surface brightness profile and Faraday rotation measure to observations. An earlier model proposed in Chapter 2 with adiabatic accretion of turbulent magnetized medium cannot be tweaked to match the observations. Its accretion rate appears too large, so turbulent magnetic field cannot stop gas from falling in. Low accretion rate leads to a peculiar radiation pattern from near the BH: cyclo-synchrotron polarized radiation is observed in radio/sub-mm. Since it comes from several Schwarzschild radii, the BH spin can be determined, when we overcome all modeling challenges. I fit the average observed radiation spectrum with a theoretical spectrum, which is computed by radiative transfer over a simulation-based model. Relevant plasma effects responsible for the observed polarization state are accurately computed for thermal plasma in Chapter 4. The prescription of how to perform the correct general relativistic polarized radiative transfer is elaborated in Chapter 5. Application of this technique to three-dimensional general relativistic magneto hydrodynamic numerical simulations is reported in Chapter 6. The main results of analysis are that the spin inclination angle is estimated to lie within a narrow range theta est = 50° -- 59°, and most probable value of BH spin is a* = 0.9. I believe the researched topics will play a central role in future modeling of typical SMBH accretion and will lead to effective ways to determine the spins of these starving eaters. Computations of plasma effects reported here will also find applications when comparing models of jets to observations.

Modeling Radiation Fog

NASA Astrophysics Data System (ADS)

K R, Sreenivas; Mohammad, Rafiuddin

2016-11-01

Predicting the fog-onset, its growth and dissipation helps in managing airports and other modes of transport. After sunset, occurrence of fog requires moist air, low wind and clear-sky conditions. Under these circumstances radiative heat transfer plays a vital role in the NBL. Locally, initiation of fog happens when the air temperature falls below the dew-point. Thus, to predict the onset of fog at a given location, one has to compute evolution of vertical temperature profile. Earlier,our group has shown that the presence of aerosols and vertical variation in their number density determines the radiative-cooling and hence development of vertical temperature profile. Aerosols, through radiation in the window-band, provides an efficient path for air layers to lose heat to the cold, upper atmosphere. This process creates cooler air layer between warmer ground and upper air layers and resulting temperature profile facilitate the initiation of fog. Our results clearly indicates that accounting for the presence of aerosols and their radiative-transfer is important in modeling micro-meteorological process of fog formation and its evolution. DST, Govt. INDIA.

Radiative transfer and spectroscopic databases: A line-sampling Monte Carlo approach

NASA Astrophysics Data System (ADS)

Galtier, Mathieu; Blanco, Stéphane; Dauchet, Jérémi; El Hafi, Mouna; Eymet, Vincent; Fournier, Richard; Roger, Maxime; Spiesser, Christophe; Terrée, Guillaume

2016-03-01

Dealing with molecular-state transitions for radiative transfer purposes involves two successive steps that both reach the complexity level at which physicists start thinking about statistical approaches: (1) constructing line-shaped absorption spectra as the result of very numerous state-transitions, (2) integrating over optical-path domains. For the first time, we show here how these steps can be addressed simultaneously using the null-collision concept. This opens the door to the design of Monte Carlo codes directly estimating radiative transfer observables from spectroscopic databases. The intermediate step of producing accurate high-resolution absorption spectra is no longer required. A Monte Carlo algorithm is proposed and applied to six one-dimensional test cases. It allows the computation of spectrally integrated intensities (over 25 cm-1 bands or the full IR range) in a few seconds, regardless of the retained database and line model. But free parameters need to be selected and they impact the convergence. A first possible selection is provided in full detail. We observe that this selection is highly satisfactory for quite distinct atmospheric and combustion configurations, but a more systematic exploration is still in progress.

Probability theory for 3-layer remote sensing radiative transfer model: univariate case.

PubMed

Ben-David, Avishai; Davidson, Charles E

2012-04-23

A probability model for a 3-layer radiative transfer model (foreground layer, cloud layer, background layer, and an external source at the end of line of sight) has been developed. The 3-layer model is fundamentally important as the primary physical model in passive infrared remote sensing. The probability model is described by the Johnson family of distributions that are used as a fit for theoretically computed moments of the radiative transfer model. From the Johnson family we use the SU distribution that can address a wide range of skewness and kurtosis values (in addition to addressing the first two moments, mean and variance). In the limit, SU can also describe lognormal and normal distributions. With the probability model one can evaluate the potential for detecting a target (vapor cloud layer), the probability of observing thermal contrast, and evaluate performance (receiver operating characteristics curves) in clutter-noise limited scenarios. This is (to our knowledge) the first probability model for the 3-layer remote sensing geometry that treats all parameters as random variables and includes higher-order statistics. © 2012 Optical Society of America

Comparison of discrete ordinate and Monte Carlo simulations of polarized radiative transfer in two coupled slabs with different refractive indices.

PubMed

Cohen, D; Stamnes, S; Tanikawa, T; Sommersten, E R; Stamnes, J J; Lotsberg, J K; Stamnes, K

2013-04-22

A comparison is presented of two different methods for polarized radiative transfer in coupled media consisting of two adjacent slabs with different refractive indices, each slab being a stratified medium with no change in optical properties except in the direction of stratification. One of the methods is based on solving the integro-differential radiative transfer equation for the two coupled slabs using the discrete ordinate approximation. The other method is based on probabilistic and statistical concepts and simulates the propagation of polarized light using the Monte Carlo approach. The emphasis is on non-Rayleigh scattering for particles in the Mie regime. Comparisons with benchmark results available for a slab with constant refractive index show that both methods reproduce these benchmark results when the refractive index is set to be the same in the two slabs. Computed results for test cases with coupling (different refractive indices in the two slabs) show that the two methods produce essentially identical results for identical input in terms of absorption and scattering coefficients and scattering phase matrices.

Enhancing Cloud Radiative Processes and Radiation Efficiency in the Advanced Research Weather Research and Forecasting (WRF) Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iacono, Michael J.

The objective of this research has been to evaluate and implement enhancements to the computational performance of the RRTMG radiative transfer option in the Advanced Research version of the Weather Research and Forecasting (WRF) model. Efficiency is as essential as accuracy for effective numerical weather prediction, and radiative transfer is a relatively time-consuming component of dynamical models, taking up to 30-50 percent of the total model simulation time. To address this concern, this research has implemented and tested a version of RRTMG that utilizes graphics processing unit (GPU) technology (hereinafter RRTMGPU) to greatly improve its computational performance; thereby permitting eithermore » more frequent simulation of radiative effects or other model enhancements. During the early stages of this project the development of RRTMGPU was completed at AER under separate NASA funding to accelerate the code for use in the Goddard Space Flight Center (GSFC) Goddard Earth Observing System GEOS-5 global model. It should be noted that this final report describes results related to the funded portion of the originally proposed work concerning the acceleration of RRTMG with GPUs in WRF. As a k-distribution model, RRTMG is especially well suited to this modification due to its relatively large internal pseudo-spectral (g-point) dimension that, when combined with the horizontal grid vector in the dynamical model, can take great advantage of the GPU capability. Thorough testing under several model configurations has been performed to ensure that RRTMGPU improves WRF model run time while having no significant impact on calculated radiative fluxes and heating rates or on dynamical model fields relative to the RRTMG radiation. The RRTMGPU codes have been provided to NCAR for possible application to the next public release of the WRF forecast model.« less

A numerical analysis for non-linear radiation in MHD flow around a cylindrical surface with chemically reactive species

NASA Astrophysics Data System (ADS)

Khan, Junaid Ahmad; Mustafa, M.

2018-03-01

Boundary layer flow around a stretchable rough cylinder is modeled by taking into account boundary slip and transverse magnetic field effects. The main concern is to resolve heat/mass transfer problem considering non-linear radiative heat transfer and temperature/concentration jump aspects. Using conventional similarity approach, the equations of motion and heat transfer are converted into a boundary value problem whose solution is computed by shooting method for broad range of slip coefficients. The proposed numerical scheme appears to improve as the strengths of magnetic field and slip coefficients are enhanced. Axial velocity and temperature are considerably influenced by a parameter M which is inversely proportional to the radius of cylinder. A significant change in temperature profile is depicted for growing wall to ambient temperature ratio. Relevant physical quantities such as wall shear stress, local Nusselt number and local Sherwood number are elucidated in detail.

Combining ray tracing and CFD in the thermal analysis of a parabolic dish tubular cavity receiver

NASA Astrophysics Data System (ADS)

Craig, Ken J.; Marsberg, Justin; Meyer, Josua P.

2016-05-01

This paper describes the numerical evaluation of a tubular receiver used in a dish Brayton cycle. In previous work considering the use of Computational Fluid Dynamics (CFD) to perform the calculation of the absorbed radiation from the parabolic dish into the cavity as well as the resulting conjugate heat transfer, it was shown that an axi-symmetric model of the dish and receiver absorbing surfaces was useful in reducing the computational cost required for a full 3-D discrete ordinates solution, but concerns remained about its accuracy. To increase the accuracy, the Monte Carlo ray tracer SolTrace is used to perform the calculation of the absorbed radiation profile to be used in the conjugate heat transfer CFD simulation. The paper describes an approach for incorporating a complex geometry like a tubular receiver generated using CFD software into SolTrace. The results illustrate the variation of CFD mesh density that translates into the number of elements in SolTrace as well as the number of rays used in the Monte Carlo approach and their effect on obtaining a resolution-independent solution. The conjugate heat transfer CFD simulation illustrates the effect of applying the SolTrace surface heat flux profile solution as a volumetric heat source to heat up the air inside the tube. Heat losses due to convection and thermal re-radiation are also determined as a function of different tube absorptivities.

Simulation of the Microwave Emission of Multi-layered Snowpacks Using the Dense Media Radiative Transfer Theory: the DMRT-ML Model

NASA Technical Reports Server (NTRS)

Picard, G.; Brucker, Ludovic; Roy, A.; Dupont, F.; Fily, M.; Royer, A.; Harlow, C.

2013-01-01

DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by spacebased microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large icesheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

Self-consistent radiation-based simulation of electric arcs: II. Application to gas circuit breakers

NASA Astrophysics Data System (ADS)

Iordanidis, A. A.; Franck, C. M.

2008-07-01

An accurate and robust method for radiative heat transfer simulation for arc applications was presented in the previous paper (part I). In this paper a self-consistent mathematical model based on computational fluid dynamics and a rigorous radiative heat transfer model is described. The model is applied to simulate switching arcs in high voltage gas circuit breakers. The accuracy of the model is proven by comparison with experimental data for all arc modes. The ablation-controlled arc model is used to simulate high current PTFE arcs burning in cylindrical tubes. Model accuracy for the lower current arcs is evaluated using experimental data on the axially blown SF6 arc in steady state and arc resistance measurements close to current zero. The complete switching process with the arc going through all three phases is also simulated and compared with the experimental data from an industrial circuit breaker switching test.

Intercomparison of three microwave/infrared high resolution line-by-line radiative transfer codes

NASA Astrophysics Data System (ADS)

Schreier, F.; Garcia, S. Gimeno; Milz, M.; Kottayil, A.; Höpfner, M.; von Clarmann, T.; Stiller, G.

2013-05-01

An intercomparison of three line-by-line (lbl) codes developed independently for atmospheric sounding - ARTS, GARLIC, and KOPRA - has been performed for a thermal infrared nadir sounding application assuming a HIRS-like (High resolution Infrared Radiation Sounder) setup. Radiances for the HIRS infrared channels and a set of 42 atmospheric profiles from the "Garand dataset" have been computed. Results of this intercomparison and a discussion of reasons of the observed differences are presented.

Characterization of cirrus clouds and atmospheric state using a new hyper-spectral optimal estimation retrieval

NASA Astrophysics Data System (ADS)

Veglio, P.; Holz, R.

2016-12-01

The importance of cirrus clouds as regulators of Earth's climate and radiation budget has been widely demonstrated, but still their characterization remains challenging. In order to derive cirrus properties, many retrieval techniques rely on prior assumptions on the atmospheric state or on the ice microphysics, either because the computational cost is too high or because the measurements do not have enough information, as in the case of broadband sensors. In this work we present a novel infrared hyper-spectral optimal estimation retrieval capable of simultaneously deriving cirrus cloud parameters (optical depth, effective radius, cloud top height) and atmospheric state (temperature and water vapor profiles) with their associated uncertainties by using a fast forward radiative transfer code. The use of hyperspectral data help overcoming the problem of the information content while the computational cost can be addressed by using a fast radiative transfer model. The tradeoff of this choice is an increasing in the complexity of the problem. Also, it is important to consider that by using a fast, approximate radiative transfer model, the uncertainties must be carefully evaluated in order to prevent or minimize any biases that could negatively affect the results. For this application data from the HS3 field campaign are used, which provide high quality hyper-spectral measurements from Scanning HIS along with CPL and possibly also dropsonde data and GDAS reanalysis to help validate the results. The future of this work will be to move from aircraft to satellite observations, and the natural choice is AIRS and CALIOP that offer a similar setup to what is currently used for this study.

Current Status on the use of Parallel Computing in Turbulent Reacting Flow Computations Involving Sprays, Monte Carlo PDF and Unstructured Grids. Chapter 4

NASA Technical Reports Server (NTRS)

Raju, M. S.

1998-01-01

The state of the art in multidimensional combustor modeling as evidenced by the level of sophistication employed in terms of modeling and numerical accuracy considerations, is also dictated by the available computer memory and turnaround times afforded by present-day computers. With the aim of advancing the current multi-dimensional computational tools used in the design of advanced technology combustors, a solution procedure is developed that combines the novelty of the coupled CFD/spray/scalar Monte Carlo PDF (Probability Density Function) computations on unstructured grids with the ability to run on parallel architectures. In this approach, the mean gas-phase velocity and turbulence fields are determined from a standard turbulence model, the joint composition of species and enthalpy from the solution of a modeled PDF transport equation, and a Lagrangian-based dilute spray model is used for the liquid-phase representation. The gas-turbine combustor flows are often characterized by a complex interaction between various physical processes associated with the interaction between the liquid and gas phases, droplet vaporization, turbulent mixing, heat release associated with chemical kinetics, radiative heat transfer associated with highly absorbing and radiating species, among others. The rate controlling processes often interact with each other at various disparate time 1 and length scales. In particular, turbulence plays an important role in determining the rates of mass and heat transfer, chemical reactions, and liquid phase evaporation in many practical combustion devices.

Case Studies of the Vertical Structure of the Direct Shortwave Aerosol Radiative Forcing During TARFOX

NASA Technical Reports Server (NTRS)

Redemann, J.; Turco, R. P.; Liou, K. N.; Hobbs, P. V.; Hartley, W. S.; Bergstrom, R. W.; Browell, E. V.; Russell, P. B.

2000-01-01

The vertical structure of aerosol-induced radiative flux changes in the Earth's troposphere affects local heating rates and thereby convective processes, the formation and lifetime of clouds, and hence the distribution of chemical constituents. We present observationally based estimates of the vertical structure of direct shortwave aerosol radiative forcing for two case studies from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) which took place on the U.S. east coast in July 1996. The aerosol radiative forcings are computed using the Fu-Liou broadband radiative transfer model. The aerosol optical properties used in the radiative transfer simulations are calculated from independent vertically resolved estimates of the complex aerosol indices of refraction in two to three distinct vertical layers, using profiles of in situ particle size distributions measured aboard the University of Washington research aircraft. Aerosol single-scattering albedos at 450 nm thus determined range from 0.9 to 0.985, while the asymmetry factor varies from 0.6 to 0.8. The instantaneous shortwave aerosol radiative forcings derived from the optical properties of the aerosols are of the order of -36 Wm(exp -2) at the top of the atmosphere and about -56 Wm(exp -2) at the surface for both case studies.

Validation experiments to determine radiation partitioning of heat flux to an object in a fully turbulent fire.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ricks, Allen; Blanchat, Thomas K.; Jernigan, Dann A.

2006-06-01

It is necessary to improve understanding and develop validation data of the heat flux incident to an object located within the fire plume for the validation of SIERRA/ FUEGO/SYRINX fire and SIERRA/CALORE. One key aspect of the validation data sets is the determination of the relative contribution of the radiative and convective heat fluxes. To meet this objective, a cylindrical calorimeter with sufficient instrumentation to measure total and radiative heat flux had been designed and fabricated. This calorimeter will be tested both in the controlled radiative environment of the Penlight facility and in a fire environment in the FLAME/Radiant Heatmore » (FRH) facility. Validation experiments are specifically designed for direct comparison with the computational predictions. Making meaningful comparisons between the computational and experimental results requires careful characterization and control of the experimental features or parameters used as inputs into the computational model. Validation experiments must be designed to capture the essential physical phenomena, including all relevant initial and boundary conditions. A significant question of interest to modeling heat flux incident to an object in or near a fire is the contribution of the radiation and convection modes of heat transfer. The series of experiments documented in this test plan is designed to provide data on the radiation partitioning, defined as the fraction of the total heat flux that is due to radiation.« less

A Novel Method for Estimating Shortwave Direct Radiative Effect of Above-cloud Aerosols over Ocean Using CALIOP and MODIS Data

NASA Technical Reports Server (NTRS)

Zhang, Z.; Meyer, K.; Platnick, S.; Oreopoulos, L.; Lee, D.; Yu, H.

2013-01-01

This paper describes an efficient and unique method for computing the shortwave direct radiative effect (DRE) of aerosol residing above low-level liquid-phase clouds using CALIOP and MODIS data. It accounts for the overlapping of aerosol and cloud rigorously by utilizing the joint histogram of cloud optical depth and cloud top pressure. Effects of sub-grid scale cloud and aerosol variations on DRE are accounted for. It is computationally efficient through using grid-level cloud and aerosol statistics, instead of pixel-level products, and a pre-computed look-up table in radiative transfer calculations. We verified that for smoke over the southeast Atlantic Ocean the method yields a seasonal mean instantaneous shortwave DRE that generally agrees with more rigorous pixel-level computation within 4%. We have also computed the annual mean instantaneous shortwave DRE of light-absorbing aerosols (i.e., smoke and polluted dust) over global ocean based on 4 yr of CALIOP and MODIS data. We found that the variability of the annual mean shortwave DRE of above-cloud light-absorbing aerosol is mainly driven by the optical depth of the underlying clouds.

A Novel Method for Estimating Shortwave Direct Radiative Effect of Above-Cloud Aerosols Using CALIOP and MODIS Data

NASA Technical Reports Server (NTRS)

Zhang, Z.; Meyer, K.; Platnick, S.; Oreopoulos, L.; Lee, D.; Yu, H.

2014-01-01

This paper describes an efficient and unique method for computing the shortwave direct radiative effect (DRE) of aerosol residing above low-level liquid-phase clouds using CALIOP and MODIS data. It accounts for the overlapping of aerosol and cloud rigorously by utilizing the joint histogram of cloud optical depth and cloud top pressure. Effects of sub-grid scale cloud and aerosol variations on DRE are accounted for. It is computationally efficient through using grid-level cloud and aerosol statistics, instead of pixel-level products, and a pre-computed look-up table in radiative transfer calculations. We verified that for smoke over the southeast Atlantic Ocean the method yields a seasonal mean instantaneous shortwave DRE that generally agrees with more rigorous pixel-level computation within 4. We have also computed the annual mean instantaneous shortwave DRE of light-absorbing aerosols (i.e., smoke and polluted dust) over global ocean based on 4 yr of CALIOP and MODIS data. We found that the variability of the annual mean shortwave DRE of above-cloud light-absorbing aerosol is mainly driven by the optical depth of the underlying clouds.

HELIOS: An Open-source, GPU-accelerated Radiative Transfer Code for Self-consistent Exoplanetary Atmospheres

NASA Astrophysics Data System (ADS)

Malik, Matej; Grosheintz, Luc; Mendonça, João M.; Grimm, Simon L.; Lavie, Baptiste; Kitzmann, Daniel; Tsai, Shang-Min; Burrows, Adam; Kreidberg, Laura; Bedell, Megan; Bean, Jacob L.; Stevenson, Kevin B.; Heng, Kevin

2017-02-01

We present the open-source radiative transfer code named HELIOS, which is constructed for studying exoplanetary atmospheres. In its initial version, the model atmospheres of HELIOS are one-dimensional and plane-parallel, and the equation of radiative transfer is solved in the two-stream approximation with nonisotropic scattering. A small set of the main infrared absorbers is employed, computed with the opacity calculator HELIOS-K and combined using a correlated-k approximation. The molecular abundances originate from validated analytical formulae for equilibrium chemistry. We compare HELIOS with the work of Miller-Ricci & Fortney using a model of GJ 1214b, and perform several tests, where we find: model atmospheres with single-temperature layers struggle to converge to radiative equilibrium; k-distribution tables constructed with ≳ 0.01 cm-1 resolution in the opacity function (≲ {10}3 points per wavenumber bin) may result in errors ≳ 1%-10% in the synthetic spectra; and a diffusivity factor of 2 approximates well the exact radiative transfer solution in the limit of pure absorption. We construct “null-hypothesis” models (chemical equilibrium, radiative equilibrium, and solar elemental abundances) for six hot Jupiters. We find that the dayside emission spectra of HD 189733b and WASP-43b are consistent with the null hypothesis, while the latter consistently underpredicts the observed fluxes of WASP-8b, WASP-12b, WASP-14b, and WASP-33b. We demonstrate that our results are somewhat insensitive to the choice of stellar models (blackbody, Kurucz, or PHOENIX) and metallicity, but are strongly affected by higher carbon-to-oxygen ratios. The code is publicly available as part of the Exoclimes Simulation Platform (exoclime.net).

3D optical digitation applied to orthodontics: analysis of unilateral cleft lip and palate in newborn infants

NASA Astrophysics Data System (ADS)

Canal, Fernando; Garcia-Mateos, Jorge; Rodriguez-Larena, Jorge; Rivera, Alejandro; Aparicio, E.

2000-12-01

Medical therapeutic applications using lasers involves understanding the light tissue interaction, in particular the rate ofphotochemical and thermal reactions. Tissue is composed ofa mix ofturbid media. Light propagation in turbid media can be described by the so-called Equation of Radiative Transfer, an integro-differential equation where scattering, absorption and internal reflection are significant factors in determining the light distribution in tissue. The Equation of Radiative Transfer however can not commonly be solved analytically.' In order to visualize and simulate the effects of laser light on heart tissues (myocardium) in relation to the treatment of irregular heart rates or so called arrhythmias, a fast interactive computer program has been developed in Java.

Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data

NASA Technical Reports Server (NTRS)

Barker, Howard W.; Kato, Serji; Wehr, T.

2012-01-01

The main point of this study was to use realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE satellite mission, was applied to CloudSat, CALIPSO, and MODIS satellite data thus producing 3D cloudy atmospheres measuring 60 km wide by 13,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances for each (1 km)2 column where then produced by a Monte Carlo photon transfer model run in both full 3D and independent column approximation mode (i.e., a 1D model).

Impact of anthropogenic aerosols on regional climate change in Beijing, China

NASA Astrophysics Data System (ADS)

Zhao, B.; Liou, K. N.; He, C.; Lee, W. L.; Gu, Y.; Li, Q.; Leung, L. R.

2015-12-01

Anthropogenic aerosols affect regional climate significantly through radiative (direct and semi-direct) and indirect effects, but the magnitude of these effects over megacities are subject to large uncertainty. In this study, we evaluated the effects of anthropogenic aerosols on regional climate change in Beijing, China using the online-coupled Weather Research and Forecasting/Chemistry Model (WRF/Chem) with the Fu-Liou-Gu radiation scheme and a spatial resolution of 4km. We further updated this radiation scheme with a geometric-optics surface-wave (GOS) approach for the computation of light absorption and scattering by black carbon (BC) particles in which aggregation shape and internal mixing properties are accounted for. In addition, we incorporated in WRF/Chem a 3D radiative transfer parameterization in conjunction with high-resolution digital data for city buildings and landscape to improve the simulation of boundary-layer, surface solar fluxes and associated sensible/latent heat fluxes. Preliminary simulated meteorological parameters, fine particles (PM2.5) and their chemical components agree well with observational data in terms of both magnitude and spatio-temporal variations. The effects of anthropogenic aerosols, including BC, on radiative forcing, surface temperature, wind speed, humidity, cloud water path, and precipitation are quantified on the basis of simulation results. With several preliminary sensitivity runs, we found that meteorological parameters and aerosol radiative effects simulated with the incorporation of improved BC absorption and 3-D radiation parameterizations deviate substantially from simulation results using the conventional homogeneous/core-shell configuration for BC and the plane-parallel model for radiative transfer. Understanding of the aerosol effects on regional climate change over megacities must consider the complex shape and mixing state of aerosol aggregates and 3D radiative transfer effects over city landscape.

Nonequilibrium air radiation (Nequair) program: User's manual

NASA Technical Reports Server (NTRS)

Park, C.

1985-01-01

A supplement to the data relating to the calculation of nonequilibrium radiation in flight regimes of aeroassisted orbital transfer vehicles contains the listings of the computer code NEQAIR (Nonequilibrium Air Radiation), its primary input data, and explanation of the user-supplied input variables. The user-supplied input variables are the thermodynamic variables of air at a given point, i.e., number densities of various chemical species, translational temperatures of heavy particles and electrons, and vibrational temperature. These thermodynamic variables do not necessarily have to be in thermodynamic equilibrium. The code calculates emission and absorption characteristics of air under these given conditions.

Transitional flow in thin tubes for space station freedom radiator

NASA Technical Reports Server (NTRS)

Loney, Patrick; Ibrahim, Mounir

1995-01-01

A two dimensional finite volume method is used to predict the film coefficients in the transitional flow region (laminar or turbulent) for the radiator panel tubes. The code used to perform this analysis is CAST (Computer Aided Simulation of Turbulent Flows). The information gathered from this code is then used to augment a Sinda85 model that predicts overall performance of the radiator. A final comparison is drawn between the results generated with a Sinda85 model using the Sinda85 provided transition region heat transfer correlations and the Sinda85 model using the CAST generated data.

A system for monitoring the radiation effects of a proton linear accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skorkin, V. M., E-mail: skorkin@inr.ru; Belyanski, K. L.; Skorkin, A. V.

2016-12-15

The system for real-time monitoring of radioactivity of a high-current proton linear accelerator detects secondary neutron emission from proton beam losses in transport channels and measures the activity of radionuclides in gas and aerosol emissions and the radiation background in the environment affected by a linear accelerator. The data provided by gamma, beta, and neutron detectors are transferred over a computer network to the central server. The system allows one to monitor proton beam losses, the activity of gas and aerosol emissions, and the radiation emission level of a linear accelerator in operation.

2-Dimensional B-Spline Algorithms with Applications to Ray Tracing in Media of Spatially-Varying Refractive Index

DTIC Science & Technology

2007-08-01

In the approach, photon trajectories are computed using a solution of the Eikonal equation (ray-tracing methods) rather than linear trajectories. The...coupling the radiative transport solution into heat transfer and damage models. 15. SUBJECT TERMS: B-Splines, Ray-Tracing, Eikonal Equation...multi-layer biological tissue model. In the approach, photon trajectories are computed using a solution of the Eikonal equation (ray-tracing methods

On the use of Lineal Energy Measurements to Estimate Linear Energy Transfer Spectra

NASA Technical Reports Server (NTRS)

Adams, David A.; Howell, Leonard W., Jr.; Adam, James H., Jr.

2007-01-01

This paper examines the error resulting from using a lineal energy spectrum to represent a linear energy transfer spectrum for applications in the space radiation environment. Lineal energy and linear energy transfer spectra are compared in three diverse but typical space radiation environments. Different detector geometries are also studied to determine how they affect the error. LET spectra are typically used to compute dose equivalent for radiation hazard estimation and single event effect rates to estimate radiation effects on electronics. The errors in the estimations of dose equivalent and single event rates that result from substituting lineal energy spectra for linear energy spectra are examined. It is found that this substitution has little effect on dose equivalent estimates in interplanetary quiet-time environment regardless of detector shape. The substitution has more of an effect when the environment is dominated by solar energetic particles or trapped radiation, but even then the errors are minor especially if a spherical detector is used. For single event estimation, the effect of the substitution can be large if the threshold for the single event effect is near where the linear energy spectrum drops suddenly. It is judged that single event rate estimates made from lineal energy spectra are unreliable and the use of lineal energy spectra for single event rate estimation should be avoided.

Effect of surface radiation on natural convection in an asymmetrically heated channel-chimney system

NASA Astrophysics Data System (ADS)

Nasri, Zied; Derouich, Youssef; Laatar, Ali Hatem; Balti, Jalloul

2018-05-01

In this paper, a more realistic numerical approach that takes into account the effect of surface radiation on the laminar air flow induced by natural convection in a channel-chimney system asymmetrically heated at uniform heat flux is used. The aim is to enrich the results given in Nasri et al. (Int J Therm Sci 90:122-134, 2015) by varying all the geometric parameters of the system and by taking into account the effect of surface radiation on the flows. The numerical results are first validated against experimental and numerical data available in the literature. The computations have allowed the determination of optimal configurations that maximize the mass flow rate and the convective heat transfer and minimize the heated wall temperatures. The analysis of the temperature fields with the streamlines and the pressure fields has helped to explain the effects of surface radiation and of the different thermo-geometrical parameters on the system performances to improve the mass flow rate and the heat transfer with respect to the simple channel. It is shown that the thermal performance of the channel-chimney system in terms of lower heated wall temperatures is little affected by the surface radiation. At the end, simple correlation equations have been proposed for quickly and easily predict the optimal configurations as well as the corresponding enhancement rates of the induced mass flow rate and the convective heat transfer.

A statewide teleradiology system reduces radiation exposure and charges in transferred trauma patients.

PubMed

Watson, Justin J J; Moren, Alexis; Diggs, Brian; Houser, Ben; Eastes, Lynn; Brand, Dawn; Bilyeu, Pamela; Schreiber, Martin; Kiraly, Laszlo

2016-05-01

Trauma transfer patients routinely undergo repeat imaging because of inefficiencies within the radiology system. In 2009, the virtual private network (VPN) telemedicine system was adopted throughout Oregon allowing virtual image transfer between hospitals. The startup cost was a nominal $3,000 per hospital. A retrospective review from 2007 to 2012 included 400 randomly selected adult trauma transfer patients based on a power analysis (200 pre/200 post). The primary outcome evaluated was reduction in repeat computed tomography (CT) scans. Secondary outcomes included cost savings, emergency department (ED) length of stay (LOS), and spared radiation. All data were analyzed using Mann-Whitney U and chi-square tests. P less than .05 indicated significance. Spared radiation was calculated as a weighted average per body region, and savings was calculated using charges obtained from Oregon Health and Science University radiology current procedural terminology codes. Four-hundred patients were included. Injury Severity Score, age, ED and overall LOS, mortality, trauma type, and gender were not statistically different between groups. The percentage of patients with repeat CT scans decreased after VPN implementation: CT abdomen (13.2% vs 2.8%, P < .01) and cervical spine (34.4% vs 18.2%, P < .01). Post-VPN, the total charges saved in 2012 for trauma transfer patients was $333,500, whereas the average radiation dose spared per person was 1.8 mSV. Length of stay in the ED for patients with Injury Severity Score less than 15 transferring to the ICU was decreased (P < .05). Implementation of a statewide teleradiology network resulted in fewer total repeat CT scans, significant savings, decrease in radiation exposure, and decreased LOS in the ED for patients with less complex injuries. The potential for health care savings by widespread adoption of a VPN is significant. Copyright © 2016 Elsevier Inc. All rights reserved.

Adiabatic Quantum Computation: Coherent Control Back Action.

PubMed

Goswami, Debabrata

2006-11-22

Though attractive from scalability aspects, optical approaches to quantum computing are highly prone to decoherence and rapid population loss due to nonradiative processes such as vibrational redistribution. We show that such effects can be reduced by adiabatic coherent control, in which quantum interference between multiple excitation pathways is used to cancel coupling to the unwanted, non-radiative channels. We focus on experimentally demonstrated adiabatic controlled population transfer experiments wherein the details on the coherence aspects are yet to be explored theoretically but are important for quantum computation. Such quantum computing schemes also form a back-action connection to coherent control developments.

Implementation of radiation shielding calculation methods. Volume 1: Synopsis of methods and summary of results

NASA Technical Reports Server (NTRS)

Capo, M. A.; Disney, R. K.

1971-01-01

The work performed in the following areas is summarized: (1) Analysis of Realistic nuclear-propelled vehicle was analyzed using the Marshall Space Flight Center computer code package. This code package includes one and two dimensional discrete ordinate transport, point kernel, and single scatter techniques, as well as cross section preparation and data processing codes, (2) Techniques were developed to improve the automated data transfer in the coupled computation method of the computer code package and improve the utilization of this code package on the Univac-1108 computer system. (3) The MSFC master data libraries were updated.

Training and Validation of the Fast PCRTM_Solar Model

NASA Astrophysics Data System (ADS)

Yang, Q.; Liu, X.; Wu, W.; Yang, P.; Wang, C.

2015-12-01

Fast and accurate radiative transfer model is the key for satellite data assimilation for remote sensing application. The simulation of the satellite remote sensing radiances is very complicated since many physical processes, such as absorption, emission, and scattering, are involved due to the interactions between electromagnetic radiation and earth surface, water vapor, clouds, aerosols, and gas molecules in the sky. The principal component-based radiative transfer model (PCRTM) has been developed for various passive IR and MW instruments. In this work, we extended PCRTM to including the contribution from solar radiation. The cloud/aerosol bidirectional reflectances have been carefully calculated using the well-known Discrete-Ordinate-Method Radiative Transfer (DISORT) model under over 10 millions of diverse conditions with varying cloud particle size, wavelength, satellite viewing direction, and solar angles. The obtained results were compressed significantly using principal component analysis and used in the mono domain radiance calculation. We used 1352 different atmosphere profiles, each of them has different surface skin temperatures and surface pressures in our training. Different surface emissivity spectra were derived from ASTER database and emissivity models. Some artificially generated emissivity spectra were also used to account for diverse surface types of the earth. Concentrations of sixteen trace gases were varied systematically in the training and the remaining trace gas contributions were accounted for as a fixed gas. Training was done in both clear and cloudy skies conditions. Finally the nonlocal thermal equilibrium (NLTE) induced radiance change was included for daytime conditions. We have updated the PCRTM model for instruments such as IASI, NASTI, CrIS, AIRS, and SHIS. The training results show that the PCRTM model can calculate thousands of channel radiances by computing only a few hundreds of mono radiances. This greatly increased the computation efficiency since we do not need to calculate the millions of mono radiances and do the convolution process. The results from fast PCRTM_Solar simulation were compared to the instrument observed data. The simulated results were excellently agreed with the observations.

Computational Model of the Modulation of Gene Expression Following DNA Damage

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Dicello, J. F.; Nikjoo, H.; Cherubini, R.

2002-01-01

High linear energy transfer (LET) radiation, such as heavy ions or neutrons, has an increased biological effectiveness compared to X rays for gene mutation, genomic instability, and carcinogenesis. In the traditional paradigm, mutations or chromosomal aberrations are causative of late effects. However, in recent years experimental evidence has demonstrated the important role of the description of the modification of gene expression by radiation in understanding the mechanisms of radiation action. In this report, approaches are discussed to the mathematical description of mRNA and protein expression kinetics following DNA damage. Several hypotheses for models of radiation modulation of protein expression are discussed including possible non-linear processes that evolve from the linear dose responses that follow the initial DNA damage produced by radiation.

Modeling UV Radiation Feedback from Massive Stars. I. Implementation of Adaptive Ray-tracing Method and Tests

NASA Astrophysics Data System (ADS)

Kim, Jeong-Gyu; Kim, Woong-Tae; Ostriker, Eve C.; Skinner, M. Aaron

2017-12-01

We present an implementation of an adaptive ray-tracing (ART) module in the Athena hydrodynamics code that accurately and efficiently handles the radiative transfer involving multiple point sources on a three-dimensional Cartesian grid. We adopt a recently proposed parallel algorithm that uses nonblocking, asynchronous MPI communications to accelerate transport of rays across the computational domain. We validate our implementation through several standard test problems, including the propagation of radiation in vacuum and the expansions of various types of H II regions. Additionally, scaling tests show that the cost of a full ray trace per source remains comparable to that of the hydrodynamics update on up to ∼ {10}3 processors. To demonstrate application of our ART implementation, we perform a simulation of star cluster formation in a marginally bound, turbulent cloud, finding that its star formation efficiency is 12% when both radiation pressure forces and photoionization by UV radiation are treated. We directly compare the radiation forces computed from the ART scheme with those from the M1 closure relation. Although the ART and M1 schemes yield similar results on large scales, the latter is unable to resolve the radiation field accurately near individual point sources.

Hyperfine excitation of C2H in collisions with ortho- and para-H2

NASA Astrophysics Data System (ADS)

Dagdigian, Paul J.

2018-06-01

Accurate estimation of the abundance of the ethynyl (C2H) radical requires accurate radiative and collisional rate coefficients. Hyperfine-resolved rate coefficients for (de-)excitation of C2H in collisions with ortho- and para-H2 are presented in this work. These rate coefficients were computed in time-independent close-coupling quantum scattering calculations that employed a potential energy surface recently computed at the coupled-clusters level of theory that describes the interaction of C2H with H2. Rate coefficients for temperatures from 10 to 300 K were computed for all transitions among the first 40 hyperfine energy levels of C2H in collisions with ortho- and para-H2. These rate coefficients were employed in simple radiative transfer calculations to simulate the excitation of C2H in typical molecular clouds.

Chapter 13. Exploring Use of the Reserved Core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holmen, John; Humphrey, Alan; Berzins, Martin

2015-07-29

In this chapter, we illustrate benefits of thinking in terms of thread management techniques when using a centralized scheduler model along with interoperability of MPI and PThread. This is facilitated through an exploration of thread placement strategies for an algorithm modeling radiative heat transfer with special attention to the 61st core. This algorithm plays a key role within the Uintah Computational Framework (UCF) and current efforts taking place at the University of Utah to model next-generation, large-scale clean coal boilers. In such simulations, this algorithm models the dominant form of heat transfer and consumes a large portion of compute time.more » Exemplified by a real-world example, this chapter presents our early efforts in porting a key portion of a scalability-centric codebase to the Intel Xeon Phi coprocessor. Specifically, this chapter presents results from our experiments profiling the native execution of a reverse Monte-Carlo ray tracing-based radiation model on a single coprocessor. These results demonstrate that our fastest run configurations utilized the 61st core and that performance was not profoundly impacted when explicitly oversubscribing the coprocessor operating system thread. Additionally, this chapter presents a portion of radiation model source code, a MIC-centric UCF cross-compilation example, and less conventional thread management technique for developers utilizing the PThreads threading model.« less

Radiative transfer and radiative driving of outflows in active galactic nuclei and starbursts

NASA Astrophysics Data System (ADS)

Novak, G. S.; Ostriker, J. P.; Ciotti, L.

2012-12-01

To facilitate the study of black hole fuelling, star formation and feedback in galaxies, we outline a method for treating the radial forces on interstellar gas due to absorption of photons by dust grains. The method gives the correct behaviour in all of the relevant limits [dominated by the central point source; dominated by the distributed isotropic source; optically thin; optically thick to ultraviolet (UV)/optical; optically thick to infrared (IR)] and reasonably interpolates between the limits when necessary. The method is explicitly energy conserving so that UV/optical photons that are absorbed are not lost, but are rather redistributed to the IR where they may scatter out of the galaxy. We implement the radiative transfer algorithm in a two-dimensional hydrodynamical code designed to study feedback processes in the context of early-type galaxies. We find that the dynamics and final state of simulations are measurably but only moderately affected by radiative forces on dust, even when assumptions about the dust-to-gas ratio are varied from zero to a value appropriate for the Milky Way. In simulations with high gas densities designed to mimic ultraluminous IR galaxies with a star formation rate of several hundred solar masses per year, dust makes a more substantial contribution to the dynamics and outcome of the simulation. We find that, despite the large opacity of dust to UV radiation, the momentum input to the flow from radiation very rarely exceeds L/c due to two factors: the low opacity of dust to the re-radiated IR and the tendency for dust to be destroyed by sputtering in hot gas environments. We also develop a simplification of our radiative transfer algorithm that respects the essential physics but is much easier to implement and requires a fraction of the computational cost.

Finite element computation of multi-physical micropolar transport phenomena from an inclined moving plate in porous media

NASA Astrophysics Data System (ADS)

Shamshuddin, MD.; Anwar Bég, O.; Sunder Ram, M.; Kadir, A.

2018-02-01

Non-Newtonian flows arise in numerous industrial transport processes including materials fabrication systems. Micropolar theory offers an excellent mechanism for exploring the fluid dynamics of new non-Newtonian materials which possess internal microstructure. Magnetic fields may also be used for controlling electrically-conducting polymeric flows. To explore numerical simulation of transport in rheological materials processing, in the current paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium. Heat generation/absorption effects are included. Rosseland's diffusion approximation is used to describe the radiative heat flux in the energy equation. A Darcy model is employed to simulate drag effects in the porous medium. The governing transport equations are rendered into non-dimensional form under the assumption of low Reynolds number and also low magnetic Reynolds number. Using a Galerkin formulation with a weighted residual scheme, finite element solutions are presented to the boundary value problem. The influence of plate inclination, Eringen coupling number, radiation-conduction number, heat absorption/generation parameter, chemical reaction parameter, plate moving velocity parameter, magnetic parameter, thermal Grashof number, species (solutal) Grashof number, permeability parameter, Eckert number on linear velocity, micro-rotation, temperature and concentration profiles. Furthermore, the influence of selected thermo-physical parameters on friction factor, surface heat transfer and mass transfer rate is also tabulated. The finite element solutions are verified with solutions from several limiting cases in the literature. Interesting features in the flow are identified and interpreted.

Machine learning based cloud mask algorithm driven by radiative transfer modeling

NASA Astrophysics Data System (ADS)

Chen, N.; Li, W.; Tanikawa, T.; Hori, M.; Shimada, R.; Stamnes, K. H.

2017-12-01

Cloud detection is a critically important first step required to derive many satellite data products. Traditional threshold based cloud mask algorithms require a complicated design process and fine tuning for each sensor, and have difficulty over snow/ice covered areas. With the advance of computational power and machine learning techniques, we have developed a new algorithm based on a neural network classifier driven by extensive radiative transfer modeling. Statistical validation results obtained by using collocated CALIOP and MODIS data show that its performance is consistent over different ecosystems and significantly better than the MODIS Cloud Mask (MOD35 C6) during the winter seasons over mid-latitude snow covered areas. Simulations using a reduced number of satellite channels also show satisfactory results, indicating its flexibility to be configured for different sensors.

Radiative flow of Carreau liquid in presence of Newtonian heating and chemical reaction

NASA Astrophysics Data System (ADS)

Hayat, T.; Ullah, Ikram; Ahmad, B.; Alsaedi, A.

Objective of this article is to investigate the magnetohydrodynamic (MHD) boundary layer stretched flow of Carreau fluid in the presence of Newtonian heating. Sheet is presumed permeable. Analysis is studied in the presence of chemical reaction and thermal radiation. Mathematical formulation is established by using the boundary layer approximations. The resultant nonlinear flow analysis is computed for the convergent solutions. Interval of convergence via numerical data and plots are obtained and verified. Impact of numerous pertinent variables on the velocity, temperature and concentration is outlined. Numerical data for surface drag coefficient, surface heat transfer (local Nusselt number) and mass transfer (local Sherwood number) is executed and inspected. Comparison of skin friction coefficient in limiting case is made for the verification of current derived solutions.

A review of the matrix-exponential formalism in radiative transfer

NASA Astrophysics Data System (ADS)

Efremenko, Dmitry S.; Molina García, Víctor; Gimeno García, Sebastián; Doicu, Adrian

2017-07-01

This paper outlines the matrix exponential description of radiative transfer. The eigendecomposition method which serves as a basis for computing the matrix exponential and for representing the solution in a discrete ordinate setting is considered. The mathematical equivalence of the discrete ordinate method, the matrix operator method, and the matrix Riccati equations method is proved rigorously by means of the matrix exponential formalism. For optically thin layers, approximate solution methods relying on the Padé and Taylor series approximations to the matrix exponential, as well as on the matrix Riccati equations, are presented. For optically thick layers, the asymptotic theory with higher-order corrections is derived, and parameterizations of the asymptotic functions and constants for a water-cloud model with a Gamma size distribution are obtained.

SIERRA Low Mach Module: Fuego User Manual Version 4.46.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierra Thermal/Fluid Team

2017-09-01

The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASCI fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the coremore » architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.« less

Fast forward modeling of Titan's infrared spectra to invert VIMS/Cassini hyperspectral images

USGS Publications Warehouse

Rodriguez, S.; Le Mouélic, Stéphane; Rannou, P.; Combe, J.-P.; Corre, L.L.; Tobie, G.; Barnes, J.W.; Sotin, Christophe; Brown, R.H.; Baines, K.H.; Buratti, B.J.; Clark, R.N.; Nicholson, P.D.

2009-01-01

The surface of Titan, the largest icy moon of Saturn, is veiled by a very thick and hazy atmosphere. The Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft, in orbit around Saturn since July 2004, conduct an intensive survey of Titan with the objective to understand the complex nature of the atmosphere and surface of the mysterious moon and the way they interact. Accurate radiative transfer modeling is necessary to analyze Titan's infrared spectra, but are often very computer resources demanding. As Cassini has gathered hitherto millions of spectra of Titan and will still observe it until at least 2010, we report here on the development of a new rapid, simple and versatile radiative transfer model specially designed to invert VIMS datacubes. ?? 2009 IEEE.

SIERRA Low Mach Module: Fuego Theory Manual Version 4.44

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierra Thermal /Fluid Team

2017-04-01

The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASCI fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the coremore » architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.« less

SIERRA Low Mach Module: Fuego Theory Manual Version 4.46.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierra Thermal/Fluid Team

The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASCI fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the coremore » architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.« less

Integration of Monte-Carlo ray tracing with a stochastic optimisation method: application to the design of solar receiver geometry.

PubMed

Asselineau, Charles-Alexis; Zapata, Jose; Pye, John

2015-06-01

A stochastic optimisation method adapted to illumination and radiative heat transfer problems involving Monte-Carlo ray-tracing is presented. A solar receiver shape optimisation case study illustrates the advantages of the method and its potential: efficient receivers are identified using a moderate computational cost.

Estimation of photosynthetically available radiation (PAR) from OCEANSAT-I OCM using a simple atmospheric radiative transfer model

NASA Astrophysics Data System (ADS)

Tripathy, Madhumita; Raman, Mini; Chauhan, Prakash

2015-10-01

Photosynthetically available radiation (PAR) is an important variable for radiation budget, marine and terrestrial ecosystem models. OCEANSAT-1 Ocean Color Monitor (OCM) PAR was estimated using two different methods under both clear and cloudy sky conditions. In the first approach, aerosol optical depth (AOD) and cloud optical depth (COD) were estimated from OCEANSAT-1 OCM TOA (top-of-atmosphere) radiance data on a pixel by pixel basis and PAR was estimated from extraterrestrial solar flux for fifteen spectral bands using a radiative transfer model. The second approach used TOA radiances measured by OCM in the PAR spectral range to compute PAR. This approach also included surface albedo and cloud albedo as inputs. Comparison between OCEANSAT-1 OCM PAR at noon with in situ measured PAR shows that root mean square difference was 5.82% for the method I and 7.24% for the method II in daily time scales. Results indicate that methodology adopted to estimate PAR from OCEANSAT-1 OCM can produce reasonably accurate PAR estimates over the tropical Indian Ocean region. This approach can be extended to OCEANSAT-2 OCM and future OCEANSAT-3 OCM data for operational estimation of PAR for regional marine ecosystem applications.

A Fast Visible-Infrared Imaging Radiometer Suite Simulator for Cloudy Atmopheres

NASA Technical Reports Server (NTRS)

Liu, Chao; Yang, Ping; Nasiri, Shaima L.; Platnick, Steven; Meyer, Kerry G.; Wang, Chen Xi; Ding, Shouguo

2015-01-01

A fast instrument simulator is developed to simulate the observations made in cloudy atmospheres by the Visible Infrared Imaging Radiometer Suite (VIIRS). The correlated k-distribution (CKD) technique is used to compute the transmissivity of absorbing atmospheric gases. The bulk scattering properties of ice clouds used in this study are based on the ice model used for the MODIS Collection 6 ice cloud products. Two fast radiative transfer models based on pre-computed ice cloud look-up-tables are used for the VIIRS solar and infrared channels. The accuracy and efficiency of the fast simulator are quantify in comparison with a combination of the rigorous line-by-line (LBLRTM) and discrete ordinate radiative transfer (DISORT) models. Relative errors are less than 2 for simulated TOA reflectances for the solar channels and the brightness temperature differences for the infrared channels are less than 0.2 K. The simulator is over three orders of magnitude faster than the benchmark LBLRTM+DISORT model. Furthermore, the cloudy atmosphere reflectances and brightness temperatures from the fast VIIRS simulator compare favorably with those from VIIRS observations.

Optimal low thrust geocentric transfer. [mission analysis computer program

NASA Technical Reports Server (NTRS)

Edelbaum, T. N.; Sackett, L. L.; Malchow, H. L.

1973-01-01

A computer code which will rapidly calculate time-optimal low thrust transfers is being developed as a mission analysis tool. The final program will apply to NEP or SEP missions and will include a variety of environmental effects. The current program assumes constant acceleration. The oblateness effect and shadowing may be included. Detailed state and costate equations are given for the thrust effect, oblateness effect, and shadowing. A simple but adequate model yields analytical formulas for power degradation due to the Van Allen radiation belts for SEP missions. The program avoids the classical singularities by the use of equinoctial orbital elements. Kryloff-Bogoliuboff averaging is used to facilitate rapid calculation. Results for selected cases using the current program are given.

Green's function solution to heat transfer of a transparent gas through a tube

NASA Technical Reports Server (NTRS)

Frankel, J. I.

1989-01-01

A heat transfer analysis of a transparent gas flowing through a circular tube of finite thickness is presented. This study includes the effects of wall conduction, internal radiative exchange, and convective heat transfer. The natural mathematical formulation produces a nonlinear, integrodifferential equation governing the wall temperature and an ordinary differential equation describing the gas temperature. This investigation proposes to convert the original system of equations into an equivalent system of integral equations. The Green's function method permits the conversion of an integrodifferential equation into a pure integral equation. The proposed integral formulation and subsequent computational procedure are shown to be stable and accurate.

A non-LTE study of silicon line formation in early-type main-sequence atmospheres.

NASA Technical Reports Server (NTRS)

Kamp, L. W.

1973-01-01

We have computed populations of 16 levels of Si III-V and radiation fields in all connecting transitions; in particular the first six Si III triplet levels, including the 4553 line, and the first six Si IV levels including 4089. The computations were done for four non-LTE H-He model atmospheres, provided by Auer and Mihalas. Estimates of corresponding MK types are B1.5 V, B0.5 V, O9 V, and O6. Solutions were obtained by iterating the linearized equations of radiative transfer and statistical equilibrium, except that for less important lines an approximate equivalent two-level atom treatment was used. Continuous opacities of C, N, O, and Ne were included. All abundances were solar values.

Optimization by means of an analytical heat transfer model of a thermal insulation for CSP applications based on radiative shields

NASA Astrophysics Data System (ADS)

Gaetano, A.; Roncolato, J.; Montorfano, D.; Barbato, M. C.; Ambrosetti, G.; Pedretti, A.

2016-05-01

The employment of new gaseous heat transfer fluids as air or CO2, which are cheaper and environmentally friendly, is drawing more and more attention within the field of Concentrated Solar Power applications. However, despite the advantages, their use requires receivers with a larger heat transfer area and flow cross section with a consequent greater volume of thermal insulation. Solid thermal insulations currently used present high thermal inertia which is energetically penalizing during the daily transient phases faced by the main plant components (e.g. receivers). With the aim of overcoming this drawback a thermal insulation based on radiative shields is presented in this study. Starting from an initial layout comprising a solid thermal insulation layer, the geometry was optimized avoiding the use of the solid insulation keeping performance and fulfilling the geometrical constraints. An analytical Matlab model was implemented to assess the system thermal behavior in terms of heat loss taking into account conductive, convective and radiative contributions. Accurate 2D Computational Fluid Dynamics (CFD) simulations were run to validate the Matlab model which was then used to select the most promising among three new different designs.

An Analysis and Procedure for Determining Space Environmental Sink Temperatures With Selected Computational Results

NASA Technical Reports Server (NTRS)

Juhasz, Albert J.

2001-01-01

The purpose of this report was to analyze the heat-transfer problem posed by the determination of spacecraft temperatures and to incorporate the theoretically derived relationships in the computational code TSCALC. The basis for the code was a theoretical analysis of the thermal radiative equilibrium in space, particularly in the Solar System. Beginning with the solar luminosity, the code takes into account these key variables: (1) the spacecraft-to-Sun distance expressed in astronomical units (AU), where 1 AU represents the average Sun-to-Earth distance of 149.6 million km; (2) the angle (arc degrees) at which solar radiation is incident upon a spacecraft surface (ILUMANG); (3) the spacecraft surface temperature (a radiator or photovoltaic array) in kelvin, the surface absorptivity-to-emissivity ratio alpha/epsilon with respect to the solar radiation and (alpha/epsilon)(sub 2) with respect to planetary radiation; and (4) the surface view factor to space F. Outputs from the code have been used to determine environmental temperatures in various Earth orbits. The code was also utilized as a subprogram in the design of power system radiators for deep-space probes.

Sensitivity of Cirrus Bidirectional Reflectance at MODIS Bands to Vertical Inhomogeneity of Ice Crystal Habits and Size Distribution

NASA Technical Reports Server (NTRS)

Yang, P.; Gao, B.-C.; Baum, B. A.; Wiscombe, W.; Hu, Y.; Nasiri, S. L.; Soulen, P. F.; Heymsfield, A. J.; McFarquhar, G. M.; Miloshevich, L. M.

2000-01-01

A common assumption in satellite imager-based cirrus retrieval algorithms is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal shape (or habit) and a single particle size distribution. However, observations of cirrus clouds have shown that the shapes and sizes of ice crystals may vary substantially with height within the clouds. In this study we investigate the sensitivity of the top-of-atmosphere bidirectional reflectances at two MODIS bands centered at 0.65 micron and 2.11 micron to the cirrus models assumed to be either a single homogeneous layer or three distinct but contiguous, layers. First, we define the single- and three-layer cirrus cloud models with respect to ice crystal habit and size distribution on the basis of in situ replicator data acquired during the First ISCCP Regional Experiment (FIRE-II), held in Kansas during the fall of 1991. Subsequently, fundamental light scattering and radiative transfer theory is employed to determine the single scattering and the bulk radiative properties of the cirrus cloud. Regarding the radiative transfer computations, we present a discrete form of the adding/doubling principle by introducing a direct transmission function, which is computationally straightforward and efficient an improvement over previous methods. For the 0.65 micron band, at which absorption by ice is negligible, there is little difference between the bidirectional reflectances calculated for the one- and three-layer cirrus models, suggesting that the vertical inhomogeneity effect is relatively unimportant. At the 2.11 micron band, the bidirectional reflectances computed for both optically thin (tau = 1) and thick (tau = 10) cirrus clouds show significant differences between the results for the one- and three-layer models. The reflectances computed for the three-layer cirrus model are substantially larger than those computed for the single-layer cirrus. Finally, we find that cloud reflectance is very sensitive to the optical properties of the small crystals that predominate in the top layer of the three-layer cirrus model. It is critical to define the most realistic geometric shape for the small "quasi-spherical" ice crystals in the top layer for obtaining reliable single-scattering parameters and bulk radiative properties of cirrus.

Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ito, Kota, E-mail: kotaito@mosk.tytlabs.co.jp; Nishikawa, Kazutaka; Iizuka, Hideo

Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO{sub 2}) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO{sub 2} film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

An asymptotic preserving unified gas kinetic scheme for frequency-dependent radiative transfer equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Wenjun, E-mail: sun_wenjun@iapcm.ac.cn; Jiang, Song, E-mail: jiang@iapcm.ac.cn; Xu, Kun, E-mail: makxu@ust.hk

This paper presents an extension of previous work (Sun et al., 2015 [22]) of the unified gas kinetic scheme (UGKS) for the gray radiative transfer equations to the frequency-dependent (multi-group) radiative transfer system. Different from the gray radiative transfer equations, where the optical opacity is only a function of local material temperature, the simulation of frequency-dependent radiative transfer is associated with additional difficulties from the frequency-dependent opacity. For the multiple frequency radiation, the opacity depends on both the spatial location and the frequency. For example, the opacity is typically a decreasing function of frequency. At the same spatial region themore » transport physics can be optically thick for the low frequency photons, and optically thin for high frequency ones. Therefore, the optical thickness is not a simple function of space location. In this paper, the UGKS for frequency-dependent radiative system is developed. The UGKS is a finite volume method and the transport physics is modeled according to the ratio of the cell size to the photon's frequency-dependent mean free path. When the cell size is much larger than the photon's mean free path, a diffusion solution for such a frequency radiation will be obtained. On the other hand, when the cell size is much smaller than the photon's mean free path, a free transport mechanism will be recovered. In the regime between the above two limits, with the variation of the ratio between the local cell size and photon's mean free path, the UGKS provides a smooth transition in the physical and frequency space to capture the corresponding transport physics accurately. The seemingly straightforward extension of the UGKS from the gray to multiple frequency radiation system is due to its intrinsic consistent multiple scale transport modeling, but it still involves lots of work to properly discretize the multiple groups in order to design an asymptotic preserving (AP) scheme in all regimes. The current scheme is tested in a few frequency-dependent radiation problems, and the results are compared with the solutions from the well-defined implicit Monte Carlo (IMC) method. The UGKS is much more efficient than IMC, and the computational times of both schemes for all test cases are listed. The UGKS seems to be the first discrete ordinate method (DOM) for the accurate capturing of multiple frequency radiative transport physics from ballistic particle motion to the diffusive wave propagation.« less

A simple method for computing the relativistic Compton scattering kernel for radiative transfer

NASA Technical Reports Server (NTRS)

Prasad, M. K.; Kershaw, D. S.; Beason, J. D.

1986-01-01

Correct computation of the Compton scattering kernel (CSK), defined to be the Klein-Nishina differential cross section averaged over a relativistic Maxwellian electron distribution, is reported. The CSK is analytically reduced to a single integral, which can then be rapidly evaluated using a power series expansion, asymptotic series, and rational approximation for sigma(s). The CSK calculation has application to production codes that aim at understanding certain astrophysical, laser fusion, and nuclear weapons effects phenomena.

Single-footprint retrievals for AIRS using a fast TwoSlab cloud-representation model and the SARTA all-sky infrared radiative transfer algorithm

NASA Astrophysics Data System (ADS)

DeSouza-Machado, Sergio; Larrabee Strow, L.; Tangborn, Andrew; Huang, Xianglei; Chen, Xiuhong; Liu, Xu; Wu, Wan; Yang, Qiguang

2018-01-01

One-dimensional variational retrievals of temperature and moisture fields from hyperspectral infrared (IR) satellite sounders use cloud-cleared radiances (CCRs) as their observation. These derived observations allow the use of clear-sky-only radiative transfer in the inversion for geophysical variables but at reduced spatial resolution compared to the native sounder observations. Cloud clearing can introduce various errors, although scenes with large errors can be identified and ignored. Information content studies show that, when using multilayer cloud liquid and ice profiles in infrared hyperspectral radiative transfer codes, there are typically only 2-4 degrees of freedom (DOFs) of cloud signal. This implies a simplified cloud representation is sufficient for some applications which need accurate radiative transfer. Here we describe a single-footprint retrieval approach for clear and cloudy conditions, which uses the thermodynamic and cloud fields from numerical weather prediction (NWP) models as a first guess, together with a simple cloud-representation model coupled to a fast scattering radiative transfer algorithm (RTA). The NWP model thermodynamic and cloud profiles are first co-located to the observations, after which the N-level cloud profiles are converted to two slab clouds (TwoSlab; typically one for ice and one for water clouds). From these, one run of our fast cloud-representation model allows an improvement of the a priori cloud state by comparing the observed and model-simulated radiances in the thermal window channels. The retrieval yield is over 90 %, while the degrees of freedom correlate with the observed window channel brightness temperature (BT) which itself depends on the cloud optical depth. The cloud-representation and scattering package is benchmarked against radiances computed using a maximum random overlap (RMO) cloud scheme. All-sky infrared radiances measured by NASA's Atmospheric Infrared Sounder (AIRS) and NWP thermodynamic and cloud profiles from the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast model are used in this paper.

Impact of heat source/sink on radiative heat transfer to Maxwell nanofluid subject to revised mass flux condition

NASA Astrophysics Data System (ADS)

Khan, M.; Irfan, M.; Khan, W. A.

2018-06-01

Nanofluids retain noteworthy structure that have absorbed attentions of numerous investigators because of their exploration in nanotechnology and nanoscience. In this scrutiny a mathematical computation of 2D flows of Maxwell nanoliquid influenced by a stretched cylinder has been established. The heat transfer structure is conceded out in the manifestation of thermal radiation and heat source/sink. Moreover, the nanoparticles mass flux condition is engaged in this exploration. This newly endorsed tactic is more realistic where the conjecture is made that the nanoparticle flux is zero and nanoparticle fraction regulates itself on the restrictions consequently. By utilizing apposite conversion the governing PDEs are transformed into ODEs and then tackled analytically via HAM. The attained outcomes are plotted and deliberated in aspect for somatic parameters. It is remarked that with an intensification in the Deborah number β diminish the liquid temperature while it boosts for radiation parameter Rd . Furthermore, the concentration of Maxwell liquid has conflicting impact for Brownian motion Nb and thermophoresis parameters Nt .

CTRANS: A Monte Carlo program for radiative transfer in plane parallel atmospheres with imbedded finite clouds: Development, testing and user's guide

NASA Technical Reports Server (NTRS)

1976-01-01

The program called CTRANS is described which was designed to perform radiative transfer computations in an atmosphere with horizontal inhomogeneities (clouds). Since the atmosphere-ground system was to be richly detailed, the Monte Carlo method was employed. This means that results are obtained through direct modeling of the physical process of radiative transport. The effects of atmopheric or ground albedo pattern detail are essentially built up from their impact upon the transport of individual photons. The CTRANS program actually tracks the photons backwards through the atmosphere, initiating them at a receiver and following them backwards along their path to the Sun. The pattern of incident photons generated through backwards tracking automatically reflects the importance to the receiver of each region of the sky. Further, through backwards tracking, the impact of the finite field of view of the receiver and variations in its response over the field of view can be directly simulated.

Solution of magnetohydrodynamic flow and heat transfer of radiative viscoelastic fluid with temperature dependent viscosity in wire coating analysis

PubMed Central

Khan, Muhammad Altaf; Siddiqui, Nasir; Ullah, Murad; Shah, Qayyum

2018-01-01

Wire coating process is a continuous extrusion process for primary insulation of conducting wires with molten polymers for mechanical strength and protection in aggressive environments. In the present study, radiative melt polymer satisfying third grade fluid model is used for wire coating process. The effect of magnetic parameter, thermal radiation parameter and temperature dependent viscosity on wire coating analysis has been investigated. Reynolds model and Vogel’s models have been incorporated for variable viscosity. The governing equations characterizing the flow and heat transfer phenomena are solved analytically by utilizing homotopy analysis method (HAM). The computed results are also verified by ND-Solve method (Numerical technique) and Adomian Decomposition Method (ADM). The effect of pertinent parameters is shown graphically. In addition, the instability of the flow in the flows of the wall of the extrusion die is well marked in the case of the Vogel model as pointed by Nhan-Phan-Thien. PMID:29596448

3D Radiative Transfer in Cloudy Atmospheres

NASA Astrophysics Data System (ADS)

Marshak, Alexander; Davis, Anthony

Developments in three-dimensional cloud radiation over the past few decades are assessed and distilled into this contributed volume. Chapters are authored by subject-matter experts who address a broad audience of graduate students, researchers, and anyone interested in cloud-radiation processes in the solar and infrared spectral regions. After two introductory chapters and a section on the fundamental physics and computational techniques, the volume extensively treats two main application areas: the impact of clouds on the Earth's radiation budget, which is an essential aspect of climate modeling; and remote observation of clouds, especially with the advanced sensors on current and future satellite missions. http://www.springeronline.com/alert/article?a=3D1_1fva7w_1j826l_41z_6

Estimation of land photosynthetically active radiation in clear sky using MODIS atmosphere and land products

NASA Astrophysics Data System (ADS)

Xie, Xiaoping; Gao, Wei; Gao, Zhiqiang

2008-08-01

Photosynthetically active radiation (PAR) is an essential parameter in vegetation growth model and soil carbon sequestration models. A method is presented with which instantaneous PAR can be calculated with high accuracy from Moderate Resolution Imaging Spectroradiometer (MODIS) atmosphere and land products. The method is based on a simplification of the general radiative transfer equation, which considers five major processes of attenuation of solar radiation: Rayleigh scattering, absorption by ozone and water vapor, aerosol scattering, multiply reflectance between surface and atmosphere. Comparing 108 retrieveled results to filed measured PAR in Yucheng station of Chinese Ecosystem Research Network (CERN) in 2006, and the r-square of 0.855 indicates that the computed results can interpret actual PAR well.

A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5

NASA Astrophysics Data System (ADS)

Hsu, Juno; Prather, Michael J.; Cameron-Smith, Philip; Veidenbaum, Alex; Nicolau, Alex

2017-07-01

Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18-0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere.The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20-40 % depending on the solar zenith angles and occur throughout the atmosphere.Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components - wavelength integration, scattering, and averaging over cloud fields - all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.

A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, Juno; Prather, Michael J.; Cameron-Smith, Philip

Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. Themore » spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere. Furthermore, the Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. Here, we compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere. Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.« less

A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5

DOE PAGES

Hsu, Juno; Prather, Michael J.; Cameron-Smith, Philip; ...

2017-01-01

Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. Themore » spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere. Furthermore, the Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. Here, we compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere. Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.« less

Pushing, pulling and electromagnetic radiation force cloaking by a pair of conducting cylindrical particles

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2018-02-01

The present analysis shows that two conducting cylindrical particles illuminated by an axially-polarized electric field of plane progressive waves at arbitrary incidence will attract, repel or become totally cloaked (i.e., invisible to the transfer of linear momentum carried by the incident waves), depending on their sizes, the interparticle distance as well as the angle of incidence of the incident field. Based on the rigorous multipole expansion method and the translational addition theorem of cylindrical wave functions, the electromagnetic (EM) radiation forces arising from multiple scattering effects between a pair of perfectly conducting cylindrical particles of circular cross-sections are derived and computed. An effective incident field on a particular particle is determined first, and used subsequently with its corresponding scattered field to derive the closed-form analytical expressions for the radiation force vector components. The mathematical expressions for the EM radiation force components (i.e. longitudinal and transverse) are exact, and have been formulated in partial-wave series expansions in cylindrical coordinates involving the angle of incidence, the interparticle distance and the expansion coefficients. Numerical examples illustrate the analysis for two perfectly conducting circular cylinders in a homogeneous nonmagnetic medium of wave propagation. The computations for the dimensionless radiation force functions are performed with particular emphasis on varying the angle of incidence, the interparticle distance, and the sizes of the particles. Depending on the interparticle distance and angle of incidence, the cylinders yield total neutrality (or invisibility); they experience no force and become unresponsive to the transfer of the EM linear momentum due to multiple scattering cancellation effects. Moreover, pushing or pulling EM forces between the two cylinders arise depending on the interparticle distance, the angle of incidence and their size parameters. This study provides a complete analytical method and computations for the longitudinal and transverse radiation force components in the multiple scattering of EM plane progressive waves with potential applications in particle manipulation, optically-engineered metamaterials with reconfigurable periodicities and cloaking devices to name a few examples.

Surveys of research in the Chemistry Division, Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grazis, B.M.

1992-01-01

Research reports are presented on reactive intermediates in condensed phase (radiation chemistry, photochemistry), electron transfer and energy conversion, photosynthesis and solar energy conversion, metal cluster chemistry, chemical dynamics in gas phase, photoionization-photoelectrons, characterization and reactivity of coal and coal macerals, premium coal sample program, chemical separations, heavy elements coordination chemistry, heavy elements photophysics/photochemistry, f-electron interactions, radiation chemistry of high-level wastes (gas generation in waste tanks), ultrafast molecular electronic devices, and nuclear medicine. Separate abstracts have been prepared. Accelerator activites and computer system/network services are also reported.

Surveys of research in the Chemistry Division, Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grazis, B.M.

1992-11-01

Research reports are presented on reactive intermediates in condensed phase (radiation chemistry, photochemistry), electron transfer and energy conversion, photosynthesis and solar energy conversion, metal cluster chemistry, chemical dynamics in gas phase, photoionization-photoelectrons, characterization and reactivity of coal and coal macerals, premium coal sample program, chemical separations, heavy elements coordination chemistry, heavy elements photophysics/photochemistry, f-electron interactions, radiation chemistry of high-level wastes (gas generation in waste tanks), ultrafast molecular electronic devices, and nuclear medicine. Separate abstracts have been prepared. Accelerator activites and computer system/network services are also reported.

Transient thermal modeling of the nonscanning ERBE detector

NASA Technical Reports Server (NTRS)

Mahan, J. R.

1983-01-01

A numerical model to predict the transient thermal response of the ERBE nonscanning wide field of view total radiometer channel was developed. The model, which uses Monte Carlo techniques to characterize the radiative component of heat transfer, is described and a listing of the computer program is provided. Application of the model to simulate the actual blackbody calibration procedure is discussed. The use of the model to establish a real time flight data interpretation strategy is recommended. Modification of the model to include a simulated Earth radiation source field and a filter dome is indicated.

FESTR: Finite-Element Spectral Transfer of Radiation spectroscopic modeling and analysis code

DOE PAGES

Hakel, Peter

2016-10-01

Here we report on the development of a new spectral postprocessor of hydrodynamic simulations of hot, dense plasmas. Based on given time histories of one-, two-, and three-dimensional spatial distributions of materials, and their local temperature and density conditions, spectroscopically-resolved signals are computed. The effects of radiation emission and absorption by the plasma on the emergent spectra are simultaneously taken into account. This program can also be used independently of hydrodynamic calculations to analyze available experimental data with the goal of inferring plasma conditions.

Calculation of TIR Canopy Hot Spot and Implications for Earth Radiation Budget

NASA Technical Reports Server (NTRS)

Smith, J. A.; Ballard, J. R., Jr.

2000-01-01

Using a 3-D model for thermal infrared exitance and the Lowtran 7 atmospheric radiative transfer model, we compute the variation in brightness temperature with view direction and, in particular, the canopy thermal hot spot. We then perform a sensitivity analysis of surface energy balance components for a nominal case using a simple SVAT model given the uncertainty in canopy temperature arising from the thermal hot spot effect. Canopy thermal hot spot variations of two degrees C lead to differences of plus or minus 24% in the midday available energy.

FESTR: Finite-Element Spectral Transfer of Radiation spectroscopic modeling and analysis code

NASA Astrophysics Data System (ADS)

Hakel, Peter

2016-10-01

We report on the development of a new spectral postprocessor of hydrodynamic simulations of hot, dense plasmas. Based on given time histories of one-, two-, and three-dimensional spatial distributions of materials, and their local temperature and density conditions, spectroscopically-resolved signals are computed. The effects of radiation emission and absorption by the plasma on the emergent spectra are simultaneously taken into account. This program can also be used independently of hydrodynamic calculations to analyze available experimental data with the goal of inferring plasma conditions.

Comparison of DSMC and CFD Solutions of Fire II Including Radiative Heating

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Johnston, Christopher O.; Lewis, Mark J.

2011-01-01

The ability to compute rarefied, ionized hypersonic flows is becoming more important as missions such as Earth reentry, landing high mass payloads on Mars, and the exploration of the outer planets and their satellites are being considered. These flows may also contain significant radiative heating. To prepare for these missions, NASA is developing the capability to simulate rarefied, ionized flows and to then calculate the resulting radiative heating to the vehicle's surface. In this study, the DSMC codes DAC and DS2V are used to obtain charge-neutral ionization solutions. NASA s direct simulation Monte Carlo code DAC is currently being updated to include the ability to simulate charge-neutral ionized flows, take advantage of the recently introduced Quantum-Kinetic chemistry model, and to include electronic energy levels as an additional internal energy mode. The Fire II flight test is used in this study to assess these new capabilities. The 1634 second data point was chosen for comparisons to be made in order to include comparisons to computational fluid dynamics solutions. The Knudsen number at this point in time is such that the DSMC simulations are still tractable and the CFD computations are at the edge of what is considered valid. It is shown that there can be quite a bit of variability in the vibrational temperature inferred from DSMC solutions and that, from how radiative heating is computed, the electronic temperature is much better suited for radiative calculations. To include the radiative portion of heating, the flow-field solutions are post-processed by the non-equilibrium radiation code HARA. Acceptable agreement between CFD and DSMC flow field solutions is demonstrated and the progress of the updates to DAC, along with an appropriate radiative heating solution, are discussed. In addition, future plans to generate more high fidelity radiative heat transfer solutions are discussed.

Aerosol Radiative Forcing over North India during Pre-Monsoon Season using WRF-Chem

NASA Astrophysics Data System (ADS)

Misra, A.; Kumar, K.; Michael, M.; Tripathi, S. N.

2013-12-01

Study of aerosols is important for a fair understanding of the Earth climate system. This requires knowledge of the physical, chemical, optical, and morphological properties of aerosols. Aerosol radiative forcing provides information on the effect of aerosols on the Earth radiation budget. Radiative forcing estimates using model data provide an opportunity to examine the contribution of individual aerosol species to overall radiative forcing. We have used Weather Research and Forecast with Online Chemistry (WRF-Chem) derived aerosol concentration data to compute aerosol radiative forcing over north India during pre-monsoon season of 2008, 2009, and 2010. WRF-Chem derived mass concentrations are converted to number concentrations using standard procedure. Optical Properties of Aerosol and Cloud (OPAC) software package is used to compute extinction and scattering coefficients, and asymmetry parameter. Computations are performed at different altitudes and the obtained values are integrated to get the column optical properties. Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model is used to calculate the radiative forcing at surface and top-of-atmosphere. Higher values of aerosol radiative forcing are observed over desert region in western Indian state of Rajasthan, and Punjab of Pakistan. Contribution of individual aerosol species to atmospheric radiative forcing is also assessed. Dust radiative forcing is high over western India. Radiative forcing due to BC and water-soluble (WASO) aerosols are higher over north-west Indian states of Punjab and Haryana, and the Indo-Gangetic Basin. A pool of high WASO optical depth and radiative forcing is observed over the Indo-Bangladesh border. The findings of aerosol optical depth and radiative forcing are consistent with the geography and prevailing aerosol climatology of various regions. Heating rate profiles due to total aerosols and only due to BC have been evaluated at selected stations in north India. They show variation between various stations and seasons.

FluorWPS: A Monte Carlo ray-tracing model to compute sun-induced chlorophyll fluorescence of three-dimensional canopy

USDA-ARS?s Scientific Manuscript database

A model to simulate radiative transfer (RT) of sun-induced chlorophyll fluorescence (SIF) of three-dimensional (3-D) canopy, FluorWPS, was proposed and evaluated. The inclusion of fluorescence excitation was implemented with the ‘weight reduction’ and ‘photon spread’ concepts based on Monte Carlo ra...

AOI 1— COMPUTATIONAL ENERGY SCIENCES:MULTIPHASE FLOW RESEARCH High-fidelity multi-phase radiation module for modern coal combustion systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Modest, Michael

The effects of radiation in particle-laden flows were the object of the present research. The presence of particles increases optical thickness substantially, making the use of the “optically thin” approximation in most cases a very poor assumption. However, since radiation fluxes peak at intermediate optical thicknesses, overall radiative effects may not necessarily be stronger than in gas combustion. Also, the spectral behavior of particle radiation properties is much more benign, making spectral models simpler (and making the assumption of a gray radiator halfway acceptable, at least for fluidized beds when gas radiation is not large). On the other hand, particlesmore » scatter radiation, making the radiative transfer equation (RTE) much more di fficult to solve. The research carried out in this project encompassed three general areas: (i) assessment of relevant radiation properties of particle clouds encountered in fluidized bed and pulverized coal combustors, (ii) development of proper spectral models for gas–particulate mixtures for various types of two-phase combustion flows, and (iii) development of a Radiative Transfer Equation (RTE) solution module for such applications. The resulting models were validated against artificial cases since open literature experimental data were not available. The final models are in modular form tailored toward maximum portability, and were incorporated into two research codes: (i) the open-source CFD code OpenFOAM, which we have extensively used in our previous work, and (ii) the open-source multi-phase flow code MFIX, which is maintained by NETL.« less

Effects of magnetic, radiation and chemical reaction on unsteady heat and mass transfer flow of an oscillating cylinder

NASA Astrophysics Data System (ADS)

Ahmed, Rubel; Rana, B. M. Jewel; Ahmmed, S. F.

2017-06-01

The effects of magnetic, radiation and chemical reaction parameters on the unsteady heat and mass transfer boundary layer flow past an oscillating cylinder is considered. The dimensionless momentum, energy and concentration equations are solved numerically by using explicit finite difference method with the help of a computer programming language Compaq visual FORTRAN 6.6a. The obtained results of this study have been discussed for different values of well-known parameters with different time steps. The effect of these parameters on the velocity field, temperature field and concentration field, skin-friction, Nusselt number, streamlines and isotherms has been studied and results are presented by graphically represented by the tabular form quantitatively. The stability and convergence analysis of the solution parameters that have been used in the mathematical model have been tested.

Python Radiative Transfer Emission code (PyRaTE): non-LTE spectral lines simulations

NASA Astrophysics Data System (ADS)

Tritsis, A.; Yorke, H.; Tassis, K.

2018-05-01

We describe PyRaTE, a new, non-local thermodynamic equilibrium (non-LTE) line radiative transfer code developed specifically for post-processing astrochemical simulations. Population densities are estimated using the escape probability method. When computing the escape probability, the optical depth is calculated towards all directions with density, molecular abundance, temperature and velocity variations all taken into account. A very easy-to-use interface, capable of importing data from simulations outputs performed with all major astrophysical codes, is also developed. The code is written in PYTHON using an "embarrassingly parallel" strategy and can handle all geometries and projection angles. We benchmark the code by comparing our results with those from RADEX (van der Tak et al. 2007) and against analytical solutions and present case studies using hydrochemical simulations. The code will be released for public use.

New numerical method for radiation heat transfer in nonhomogeneous participating media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howell, J.R.; Tan, Zhiqiang

A new numerical method, which solves the exact integral equations of distance-angular integration form for radiation transfer, is introduced in this paper. By constructing and prestoring the numerical integral formulas for the distance integral for appropriate kernel functions, this method eliminates the time consuming evaluations of the kernels of the space integrals in the formal computations. In addition, when the number of elements in the system is large, the resulting coefficient matrix is quite sparse. Thus, either considerable time or much storage can be saved. A weakness of the method is discussed, and some remedies are suggested. As illustrations, somemore » one-dimensional and two-dimensional problems in both homogeneous and inhomogeneous emitting, absorbing, and linear anisotropic scattering media are studied. Some results are compared with available data. 13 refs.« less

Optical properties reconstruction using the adjoint method based on the radiative transfer equation

NASA Astrophysics Data System (ADS)

Addoum, Ahmad; Farges, Olivier; Asllanaj, Fatmir

2018-01-01

An efficient algorithm is proposed to reconstruct the spatial distribution of optical properties in heterogeneous media like biological tissues. The light transport through such media is accurately described by the radiative transfer equation in the frequency-domain. The adjoint method is used to efficiently compute the objective function gradient with respect to optical parameters. Numerical tests show that the algorithm is accurate and robust to retrieve simultaneously the absorption μa and scattering μs coefficients for lowly and highly absorbing medium. Moreover, the simultaneous reconstruction of μs and the anisotropy factor g of the Henyey-Greenstein phase function is achieved with a reasonable accuracy. The main novelty in this work is the reconstruction of g which might open the possibility to image this parameter in tissues as an additional contrast agent in optical tomography.

Nonlinear Gravitational and Radiation Aspects in Nanoliquid with Exponential Space Dependent Heat Source and Variable Viscosity

NASA Astrophysics Data System (ADS)

Gireesha, B. J.; Kumar, P. B. Sampath; Mahanthesh, B.; Shehzad, S. A.; Abbasi, F. M.

2018-05-01

The nonlinear convective flow of kerosene-Alumina nanoliquid subjected to an exponential space dependent heat source and temperature dependent viscosity is investigated here. This study is focuses on augmentation of heat transport rate in liquid propellant rocket engine. The kerosene-Alumina nanoliquid is considered as the regenerative coolant. Aspects of radiation and viscous dissipation are also covered. Relevant nonlinear system is solved numerically via RK based shooting scheme. Diverse flow fields are computed and examined for distinct governing variables. We figured out that the nanoliquid's temperature increased due to space dependent heat source and radiation aspects. The heat transfer rate is higher in case of changeable viscosity than constant viscosity.

Numerical study of Free Convective Viscous Dissipative flow along Vertical Cone with Influence of Radiation using Network Simulation method

NASA Astrophysics Data System (ADS)

Kannan, R. M.; Pullepu, Bapuji; Immanuel, Y.

2018-04-01

A two dimensional mathematical model is formulated for the transient laminar free convective flow with heat transfer over an incompressible viscous fluid past a vertical cone with uniform surface heat flux with combined effects of viscous dissipation and radiation. The dimensionless boundary layer equations of the flow which are transient, coupled and nonlinear Partial differential equations are solved using the Network Simulation Method (NSM), a powerful numerical technique which demonstrates high efficiency and accuracy by employing the network simulator computer code Pspice. The velocity and temperature profiles have been investigated for various factors, namely viscous dissipation parameter ε, Prandtl number Pr and radiation Rd are analyzed graphically.

Nonlinear Gravitational and Radiation Aspects in Nanoliquid with Exponential Space Dependent Heat Source and Variable Viscosity

NASA Astrophysics Data System (ADS)

Gireesha, B. J.; Kumar, P. B. Sampath; Mahanthesh, B.; Shehzad, S. A.; Abbasi, F. M.

2018-02-01

The nonlinear convective flow of kerosene-Alumina nanoliquid subjected to an exponential space dependent heat source and temperature dependent viscosity is investigated here. This study is focuses on augmentation of heat transport rate in liquid propellant rocket engine. The kerosene-Alumina nanoliquid is considered as the regenerative coolant. Aspects of radiation and viscous dissipation are also covered. Relevant nonlinear system is solved numerically via RK based shooting scheme. Diverse flow fields are computed and examined for distinct governing variables. We figured out that the nanoliquid's temperature increased due to space dependent heat source and radiation aspects. The heat transfer rate is higher in case of changeable viscosity than constant viscosity.

The Effect of Cumulus Cloud Field Anisotropy on Domain-Averaged Solar Fluxes and Atmospheric Heating Rates

NASA Technical Reports Server (NTRS)

Hinkelman, Laura M.; Evans, K. Franklin; Clothiaux, Eugene E.; Ackerman, Thomas P.; Stackhouse, Paul W., Jr.

2006-01-01

Cumulus clouds can become tilted or elongated in the presence of wind shear. Nevertheless, most studies of the interaction of cumulus clouds and radiation have assumed these clouds to be isotropic. This paper describes an investigation of the effect of fair-weather cumulus cloud field anisotropy on domain-averaged solar fluxes and atmospheric heating rate profiles. A stochastic field generation algorithm was used to produce twenty three-dimensional liquid water content fields based on the statistical properties of cloud scenes from a large eddy simulation. Progressively greater degrees of x-z plane tilting and horizontal stretching were imposed on each of these scenes, so that an ensemble of scenes was produced for each level of distortion. The resulting scenes were used as input to a three-dimensional Monte Carlo radiative transfer model. Domain-average transmission, reflection, and absorption of broadband solar radiation were computed for each scene along with the average heating rate profile. Both tilt and horizontal stretching were found to significantly affect calculated fluxes, with the amount and sign of flux differences depending strongly on sun position relative to cloud distortion geometry. The mechanisms by which anisotropy interacts with solar fluxes were investigated by comparisons to independent pixel approximation and tilted independent pixel approximation computations for the same scenes. Cumulus anisotropy was found to most strongly impact solar radiative transfer by changing the effective cloud fraction, i.e., the cloud fraction when the field is projected on a surface perpendicular to the direction of the incident solar beam.

Evaluation of FSK models for radiative heat transfer under oxyfuel conditions

NASA Astrophysics Data System (ADS)

Clements, Alastair G.; Porter, Rachael; Pranzitelli, Alessandro; Pourkashanian, Mohamed

2015-01-01

Oxyfuel is a promising technology for carbon capture and storage (CCS) applied to combustion processes. It would be highly advantageous in the deployment of CCS to be able to model and optimise oxyfuel combustion, however the increased concentrations of CO2 and H2O under oxyfuel conditions modify several fundamental processes of combustion, including radiative heat transfer. This study uses benchmark narrow band radiation models to evaluate the influence of assumptions in global full-spectrum k-distribution (FSK) models, and whether they are suitable for modelling radiation in computational fluid dynamics (CFD) calculations of oxyfuel combustion. The statistical narrow band (SNB) and correlated-k (CK) models are used to calculate benchmark data for the radiative source term and heat flux, which are then compared to the results calculated from FSK models. Both the full-spectrum correlated k (FSCK) and the full-spectrum scaled k (FSSK) models are applied using up-to-date spectral data. The results show that the FSCK and FSSK methods achieve good agreement in the test cases. The FSCK method using a five-point Gauss quadrature scheme is recommended for CFD calculations in oxyfuel conditions, however there are still potential inaccuracies in cases with very wide variations in the ratio between CO2 and H2O concentrations.

A fast code for channel limb radiances with gas absorption and scattering in a spherical atmosphere

NASA Astrophysics Data System (ADS)

Eluszkiewicz, Janusz; Uymin, Gennady; Flittner, David; Cady-Pereira, Karen; Mlawer, Eli; Henderson, John; Moncet, Jean-Luc; Nehrkorn, Thomas; Wolff, Michael

2017-05-01

We present a radiative transfer code capable of accurately and rapidly computing channel limb radiances in the presence of gaseous absorption and scattering in a spherical atmosphere. The code has been prototyped for the Mars Climate Sounder measuring limb radiances in the thermal part of the spectrum (200-900 cm-1) where absorption by carbon dioxide and water vapor and absorption and scattering by dust and water ice particles are important. The code relies on three main components: 1) The Gauss Seidel Spherical Radiative Transfer Model (GSSRTM) for scattering, 2) The Planetary Line-By-Line Radiative Transfer Model (P-LBLRTM) for gas opacity, and 3) The Optimal Spectral Sampling (OSS) for selecting a limited number of spectral points to simulate channel radiances and thus achieving a substantial increase in speed. The accuracy of the code has been evaluated against brute-force line-by-line calculations performed on the NASA Pleiades supercomputer, with satisfactory results. Additional improvements in both accuracy and speed are attainable through incremental changes to the basic approach presented in this paper, which would further support the use of this code for real-time retrievals and data assimilation. Both newly developed codes, GSSRTM/OSS for MCS and P-LBLRTM, are available for additional testing and user feedback.

A review of research and development on the microwave-plasma electrothermal rocket

NASA Technical Reports Server (NTRS)

Hawley, Martin C.; Asmussen, Jes; Filpus, John W.; Frasch, Lydell L.; Whitehair, Stanley; Morin, T. J.; Chapman, R.

1987-01-01

The microwave-plasma electrothermal rocket (MWPETR) shows promise for spacecraft propulsion and maneuvering, without some of the drawbacks of competitive electric propulsion systems. In the MWPETR, the electric power is first converted to microwave-frequency radiation. In a specially-designed microwave cavity system, the electromagnetic energy of the radiation is transferred to the electrons in a plasma sustained in the working fluid. The resulting high-energy electrons transfer their energy to the atoms and molecules of the working fluid by collisions. The working fluid, thus heated, expands through a nozzle to generate thrust. In the MWPETR, no electrodes are in contact with the working fluid, the energy is transferred into the working fluid by nonthermal mechanisms, and the main requirement for the materials of construction is that the walls of the plasma chamber be insulating and transparent to microwave radiation at operating conditions. In this survey of work on the MWPETR, several experimental configurations are described and compared. Diagnostic methods used in the study are described and compared, including titration, spectroscopy, calorimetry, electric field measurements, gas-dynamic methods, and thrust measurements. Measured and estimated performance efficiencies are reported. Results of computer modeling of the plasma and of the gas flowing from the plasma are summarized.

Radiative transfer model for aerosols at infrared wavelengths for passive remote sensing applications: revisited.

PubMed

Ben-David, Avishai; Davidson, Charles E; Embury, Janon F

2008-11-01

We introduced a two-dimensional radiative transfer model for aerosols in the thermal infrared [Appl. Opt.45, 6860-6875 (2006)APOPAI0003-693510.1364/AO.45.006860]. In that paper we superimposed two orthogonal plane-parallel layers to compute the radiance due to a two-dimensional (2D) rectangular aerosol cloud. In this paper we revisit the model and correct an error in the interaction of the two layers. We derive new expressions relating to the signal content of the radiance from an aerosol cloud based on the concept of five directional thermal contrasts: four for the 2D diffuse radiance and one for direct radiance along the line of sight. The new expressions give additional insight on the radiative transfer processes within the cloud. Simulations for Bacillus subtilis var. niger (BG) bioaerosol and dustlike kaolin aerosol clouds are compared and contrasted for two geometries: an airborne sensor looking down and a ground-based sensor looking up. Simulation results suggest that aerosol cloud detection from an airborne platform may be more challenging than for a ground-based sensor and that the detection of an aerosol cloud in emission mode (negative direct thermal contrast) is not the same as the detection of an aerosol cloud in absorption mode (positive direct thermal contrast).

The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer

NASA Astrophysics Data System (ADS)

Drummond, B.; Mayne, N. J.; Baraffe, I.; Tremblin, P.; Manners, J.; Amundsen, D. S.; Goyal, J.; Acreman, D.

2018-05-01

In this work, we have performed a series of simulations of the atmosphere of GJ 1214b assuming different metallicities using the Met Office Unified Model (UM). The UM is a general circulation model (GCM) that solves the deep, non-hydrostatic equations of motion and uses a flexible and accurate radiative transfer scheme, based on the two-stream and correlated-k approximations, to calculate the heating rates. In this work we consistently couple a well-tested Gibbs energy minimisation scheme to solve for the chemical equilibrium abundances locally in each grid cell for a general set of elemental abundances, further improving the flexibility and accuracy of the model. As the metallicity of the atmosphere is increased we find significant changes in the dynamical and thermal structure, with subsequent implications for the simulated phase curve. The trends that we find are qualitatively consistent with previous works, though with quantitative differences. We investigate in detail the effect of increasing the metallicity by splitting the mechanism into constituents, involving the mean molecular weight, the heat capacity and the opacities. We find the opacity effect to be the dominant mechanism in altering the circulation and thermal structure. This result highlights the importance of accurately computing the opacities and radiative transfer in 3D GCMs.

Assessing Spectral Shortwave Cloud Observations at the Southern Great Plains Facility

NASA Technical Reports Server (NTRS)

McBride, P. J.; Marshak, A.; Wiscombe, W. J.; Flynn, C. J.; Vogelmann, A. M.

2012-01-01

The Atmospheric Radiation Measurement (ARM) program (now Atmospheric System Research) was established, in part, to improve radiation models so that they could be used reliably to compute radiation fluxes through the atmosphere, given knowledge of the surface albedo, atmospheric gases, and the aerosol and cloud properties. Despite years of observations, discrepancies still exist between radiative transfer models and observations, particularly in the presence of clouds. Progress has been made at closing discrepancies in the spectral region beyond 3 micron, but the progress lags at shorter wavelengths. Ratios of observed visible and near infrared cloud albedo from aircraft and satellite have shown both localized and global discrepancies between model and observations that are, thus far, unexplained. The capabilities of shortwave surface spectrometry have been improved in recent years at the Southern Great Plains facility (SGP) of the ARM Climate Research Facility through the addition of new instrumentation, the Shortwave Array Spectroradiometer, and upgrades to existing instrumentation, the Shortwave Spectroradiometer and the Rotating Shadowband Spectroradiometer. An airborne-based instrument, the HydroRad Spectroradiometer, was also deployed at the ARM site during the Routine ARM Aerial Facility Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign. Using the new and upgraded spectral observations along with radiative transfer models, cloud scenes at the SGP are presented with the goal of characterizing the instrumentation and the cloud fields themselves.

Assessment of radiation awareness training in immersive virtual environments

NASA Astrophysics Data System (ADS)

Whisker, Vaughn E., III

The prospect of new nuclear power plant orders in the near future and the graying of the current workforce create a need to train new personnel faster and better. Immersive virtual reality (VR) may offer a solution to the training challenge. VR technology presented in a CAVE Automatic Virtual Environment (CAVE) provides a high-fidelity, one-to-one scale environment where areas of the power plant can be recreated and virtual radiation environments can be simulated, making it possible to safely expose workers to virtual radiation in the context of the actual work environment. The use of virtual reality for training is supported by many educational theories; constructivism and discovery learning, in particular. Educational theory describes the importance of matching the training to the task. Plant access training and radiation worker training, common forms of training in the nuclear industry, rely on computer-based training methods in most cases, which effectively transfer declarative knowledge, but are poor at transferring skills. If an activity were to be added, the training would provide personnel with the opportunity to develop skills and apply their knowledge so they could be more effective when working in the radiation environment. An experiment was developed to test immersive virtual reality's suitability for training radiation awareness. Using a mixed methodology of quantitative and qualitative measures, the subjects' performances before and after training were assessed. First, subjects completed a pre-test to measure their knowledge prior to completing any training. Next they completed unsupervised computer-based training, which consisted of a PowerPoint presentation and a PDF document. After completing a brief orientation activity in the virtual environment, one group of participants received supplemental radiation awareness training in a simulated radiation environment presented in the CAVE, while a second group, the control group, moved directly to the assessment phase of the experiment. The CAVE supplied an activity-based training environment where learners were able to use a virtual survey meter to explore the properties of radiation sources and the effects of time and distance on radiation exposure. Once the training stage had ended, the subjects completed an assessment activity where they were asked to complete four tasks in a simulated radiation environment in the CAVE, which was designed to provide a more authentic assessment than simply testing understanding using a quiz. After the practicum, the subjects completed a post-test. Survey information was also collected to assist the researcher with interpretation of the collected data. Response to the training was measured by completion time, radiation exposure received, successful completion of the four tasks in the practicum, and scores on the post-test. These results were combined to create a radiation awareness score. In addition, observational data was collected as the subjects completed the tasks. The radiation awareness scores of the control group and the group that received supplemental training in the virtual environment were compared. T-tests showed that the effect of the supplemental training was not significant; however, calculation of the effect size showed a small-to-medium effect of the training. The CAVE group received significantly less radiation exposure during the assessment activity, and they completed the activities on an average of one minute faster. These results indicate that the training was effective, primarily for instilling radiation sensitivity. Observational data collected during the assessment supports this conclusion. The training environment provided by the immersive virtual reality recreated a radiation environment where learners could apply knowledge they had been taught by computer-based training. Activity-based training has been shown to be a more effective way to transfer skills because of the similarity between the training environment and the application environment. Virtual reality enables the training environment to look and feel like the application environment. Because of this, radiation awareness training in an immersive virtual environment should be considered by the nuclear industry, which is supported by the results of this experiment.

Introduction to IdentiFINDERs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rees, Brian G.

These are slides from a presentation. The identiFINDER provides information on radiation levels. It can automatically identify isotopes in its library. It can save spectra for transfer to a computer, and has a 4-8 hour battery life. The following is covered: an overview, operating modes, getting started, finder mode, search, identification mode, dose & rate, warning & alarm, options (ultra LGH), options (identifinder2), and general procedure.

Technology transfer of military space microprocessor developments

NASA Astrophysics Data System (ADS)

Gorden, C.; King, D.; Byington, L.; Lanza, D.

1999-01-01

Over the past 13 years the Air Force Research Laboratory (AFRL) has led the development of microprocessors and computers for USAF space and strategic missile applications. As a result of these Air Force development programs, advanced computer technology is available for use by civil and commercial space customers as well. The Generic VHSIC Spaceborne Computer (GVSC) program began in 1985 at AFRL to fulfill a deficiency in the availability of space-qualified data and control processors. GVSC developed a radiation hardened multi-chip version of the 16-bit, Mil-Std 1750A microprocessor. The follow-on to GVSC, the Advanced Spaceborne Computer Module (ASCM) program, was initiated by AFRL to establish two industrial sources for complete, radiation-hardened 16-bit and 32-bit computers and microelectronic components. Development of the Control Processor Module (CPM), the first of two ASCM contract phases, concluded in 1994 with the availability of two sources for space-qualified, 16-bit Mil-Std-1750A computers, cards, multi-chip modules, and integrated circuits. The second phase of the program, the Advanced Technology Insertion Module (ATIM), was completed in December 1997. ATIM developed two single board computers based on 32-bit reduced instruction set computer (RISC) processors. GVSC, CPM, and ATIM technologies are flying or baselined into the majority of today's DoD, NASA, and commercial satellite systems.

Influence of thermal radiation on soot production in Laminar axisymmetric diffusion flames

NASA Astrophysics Data System (ADS)

Demarco, R.; Nmira, F.; Consalvi, J. L.

2013-05-01

The aim of this paper is to study the effect of radiative heat transfer on soot production in laminar axisymmetric diffusion flames. Twenty-four C1-C3 hydrocarbon-air flames, consisting of normal (NDF) and inverse (IDF) diffusion flames at both normal gravity (1 g) and microgravity (0 g), and covering a wide range of conditions affecting radiative heat transfer, were simulated. The numerical model is based on the Steady Laminar Flamelet (SLF) model, a semi-empirical two-equation acetylene/benzene based soot model and the Statistical Narrow Band Correlated K (SNBCK) model coupled to the Finite Volume Method (FVM) to compute thermal radiation. Predictions relative to velocity, temperature, soot volume fraction and radiative losses are on the whole in good agreement with the available experimental data. Model results show that, for all the flames considered, thermal radiation is a crucial process with a view to providing accurate predictions for temperatures and soot concentrations. It becomes increasingly significant from IDFs to NDFs and its influence is much greater as gravity is reduced. The radiative contribution of gas prevails in the weakly-sooting IDFs and in the methane and ethane NDFs, whereas soot radiation dominates in the other flames. However, both contributions are significant in all cases, with the exception of the 1 g IDFs investigated where soot radiation can be ignored. The optically-thin approximation (OTA) was also tested and found to be applicable as long as the optical thickness, based on flame radius and Planck mean absorption coefficient, is less than 0.05. The OTA is reasonable for the IDFs and for most of the 1 g NDFs, but it fails to predict the radiative heat transfer for the 0 g NDFs. The accuracy of radiative-property models was then assessed in the latter cases. Simulations show that the gray approximation can be applied to soot but not to combustion gases. Both the non-gray and gray soot versions of the Full Spectrum Correlated k (FSCK) model can be then substituted for the SNBCK with a reduction in CPU time by a factor of about 20 in the latter case.

Open-source Software for Exoplanet Atmospheric Modeling

NASA Astrophysics Data System (ADS)

Cubillos, Patricio; Blecic, Jasmina; Harrington, Joseph

2018-01-01

I will present a suite of self-standing open-source tools to model and retrieve exoplanet spectra implemented for Python. These include: (1) a Bayesian-statistical package to run Levenberg-Marquardt optimization and Markov-chain Monte Carlo posterior sampling, (2) a package to compress line-transition data from HITRAN or Exomol without loss of information, (3) a package to compute partition functions for HITRAN molecules, (4) a package to compute collision-induced absorption, and (5) a package to produce radiative-transfer spectra of transit and eclipse exoplanet observations and atmospheric retrievals.

3-D Inhomogeous Radiative Transfer Model using a Planar-stratified Forward RT Model and Horizontal Perturbation Series

NASA Astrophysics Data System (ADS)

Zhang, K.; Gasiewski, A. J.

2017-12-01

A horizontally inhomogeneous unified microwave radiative transfer (HI-UMRT) model based upon a nonspherical hydrometeor scattering model is being developed at the University of Colorado at Boulder to facilitate forward radiative simulations for 3-dimensionally inhomogeneous clouds in severe weather. The HI-UMRT 3-D analytical solution is based on incorporating a planar-stratified 1-D UMRT algorithm within a horizontally inhomogeneous iterative perturbation scheme. Single-scattering parameters are computed using the Discrete Dipole Scattering (DDSCAT v7.3) program for hundreds of carefully selected nonspherical complex frozen hydrometeors from the NASA/GSFC DDSCAT database. The required analytic factorization symmetry of transition matrix in a normalized RT equation was analytically proved and validated numerically using the DDSCAT-based full Stokes matrix of randomly oriented hydrometeors. The HI-UMRT model thus inherits the properties of unconditional numerical stability, efficiency, and accuracy from the UMRT algorithm and provides a practical 3-D two-Stokes parameter radiance solution with Jacobian to be used within microwave retrievals and data assimilation schemes. In addition, a fast forward radar reflectivity operator with Jacobian based on DDSCAT backscatter efficiency computed for large hydrometeors is incorporated into the HI-UMRT model to provide applicability to active radar sensors. The HI-UMRT will be validated strategically at two levels: 1) intercomparison of brightness temperature (Tb) results with those of several 1-D and 3-D RT models, including UMRT, CRTM and Monte Carlo models, 2) intercomparison of Tb with observed data from combined passive and active spaceborne sensors (e.g. GPM GMI and DPR). The precise expression for determining the required number of 3-D iterations to achieve an error bound on the perturbation solution will be developed to facilitate the numerical verification of the HI-UMRT code complexity and computation performance.

Study of a fail-safe abort system for an actively cooled hypersonic aircraft: Computer program documentation

NASA Technical Reports Server (NTRS)

Haas, L. A., Sr.

1976-01-01

The Fail-Safe Abort System TEMPerature Analysis Program, (FASTEMP), user's manual is presented. This program was used to analyze fail-safe abort systems for an actively cooled hypersonic aircraft. FASTEMP analyzes the steady state or transient temperature response of a thermal model defined in rectangular, cylindrical, conical and/or spherical coordinate system. FASTEMP provides the user with a large selection of subroutines for heat transfer calculations. The various modes of heat transfer available from these subroutines are: heat storage, conduction, radiation, heat addition or generation, convection, and fluid flow.

Towards quantifying global aerosol radiative effects using lidar

NASA Astrophysics Data System (ADS)

Thorsen, T. J.

2017-12-01

Spaceborne lidar observations alleviate many of the limitations of passivesensors and have great potential to provide accurate global all-sky estimatesof the aerosol direct radiative effect (DRE). However, analysis of CALIPSOlidar observations show that CALIPSO does not detect allradiatively-significant aerosol, i.e. aerosol that directly modifies theEarth's radiation budget. We estimated that using CALIPSO observationsresults in an underestimate of the magnitude of the global mean aerosol DREby up to 54%. The CATS lidar on-board the ISS is shown to have a poorersensitivity than CALIPSO and the expected sensitivity of the upcoming ATLIDlidar on EarthCARE indicates that calculations of the aerosol DRE willcontinue to be significantly biased. Improvements to our knowledge of aerosol forcing, which contributes thelargest uncertainty to climate sensitivity, could be achieved by a futurespace-based HSRL mission. To this end, high-accuracy ground-based andairborne lidar datasets have been used to compute the detection sensitivityrequired to accurately resolve the aerosol DRE. Multiwavelength HSRLmeasurements also can retrieve vertically-resolved aerosol optical propertiesneeded for radiative transfer calculations which are not provided by currentsatellite observations. Current satellite observations also do not provideall the quantities needed to compute the aerosol direct radiative forcing,i.e. the radiative effect of just anthropogenic aerosols. A multiwavelengthHSRL allows for a more refined aerosol classification to be made enablingboth calculations of anthropogenic aerosol radiative effects and betterconstraints on global models.

Multiphysics Modeling for Dimensional Analysis of a Self-Heated Molten Regolith Electrolysis Reactor for Oxygen and Metals Production on the Moon and Mars

NASA Technical Reports Server (NTRS)

Dominguez, Jesus A.; Sibille, Laurent

2010-01-01

The technology of direct electrolysis of molten lunar regolith to produce oxygen and molten metal alloys has progressed greatly in the last few years. The development of long-lasting inert anodes and cathode designs as well as techniques for the removal of molten products from the reactor has been demonstrated. The containment of chemically aggressive oxide and metal melts is very difficult at the operating temperatures ca 1600 C. Containing the molten oxides in a regolith shell can solve this technical issue and can be achieved by designing a self-heating reactor in which the electrolytic currents generate enough Joule heat to create a molten bath. In a first phase, a thermal analysis model was built to study the formation of a melt of lunar basaltic regolith irradiated by a focused solar beam This mode of heating was selected because it relies on radiative heat transfer, which is the dominant mode of transfer of energy in melts at 1600 C. Knowing and setting the Gaussian-type heat flux from the concentrated solar beam and the phase and temperature dependent thermal properties, the model predicts the dimensions and temperature profile of the melt. A validation of the model is presented in this paper through the experimental formation of a spherical cap melt realized by others. The Orbitec/PSI experimental setup uses an 3.6-cm diameter concentrated solar beam to create a hemispheric melt in a bed of lunar regolith simulant contained in a large pot. Upon cooling, the dimensions of the vitrified melt are measured to validate the thermal model. In a second phase, the model is augmented by multiphysics components to compute the passage of electrical currents between electrodes inserted in the molten regolith. The current through the melt generates Joule heating due to the high resistivity of the medium and this energy is transferred into the melt by conduction, convection and primarily by radiation. The model faces challenges in two major areas, the change of phase as temperature increases, and the dominance of radiative heat flux as heat transfer mechanism within the melt the change of phase concerns the regolith itself which is present in states ranging from a fine grain regolith with low thermal conductivity and low density to a vitrified melt with much higher thermal conductivity, and higher density. As the regolith is heated, it starts to soften around 1300 C the melt iS very viscous and evolving gas bubbles out in thick, lava-like fashion. By 1600 C the regolith is completely melted and the viscosity is low The second challenge resides in the proper modeling of the radiative heat flux requiring the addition of the computing-demanding radiative-heat-transfer function to the general heat transfer equation. The model Includes temperature-dependent properties (density, thermal conductivity, heat capacity, and viscosity, and absorption coefficients) and solves the radiative heat flux equation assuming gray (fine grains) and semi-transparent (melt) media and using an absorption coefficient spectral found in the literature for terrestrial minerals similar in composition to those of lunar regolith simulant

Spectral modeling of radiation in combustion systems

NASA Astrophysics Data System (ADS)

Pal, Gopalendu

Radiation calculations are important in combustion due to the high temperatures encountered but has not been studied in sufficient detail in the case of turbulent flames. Radiation calculations for such problems require accurate, robust, and computationally efficient models for the solution of radiative transfer equation (RTE), and spectral properties of radiation. One more layer of complexity is added in predicting the overall heat transfer in turbulent combustion systems due to nonlinear interactions between turbulent fluctuations and radiation. The present work is aimed at the development of finite volume-based high-accuracy thermal radiation modeling, including spectral radiation properties in order to accurately capture turbulence-radiation interactions (TRI) and predict heat transfer in turbulent combustion systems correctly and efficiently. The turbulent fluctuations of temperature and chemical species concentrations have strong effects on spectral radiative intensities, and TRI create a closure problem when the governing partial differential equations are averaged. Recently, several approaches have been proposed to take TRI into account. Among these attempts the most promising approaches are the probability density function (PDF) methods, which can treat nonlinear coupling between turbulence and radiative emission exactly, i.e., "emission TRI". The basic idea of the PDF method is to treat physical variables as random variables and to solve the PDF transport equation stochastically. The actual reacting flow field is represented by a large number of discrete stochastic particles each carrying their own random variable values and evolving with time. The mean value of any function of those random variables, such as the chemical source term, can be evaluated exactly by taking the ensemble average of particles. The local emission term belongs to this class and thus, can be evaluated directly and exactly from particle ensembles. However, the local absorption term involves interactions between the local particle and energy emitted by all other particles and, hence, cannot be obtained from particle ensembles directly. To close the nonlinear coupling between turbulence and absorption, i.e., "absorption TRI", an optically thin fluctuation approximation can be applied to virtually all combustion problems and obtain acceptable accuracy. In the present study a composition-PDF method is applied, in which only the temperature and the species concentrations are treated as random variables. A closely coupled hybrid finite-volume/Monte Carlo scheme is adopted, in which the Monte Carlo method is used to solve the composition-PDF for chemical reactions and the finite volume method is used to solve for the flow field and radiation. Spherical harmonics method-based finite volume solvers (P-1 and P-3) are developed using the data structures of the high fidelity open-source code flow software OpenFOAM. Spectral radiative properties of the participating medium are modeled using full-spectrum k-distribution methods. Advancements of basic k-distribution methods are performed for nongray nonhomogeneous gas- and particulate-phase (soot, fuel droplets, ash, etc.) participating media using multi-scale and multi-group based approaches. These methods achieve close-to benchmark line-by-line (LBL) accuracy in strongly inhomogeneous media at a tiny fraction of LBL's computational cost. A portable spectral module is developed, which includes all the basic to advanced k-distribution methods along with the precompiled accurate and compact k-distribution databases. The P-1 /P-3 RTE solver coupled with the spectral module is used in conjunction with the combined Reynolds-averaged Navier-Stokes (RANS) and composition-PDF-based turbulence-chemistry solver to investigate TRI in multiphase turbulent combustion systems. The combustion solvers developed in this study is employed to simulate several turbulent jet flames, such as Sandia Flame D, and artificial nonsooting and sooting flames derived from Flame D. The effects of combustion chemistry, radiation and TRI on total heat transfer and pollutant (such as NO x) generation are studied for the above flames. The accuracy of the overall combustion solver is assessed by comparing it with the experimental data for Flame D. Comparison of the accuracy and the computational cost among various spectral models and RTE solvers is extensively done on the artificial flames derived from Flame D to demonstrate the necessity of accurate modeling of radiation in combustion problems.

Technical report series on global modeling and data assimilation. Volume 3: An efficient thermal infrared radiation parameterization for use in general circulation models

NASA Technical Reports Server (NTRS)

Suarex, Max J. (Editor); Chou, Ming-Dah

1994-01-01

A detailed description of a parameterization for thermal infrared radiative transfer designed specifically for use in global climate models is presented. The parameterization includes the effects of the main absorbers of terrestrial radiation: water vapor, carbon dioxide, and ozone. While being computationally efficient, the schemes compute very accurately the clear-sky fluxes and cooling rates from the Earth's surface to 0.01 mb. This combination of accuracy and speed makes the parameterization suitable for both tropospheric and middle atmospheric modeling applications. Since no transmittances are precomputed the atmospheric layers and the vertical distribution of the absorbers may be freely specified. The scheme can also account for any vertical distribution of fractional cloudiness with arbitrary optical thickness. These features make the parameterization very flexible and extremely well suited for use in climate modeling studies. In addition, the numerics and the FORTRAN implementation have been carefully designed to conserve both memory and computer time. This code should be particularly attractive to those contemplating long-term climate simulations, wishing to model the middle atmosphere, or planning to use a large number of levels in the vertical.

Rapid calculation of radiative heating rates and photodissociation rates in inhomogeneous multiple scattering atmospheres

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Mckay, C. P.; Ackerman, T. P.; Santhanam, K.

1989-01-01

The solution of the generalized two-stream approximation for radiative transfer in homogeneous multiple scattering atmospheres is extended to vertically inhomogeneous atmospheres in a manner which is numerically stable and computationally efficient. It is shown that solar energy deposition rates, photolysis rates, and infrared cooling rates all may be calculated with the simple modifications of a single algorithm. The accuracy of the algorithm is generally better than 10 percent, so that other uncertainties, such as in absorption coefficients, may often dominate the error in calculation of the quantities of interest to atmospheric studies.

Modelling the performance of the tapered artery heat pipe design for use in the radiator of the solar dynamic power system of the NASA Space Station

NASA Technical Reports Server (NTRS)

Evans, Austin Lewis

1988-01-01

The paper presents a computer program developed to model the steady-state performance of the tapered artery heat pipe for use in the radiator of the solar dynamic power system of the NASA Space Station. The program solves six governing equations to ascertain which one is limiting the maximum heat transfer rate of the heat pipe. The present model appeared to be slightly better than the LTV model in matching the 1-g data for the standard 15-ft test heat pipe.

Laser Induced Aluminum Surface Breakdown Model

NASA Technical Reports Server (NTRS)

Chen, Yen-Sen; Liu, Jiwen; Zhang, Sijun; Wang, Ten-See (Technical Monitor)

2002-01-01

Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Based on an unstructured grid, pressure-based computational aerothermodynamics; platform, several sub-models describing such underlying physics as laser ray tracing and focusing, thermal non-equilibrium, plasma radiation and air spark ignition have been developed. This proposed work shall extend the numerical platform and existing sub-models to include the aluminum wall surface Inverse Bremsstrahlung (IB) effect from which surface ablation and free-electron generation can be initiated without relying on the air spark ignition sub-model. The following tasks will be performed to accomplish the research objectives.

Study of the atmospheric effects on the radiation detected by the sensor aboard orbiting platforms (ERTS/LANDSAT). M.S. Thesis - October 1978; [Ribeirao Preto and Brasilia, Brazil

NASA Technical Reports Server (NTRS)

Dejesusparada, N. (Principal Investigator); Morimoto, T.

1980-01-01

The author has identified the following significant results. Multispectral scanner data for Brasilia was corrected for atmospheric interference using the LOWTRAN-3 computer program and the analytical solution of the radiative transfer equation. This improved the contrast between two natural targets and the corrected images of two different dates were more similar than the original ones. Corrected images of MSS data for Ribeirao Preto gave a classification accuracy for sugar cane about 10% higher as compared to the original images.

Development of a model to compute the extension of life supporting zones for Earth-like exoplanets.

PubMed

Neubauer, David; Vrtala, Aron; Leitner, Johannes J; Firneis, Maria G; Hitzenberger, Regina

2011-12-01

A radiative convective model to calculate the width and the location of the life supporting zone (LSZ) for different, alternative solvents (i.e. other than water) is presented. This model can be applied to the atmospheres of the terrestrial planets in the solar system as well as (hypothetical, Earth-like) terrestrial exoplanets. Cloud droplet formation and growth are investigated using a cloud parcel model. Clouds can be incorporated into the radiative transfer calculations. Test runs for Earth, Mars and Titan show a good agreement of model results with observations.

Three dimensional radiative flow of magnetite-nanofluid with homogeneous-heterogeneous reactions

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Rashid, Madiha; Alsaedi, Ahmed

2018-03-01

Present communication deals with the effects of homogeneous-heterogeneous reactions in flow of nanofluid by non-linear stretching sheet. Water based nanofluid containing magnetite nanoparticles is considered. Non-linear radiation and non-uniform heat sink/source effects are examined. Non-linear differential systems are computed by Optimal homotopy analysis method (OHAM). Convergent solutions of nonlinear systems are established. The optimal data of auxiliary variables is obtained. Impact of several non-dimensional parameters for velocity components, temperature and concentration fields are examined. Graphs are plotted for analysis of surface drag force and heat transfer rate.

Why Hart found narrow ecospheres--a minor science mystery solved.

PubMed

Levenson, Barton Paul

2015-05-01

To explain why two NASA computer simulation studies in the 1970s (Hart, 1978 , 1979 ) briefly rocked the subfield of astrobiology and SETI studies by showing very narrow habitable zones (HZs) for solar-type stars. Although other studies later supported wider HZs, it was never clear why the Hart simulations found the narrow limits they did. Investigation of the state of climate studies and radiative transfer models in the period 1960-1970 provides a likely explanation. Hart's findings were in line with earlier results, preventing him from noticing that his radiation model was inadequate.

Temperature Distribution in a Composite of Opaque and Semitransparent Spectral Layers

NASA Technical Reports Server (NTRS)

Siegel, Robert

1997-01-01

The analysis of radiative transfer becomes computationally complex for a composite when there are multiple layers and multiple spectral bands. A convenient analytical method is developed for combined radiation and conduction in a composite of alternating semitransparent and opaque layers. The semi- transparent layers absorb, scatter, and emit radiation, and spectral properties with large scattering are included. The two-flux method is used, and its applicability is verified by comparison with a basic solution in the literature. The differential equation in the two-flux method Is solved by deriving a Green's function. The solution technique is applied to analyze radiation effects in a multilayer zirconia thermal barrier coating with internal radiation shields for conditions in an aircraft engine combustor. The zirconia radiative properties are modeled by two spectral bands. Thin opaque layers within the coating are used to decrease radiant transmission that can degrade the zirconia insulating ability. With radiation shields, the temperature distributions more closely approach the opaque limit that provides the lowest metal wall temperatures.

Ethane and acetylene abundances in the Jovian atmosphere

NASA Technical Reports Server (NTRS)

Tokunaga, A.; Knacke, R. F.; Owen, T.

1976-01-01

The paper reports spectra of Jupiter in the spectral region from 755 to 850 kaysers, which covers the nu-9 fundamental of ethane and contains lines from the R branch of the nu-5 fundamental of acetylene. The monochromatic absorption coefficient of the central Q branch of the nu-9 fundamental of ethane, which was determined in the laboratory, is applied in a radiative-transfer calculation to evaluate the ethane mixing ratio in the Jovian atmosphere; the present data are also used to place an upper limit on the acetylene mixing ratio. For the radiative-transfer calculation, emission intensity is computed for the region above the 0.02-atm level assuming both an isothermal inversion layer and a previously reported temperature profile. The resulting maximum mixing ratios consistent with the observations are 0.00003 for ethane and 7.5 by 10 to the -8th power for acetylene.

Effects of virtualization on a scientific application - Running a hyperspectral radiative transfer code on virtual machines.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tikotekar, Anand A; Vallee, Geoffroy R; Naughton III, Thomas J

2008-01-01

The topic of system-level virtualization has recently begun to receive interest for high performance computing (HPC). This is in part due to the isolation and encapsulation offered by the virtual machine. These traits enable applications to customize their environments and maintain consistent software configurations in their virtual domains. Additionally, there are mechanisms that can be used for fault tolerance like live virtual machine migration. Given these attractive benefits to virtualization, a fundamental question arises, how does this effect my scientific application? We use this as the premise for our paper and observe a real-world scientific code running on a Xenmore » virtual machine. We studied the effects of running a radiative transfer simulation, Hydrolight, on a virtual machine. We discuss our methodology and report observations regarding the usage of virtualization with this application.« less

Radiative Transfer Theory Verified by Controlled Laboratory Experiments

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Goldstein, Dennis H.; Chowdhary, Jacek; Lompado, Arthur

2013-01-01

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2 to 10. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to 2. VRTE results for packing densities of the order of 5 should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination.

Grid of Supergiant B[e] Models from HDUST Radiative Transfer

NASA Astrophysics Data System (ADS)

Domiciano de Souza, A.; Carciofi, A. C.

2012-12-01

By using the Monte Carlo radiative transfer code HDUST (developed by A. C. Carciofi and J..E. Bjorkman) we have built a grid of models for stars presenting the B[e] phenomenon and a bimodal outflowing envelope. The models are particularly adapted to the study of B[e] supergiants and FS CMa type stars. The adopted physical parameters of the calculated models make the grid well adapted to interpret high angular and high spectral observations, in particular spectro-interferometric data from ESO-VLTI instruments AMBER (near-IR at low and medium spectral resolution) and MIDI (mid-IR at low spectral resolution). The grid models include, for example, a central B star with different effective temperatures, a gas (hydrogen) and silicate dust circumstellar envelope with a bimodal mass loss presenting dust in the denser equatorial regions. The HDUST grid models were pre-calculated using the high performance parallel computing facility Mésocentre SIGAMM, located at OCA, France.

A Two-moment Radiation Hydrodynamics Module in ATHENA Using a Godunov Method

NASA Astrophysics Data System (ADS)

Skinner, M. A.; Ostriker, E. C.

2013-04-01

We describe a module for the Athena code that solves the grey equations of radiation hydrodynamics (RHD) using a local variable Eddington tensor (VET) based on the M1 closure of the two-moment hierarchy of the transfer equation. The variables are updated via a combination of explicit Godunov methods to advance the gas and radiation variables including the non-stiff source terms, and a local implicit method to integrate the stiff source terms. We employ the reduced speed of light approximation (RSLA) with subcycling of the radiation variables in order to reduce computational costs. The streaming and diffusion limits are well-described by the M1 closure model, and our implementation shows excellent behavior for problems containing both regimes simultaneously. Our operator-split method is ideally suited for problems with a slowly-varying radiation field and dynamical gas flows, in which the effect of the RSLA is minimal.

Heat Transfer Modelling of Glass Media within TPV Systems

NASA Astrophysics Data System (ADS)

Bauer, Thomas; Forbes, Ian; Penlington, Roger; Pearsall, Nicola

2004-11-01

Understanding and optimisation of heat transfer, and in particular radiative heat transfer in terms of spectral, angular and spatial radiation distributions is important to achieve high system efficiencies and high electrical power densities for thermophtovoltaics (TPV). This work reviews heat transfer models and uses the Discrete Ordinates method. Firstly one-dimensional heat transfer in fused silica (quartz glass) shields was examined for the common arrangement, radiator-air-glass-air-PV cell. It has been concluded that an alternative arrangement radiator-glass-air-PV cell with increased thickness of fused silica should have advantages in terms of improved transmission of convertible radiation and enhanced suppression of non-convertible radiation.

Light scattering and absorption by space weathered planetary bodies: Novel numerical solution

NASA Astrophysics Data System (ADS)

Markkanen, Johannes; Väisänen, Timo; Penttilä, Antti; Muinonen, Karri

2017-10-01

Airless planetary bodies are exposed to space weathering, i.e., energetic electromagnetic and particle radiation, implantation and sputtering from solar wind particles, and micrometeorite bombardment.Space weathering is known to alter the physical and chemical composition of the surface of an airless body (C. Pieters et al., J. Geophys. Res. Planets, 121, 2016). From the light scattering perspective, one of the key effects is the production of nanophase iron (npFe0) near the exposed surfaces (B. Hapke, J. Geophys. Res., 106, E5, 2001). At visible and ultraviolet wavelengths these particles have a strong electromagnetic response which has a major impact on scattering and absorption features. Thus, to interpret the spectroscopic observations of space-weathered asteroids, the model should treat the contributions of the npFe0 particles rigorously.Our numerical approach is based on the hierarchical geometric optics (GO) and radiative transfer (RT). The modelled asteroid is assumed to consist of densely packed silicate grains with npFe0 inclusions. We employ our recently developed RT method for dense random media (K. Muinonen, et al., Radio Science, submitted, 2017) to compute the contributions of the npFe0 particles embedded in silicate grains. The dense media RT method requires computing interactions of the npFe0 particles in the volume element for which we use the exact fast superposition T-matrix method (J. Markkanen, and A.J. Yuffa, JQSRT 189, 2017). Reflections and refractions on the grain surface and propagation in the grain are addressed by the GO. Finally, the standard RT is applied to compute scattering by the entire asteroid.Our numerical method allows for a quantitative interpretation of the spectroscopic observations of space-weathered asteroids. In addition, it may be an important step towards more rigorous a thermophysical model of asteroids when coupled with the radiative and conductive heat transfer techniques.Acknowledgments. Research supported by European Research Council with Advanced Grant No. 320773 SAEMPL. Computational resources provided by CSC- IT Centre for Science Ltd, Finland.

Continuum Absorption Coefficient of Atoms and Ions

NASA Technical Reports Server (NTRS)

Armaly, B. F.

1979-01-01

The rate of heat transfer to the heat shield of a Jupiter probe has been estimated to be one order of magnitude higher than any previously experienced in an outer space exploration program. More than one-third of this heat load is due to an emission of continuum radiation from atoms and ions. The existing computer code for calculating the continuum contribution to the total load utilizes a modified version of Biberman's approximate method. The continuum radiation absorption cross sections of a C - H - O - N ablation system were examined in detail. The present computer code was evaluated and updated by being compared with available exact and approximate calculations and correlations of experimental data. A detailed calculation procedure, which can be applied to other atomic species, is presented. The approximate correlations can be made to agree with the available exact and experimental data.

A numerical study of three-dimensional flame propagation over thin solids in purely forced concurrent flow including gas-phase radiation

NASA Astrophysics Data System (ADS)

Feier, Ioan I., Jr.

The effect of flame radiation on concurrent-flow flame spread over a thin solid sample of finite width in a low-speed wind tunnel is modeled using three-dimensional full Navier-Stokes equations and three-dimensional flame radiation transfer equations. The formulation includes the conservation of mass, momentum, energy, and species: fuel vapor, oxygen, carbon dioxide and water vapor. The SN discrete ordinates method is used to solve the radiation transfer equation with a mean absorption coefficient kappa = Ckappa p, where kappap is the Planck mean absorption coefficient of the gas mixture. The varying parameter C has a value between 0 and 1; C represents the strength of flame radiation. In addition, the solid fuel absorptivity alpha is varied to ascertain the effect of flame radiation heat feedback to the solid. The flow tunnel modeled has a dimension of 10x10x30 cm, the solid fuel has a width of 6-cm with two 1-cm inert strips as edges. Incoming forced flow velocity (5 cm/s) of 21% oxygen is assumed. For comparison with the three-dimensional results, corresponding two-dimensional computations are also performed. Detailed spatial flame profiles, solid surface profiles, and heat fluxes are presented. Increasing the flame radiation strength decreases the flame length. Although flame radiation provides an additional heat transfer mechanism to preheat the solid, it is insufficient to offset the decreased convective heating due to the shorter flame; the net effect is a slower spread rate. The percentage of unreacted fuel vapor that escapes from the flame is under 2%. It is theorized that some of the pyrolyzed fuel vapor diffuses sideway and reacts at the flame edges. A radiative energy balance is analyzed also. Flame radiative feedback to the solid plays a more important role in two-dimensional flames. With high solid fuel absorptivity, a peak in the flame spread rate occurs at an intermediate value of flame radiation strength---due to the competition between two mechanisms: gas-radiation heat loss weakening the flame and the radiative feedback boosting the solid pyrolysis. Two-dimensional calculations suggest that a larger percentage of unreacted fuel vapor can escape from the flame when the flame radiation strength is high.

Radiative Transfer in Seagrass Canopies

DTIC Science & Technology

1999-09-30

Radiative Transfer in Seagrass Canopies Richard C. Zimmerman Moss Landing Marine Laboratories P. O. Box 450 Moss Landing, CA 95039 phone (831) 655...models of radiative transfer for optically shallow waters with benthic substrates colonized by submerged plant canopies ( seagrasses and seaweeds). Such...coastal resources. SCIENTIFIC OBJECTIVES The objectives of this study are to • Develop radiative transfer models of seagrass and seaweed canopies in

Cross diffusion and exponential space dependent heat source impacts in radiated three-dimensional (3D) flow of Casson fluid by heated surface

NASA Astrophysics Data System (ADS)

Zaigham Zia, Q. M.; Ullah, Ikram; Waqas, M.; Alsaedi, A.; Hayat, T.

2018-03-01

This research intends to elaborate Soret-Dufour characteristics in mixed convective radiated Casson liquid flow by exponentially heated surface. Novel features of exponential space dependent heat source are introduced. Appropriate variables are implemented for conversion of partial differential frameworks into a sets of ordinary differential expressions. Homotopic scheme is employed for construction of analytic solutions. Behavior of various embedding variables on velocity, temperature and concentration distributions are plotted graphically and analyzed in detail. Besides, skin friction coefficients and heat and mass transfer rates are also computed and interpreted. The results signify the pronounced characteristics of temperature corresponding to convective and radiation variables. Concentration bears opposite response for Soret and Dufour variables.

A novel approach for introducing cloud spatial structure into cloud radiative transfer parameterizations

NASA Astrophysics Data System (ADS)

Huang, Dong; Liu, Yangang

2014-12-01

Subgrid-scale variability is one of the main reasons why parameterizations are needed in large-scale models. Although some parameterizations started to address the issue of subgrid variability by introducing a subgrid probability distribution function for relevant quantities, the spatial structure has been typically ignored and thus the subgrid-scale interactions cannot be accounted for physically. Here we present a new statistical-physics-like approach whereby the spatial autocorrelation function can be used to physically capture the net effects of subgrid cloud interaction with radiation. The new approach is able to faithfully reproduce the Monte Carlo 3D simulation results with several orders less computational cost, allowing for more realistic representation of cloud radiation interactions in large-scale models.

CINE: Comet INfrared Excitation

NASA Astrophysics Data System (ADS)

de Val-Borro, Miguel; Cordiner, Martin A.; Milam, Stefanie N.; Charnley, Steven B.

2017-08-01

CINE calculates infrared pumping efficiencies that can be applied to the most common molecules found in cometary comae such as water, hydrogen cyanide or methanol. One of the main mechanisms for molecular excitation in comets is the fluorescence by the solar radiation followed by radiative decay to the ground vibrational state. This command-line tool calculates the effective pumping rates for rotational levels in the ground vibrational state scaled by the heliocentric distance of the comet. Fluorescence coefficients are useful for modeling rotational emission lines observed in cometary spectra at sub-millimeter wavelengths. Combined with computational methods to solve the radiative transfer equations based, e.g., on the Monte Carlo algorithm, this model can retrieve production rates and rotational temperatures from the observed emission spectrum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobel, R.

TRUMP is a general finite difference computer program for the solution of transient and steady state heat transfer problems. It is a very general program capable of solving heat transfer problems in one, two or three dimensions for plane, cylindrical or spherical geometry. Because of the variety of possible geometries, the effort required to describe the geometry can be large. GIFT was written to minimize this effort for one-dimensional heat flow problems. After describing the inner and outer boundaries of a region made of a single material along with the modes of heat transfer which thermally connect different regions, GIFTmore » will calculate all the geometric data (BLOCK 04) and thermal network data (BLOCK 05) required by TRUMP for one-dimensional problems. The heat transfer between layers (or shells) of a material may be by conduction or radiation; also, an interface resistance between layers can be specified. Convection between layers can be accounted for by use of an effective thermal conductivity in which the convection effect is included or by a thermal conductance coefficient. GIFT was written for the Sigma 7 computer, a small digital computer with a versatile graphic display system. This system makes it possible to input the desired data in a question and answer mode and to see both the input and the output displayed on a screen in front of the user at all times. (auth)« less

A Fast Hyperspectral Vector Radiative Transfer Model in UV to IR spectral bands

NASA Astrophysics Data System (ADS)

Ding, J.; Yang, P.; Sun, B.; Kattawar, G. W.; Platnick, S. E.; Meyer, K.; Wang, C.

2016-12-01

We develop a fast hyperspectral vector radiative transfer model with a spectral range from UV to IR with 5 nm resolutions. This model can simulate top of the atmosphere (TOA) diffuse radiance and polarized reflectance by considering gas absorption, Rayleigh scattering, and aerosol and cloud scattering. The absorption component considers several major atmospheric absorbers such as water vapor, CO2, O3, and O2 including both line and continuum absorptions. A regression-based method is used to parameterize the layer effective optical thickness for each gas, which substantially increases the computation efficiency for absorption while maintaining high accuracy. This method is over 500 times faster than the existing line-by-line method. The scattering component uses the successive order of scattering (SOS) method. For Rayleigh scattering, convergence is fast due to the small optical thickness of atmospheric gases. For cloud and aerosol layers, a small-angle approximation method is used in SOS calculations. The scattering process is divided into two parts, a forward part and a diffuse part. The scattering in the small-angle range in the forward direction is approximated as forward scattering. A cloud or aerosol layer is divided into thin layers. As the ray propagates through each thin layer, a portion diverges as diffuse radiation, while the remainder continues propagating in forward direction. The computed diffuse radiance is the sum of all of the diffuse parts. The small-angle approximation makes the SOS calculation converge rapidly even in a thick cloud layer.

Satellite Remote Sensing of Tropical Precipitation and Ice Clouds for GCM Verification

NASA Technical Reports Server (NTRS)

Evans, K. Franklin

2001-01-01

This project, supported by the NASA New Investigator Program, has primarily been funding a graduate student, Darren McKague. Since August 1999 Darren has been working part time at Raytheon, while continuing his PhD research. Darren is planning to finish his thesis work in May 2001, thus some of the work described here is ongoing. The proposed research was to use GOES visible and infrared imager data and SSM/I microwave data to obtain joint distributions of cirrus cloud ice mass and precipitation for a study region in the Eastern Tropical Pacific. These joint distributions of cirrus cloud and rainfall were to be compared to those from the CSU general circulation model to evaluate the cloud microphysical amd cumulus parameterizations in the GCM. Existing algorithms were to be used for the retrieval of cloud ice water path from GOES (Minnis) and rainfall from SSM/I (Wilheit). A theoretical study using radiative transfer models and realistic variations in cloud and precipitation profiles was to be used to estimate the retrieval errors. Due to the unavailability of the GOES satellite cloud retrieval algorithm from Dr. Minnis (a co-PI), there was a change in the approach and emphasis of the project. The new approach was to develop a completely new type of remote sensing algorithm - one to directly retrieve joint probability density functions (pdf's) of cloud properties from multi-dimensional histograms of satellite radiances. The usual approach is to retrieve individual pixels of variables (i.e. cloud optical depth), and then aggregate the information. Only statistical information is actually needed, however, and so a more direct method is desirable. We developed forward radiative transfer models for the SSM/I and GOES channels, originally for testing the retrieval algorithms. The visible and near infrared ice scattering information is obtained from geometric ray tracing of fractal ice crystals (Andreas Macke), while the mid-infrared and microwave scattering is computed with Mie scattering. The radiative transfer is performed with the Spherical Harmonic Discrete Ordinate Method (developed by the PI), and infrared molecular absorption is included with the correlated k-distribution method. The SHDOM radiances have been validated by comparison to version 2 of DISORT (the community "standard" discrete-ordinates radiative transfer model), however we use SHDOM since it is computationally more efficient.

A unified radiative magnetohydrodynamics code for lightning-like discharge simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Qiang, E-mail: cq0405@126.com; Chen, Bin, E-mail: emcchen@163.com; Xiong, Run

2014-03-15

A two-dimensional Eulerian finite difference code is developed for solving the non-ideal magnetohydrodynamic (MHD) equations including the effects of self-consistent magnetic field, thermal conduction, resistivity, gravity, and radiation transfer, which when combined with specified pulse current models and plasma equations of state, can be used as a unified lightning return stroke solver. The differential equations are written in the covariant form in the cylindrical geometry and kept in the conservative form which enables some high-accuracy shock capturing schemes to be equipped in the lightning channel configuration naturally. In this code, the 5-order weighted essentially non-oscillatory scheme combined with Lax-Friedrichs fluxmore » splitting method is introduced for computing the convection terms of the MHD equations. The 3-order total variation diminishing Runge-Kutta integral operator is also equipped to keep the time-space accuracy of consistency. The numerical algorithms for non-ideal terms, e.g., artificial viscosity, resistivity, and thermal conduction, are introduced in the code via operator splitting method. This code assumes the radiation is in local thermodynamic equilibrium with plasma components and the flux limited diffusion algorithm with grey opacities is implemented for computing the radiation transfer. The transport coefficients and equation of state in this code are obtained from detailed particle population distribution calculation, which makes the numerical model is self-consistent. This code is systematically validated via the Sedov blast solutions and then used for lightning return stroke simulations with the peak current being 20 kA, 30 kA, and 40 kA, respectively. The results show that this numerical model consistent with observations and previous numerical results. The population distribution evolution and energy conservation problems are also discussed.« less

Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies

NASA Technical Reports Server (NTRS)

Cucinotta, F. A.; Wilson, J. W.; Shinn, J. L.; Badavi, F. F.; Badhwar, G. D.

1996-01-01

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (> 100 keV/micrometer) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (> 10 g/cm2 of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.

Impact of intravenous contrast used in computed tomography on radiation dose to carotid arteries and thyroid in intensity-modulated radiation therapy planning for nasopharyngeal carcinoma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Victor Ho Fun, E-mail: vhflee@hku.hk; Ng, Sherry Chor Yi; Kwong, Dora Lai Wan

The aim of this study was to investigate if intravenous contrast injection affected the radiation doses to carotid arteries and thyroid during intensity-modulated radiation therapy (IMRT) planning for nasopharyngeal carcinoma (NPC). Thirty consecutive patients with NPC underwent plain computed tomography (CT) followed by repeated scanning after contrast injection. Carotid arteries (common, external, internal), thyroid, target volumes, and other organs-at-risk (OARs), as well as IMRT planning, were based on contrast-enhanced CT (CE-CT) images. All these structures and the IMRT plans were then copied and transferred to the non–contrast-enhanced CT (NCE-CT) images, and dose calculation without optimization was performed again. The radiationmore » doses to the carotid arteries and the thyroid based on CE-CT and NCE-CT were then compared. Based on CE-CT, no statistical differences, despite minute numeric decreases, were noted in all dosimetric parameters (minimum, maximum, mean, median, D05, and D01) of the target volumes, the OARs, the carotid arteries, and the thyroid compared with NCE-CT. Our results suggested that compared with NCE-CT planning, CE-CT scanning should be performed during IMRT for better target and OAR delineation, without discernible change in radiation doses.« less

Multiple Scattering in Clouds: Insights from Three-Dimensional Diffusion/P{sub 1} Theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davis, Anthony B.; Marshak, Alexander

2001-03-15

In the atmosphere, multiple scattering matters nowhere more than in clouds, and being a product of its turbulence, clouds are highly variable environments. This challenges three-dimensional (3D) radiative transfer theory in a way that easily swamps any available computational resources. Fortunately, the far simpler diffusion (or P{sub 1}) theory becomes more accurate as the scattering intensifies, and allows for some analytical progress as well as computational efficiency. After surveying current approaches to 3D solar cloud-radiation problems from the diffusion standpoint, a general 3D result in steady-state diffusive transport is derived relating the variability-induced change in domain-average flux (i.e., diffuse transmittance)more » to the one-point covariance of internal fluctuations in particle density and in radiative flux. These flux variations follow specific spatial patterns in deliberately hydrodynamical language: radiative channeling. The P{sub 1} theory proves even more powerful when the photon diffusion process unfolds in time as well as space. For slab geometry, characteristic times and lengths that describe normal and transverse transport phenomena are derived. This phenomenology is used to (a) explain persistent features in satellite images of dense stratocumulus as radiative channeling, (b) set limits on current cloud remote-sensing techniques, and (c) propose new ones both active and passive.« less

A comparison of three radiation models for the calculation of nozzle arcs

NASA Astrophysics Data System (ADS)

Dixon, C. M.; Yan, J. D.; Fang, M. T. C.

2004-12-01

Three radiation models, the semi-empirical model based on net emission coefficients (Zhang et al 1987 J. Phys. D: Appl. Phys. 20 386-79), the five-band P1 model (Eby et al 1998 J. Phys. D: Appl. Phys. 31 1578-88), and the method of partial characteristics (Aubrecht and Lowke 1994 J. Phys. D: Appl.Phys. 27 2066-73, Sevast'yanenko 1979 J. Eng. Phys. 36 138-48), are used to calculate the radiation transfer in an SF6 nozzle arc. The temperature distributions computed by the three models are compared with the measurements of Leseberg and Pietsch (1981 Proc. 4th Int. Symp. on Switching Arc Phenomena (Lodz, Poland) pp 236-40) and Leseberg (1982 PhD Thesis RWTH Aachen, Germany). It has been found that all three models give similar distributions of radiation loss per unit time and volume. For arcs burning in axially dominated flow, such as arcs in nozzle flow, the semi-empirical model and the P1 model give accurate predictions when compared with experimental results. The prediction by the method of partial characteristics is poorest. The computational cost is the lowest for the semi-empirical model.

A detailed numerical simulation of a liquid-propellant rocket engine ground test experiment

NASA Astrophysics Data System (ADS)

Lankford, D. W.; Simmons, M. A.; Heikkinen, B. D.

1992-07-01

A computational simulation of a Liquid Rocket Engine (LRE) ground test experiment was performed using two modeling approaches. The results of the models were compared with selected data to assess the validity of state-of-the-art computational tools for predicting the flowfield and radiative transfer in complex flow environments. The data used for comparison consisted of in-band station radiation measurements obtained in the near-field portion of the plume exhaust. The test article was a subscale LRE with an afterbody, resulting in a large base region. The flight conditions were such that afterburning regions were observed in the plume flowfield. A conventional standard modeling approach underpredicted the extent of afterburning and the associated radiation levels. These results were attributed to the absence of the base flow region which is not accounted for in this model. To assess the effects of the base region a Navier-Stokes model was applied. The results of this calculation indicate that the base recirculation effects are dominant features in the immediate expansion region and resulted in a much improved comparison. However, the downstream in-band station radiation data remained underpredicted by this model.

Radiative heat transfer in the extreme near field.

PubMed

Kim, Kyeongtae; Song, Bai; Fernández-Hurtado, Víctor; Lee, Woochul; Jeong, Wonho; Cui, Longji; Thompson, Dakotah; Feist, Johannes; Reid, M T Homer; García-Vidal, Francisco J; Cuevas, Juan Carlos; Meyhofer, Edgar; Reddy, Pramod

2015-12-17

Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4-6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.

Analysis and evaluation of WRF microphysical schemes for deep moist convection over south-eastern South America (SESA) using microwave satellite observations and radiative transfer simulations

NASA Astrophysics Data System (ADS)

Sol Galligani, Victoria; Wang, Die; Alvarez Imaz, Milagros; Salio, Paola; Prigent, Catherine

2017-10-01

In the present study, three meteorological events of extreme deep moist convection, characteristic of south-eastern South America, are considered to conduct a systematic evaluation of the microphysical parameterizations available in the Weather Research and Forecasting (WRF) model by undertaking a direct comparison between satellite-based simulated and observed microwave radiances. A research radiative transfer model, the Atmospheric Radiative Transfer Simulator (ARTS), is coupled with the WRF model under three different microphysical parameterizations (WSM6, WDM6 and Thompson schemes). Microwave radiometry has shown a promising ability in the characterization of frozen hydrometeors. At high microwave frequencies, however, frozen hydrometeors significantly scatter radiation, and the relationship between radiation and hydrometeor populations becomes very complex. The main difficulty in microwave remote sensing of frozen hydrometeor characterization is correctly characterizing this scattering signal due to the complex and variable nature of the size, composition and shape of frozen hydrometeors. The present study further aims at improving the understanding of frozen hydrometeor optical properties characteristic of deep moist convection events in south-eastern South America. In the present study, bulk optical properties are computed by integrating the single-scattering properties of the Liu(2008) discrete dipole approximation (DDA) single-scattering database across the particle size distributions parameterized by the different WRF schemes in a consistent manner, introducing the equal mass approach. The equal mass approach consists of describing the optical properties of the WRF snow and graupel hydrometeors with the optical properties of habits in the DDA database whose dimensions might be different (Dmax') but whose mass is conserved. The performance of the radiative transfer simulations is evaluated by comparing the simulations with the available coincident microwave observations up to 190 GHz (with observations from Tropical Rainfall Measuring Mission's (TRMM) Microwave Imager (TMI), Microwave Humidity Sounder (MHS) and Special Sensor Microwave Imager/Sounder (SSMI/S)) using the χ2 test. Good agreement is obtained with all observations provided special care is taken to represent the scattering properties of the snow and graupel species.

Numerical study of radiative heat transfer and effects of thermal boundary conditions on CLC fuel reactor

NASA Astrophysics Data System (ADS)

Ben-Mansour, R.; Li, H.; Habib, M. A.; Hossain, M. M.

2018-02-01

Global warming has become a worldwide concern due to its severe impacts and consequences on the climate system and ecosystem. As a promising technology proving good carbon capture ability with low-efficiency penalty, Chemical Looping Combustion technology has risen much interest. However, the radiative heat transfer was hardly studied, nor its effects were clearly declared. The present work provides a mathematical model for radiative heat transfer within fuel reactor of chemical looping combustion systems and conducts a numerical research on the effects of boundary conditions, solid particles reflectivity, particles size, and the operating temperature. The results indicate that radiative heat transfer has very limited impacts on the flow pattern. Meanwhile, the temperature variations in the static bed region (where solid particles are dense) brought by radiation are also insignificant. However, the effects of radiation on temperature profiles within free bed region (where solid particles are very sparse) are obvious, especially when convective-radiative (mixed) boundary condition is applied on fuel reactor walls. Smaller oxygen carrier particle size results in larger absorption & scattering coefficients. The consideration of radiative heat transfer within fuel reactor increases the temperature gradient within free bed region. On the other hand, the conversion performance of fuel is nearly not affected by radiation heat transfer within fuel reactor. However, the consideration of radiative heat transfer enhances the heat transfer between the gas phase and solid phase, especially when the operating temperature is low.

Radiation characteristics of water droplets in a fire-inspired environment: A Monte Carlo ray tracing study

NASA Astrophysics Data System (ADS)

Wu, Bifen; Zhao, Xinyu

2018-06-01

The effects of radiation of water mists in a fire-inspired environment are numerically investigated for different complexities of radiative media in a three-dimensional cubic enclosure. A Monte Carlo ray tracing (MCRT) method is employed to solve the radiative transfer equation (RTE). The anisotropic scattering behaviors of water mists are modeled by a combination of the Mie theory and the Henyey-Greestein relation. A tabulation method considering the size and wavelength dependencies is established for water droplets, to reduce the computational cost associated with the evaluation of the nongray spectral properties of water mists. Validation and verification of the coupled MCRT solver are performed using a one-dimensional slab with gray gas in comparison with the analytical solutions. Parametric studies are then performed using a three-dimensional cubic box to examine radiation of two monodispersed and one polydispersed water mist systems. The tabulation method can reduce the computational cost by a factor of one hundred. Results obtained without any scattering model better conform with results obtained from the anisotropic model than the isotropic scattering model, when a highly directional emissive source is applied. For isotropic emissive sources, isotropic and anisotropic scattering models predict comparable results. The addition of different volume fractions of soot shows that soot may have a negative impact on the effectiveness of water mists in absorbing radiation when its volume fraction exceeds certain threshold.

Dayglow and night glow of the Venusian upper atmosphere. Modelling and observations

NASA Astrophysics Data System (ADS)

Gronoff, G.; Lilensten, J.; Simon, C.; Barthélemy, M.; Leblanc, F.

2007-08-01

Aims. We present the modelling of the production of excited states of O, CO and N2 in the Venusian upper atmosphere, which allows to compute the nightglow emissions. In the dayside, we also compute several emissions, taking advantage of the small influence of resonant scattering for forbidden transitions. Methods. We compute the photoionisation and the photodissociation mechanisms, and thus the photoelectron production. We compute electron impact excitation and ionisation through a multi-stream stationary kinetic transport code. Finally, we compute the ion recombination with a stationary chemical model. Results.We predict altitude density profiles for O(1S) and O(1D) states and the emissions corresponding to their different transitions. They are found to be very comparable to the observations without the need for stratospheric emissions. In the nightside, we highlight the role of the N + O+2 reaction in the creation of the O(1S) state. This reaction has been suggested by Rees in 1975 (Frederick, 1976). It has been discussed several times afterwhile and in spite of different studies, is still controversial. However, when we take it in consideration in Venus, it is shown to be the cause of almost 90% of the state production. We calculate the production intensities of O(3S) and O(5S) states, which are needed for radiative transfer models. For CO we compute the Cameron band and the fourth positive band emissions. For N2 we compute the LBH, first and second positive bands. All these values are successfully compared to the experiment when data are available. Conclusions. For the first time, a comprehensive model is proposed to compute dayglow and nightglow emissions of the Venusian upper atmosphere. It relies on previous works with noticeable improvements, both on the transport and on the chemical aspects. In the near future, a radiative transfer model will be used to compute optically thick lines in the dayglow, and a fluid model will be added to compute ionosphere densities and temperatures. We will present the first observational results from the Pic du Midi telescope in June 2007, in order to compare with our modelling.

On the Compton scattering redistribution function in plasma

NASA Astrophysics Data System (ADS)

Madej, J.; Różańska, A.; Majczyna, A.; Należyty, M.

2017-08-01

Compton scattering is the dominant opacity source in hot neutron stars, accretion discs around black holes and hot coronae. We collected here a set of numerical expressions of the Compton scattering redistribution functions (RFs) for unpolarized radiation, which are more exact than the widely used Kompaneets equation. The principal aim of this paper is the presentation of the RF by Guilbert, which is corrected for the computational errors in the original paper. This corrected RF was used in the series of papers on model atmosphere computations of hot neutron stars. We have also organized four existing algorithms for the RF computations into a unified form ready to use in radiative transfer and model atmosphere codes. The exact method by Nagirner & Poutanen was numerically compared to all other algorithms in a very wide spectral range from hard X-rays to radio waves. Sample computations of the Compton scattering RFs in thermal plasma were done for temperatures corresponding to the atmospheres of bursting neutron stars and hot intergalactic medium. Our formulae are also useful to study the Compton scattering of unpolarized microwave background radiation in hot intracluster gas and the Sunyaev-Zeldovich effect. We conclude that the formulae by Guilbert and the exact quantum mechanical formulae yield practically the same RFs for gas temperatures relevant to the atmospheres of X-ray bursting neutron stars, T ≤ 108 K.

Prospective of employing high porosity open-cell metal foams in passive cryogenic radiators for space applications

NASA Astrophysics Data System (ADS)

Tisha, Dixit; Indranil, Ghosh

2017-02-01

Passive cryogenic radiators work on the principle of dissipating heat to the outer space purely by radiation. High porosity open-cell metal foams are a relatively new class of extended surfaces. These possess the advantages of high surface area density and low weight, characteristics which the space industry looks for. In case of radiative heat transfer, the porous nature of metal foams permits a deeper penetration of the incident radiation. Consequently, the heat transfer area participating in radiative heat exchange increases thereby enhancing the heat transfer rate. However, effective heat conduction in between the foam struts reduces as a result of the void spaces. These two conflicting phenomenon for radiation heat transfer in metal foams have been studied in this work. Similar to the foam conduction-convection heat transfer analysis, a conduction-radiation heat transfer model has been developed for metal foams in analogy with the conventional solid fin theory. Metal foams have been theoretically represented as simple cubic structures. A comparison of the radiative heat transfer through metal foams and solid fins attached to a surface having constant temperature has been presented. Effect of changes in foam characteristic properties such as porosity and pore density have also been studied.

Fluctuating volume-current formulation of electromagnetic fluctuations in inhomogeneous media: Incandescence and luminescence in arbitrary geometries

NASA Astrophysics Data System (ADS)

Polimeridis, Athanasios G.; Reid, M. T. H.; Jin, Weiliang; Johnson, Steven G.; White, Jacob K.; Rodriguez, Alejandro W.

2015-10-01

We describe a fluctuating volume-current formulation of electromagnetic fluctuations that extends our recent work on heat exchange and Casimir interactions between arbitrarily shaped homogeneous bodies [A. W. Rodriguez, M. T. H. Reid, and S. G. Johnson, Phys. Rev. B 88, 054305 (2013), 10.1103/PhysRevB.88.054305] to situations involving incandescence and luminescence problems, including thermal radiation, heat transfer, Casimir forces, spontaneous emission, fluorescence, and Raman scattering, in inhomogeneous media. Unlike previous scattering formulations based on field and/or surface unknowns, our work exploits powerful techniques from the volume-integral equation (VIE) method, in which electromagnetic scattering is described in terms of volumetric, current unknowns throughout the bodies. The resulting trace formulas (boxed equations) involve products of well-studied VIE matrices and describe power and momentum transfer between objects with spatially varying material properties and fluctuation characteristics. We demonstrate that thanks to the low-rank properties of the associated matrices, these formulas are susceptible to fast-trace computations based on iterative methods, making practical calculations tractable. We apply our techniques to study thermal radiation, heat transfer, and fluorescence in complicated geometries, checking our method against established techniques best suited for homogeneous bodies as well as applying it to obtain predictions of radiation from complex bodies with spatially varying permittivities and/or temperature profiles.

Solar tower cavity receiver aperture optimization based on transient optical and thermo-hydraulic modeling

NASA Astrophysics Data System (ADS)

Schöttl, Peter; Bern, Gregor; van Rooyen, De Wet; Heimsath, Anna; Fluri, Thomas; Nitz, Peter

2017-06-01

A transient simulation methodology for cavity receivers for Solar Tower Central Receiver Systems with molten salt as heat transfer fluid is described. Absorbed solar radiation is modeled with ray tracing and a sky discretization approach to reduce computational effort. Solar radiation re-distribution in the cavity as well as thermal radiation exchange are modeled based on view factors, which are also calculated with ray tracing. An analytical approach is used to represent convective heat transfer in the cavity. Heat transfer fluid flow is simulated with a discrete tube model, where the boundary conditions at the outer tube surface mainly depend on inputs from the previously mentioned modeling aspects. A specific focus is put on the integration of optical and thermo-hydraulic models. Furthermore, aiming point and control strategies are described, which are used during the transient performance assessment. Eventually, the developed simulation methodology is used for the optimization of the aperture opening size of a PS10-like reference scenario with cavity receiver and heliostat field. The objective function is based on the cumulative gain of one representative day. Results include optimized aperture opening size, transient receiver characteristics and benefits of the implemented aiming point strategy compared to a single aiming point approach. Future work will include annual simulations, cost assessment and optimization of a larger range of receiver parameters.

3D Multi-Level Non-LTE Radiative Transfer for the CO Molecule

NASA Astrophysics Data System (ADS)

Berkner, A.; Schweitzer, A.; Hauschildt, P. H.

2015-01-01

The photospheres of cool stars are both rich in molecules and an environment where the assumption of LTE can not be upheld under all circumstances. Unfortunately, detailed 3D non-LTE calculations involving molecules are hardly feasible with current computers. For this reason, we present our implementation of the super level technique, in which molecular levels are combined into super levels, to reduce the number of unknowns in the rate equations and, thus, the computational effort and memory requirements involved, and show the results of our first tests against the 1D implementation of the same method.

A scattering model for defoliated vegetation

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.

1986-01-01

A scattering model for defoliated vegetation is conceived as a layer of dielectric, finite-length cylinders with specified size and orientation distributions above an irregular ground surface. The scattering phase matrix of a single cylinder is computed, then the radiative transfer technique is applied to link volume scattering from vegetation to surface scattering from the soil surface. Polarized and depolarized scattering are computed and the effects of the cylinder size and orientation distributions are illustrated. It is found that size and orientation distributions have significant effects on the backscattered signal. The model is compared with scattering from defoliated trees and agricultural crops.

Monochromatic, Rosseland mean, and Planck mean opacity routine

NASA Astrophysics Data System (ADS)

Semenov, D.

2006-11-01

Several FORTRAN77 codes were developed to compute frequency-dependent, Rosseland and Planck mean opacities of gas and dust in protoplanetary disks. The opacities can be computed for an ensemble of dust grains having various compositions (ices, silicates, organics, etc), sizes, topologies (homogeneous/composite aggregates, homogeneous/layered/composite spheres, etc.), porosities, and dust-to-gas ratio. Several examples are available. In addition, a very fast opacity routine to be used in modeling of the radiative transfer in hydro simulations of disks is available upon request (10^8 routine calls require about 30s on Pentium 4 3.0GHz).

ENGINEERING APPLICATIONS OF ANALOG COMPUTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryant, L.T.; Janicke, M.J.; Just, L.C.

1963-10-31

Six experiments from the fields of reactor engineering, heat transfer, and dynamics are presented to illustrate the engineering applications of analog computers. The steps required for producing the analog solution are shown, as well as complete information for duplicating the solution. Graphical results are provided. The experiments include: deceleration of a reactor control rod, pressure variations through a packed bed, reactor kinetics over many decades with thermal feedback, a vibrating system with two degrees of freedom, temperature distribution in a radiating fin, temperature distribution in an infinite slab considering variable thermal properties, and iodine -xenon buildup in a reactor. (M.C.G.)

Discontinuous finite element method for vector radiative transfer

NASA Astrophysics Data System (ADS)

Wang, Cun-Hai; Yi, Hong-Liang; Tan, He-Ping

2017-03-01

The discontinuous finite element method (DFEM) is applied to solve the vector radiative transfer in participating media. The derivation in a discrete form of the vector radiation governing equations is presented, in which the angular space is discretized by the discrete-ordinates approach with a local refined modification, and the spatial domain is discretized into finite non-overlapped discontinuous elements. The elements in the whole solution domain are connected by modelling the boundary numerical flux between adjacent elements, which makes the DFEM numerically stable for solving radiative transfer equations. Several various problems of vector radiative transfer are tested to verify the performance of the developed DFEM, including vector radiative transfer in a one-dimensional parallel slab containing a Mie/Rayleigh/strong forward scattering medium and a two-dimensional square medium. The fact that DFEM results agree very well with the benchmark solutions in published references shows that the developed DFEM in this paper is accurate and effective for solving vector radiative transfer problems.

A Network Model for the Effective Thermal Conductivity of Rigid Fibrous Refractory Insulations

NASA Technical Reports Server (NTRS)

Marschall, Jochen; Cooper, D. M. (Technical Monitor)

1995-01-01

A procedure is described for computing the effective thermal conductivity of a rigid fibrous refractory insulation. The insulation is modeled as a 3-dimensional Cartesian network of thermal conductance. The values and volume distributions of the conductance are assigned to reflect the physical properties of the insulation, its constituent fibers, and any permeating gas. The effective thermal conductivity is computed by considering the simultaneous energy transport by solid conduction, gas conduction and radiation through a cubic volume of model insulation; thus the coupling between heat transfer modes is retained (within the simplifications inherent to the model), rather than suppressed by treating these heat transfer modes as independent. The model takes into account insulation composition, density and fiber anisotropy, as well as the geometric and material properties of the constituent fibers. A relatively good agreement, between calculated and experimentally derived thermal conductivity values, is obtained for a variety of rigid fibrous insulations.

Finite-element reentry heat-transfer analysis of space shuttle Orbiter

NASA Technical Reports Server (NTRS)

Ko, William L.; Quinn, Robert D.; Gong, Leslie

1986-01-01

A structural performance and resizing (SPAR) finite-element thermal analysis computer program was used in the heat-transfer analysis of the space shuttle orbiter subjected to reentry aerodynamic heating. Three wing cross sections and one midfuselage cross section were selected for the thermal analysis. The predicted thermal protection system temperatures were found to agree well with flight-measured temperatures. The calculated aluminum structural temperatures also agreed reasonably well with the flight data from reentry to touchdown. The effects of internal radiation and of internal convection were found to be significant. The SPAR finite-element solutions agreed reasonably well with those obtained from the conventional finite-difference method.

Solar electric geocentric transfer with attitude constraints: Analysis

NASA Technical Reports Server (NTRS)

Sackett, L. L.; Malchow, H. L.; Delbaum, T. N.

1975-01-01

A time optimal or nearly time optimal trajectory program was developed for solar electric geocentric transfer with or without attitude constraints and with an optional initial high thrust stage. The method of averaging reduces computation time. A nonsingular set of orbital elements is used. The constraints, which are those of one of the SERT-C designs, introduce complexities into the analysis and the solution yields possible discontinuous changes in thrust direction. The power degradation due to VanAllen radiation is modeled analytically. A wide range of solar cell characteristics is assumed. Effects such as oblateness and shadowing are included. The analysis and the results of many example runs are included.

Correlation of heat transfer for the zero pressure gradient hypersonic laminar boundary layer for several gases

NASA Technical Reports Server (NTRS)

Cook, W. J.

1973-01-01

A theoretical study of heat transfer for zero pressure gradient hypersonic laminar boundary layers for various gases with particular application to the flows produced in an expansion tube facility was conducted. A correlation based on results obtained from solutions to the governing equations for five gases was formulated. Particular attention was directed toward the laminar boundary layer shock tube splitter plates in carbon dioxide flows generated by high speed shock waves. Computer analysis of the splitter plate boundary layer flow provided information that is useful in interpreting experimental data obtained in shock tube gas radiation studies.

Impact of aerosols and clouds on decadal trends in all-sky solar radiation over the Netherlands (1966-2015)

NASA Astrophysics Data System (ADS)

Boers, Reinout; Brandsma, Theo; Pier Siebesma, A.

2017-07-01

A 50-year hourly data set of global shortwave radiation, cloudiness and visibility over the Netherlands was used to quantify the contribution of aerosols and clouds to the trend in yearly-averaged all-sky radiation (1.81 ± 1.07 W m-2 decade-1). Yearly-averaged clear-sky and cloud-base radiation data show large year-to-year fluctuations caused by yearly changes in the occurrence of clear and cloudy periods and cannot be used for trend analysis. Therefore, proxy clear-sky and cloud-base radiations were computed. In a proxy analysis hourly radiation data falling within a fractional cloudiness value are fitted by monotonic increasing functions of solar zenith angle and summed over all zenith angles occurring in a single year to produce an average. Stable trends can then be computed from the proxy radiation data. A functional expression is derived whereby the trend in proxy all-sky radiation is a linear combination of trends in fractional cloudiness, proxy clear-sky radiation and proxy cloud-base radiation. Trends (per decade) in fractional cloudiness, proxy clear-sky and proxy cloud-base radiation were, respectively, 0.0097 ± 0.0062, 2.78 ± 0.50 and 3.43 ± 1.17 W m-2. To add up to the all-sky radiation the three trends have weight factors, namely the difference between the mean cloud-base and clear-sky radiation, the clear-sky fraction and the fractional cloudiness, respectively. Our analysis clearly demonstrates that all three components contribute significantly to the observed trend in all-sky radiation. Radiative transfer calculations using the aerosol optical thickness derived from visibility observations indicate that aerosol-radiation interaction (ARI) is a strong candidate to explain the upward trend in the clear-sky radiation. Aerosol-cloud interaction (ACI) may have some impact on cloud-base radiation, but it is suggested that decadal changes in cloud thickness and synoptic-scale changes in cloud amount also play an important role.

A study of the 3D radiative transfer effect in cloudy atmospheres

NASA Astrophysics Data System (ADS)

Okata, M.; Teruyuki, N.; Suzuki, K.

2015-12-01

Evaluation of the effect of clouds in the atmosphere is a significant problem in the Earth's radiation budget study with their large uncertainties of microphysics and the optical properties. In this situation, we still need more investigations of 3D cloud radiative transer problems using not only models but also satellite observational data.For this purpose, we have developed a 3D-Monte-Carlo radiative transfer code that is implemented with various functions compatible with the OpenCLASTR R-Star radiation code for radiance and flux computation, i.e. forward and backward tracing routines, non-linear k-distribution parameterization (Sekiguchi and Nakajima, 2008) for broad band solar flux calculation, and DM-method for flux and TMS-method for upward radiance (Nakajima and Tnaka 1998). We also developed a Minimum cloud Information Deviation Profiling Method (MIDPM) as a method for a construction of 3D cloud field with MODIS/AQUA and CPR/CloudSat data. We then selected a best-matched radar reflectivity factor profile from the library for each of off-nadir pixels of MODIS where CPR profile is not available, by minimizing the deviation between library MODIS parameters and those at the pixel. In this study, we have used three cloud microphysical parameters as key parameters for the MIDPM, i.e. effective particle radius, cloud optical thickness and top of cloud temperature, and estimated 3D cloud radiation budget. We examined the discrepancies between satellite observed and mode-simulated radiances and three cloud microphysical parameter's pattern for studying the effects of cloud optical and microphysical properties on the radiation budget of the cloud-laden atmospheres.

Performance analysis of a parallel Monte Carlo code for simulating solar radiative transfer in cloudy atmospheres using CUDA-enabled NVIDIA GPU

NASA Astrophysics Data System (ADS)

Russkova, Tatiana V.

2017-11-01

One tool to improve the performance of Monte Carlo methods for numerical simulation of light transport in the Earth's atmosphere is the parallel technology. A new algorithm oriented to parallel execution on the CUDA-enabled NVIDIA graphics processor is discussed. The efficiency of parallelization is analyzed on the basis of calculating the upward and downward fluxes of solar radiation in both a vertically homogeneous and inhomogeneous models of the atmosphere. The results of testing the new code under various atmospheric conditions including continuous singlelayered and multilayered clouds, and selective molecular absorption are presented. The results of testing the code using video cards with different compute capability are analyzed. It is shown that the changeover of computing from conventional PCs to the architecture of graphics processors gives more than a hundredfold increase in performance and fully reveals the capabilities of the technology used.

Computational model for operation of 2 mum co-doped Tm,Ho solid state lasers.

PubMed

Louchev, Oleg A; Urata, Yoshiharu; Saito, Norihito; Wada, Satoshi

2007-09-17

A computational model for operation of co-doped Tm,Ho solid-state lasers is developed coupling (i) 8-level rate equations with (ii) TEM00 laser beam distribution, and (iii) complex heat dissipation model. Simulations done for Q-switched approximately 0.1 J giant pulse generation by Tm,Ho:YLF laser show that approximately 43% of the 785 nm light diode side-pumped energy is directly transformed into the heat inside the crystal, whereas approximately 45% is the spontaneously emitted radiation from (3)F(4), (5)I(7) , (3)H(4) and (3)H(5) levels. In water-cooled operation this radiation is absorbed inside the thermal boundary layer where the heat transfer is dominated by heat conduction. In high-power operation the resulting temperature increase is shown to lead to (i) significant decrease in giant pulse energy and (ii) thermal lensing.

Radiative transfer modelling inside thermal protection system using hybrid homogenization method for a backward Monte Carlo method coupled with Mie theory

NASA Astrophysics Data System (ADS)

Le Foll, S.; André, F.; Delmas, A.; Bouilly, J. M.; Aspa, Y.

2012-06-01

A backward Monte Carlo method for modelling the spectral directional emittance of fibrous media has been developed. It uses Mie theory to calculate the radiative properties of single fibres, modelled as infinite cylinders, and the complex refractive index is computed by a Drude-Lorenz model for the dielectric function. The absorption and scattering coefficient are homogenised over several fibres, but the scattering phase function of a single one is used to determine the scattering direction of energy inside the medium. Sensitivity analysis based on several Monte Carlo results has been performed to estimate coefficients for a Multi-Linear Model (MLM) specifically developed for inverse analysis of experimental data. This model concurs with the Monte Carlo method and is highly computationally efficient. In contrast, the surface emissivity model, which assumes an opaque medium, shows poor agreement with the reference Monte Carlo calculations.

Influence of daylight and noise current on cloud and aerosol observations by spaceborne elastic scattering lidar.

PubMed

Nakajima, T Y; Imai, T; Uchino, O; Nagai, T

1999-08-20

The influence of daylight and noise current on cloud and aerosol observations by realistic spaceborne lidar was examined by computer simulations. The reflected solar radiations, which contaminate the daytime return signals of lidar operations, were strictly and explicitly estimated by accurate radiative transfer calculations. It was found that the model multilayer cirrus clouds and the boundary layer aerosols could be observed during the daytime and the nighttime with only a few laser shots. However, high background noise and noise current make it difficult to observe volcanic aerosols in middle and upper atmospheric layers. Optimal combinations of the laser power and receiver field of view are proposed to compensate for the negative influence that is due to these noises. For the computer simulations, we used a realistic set of lidar parameters similar to the Experimental Lidar in-Space Equipment of the National Space Development Agency of Japan.

Thermal Analysis on Plume Heating of the Main Engine on the Crew Exploration Vehicle Service Module

NASA Technical Reports Server (NTRS)

Wang, Xiao-Yen J.; Yuko, James R.

2007-01-01

The crew exploration vehicle (CEV) service module (SM) main engine plume heating is analyzed using multiple numerical tools. The chemical equilibrium compositions and applications (CEA) code is used to compute the flow field inside the engine nozzle. The plume expansion into ambient atmosphere is simulated using an axisymmetric space-time conservation element and solution element (CE/SE) Euler code, a computational fluid dynamics (CFD) software. The thermal analysis including both convection and radiation heat transfers from the hot gas inside the engine nozzle and gas radiation from the plume is performed using Thermal Desktop. Three SM configurations, Lockheed Martin (LM) designed 604, 605, and 606 configurations, are considered. Design of multilayer insulation (MLI) for the stowed solar arrays, which is subject to plume heating from the main engine, among the passive thermal control system (PTCS), are proposed and validated.

Quantitation of heavy ion damage to the mammalian brain - Some preliminary findings

NASA Technical Reports Server (NTRS)

Cox, A. B.; Kraft, L. M.

1984-01-01

For several years, studies have been conducted regarding late effects of particulate radiations in mammalian tissues, taking into account the brains of rodents and lagomorphs. Recently, it has become feasible to quantify pathological damage and morpho-physiologic alterations accurately in large numbers of histological specimens. New investigative procedures make use of computer-assisted automated image analysis systems. Details regarding the employed methodology are discussed along with the results of the information. The radiations of high linear energy transfer (LET) cause apparently earlier and more dramatic shrinkage of olfactory glomeruli in exposed rabbit brains than comparable doses of Co-60 gamma photons.

Laser Powered Launch Vehicle Performance Analyses

NASA Technical Reports Server (NTRS)

Chen, Yen-Sen; Liu, Jiwen; Wang, Ten-See (Technical Monitor)

2001-01-01

The purpose of this study is to establish the technical ground for modeling the physics of laser powered pulse detonation phenomenon. Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Successful predictions of the performance of laser powered launch vehicle concepts depend on the sophisticate models that reflects the underlying flow physics including the laser ray tracing the focusing, inverse Bremsstrahlung (IB) effects, finite-rate air chemistry, thermal non-equilibrium, plasma radiation and detonation wave propagation, etc. The proposed work will extend the base-line numerical model to an efficient design analysis tool. The proposed model is suitable for 3-D analysis using parallel computing methods.

Relationships between chlorophyll density and ocean radiance as measured by U2/OCS: Algorithms, examples and comparison

NASA Technical Reports Server (NTRS)

Kim, H. H.; Hart, W. D.

1983-01-01

An ocean atmosphere radiative transfer process computation method which is suitable for determining lower boundary ocean albedo and other radiation components from spectral measurements of upwelling radiance taken from a high altitude platform is described. The method was applied to a set of color scanner data taken from slope water of the South Atlantic Bight to determine the influence of cholorophyll-a pigments in the sea on the ratio of upwelling radiance to down welling irradiance as a function of wavelength. The resulting chlorophyll concentrations are compared with measurements made by ships stationed along the flight path.

Power flow in normal human voice production

NASA Astrophysics Data System (ADS)

Krane, Michael

2016-11-01

The principal mechanisms of energy utilization in voicing are quantified using a simplified model, in order to better define voice efficiency. A control volume analysis of energy utilization in phonation is presented to identify the energy transfer mechanisms in terms of their function. Conversion of subglottal airstream potential energy into useful work done (vocal fold vibration, flow work, sound radiation), and into heat (sound radiation absorbed by the lungs, glottal jet dissipation) are described. An approximate numerical model is used to compute the contributions of each of these mechanisms, as a function of subglottal pressure, for normal phonation. Acknowledge support of NIH Grant 2R01DC005642-10A1.

K-distribution models for gas mixtures in hypersonic nonequilibrium flows

NASA Astrophysics Data System (ADS)

Bansal, Ankit

Calculation of nonequilibrium radiation field in plasmas around a spacecraft entering into an atmosphere at hypersonic velocities is a very complicated and computationally expensive task. The objective of this Dissertation is to collect state-of-the art spectroscopic data for the evaluation of spectral absorption and emission coefficients of atomic and molecular gases, develop efficient and accurate spectral models and databases, and study the effect of radiation on wall heat loads and flowfield around the spacecraft. The most accurate simulation of radiative transport in the shock layer requires calculating the gas properties at a large number of wavelengths and solving the Radiative Transfer Equation (RTE) in a line-by-line (LBL) fashion, which is prohibitively expensive for coupled simulations. A number of k-distribution based spectral models are developed for atomic lines, continuum and molecular bands that allow efficient evaluation of radiative properties and heat loads in hypersonic shock layer plasma. Molecular radiation poses very different challenges than atomic radiation. A molecular spectrum is governed by simultaneous electronic, vibrational and rotational transitions, making the spectrum very strongly dependent on wavelength. In contrast to an atomic spectrum, where line wings play a major role in heat transfer, most of the heat transfer in molecular spectra occurs near line centers. As the first step, k-distribution models are developed separately for atomic and molecular species, taking advantage of the fact that in the Earth's atmosphere the radiative field is dominated by atomic species (N and O) and in Titan's and Mars' atmospheres molecular bands of CN and CO are dominant. There are a number of practical applications where both atomic and molecular species are present, for example, the vacuum-ultra-violet spectrum during Earth's reentry conditions is marked by emission from atomic bound-bound lines and continuum and simultaneous absorption by strong bands of N2. For such cases, a new model is developed for the treatment of gas mixtures containing atomic lines, continuum and molecular bands. Full-spectrum k-distribution (FSK) method provides very accurate results compared to those obtained from the exact line-by-line method. For cases involving more extreme gradients in species concentrations and temperature, full-spectrum k-distribution model is relatively less accurate, and the method is refined by dividing the spectrum into a number of groups or scales, leading to the development of multi-scale models. The detailed methodology of splitting the gas mixture into scales is presented. To utilize the full potential of the k-distribution methods, pre-calculated values of k-distributions are stored in databases, which can later be interpolated at local flow conditions. Accurate and compact part-spectrum k-distribution databases are developed for atomic species and molecular bands. These databases allow users to calculate desired full-spectrum k-distributions through look-up and interpolation. Application of the new spectral models and databases to shock layer plasma radiation is demonstrated by solving the radiative transfer equation along typical one-dimensional flowfields in Earth's, Titan's and Mars' atmospheres. The k-distribution methods are vastly more efficient than the line-by-line method. The efficiency of the method is compared with the line-by-line method by measuring computational times for a number of test problems, showing typical reduction in computational time by a factor of more than 500 for property evaluation and a factor of about 32,000 for the solution of the RTE. A large percentage of radiative energy emitted in the shock-layer is likely to escape the region, resulting in cooling of the shock layer. This may change the flow parameters in the flowfield and, in turn, can affect radiative as well as convective heat loads. A new flow solver is constructed to simulate coupled hypersonic flow-radiation over a reentry vehicle. The flow solver employs a number of existing schemes and tools available in OpenFOAM; along with a number of additional features for high temperature, compressible and chemically reacting flows, and k-distribution models for radiative calculations. The radiative transport is solved with the one-dimensional tangent slab and P1 solvers, and also with the two-dimensional P1 solver. The new solver is applied to simulate flow around an entry vehicle in Martian atmosphere. Results for uncoupled and coupled flow-radiation simulations are presented, highlighting the effects of radiative cooling on flowfield and wall fluxes.

Nonequilibrium radiative hypersonic flow simulation

NASA Astrophysics Data System (ADS)

Shang, J. S.; Surzhikov, S. T.

2012-08-01

Nearly all the required scientific disciplines for computational hypersonic flow simulation have been developed on the framework of gas kinetic theory. However when high-temperature physical phenomena occur beneath the molecular and atomic scales, the knowledge of quantum physics and quantum chemical-physics becomes essential. Therefore the most challenging topics in computational simulation probably can be identified as the chemical-physical models for a high-temperature gaseous medium. The thermal radiation is also associated with quantum transitions of molecular and electronic states. The radiative energy exchange is characterized by the mechanisms of emission, absorption, and scattering. In developing a simulation capability for nonequilibrium radiation, an efficient numerical procedure is equally important both for solving the radiative transfer equation and for generating the required optical data via the ab-initio approach. In computational simulation, the initial values and boundary conditions are paramount for physical fidelity. Precise information at the material interface of ablating environment requires more than just a balance of the fluxes across the interface but must also consider the boundary deformation. The foundation of this theoretic development shall be built on the eigenvalue structure of the governing equations which can be described by Reynolds' transport theorem. Recent innovations for possible aerospace vehicle performance enhancement via an electromagnetic effect appear to be very attractive. The effectiveness of this mechanism is dependent strongly on the degree of ionization of the flow medium, the consecutive interactions of fluid dynamics and electrodynamics, as well as an externally applied magnetic field. Some verified research results in this area will be highlighted. An assessment of all these most recent advancements in nonequilibrium modeling of chemical kinetics, chemical-physics kinetics, ablation, radiative exchange, computational algorithms, and the aerodynamic-electromagnetic interaction are summarized and delineated. The critical basic research areas for physic-based hypersonic flow simulation should become self-evident through the present discussion. Nevertheless intensive basic research efforts must be sustained in these areas for fundamental knowledge and future technology advancement.

Validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving.

PubMed

Zampolli, Mario; Nijhof, Marten J J; de Jong, Christ A F; Ainslie, Michael A; Jansen, Erwin H W; Quesson, Benoit A J

2013-01-01

The acoustic radiation from a pile being driven into the sediment by a sequence of hammer strikes is studied with a linear, axisymmetric, structural acoustic frequency domain finite element model. Each hammer strike results in an impulsive sound that is emitted from the pile and then propagated in the shallow water waveguide. Measurements from accelerometers mounted on the head of a test pile and from hydrophones deployed in the water are used to validate the model results. Transfer functions between the force input at the top of the anvil and field quantities, such as acceleration components in the structure or pressure in the fluid, are computed with the model. These transfer functions are validated using accelerometer or hydrophone measurements to infer the structural forcing. A modeled hammer forcing pulse is used in the successive step to produce quantitative predictions of sound exposure at the hydrophones. The comparison between the model and the measurements shows that, although several simplifying assumptions were made, useful predictions of noise levels based on linear structural acoustic models are possible. In the final part of the paper, the model is used to characterize the pile as an acoustic radiator by analyzing the flow of acoustic energy.

High-order solution methods for grey discrete ordinates thermal radiative transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maginot, Peter G., E-mail: maginot1@llnl.gov; Ragusa, Jean C., E-mail: jean.ragusa@tamu.edu; Morel, Jim E., E-mail: morel@tamu.edu

This work presents a solution methodology for solving the grey radiative transfer equations that is both spatially and temporally more accurate than the canonical radiative transfer solution technique of linear discontinuous finite element discretization in space with implicit Euler integration in time. We solve the grey radiative transfer equations by fully converging the nonlinear temperature dependence of the material specific heat, material opacities, and Planck function. The grey radiative transfer equations are discretized in space using arbitrary-order self-lumping discontinuous finite elements and integrated in time with arbitrary-order diagonally implicit Runge–Kutta time integration techniques. Iterative convergence of the radiation equation ismore » accelerated using a modified interior penalty diffusion operator to precondition the full discrete ordinates transport operator.« less

High-order solution methods for grey discrete ordinates thermal radiative transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maginot, Peter G.; Ragusa, Jean C.; Morel, Jim E.

This paper presents a solution methodology for solving the grey radiative transfer equations that is both spatially and temporally more accurate than the canonical radiative transfer solution technique of linear discontinuous finite element discretization in space with implicit Euler integration in time. We solve the grey radiative transfer equations by fully converging the nonlinear temperature dependence of the material specific heat, material opacities, and Planck function. The grey radiative transfer equations are discretized in space using arbitrary-order self-lumping discontinuous finite elements and integrated in time with arbitrary-order diagonally implicit Runge–Kutta time integration techniques. Iterative convergence of the radiation equation ismore » accelerated using a modified interior penalty diffusion operator to precondition the full discrete ordinates transport operator.« less

High-order solution methods for grey discrete ordinates thermal radiative transfer

DOE PAGES

Maginot, Peter G.; Ragusa, Jean C.; Morel, Jim E.

2016-09-29

This paper presents a solution methodology for solving the grey radiative transfer equations that is both spatially and temporally more accurate than the canonical radiative transfer solution technique of linear discontinuous finite element discretization in space with implicit Euler integration in time. We solve the grey radiative transfer equations by fully converging the nonlinear temperature dependence of the material specific heat, material opacities, and Planck function. The grey radiative transfer equations are discretized in space using arbitrary-order self-lumping discontinuous finite elements and integrated in time with arbitrary-order diagonally implicit Runge–Kutta time integration techniques. Iterative convergence of the radiation equation ismore » accelerated using a modified interior penalty diffusion operator to precondition the full discrete ordinates transport operator.« less

Selected natural and fallout radionuclides in plant foods around the Kudankulam Nuclear Power Project, India.

PubMed

Ross, E Mahiban; Raj, Y Lenin; Wesley, S Godwin; Rajan, M P

2013-01-01

The activity concentrations of certain radionuclides were quantified in some plant foods cultivated around Kudankulam, where a mega-nuclear power plant is being established. The activity concentrations were found more in the 'pulses' group and were the lowest in 'other vegetable' category. The annual effective dose was computed based on the activity concentration of radionuclides and it was found to be higher due to the consumption of cereals and pulses. Other vegetables, cereals, pulses and nuts recorded high transfer factors for the radionuclide (228)Ra. Fruits, leafy vegetables, tubers and roots, and palm embryo registered high transfer factors for (226)Ra. Group-wise activity concentration, radiation dose to the public and soil-plant-to-transfer factor are discussed in detail. Copyright © 2012 Elsevier Ltd. All rights reserved.

Dust radiative effect over Europe, Mediterranean, Sahara and Middle East from a radiative transfer model using BSC-DREAM8b aerosol optical data

NASA Astrophysics Data System (ADS)

Papadimas, Christos; Gkikas, Antonis; Hatzianastassiou, Nikos; Matsoukas, Christos; Kazadzis, Stelios; Basart, Sara; Baldasano, Jose; Vardavas, Ilias

2013-04-01

The arid regions of Saharan desert and Middle East are the world's major dust sources. However, dust particles from these areas are transported to nearby regions, through favourable synoptic conditions, even reaching remote locations in Europe or in the Arctic. This transport is very important in numerous aspects. One of its most important effects is on the radiation budget, and more specifically on solar radiation, through the aerosol direct radiative effect (DRE). Previous studies have shown that this effect is great under dust load conditions. Therefore, it is very important to simulate dust transport processes and associated radiative effects. The simulation of dust production, transport and removal is done by numerical models, which however have their own limitations as to the consideration of physical and dynamical processes as well as their initial conditions. On the other hand, the computation of dust DRE is ideally done with radiative transfer models (RTMs), which however imply uncertainties associated with the input aerosol optical properties. The most important aerosol optical properties used in RTMs and climate models are aerosol optical depth (AOD), single scattering albedo (SSA) and asymmetry parameter (AP). The main target of the present study is to reduce the uncertainties of dust DRE by using a detailed spectral RTM and an acknowledged regional and meso-scale model describing the distribution of dust. The combined use of these tools is applied to the region covering the deserts of Sahara, Arabian Peninsula and Middle East, and the neighbouring Mediterranean basin and European continent (extending from 15°N to 60°N and from 21°W to 54°E). The computations are performed on a monthly mean basis, refer to the 11-year period 2000-2010, and quantify the effects of dust on the reflected solar radiation at the top of atmosphere (DRETOA), on the absorbed solar radiation within the atmosphere (DREatmab), and on the downwelling and absorbed solar radiation at the surface (DREsurf and DREsurfnet, respectively). The RTM takes into account all physical parameters of the Earth-Atmosphere system that interact with solar radiation, namely ozone, carbon dioxide, methane, water vapour, clouds (low, middle, high), aerosol and atmospheric molecules (Rayleigh scattering) as well as surface reflection. Emphasis is given to aerosol optical properties (AOD, SSA and AP) which are all obtained from the dust regional BSC-DREAM8b model. Detailed analysis is undertaken of the modelled aerosol properties, and the spatial and temporal (seasonal and year by year) variation of these properties and of the model DREs are thoroughly investigated. In addition, the computed DREs are inter-compared with corresponding ones obtained with the same RTM using aerosol data from satellites (e.g. MODIS) or other datasets (e.g. Global Aerosol DataSet, GADS and Hamburg Aerosol Climatology, HAC).

Analysis of the thermal performance of heat pipe radiators

NASA Technical Reports Server (NTRS)

Boo, J. H.; Hartley, J. G.

1990-01-01

A comprehensive mathematical model and computational methodology are presented to obtain numerical solutions for the transient behavior of a heat pipe radiator in a space environment. The modeling is focused on a typical radiator panel having a long heat pipe at the center and two extended surfaces attached to opposing sides of the heat pipe shell in the condenser section. In the set of governing equations developed for the model, each region of the heat pipe - shell, liquid, and vapor - is thermally lumped to the extent possible, while the fin is lumped only in the direction normal to its surface. Convection is considered to be the only significant heat transfer mode in the vapor, and the evaporation and condensation velocity at the liquid-vapor interface is calculated from kinetic theory. A finite-difference numerical technique is used to predict the transient behavior of the entire radiator in response to changing loads.

CAD-based stand-alone spacecraft radiation exposure analysis system: An application of the early man-tended Space Station

NASA Technical Reports Server (NTRS)

Appleby, M. H.; Golightly, M. J.; Hardy, A. C.

1993-01-01

Major improvements have been completed in the approach to analyses and simulation of spacecraft radiation shielding and exposure. A computer-aided design (CAD)-based system has been developed for determining the amount of shielding provided by a spacecraft and simulating transmission of an incident radiation environment to any point within or external to the vehicle. Shielding analysis is performed using a customized ray-tracing subroutine contained within a standard engineering modeling software package. This improved shielding analysis technique has been used in several vehicle design programs such as a Mars transfer habitat, pressurized lunar rover, and the redesigned international Space Station. Results of analysis performed for the Space Station astronaut exposure assessment are provided to demonastrate the applicability and versatility of the system.

The iterative thermal emission method: A more implicit modification of IMC

DOE PAGES

Long, A. R.; Gentile, N. A.; Palmer, T. S.

2014-08-19

For over 40 years, the Implicit Monte Carlo (IMC) method has been used to solve challenging problems in thermal radiative transfer. These problems typically contain regions that are optically thick and diffusive, as a consequence of the high degree of “pseudo-scattering” introduced to model the absorption and reemission of photons from a tightly-coupled, radiating material. IMC has several well-known features that could be improved: a) it can be prohibitively computationally expensive, b) it introduces statistical noise into the material and radiation temperatures, which may be problematic in multiphysics simulations, and c) under certain conditions, solutions can be nonphysical, in thatmore » they violate a maximum principle, where IMC-calculated temperatures can be greater than the maximum temperature used to drive the problem.« less

A novel approach for introducing cloud spatial structure into cloud radiative transfer parameterizations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Dong; Liu, Yangang

2014-12-18

Subgrid-scale variability is one of the main reasons why parameterizations are needed in large-scale models. Although some parameterizations started to address the issue of subgrid variability by introducing a subgrid probability distribution function for relevant quantities, the spatial structure has been typically ignored and thus the subgrid-scale interactions cannot be accounted for physically. Here we present a new statistical-physics-like approach whereby the spatial autocorrelation function can be used to physically capture the net effects of subgrid cloud interaction with radiation. The new approach is able to faithfully reproduce the Monte Carlo 3D simulation results with several orders less computational cost,more » allowing for more realistic representation of cloud radiation interactions in large-scale models.« less

Nonequilibrium radiation and chemistry models for aerocapture vehicle flowfields, volume 2

NASA Technical Reports Server (NTRS)

Carlson, Leland A.

1991-01-01

A technique was developed for predicting the character and magnitude of the shock wave precursor ahead of an entry vehicle and the effect of this precursor on the vehicle flow field was ascertained. A computational method and program were developed to properly model this precursor. Expressions were developed for the mass production rates of each species due to photodissociation and photoionization reactions. Also, consideration was given to the absorption and emission of radiation and how it affects the energy in each of the energy modes of both the atomic and diatomic species. A series of parametric studies were conducted covering a range of entry conditions in order to predict the effects of the precursor on the shock layer and the radiative heat transfer to the body.

N(+)-N and O(+)-O interaction energies, dipole transition moments, and transport cross sections

NASA Technical Reports Server (NTRS)

Partridge, H.; Stallcop, J. R.

1986-01-01

Complete sets of ion-atom interaction energies have been computed for nitrogen and oxygen with accurate large scale structure calculations. The computed energies agree well with the accurate potential curves available from spectroscopic measurement. The state functions from the nitrogen calculations have been applied to determine the transition moment for all allowed dipole transitions. These results can be combined to compute a detailed radiation spectrum such as that required to define the highly nonequilibrium environment of aeroassisted orbital transfer vehicle (AOTV). The long-range interaction energies have been used to determine the ion-atom resonance charge exchange cross sections that are important for transport processes such as diffusion. A calculation to determine reliable transport properties for energies that include the AOTV temperature range from these computed properties is described.

Numerical Investigation of Radiative Heat Transfer in Laser Induced Air Plasmas

NASA Technical Reports Server (NTRS)

Liu, J.; Chen, Y. S.; Wang, T. S.; Turner, James E. (Technical Monitor)

2001-01-01

Radiative heat transfer is one of the most important phenomena in the laser induced plasmas. This study is intended to develop accurate and efficient methods for predicting laser radiation absorption and plasma radiative heat transfer, and investigate the plasma radiation effects in laser propelled vehicles. To model laser radiation absorption, a ray tracing method along with the Beer's law is adopted. To solve the radiative transfer equation in the air plasmas, the discrete transfer method (DTM) is selected and explained. The air plasma radiative properties are predicted by the LORAN code. To validate the present nonequilibrium radiation model, several benchmark problems are examined and the present results are found to match the available solutions. To investigate the effects of plasma radiation in laser propelled vehicles, the present radiation code is coupled into a plasma aerodynamics code and a selected problem is considered. Comparisons of results at different cases show that plasma radiation plays a role of cooling plasma and it lowers the plasma temperature by about 10%. This change in temperature also results in a reduction of the coupling coefficient by about 10-20%. The present study indicates that plasma radiation modeling is very important for accurate modeling of aerodynamics in a laser propelled vehicle.

XCO2 Retrieval Errors from a PCA-based Approach to Fast Radiative Transfer

NASA Astrophysics Data System (ADS)

Somkuti, Peter; Boesch, Hartmut; Natraj, Vijay; Kopparla, Pushkar

2017-04-01

Multiple-scattering radiative transfer (RT) calculations are an integral part of forward models used to infer greenhouse gas concentrations in the shortwave-infrared spectral range from satellite missions such as GOSAT or OCO-2. Such calculations are, however, computationally expensive and, combined with the recent growth in data volume, necessitate the use of acceleration methods in order to make retrievals feasible on an operational level. The principle component analysis (PCA)-based approach to fast radiative transfer introduced by Natraj et al. 2005 is a spectral binning method, in which the many line-by-line monochromatic calculations are replaced by a small set of representative ones. From the PCA performed on the optical layer properties for a scene-dependent atmosphere, the results of the representative calculations are mapped onto all spectral points in the given band. Since this RT scheme is an approximation, the computed top-of-atmosphere radiances exhibit errors compared to the "full" line-by-line calculation. These errors ultimately propagate into the final retrieved greenhouse gas concentrations, and their magnitude depends on scene-dependent parameters such as aerosol loadings or viewing geometry. An advantage of this method is the ability to choose the degree of accuracy by increasing or decreasing the number of empirical orthogonal functions used for the reconstruction of the radiances. We have performed a large set of global simulations based on real GOSAT scenes and assess the retrieval errors induced by the fast RT approximation through linear error analysis. We find that across a wide range of geophysical parameters, the errors are for the most part smaller than ± 0.2 ppm and ± 0.06 ppm (out of roughly 400 ppm) for ocean and land scenes respectively. A fast RT scheme that produces low errors is important, since regional biases in XCO2 even in the low sub-ppm range can cause significant changes in carbon fluxes obtained from inversions (Chevallier et al. 2007).

Regional mapping of aerosol population and surface albedo of Titan by the massive inversion of the Cassini/VIMS dataset

NASA Astrophysics Data System (ADS)

Rodriguez, S.; Cornet, T.; Maltagliati, L.; Appéré, T.; Le Mouelic, S.; Sotin, C.; Barnes, J. W.; Brown, R. H.

2017-12-01

Mapping Titan's surface albedo is a necessary step to give reliable constraints on its composition. However, even after the end of the Cassini mission, surface albedo maps of Titan, especially over large regions, are still very rare, the surface windows being strongly affected by atmospheric contributions (absorption, scattering). A full radiative transfer model is an essential tool to remove these effects, but too time-consuming to treat systematically the 50000 hyperspectral images VIMS acquired since the beginning of the mission. We developed a massive inversion of VIMS data based on lookup tables computed from a state-of-the-art radiative transfer model in pseudo-spherical geometry, updated with new aerosol properties coming from our analysis of observations acquired recently by VIMS (solar occultations and emission phase curves). Once the physical properties of gases, aerosols and surface are fixed, the lookup tables are built for the remaining free parameters: the incidence, emergence and azimuth angles, given by navigation; and two products (the aerosol opacity and the surface albedo at all wavelengths). The lookup table grid was carefully selected after thorough testing. The data inversion on these pre-computed spectra (opportunely interpolated) is more than 1000 times faster than recalling the full radiative transfer at each minimization step. We present here the results from selected flybys. We invert mosaics composed by couples of flybys observing the same area at two different times. The composite albedo maps do not show significant discontinuities in any of the surface windows, suggesting a robust correction of the effects of the geometry (and thus the aerosols) on the observations. Maps of aerosol and albedo uncertainties are also provided, along with absolute errors. We are thus able to provide reliable surface albedo maps at pixel scale for entire regions of Titan and for the whole VIMS spectral range.

Integrated ray tracing simulation of annual variation of spectral bio-signatures from cloud free 3D optical Earth model

NASA Astrophysics Data System (ADS)

Ryu, Dongok; Kim, Sug-Whan; Kim, Dae Wook; Lee, Jae-Min; Lee, Hanshin; Park, Won Hyun; Seong, Sehyun; Ham, Sun-Jeong

2010-09-01

Understanding the Earth spectral bio-signatures provides an important reference datum for accurate de-convolution of collapsed spectral signals from potential earth-like planets of other star systems. This study presents a new ray tracing computation method including an improved 3D optical earth model constructed with the coastal line and vegetation distribution data from the Global Ecological Zone (GEZ) map. Using non-Lambertian bidirectional scattering distribution function (BSDF) models, the input earth surface model is characterized with three different scattering properties and their annual variations depending on monthly changes in vegetation distribution, sea ice coverage and illumination angle. The input atmosphere model consists of one layer with Rayleigh scattering model from the sea level to 100 km in altitude and its radiative transfer characteristics is computed for four seasons using the SMART codes. The ocean scattering model is a combination of sun-glint scattering and Lambertian scattering models. The land surface scattering is defined with the semi empirical parametric kernel method used for MODIS and POLDER missions. These three component models were integrated into the final Earth model that was then incorporated into the in-house built integrated ray tracing (IRT) model capable of computing both spectral imaging and radiative transfer performance of a hypothetical space instrument as it observes the Earth from its designated orbit. The IRT model simulation inputs include variation in earth orientation, illuminated phases, and seasonal sea ice and vegetation distribution. The trial simulation runs result in the annual variations in phase dependent disk averaged spectra (DAS) and its associated bio-signatures such as NDVI. The full computational details are presented together with the resulting annual variation in DAS and its associated bio-signatures.

Effects of multiple scattering and surface albedo on the photochemistry of the troposphere

NASA Technical Reports Server (NTRS)

Augustsson, T. R.; Tiwari, S. N.

1981-01-01

The effect of treatment of incoming solar radiation on the photochemistry of the troposphere is discussed. A one dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families was developed. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Vertical profiles of tropospheric species were compared with the Leighton approximation, radiative transfer, matrix inversion model. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption, and surface albedo on the transfer of incoming solar radiation. It is indicated that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with, radiative transfer, matrix inversion technique. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habte, A.; Sengupta, M.; Wilcox, S.

This report was part of a multiyear collaboration with the University of Wisconsin and the National Oceanic and Atmospheric Administration (NOAA) to produce high-quality, satellite-based, solar resource datasets for the United States. High-quality, solar resource assessment accelerates technology deployment by making a positive impact on decision making and reducing uncertainty in investment decisions. Satellite-based solar resource datasets are used as a primary source in solar resource assessment. This is mainly because satellites provide larger areal coverage and longer periods of record than ground-based measurements. With the advent of newer satellites with increased information content and faster computers that can processmore » increasingly higher data volumes, methods that were considered too computationally intensive are now feasible. One class of sophisticated methods for retrieving solar resource information from satellites is a two-step, physics-based method that computes cloud properties and uses the information in a radiative transfer model to compute solar radiation. This method has the advantage of adding additional information as satellites with newer channels come on board. This report evaluates the two-step method developed at NOAA and adapted for solar resource assessment for renewable energy with the goal of identifying areas that can be improved in the future.« less

Senstitivity analysis of horizontal heat and vapor transfer coefficients for a cloud-topped marine boundary layer during cold-air outbreaks. M.S. Thesis

NASA Technical Reports Server (NTRS)

Chang, Y. V.

1986-01-01

The effects of external parameters on the surface heat and vapor fluxes into the marine atmospheric boundary layer (MABL) during cold-air outbreaks are investigated using the numerical model of Stage and Businger (1981a). These fluxes are nondimensionalized using the horizontal heat (g1) and vapor (g2) transfer coefficient method first suggested by Chou and Atlas (1982) and further formulated by Stage (1983a). In order to simplify the problem, the boundary layer is assumed to be well mixed and horizontally homogeneous, and to have linear shoreline soundings of equivalent potential temperature and mixing ratio. Modifications of initial surface flux estimates, time step limitation, and termination conditions are made to the MABL model to obtain accurate computations. The dependence of g1 and g2 in the cloud topped boundary layer on the external parameters (wind speed, divergence, sea surface temperature, radiative sky temperature, cloud top radiation cooling, and initial shoreline soundings of temperature, and mixing ratio) is studied by a sensitivity analysis, which shows that the uncertainties of horizontal transfer coefficients caused by changes in the parameters are reasonably small.

Radiant heat exchange calculations in radiantly heated and cooled enclosures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapman, K.S.; Zhang, P.

1995-08-01

This paper presents the development of a three-dimensional mathematical model to compute the radiant heat exchange between surfaces separated by a transparent and/or opaque medium. The model formulation accommodates arbitrary arrangements of the interior surfaces, as well as arbitrary placement of obstacles within the enclosure. The discrete ordinates radiation model is applied and has the capability to analyze the effect of irregular geometries and diverse surface temperatures and radiative properties. The model is verified by comparing calculated heat transfer rates to heat transfer rates determined from the exact radiosity method for four different enclosures. The four enclosures were selected tomore » provide a wide range of verification. This three-dimensional model based on the discrete ordinates method can be applied to a building to assist the design engineer in sizing a radiant heating system. By coupling this model with a convective and conductive heat transfer model and a thermal comfort model, the comfort levels throughout the room can be easily and efficiently mapped for a given radiant heater location. In addition, objects such as airplanes, trucks, furniture, and partitions can be easily incorporated to determine their effect on the performance of the radiant heating system.« less

Evaluating radiative transfer schemes treatment of vegetation canopy architecture in land surface models

NASA Astrophysics Data System (ADS)

Braghiere, Renato; Quaife, Tristan; Black, Emily

2016-04-01

Incoming shortwave radiation is the primary source of energy driving the majority of the Earth's climate system. The partitioning of shortwave radiation by vegetation into absorbed, reflected, and transmitted terms is important for most of biogeophysical processes, including leaf temperature changes and photosynthesis, and it is currently calculated by most of land surface schemes (LSS) of climate and/or numerical weather prediction models. The most commonly used radiative transfer scheme in LSS is the two-stream approximation, however it does not explicitly account for vegetation architectural effects on shortwave radiation partitioning. Detailed three-dimensional (3D) canopy radiative transfer schemes have been developed, but they are too computationally expensive to address large-scale related studies over long time periods. Using a straightforward one-dimensional (1D) parameterisation proposed by Pinty et al. (2006), we modified a two-stream radiative transfer scheme by including a simple function of Sun zenith angle, so-called "structure factor", which does not require an explicit description and understanding of the complex phenomena arising from the presence of vegetation heterogeneous architecture, and it guarantees accurate simulations of the radiative balance consistently with 3D representations. In order to evaluate the ability of the proposed parameterisation in accurately represent the radiative balance of more complex 3D schemes, a comparison between the modified two-stream approximation with the "structure factor" parameterisation and state-of-art 3D radiative transfer schemes was conducted, following a set of virtual scenarios described in the RAMI4PILPS experiment. These experiments have been evaluating the radiative balance of several models under perfectly controlled conditions in order to eliminate uncertainties arising from an incomplete or erroneous knowledge of the structural, spectral and illumination related canopy characteristics typical of model comparisons with in-situ observations. The structure factor parameters were obtained for each canopy structure through the inversion against direct and diffuse fraction of absorbed photosynthetically active radiation (fAPAR), and albedo PAR. Overall, the modified two-stream approximation consistently showed a good agreement with the RAMI4PILPS reference values under direct and diffuse illumination conditions. It is an efficient and accurate tool to derive PAR absorptance and reflectance for scenarios with different canopy densities, leaf densities and soil background albedos, with especial attention to brighter backgrounds, i.e., snowy. The major difficulty of its applicability in the real world is to acquire the parameterisation parameters from in-situ observations. The derivation of parameters from Digital Hemispherical Photographs (DHP) is highly promising at forest stands scales. DHP provide a permanent record and are a valuable information source for position, size, density, and distribution of canopy gaps. The modified two-stream approximation parameters were derived from gap probability data extracted from DHP obtained in a woody savannah in California, USA. Values of fAPAR and albedo PAR were evaluated against a tree-based vegetation canopy model, MAESPA, which used airborne LiDAR data to define the individual-tree locations, and extract structural information such as tree height and crown diameter. The parameterisation improved the performance of a two-stream approximation by making it achieves comparable results to complex 3D model calculations under observed conditions.

Bidirectional plant canopy reflection models derived from the radiation transfer equation

NASA Technical Reports Server (NTRS)

Beeth, D. R.

1975-01-01

A collection of bidirectional canopy reflection models was obtained from the solution of the radiation transfer equation for a horizontally homogeneous canopy. A phase function is derived for a collection of bidirectionally reflecting and transmitting planar elements characterized geometrically by slope and azimuth density functions. Two approaches to solving the radiation transfer equation for the canopy are presented. One approach factors the radiation transfer equation into a solvable set of three first-order linear differential equations by assuming that the radiation field within the canopy can be initially approximated by three components: uniformly diffuse downwelling, uniformly diffuse upwelling, and attenuated specular. The solution to these equations, which can be iterated to any degree of accuracy, was used to obtain overall canopy reflection from the formal solution to the radiation transfer equation. A programable solution to canopy overall bidirectional reflection is given for this approach. The special example of Lambertian leaves with constant leaf bidirectional reflection and scattering functions is considered, and a programmable solution for this example is given. The other approach to solving the radiation transfer equation, a generalized Chandrasekhar technique, is presented in the appendix.

Spectrally-Invariant Approximation Within Atmospheric Radiative Transfer

NASA Technical Reports Server (NTRS)

Marshak, A.; Knyazikhin, Y.; Chiu, J. C.; Wiscombe, W. J.

2011-01-01

Certain algebraic combinations of single scattering albedo and solar radiation reflected from, or transmitted through, vegetation canopies do not vary with wavelength. These "spectrally invariant relationships" are the consequence of wavelength independence of the extinction coefficient and scattering phase function in vegetation. In general, this wavelength independence does not hold in the atmosphere, but in clouddominated atmospheres the total extinction and total scattering phase function vary only weakly with wavelength. This paper identifies the atmospheric conditions under which the spectrally invariant approximation can accurately describe the extinction. and scattering properties of cloudy atmospheres. The validity of the assumptions and the accuracy of the approximation are tested with ID radiative transfer calculations using publicly available radiative transfer models: Discrete Ordinate Radiative Transfer (DISORT) and Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). It is shown for cloudy atmospheres with cloud optical depth above 3, and for spectral intervals that exclude strong water vapor absorption, that the spectrally invariant relationships found in vegetation canopy radiative transfer are valid to better than 5%. The physics behind this phenomenon, its mathematical basis, and possible applications to remote sensing and climate are discussed.

Characterization of supersonic radiation diffusion waves

DOE PAGES

Moore, Alastair S.; Guymer, Thomas M.; Morton, John; ...

2015-02-27

Supersonic and diffusive radiation flow is an important test problem for the radiative transfer models used in radiation-hydrodynamics computer codes owing to solutions being accessible via analytic and numeric methods. We present experimental results with which we compare these solutions by studying supersonic and diffusive flow in the laboratory. Here, we present results of higher-accuracy experiments than previously possible studying radiation flow through up to 7 high-temperature mean free paths of low-density, chlorine-doped polystyrene foam and silicon dioxide aerogel contained by an Au tube. Measurements of the heat front position and absolute measurements of the x-ray emission arrival at themore » end of the tube are used to test numerical and analytical models. We find excellent absolute agreement with simulations provided that the opacity and the equation of state are adjusted within expected uncertainties; analytical models provide a good phenomenological match to measurements but are not in quantitative agreement due to their limited scope.« less

Discrimination of radiation quality through second harmonic out-of-phase cw-ESR detection.

PubMed

Marrale, Maurizio; Longo, Anna; Brai, Maria; Barbon, Antonio; Brustolon, Marina

2014-02-01

The ability to discriminate the quality of ionizing radiation is important because the biological effects produced in tissue strongly depends on both absorbed dose and linear energy transfer (LET) of ionizing particles. Here we present an experimental electron spin resonance (ESR) analysis aimed at discriminating the effective LETs of various radiation beams (e.g., 19.3 MeV protons, (60)Co photons and thermal neutrons). The measurement of the intensities of the continuous wave spectrometer signal channel first harmonic in-phase and the second harmonic out-of-phase components are used to distinguish the radiation quality. A computational analysis, was carried out to evaluate the dependence of the first harmonic in-phase and second harmonic out-of-phase components on microwave power, modulation amplitude and relaxation times, and highlights that these components could be used to point out differences in the relaxation times. On the basis of this numerical analysis the experimental results are discussed. The methodology described in this study has the potential to provide information on radiation quality.

Analysis of stray radiation for infrared optical system

NASA Astrophysics Data System (ADS)

Li, Yang; Zhang, Tingcheng; Liao, Zhibo; Mu, Shengbo; Du, Jianxiang; Wang, Xiangdong

2016-10-01

Based on the theory of radiation energy transfer in the infrared optical system, two methods for stray radiation analysis caused by interior thermal radiation in infrared optical system are proposed, one of which is important sampling method technique using forward ray trace, another of which is integral computation method using reverse ray trace. The two methods are discussed in detail. A concrete infrared optical system is provided. Light-tools is used to simulate the passage of radiation from the mirrors and mounts. Absolute values of internal irradiance on the detector are received. The results shows that the main part of the energy on the detector is due to the critical objects which were consistent with critical objects obtained by reverse ray trace, where mirror self-emission contribution is about 87.5% of the total energy. Corresponding to the results, the irradiance on the detector calculated by the two methods are in good agreement. So the validity and rationality of the two methods are proved.

Characterization of supersonic radiation diffusion waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, Alastair S.; Guymer, Thomas M.; Morton, John

Supersonic and diffusive radiation flow is an important test problem for the radiative transfer models used in radiation-hydrodynamics computer codes owing to solutions being accessible via analytic and numeric methods. We present experimental results with which we compare these solutions by studying supersonic and diffusive flow in the laboratory. Here, we present results of higher-accuracy experiments than previously possible studying radiation flow through up to 7 high-temperature mean free paths of low-density, chlorine-doped polystyrene foam and silicon dioxide aerogel contained by an Au tube. Measurements of the heat front position and absolute measurements of the x-ray emission arrival at themore » end of the tube are used to test numerical and analytical models. We find excellent absolute agreement with simulations provided that the opacity and the equation of state are adjusted within expected uncertainties; analytical models provide a good phenomenological match to measurements but are not in quantitative agreement due to their limited scope.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kakoniti, Androula; Georgiou, Gregoria; Neophytou, Marina

Two-dimensional steady-state simulations have been performed using the standard k-e turbulence model coupled with the heat transfer models available in the CFD software FLUENT 6.1, in order to examine the impact of radiation on the Urban Heat Island phenomenon. Specifically, the impact of radiation in three typical urban areas of Cyprus during the summer period is examined. The first geometry considered represents a typical suburban area and is termed as the reference geometry. The second geometry represents an area at the centre of a town with higher buildings and relatively narrower roads. The third geometry, on the other hand, describesmore » a suburban area with wider roads and larger houses than the reference model. Computed values for air temperature in the urban street canyon have indicated that the increase in temperature associated with radiative heat transfer can be reduced by optimising the canyon geometry and, ultimately, help to mitigate the human thermal discomfort. The present study has also revealed that the selection of construction materials can be optimised to offer further reductions in the air temperature of the urban environment. It can be concluded that the combined effect of these remedies can lead to reductions in the energy consumption for building air-conditioning over the summer period.« less

The Scaled SLW model of gas radiation in non-uniform media based on Planck-weighted moments of gas absorption cross-section

NASA Astrophysics Data System (ADS)

Solovjov, Vladimir P.; Andre, Frederic; Lemonnier, Denis; Webb, Brent W.

2018-02-01

The Scaled SLW model for prediction of radiation transfer in non-uniform gaseous media is presented. The paper considers a new approach for construction of a Scaled SLW model. In order to maintain the SLW method as a simple and computationally efficient engineering method special attention is paid to explicit non-iterative methods of calculation of the scaling coefficient. The moments of gas absorption cross-section weighted by the Planck blackbody emissive power (in particular, the first moment - Planck mean, and first inverse moment - Rosseland mean) are used as the total characteristics of the absorption spectrum to be preserved by scaling. Generalized SLW modelling using these moments including both discrete gray gases and the continuous formulation is presented. Application of line-by-line look-up table for corresponding ALBDF and inverse ALBDF distribution functions (such that no solution of implicit equations is needed) ensures that the method is flexible and efficient. Predictions for radiative transfer using the Scaled SLW model are compared to line-by-line benchmark solutions, and predictions using the Rank Correlated SLW model and SLW Reference Approach. Conclusions and recommendations regarding application of the Scaled SLW model are made.

IPRT polarized radiative transfer model intercomparison project - Three-dimensional test cases (phase B)

NASA Astrophysics Data System (ADS)

Emde, Claudia; Barlakas, Vasileios; Cornet, Céline; Evans, Frank; Wang, Zhen; Labonotte, Laurent C.; Macke, Andreas; Mayer, Bernhard; Wendisch, Manfred

2018-04-01

Initially unpolarized solar radiation becomes polarized by scattering in the Earth's atmosphere. In particular molecular scattering (Rayleigh scattering) polarizes electromagnetic radiation, but also scattering of radiation at aerosols, cloud droplets (Mie scattering) and ice crystals polarizes. Each atmospheric constituent produces a characteristic polarization signal, thus spectro-polarimetric measurements are frequently employed for remote sensing of aerosol and cloud properties. Retrieval algorithms require efficient radiative transfer models. Usually, these apply the plane-parallel approximation (PPA), assuming that the atmosphere consists of horizontally homogeneous layers. This allows to solve the vector radiative transfer equation (VRTE) efficiently. For remote sensing applications, the radiance is considered constant over the instantaneous field-of-view of the instrument and each sensor element is treated independently in plane-parallel approximation, neglecting horizontal radiation transport between adjacent pixels (Independent Pixel Approximation, IPA). In order to estimate the errors due to the IPA approximation, three-dimensional (3D) vector radiative transfer models are required. So far, only a few such models exist. Therefore, the International Polarized Radiative Transfer (IPRT) working group of the International Radiation Commission (IRC) has initiated a model intercomparison project in order to provide benchmark results for polarized radiative transfer. The group has already performed an intercomparison for one-dimensional (1D) multi-layer test cases [phase A, 1]. This paper presents the continuation of the intercomparison project (phase B) for 2D and 3D test cases: a step cloud, a cubic cloud, and a more realistic scenario including a 3D cloud field generated by a Large Eddy Simulation (LES) model and typical background aerosols. The commonly established benchmark results for 3D polarized radiative transfer are available at the IPRT website (http://www.meteo.physik.uni-muenchen.de/ iprt).

Discontinuous Galerkin finite element methods for radiative transfer in spherical symmetry

NASA Astrophysics Data System (ADS)

Kitzmann, D.; Bolte, J.; Patzer, A. B. C.

2016-11-01

The discontinuous Galerkin finite element method (DG-FEM) is successfully applied to treat a broad variety of transport problems numerically. In this work, we use the full capacity of the DG-FEM to solve the radiative transfer equation in spherical symmetry. We present a discontinuous Galerkin method to directly solve the spherically symmetric radiative transfer equation as a two-dimensional problem. The transport equation in spherical atmospheres is more complicated than in the plane-parallel case owing to the appearance of an additional derivative with respect to the polar angle. The DG-FEM formalism allows for the exact integration of arbitrarily complex scattering phase functions, independent of the angular mesh resolution. We show that the discontinuous Galerkin method is able to describe accurately the radiative transfer in extended atmospheres and to capture discontinuities or complex scattering behaviour which might be present in the solution of certain radiative transfer tasks and can, therefore, cause severe numerical problems for other radiative transfer solution methods.

A mathematical characterization of vegetation effect on microwave remote sensing from the Earth

NASA Technical Reports Server (NTRS)

Choe, Y.; Tsang, L.

1983-01-01

In passive microwave remote sensing of the earth, a theoretical model that utilizes the radiative transfer equations was developed to account for the volume scattering effects of the vegetation canopy. Vegetation canopies such as alfalfa, sorghum, and corn are simulated by a layer of ellipsoidal scatterers and cylindrical structures. The ellipsoidal scatterers represent the leaves of vegetation and are randomly positioned and oriented. The orientation of ellipsoids is characterized by a probability density function of Eulerian angles of rotation. The cylindrical structures represent the stalks of vegetation and their radii are assumed to be much smaller than their lengths. The underlying soil is represented by a half-space medium with a homogeneous permittivity and uniform temperature profile. The radiative transfer quations are solved by a numerical method using a Gaussian quadrature formula to compute both the vertical and horizontal polarized brightness temperature as a function of observation angle. The theory was applied to the interpretation of experimental data obtained from sorghum covered fields near College Station, Texas.

Study on the CFD simulation of refrigerated container

NASA Astrophysics Data System (ADS)

Arif Budiyanto, Muhammad; Shinoda, Takeshi; Nasruddin

2017-10-01

The objective this study is to performed Computational Fluid Dynamic (CFD) simulation of refrigerated container in the container port. Refrigerated container is a thermal cargo container constructed from an insulation wall to carry kind of perishable goods. CFD simulation was carried out use cross sectional of container walls to predict surface temperatures of refrigerated container and to estimate its cooling load. The simulation model is based on the solution of the partial differential equations governing the fluid flow and heat transfer processes. The physical model of heat-transfer processes considered in this simulation are consist of solar radiation from the sun, heat conduction on the container walls, heat convection on the container surfaces and thermal radiation among the solid surfaces. The validation of simulation model was assessed uses surface temperatures at center points on each container walls obtained from the measurement experimentation in the previous study. The results shows the surface temperatures of simulation model has good agreement with the measurement data on all container walls.

Dust emission in simulated dwarf galaxies using GRASIL-3D

NASA Astrophysics Data System (ADS)

Santos-Santos, I. M.; Domínguez-Tenreiro, R.; Granato, G. L.; Brook, C. B.; Obreja, A.

2017-03-01

Recent Herschel observations of dwarf galaxies have shown a wide diversity in the shapes of their IR-submm spectral energy distributions as compared to more massive galaxies, presenting features that cannot be explained with the current models. In order to understand the physics driving these differences, we have computed the emission of a sample of simulated dwarf galaxies using the radiative transfer code GRASIL-3D. This code separately treats the radiative transfer in dust grains from molecular clouds and cirri. The simulated galaxies have masses ranging from 10^6-10^9 M_⊙ and have evolved within a Local Group environment by using CLUES initial conditions. We show that their IR band luminosities are in agreement with observations, with their SEDs reproducing naturally the particular spectral features observed. We conclude that the GRASIL-3D two-component model gives a physical interpretation to the emission of dwarf galaxies, with molecular clouds (cirri) as the warm (cold) dust components needed to recover observational data.

Numerical treatment for Carreau nanofluid flow over a porous nonlinear stretching surface

NASA Astrophysics Data System (ADS)

Eid, Mohamed R.; Mahny, Kasseb L.; Muhammad, Taseer; Sheikholeslami, Mohsen

2018-03-01

The impact of magnetic field and nanoparticles on the two-phase flow of a generalized non-Newtonian Carreau fluid over permeable non-linearly stretching surface has been analyzed in the existence of all suction/injection and thermal radiation. The governing PDEs with congruous boundary condition are transformed into a system of non-linear ODEs with appropriate boundary conditions by using similarity transformation. It solved numerically by using 4th-5th order Runge-Kutta-Fehlberg method based on shooting technique. The impacts of non-dimensional controlling parameters on velocity, temperature, and nanoparticles volume concentration profiles are scrutinized with aid of graphs. The Nusselt and the Sherwood numbers are studied at the different situations of the governing parameters. The numerical computations are in excellent consent with previously reported studies. It is found that the heat transfer rate is reduced with an increment of thermal radiation parameter and on contrary of the rising of magnetic field. The opposite trend happens in the mass transfer rate.

User's manual for CNVUFAC, the general dynamics heat-transfer radiation view factor program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wong, R. L.

CNVUFAC, the General Dynamics heat-transfer radiation veiw factor program, has been adapted for use on the LLL CDC 7600 computer system. The input and output have been modified, and a node incrementing logic was included to make the code compatible with the TRUMP thermal analyzer and related codes. The program performs the multiple integration necessary to evaluate the geometric black-body radiaton node to node view factors. Card image output that contains node number and view factor information is generated for input into the related program GRAY. Program GRAY is then used to include the effects of gray-body emissivities and multiplemore » reflections, generating the effective gray-body view factors usable in TRUMP. CNVUFAC uses an elemental area summation scheme to evaluate the multiple integrals. The program permits shadowing and self-shadowing. The basic configuration shapes that can be considered are cylinders, cones, spheres, ellipsoids, flat plates, disks, toroids, and polynomials of revolution. Portions of these shapes can also be considered.« less

DustEM: Dust extinction and emission modelling

NASA Astrophysics Data System (ADS)

Compiègne, M.; Verstraete, L.; Jones, A.; Bernard, J.-P.; Boulanger, F.; Flagey, N.; Le Bourlot, J.; Paradis, D.; Ysard, N.

2013-07-01

DustEM computes the extinction and the emission of interstellar dust grains heated by photons. It is written in Fortran 95 and is jointly developed by IAS and CESR. The dust emission is calculated in the optically thin limit (no radiative transfer) and the default spectral range is 40 to 108 nm. The code is designed so dust properties can easily be changed and mixed and to allow for the inclusion of new grain physics.

A passive and active microwave-vector radiative transfer (PAM-VRT) model

NASA Astrophysics Data System (ADS)

Yang, Jun; Min, Qilong

2015-11-01

A passive and active microwave vector radiative transfer (PAM-VRT) package has been developed. This fast and accurate forward microwave model, with flexible and versatile input and output components, self-consistently and realistically simulates measurements/radiation of passive and active microwave sensors. The core PAM-VRT, microwave radiative transfer model, consists of five modules: gas absorption (two line-by-line databases and four fast models); hydrometeor property of water droplets and ice (spherical and nonspherical) particles; surface emissivity (from Community Radiative Transfer Model (CRTM)); vector radiative transfer of successive order of scattering (VSOS); and passive and active microwave simulation. The PAM-VRT package has been validated against other existing models, demonstrating good accuracy. The PAM-VRT not only can be used to simulate or assimilate measurements of existing microwave sensors, but also can be used to simulate observation results at some new microwave sensors.

The vector radiative transfer numerical model of coupled ocean-atmosphere system using the matrix-operator method

NASA Astrophysics Data System (ADS)

Xianqiang, He; Delu, Pan; Yan, Bai; Qiankun, Zhu

2005-10-01

The numerical model of the vector radiative transfer of the coupled ocean-atmosphere system is developed based on the matrix-operator method, which is named PCOART. In PCOART, using the Fourier analysis, the vector radiative transfer equation (VRTE) splits up into a set of independent equations with zenith angle as only angular coordinate. Using the Gaussian-Quadrature method, VRTE is finally transferred into the matrix equation, which is calculated by using the adding-doubling method. According to the reflective and refractive properties of the ocean-atmosphere interface, the vector radiative transfer numerical model of ocean and atmosphere is coupled in PCOART. By comparing with the exact Rayleigh scattering look-up-table of MODIS(Moderate-resolution Imaging Spectroradiometer), it is shown that PCOART is an exact numerical calculation model, and the processing methods of the multi-scattering and polarization are correct in PCOART. Also, by validating with the standard problems of the radiative transfer in water, it is shown that PCOART could be used to calculate the underwater radiative transfer problems. Therefore, PCOART is a useful tool to exactly calculate the vector radiative transfer of the coupled ocean-atmosphere system, which can be used to study the polarization properties of the radiance in the whole ocean-atmosphere system and the remote sensing of the atmosphere and ocean.

Influence of Ice Cloud Microphysics on Imager-Based Estimates of Earth's Radiation Budget

NASA Astrophysics Data System (ADS)

Loeb, N. G.; Kato, S.; Minnis, P.; Yang, P.; Sun-Mack, S.; Rose, F. G.; Hong, G.; Ham, S. H.

2016-12-01

A central objective of the Clouds and the Earth's Radiant Energy System (CERES) is to produce a long-term global climate data record of Earth's radiation budget from the TOA down to the surface along with the associated atmospheric and surface properties that influence it. CERES relies on a number of data sources, including broadband radiometers measuring incoming and reflected solar radiation and OLR, high-resolution spectral imagers, meteorological, aerosol and ozone assimilation data, and snow/sea-ice maps based on microwave radiometer data. While the TOA radiation budget is largely determined directly from accurate broadband radiometer measurements, the surface radiation budget is derived indirectly through radiative transfer model calculations initialized using imager-based cloud and aerosol retrievals and meteorological assimilation data. Because ice cloud particles exhibit a wide range of shapes, sizes and habits that cannot be independently retrieved a priori from passive visible/infrared imager measurements, assumptions about the scattering properties of ice clouds are necessary in order to retrieve ice cloud optical properties (e.g., optical depth) from imager radiances and to compute broadband radiative fluxes. This presentation will examine how the choice of an ice cloud particle model impacts computed shortwave (SW) radiative fluxes at the top-of-atmosphere (TOA) and surface. The ice cloud particle models considered correspond to those from prior, current and future CERES data product versions. During the CERES Edition2 (and Edition3) processing, ice cloud particles were assumed to be smooth hexagonal columns. In the Edition4, roughened hexagonal columns are assumed. The CERES team is now working on implementing in a future version an ice cloud particle model comprised of a two-habit ice cloud model consisting of roughened hexagonal columns and aggregates of roughened columnar elements. In each case, we use the same ice particle model in both the imager-based cloud retrievals (inverse problem) and the computed radiative fluxes (forward calculation). In addition to comparing radiative fluxes using the different ice cloud particle models, we also compare instantaneous TOA flux calculations with those observed by the CERES instrument.

A three-dimensional model of solar radiation transfer in a non-uniform plant canopy

NASA Astrophysics Data System (ADS)

Levashova, N. T.; Mukhartova, Yu V.

2018-01-01

A three-dimensional (3D) model of solar radiation transfer in a non-uniform plant canopy was developed. It is based on radiative transfer equations and a so-called turbid medium assumption. The model takes into account the multiple scattering contributions of plant elements in radiation fluxes. These enable more accurate descriptions of plant canopy reflectance and transmission in different spectral bands. The model was applied to assess the effects of plant canopy heterogeneity on solar radiation transmission and to quantify the difference in a radiation transfer between photosynthetically active radiation PAR (=0.39-0.72 μm) and near infrared solar radiation NIR (Δλ = 0.72-3.00 μm). Comparisons of the radiative transfer fluxes simulated by the 3D model within a plant canopy consisted of sparsely planted fruit trees (plant area index, PAI - 0.96 m2 m-2) with radiation fluxes simulated by a one-dimensional (1D) approach, assumed horizontal homogeneity of plant and leaf area distributions, showed that, for sunny weather conditions with a high solar elevation angle, an application of a simplified 1D approach can result in an underestimation of transmitted solar radiation by about 22% for PAR, and by about 26% for NIR.

The calculating study of the moisture transfer influence at the temperature field in a porous wet medium with internal heat sources

NASA Astrophysics Data System (ADS)

Kuzevanov, V. S.; Garyaev, A. B.; Zakozhurnikova, G. S.; Zakozhurnikov, S. S.

2017-11-01

A porous wet medium with solid and gaseous components, with distributed or localized heat sources was considered. The regimes of temperature changes at the heating at various initial material moisture were studied. Mathematical model was developed applied to the investigated wet porous multicomponent medium with internal heat sources, taking into account the transfer of the heat by heat conductivity with variable thermal parameters and porosity, heat transfer by radiation, chemical reactions, drying and moistening of solids, heat and mass transfer of volatile products of chemical reactions by flows filtration, transfer of moisture. The algorithm of numerical calculation and the computer program that implements the proposed mathematical model, allowing to study the dynamics of warming up at a local or distributed heat release, in particular the impact of the transfer of moisture in the medium on the temperature field were created. Graphs of temperature change were obtained at different points of the graphics with different initial moisture. Conclusions about the possible control of the regimes of heating a solid porous body by the initial moisture distribution were made.

A scalable plant-resolving radiative transfer model based on optimized GPU ray tracing

USDA-ARS?s Scientific Manuscript database

A new model for radiative transfer in participating media and its application to complex plant canopies is presented. The goal was to be able to efficiently solve complex canopy-scale radiative transfer problems while also representing sub-plant heterogeneity. In the model, individual leaf surfaces ...

In Vivo 18-FDG/18-Choline-Mediated Cerenkov Radiation Energy Transfer (CRET) Multiplexed Optical Imaging for Human Prostate Carcinoma Detection and Staging

DTIC Science & Technology

2017-12-01

AWARD NUMBER: W81XWH-13-1-0138 TITLE: In Vivo 18-FDG/18-Choline-Mediated Cerenkov Radiation Energy Transfer (CRET) Multiplexed Optical...18Ffluorocholine/ 18F-FDG Cerenkov radiation energy transfer (CRET) coupled with TF- and ErbB2/3- molecularly targeted nearinfrared (NIR) QDs can be used to detect...to examine whether internal illumination via 18F-fluorocholine Cerenkov radiation energy transfer (CRET) coupled with TF- and ErbB2/3- molecularly

Atmospheric Radiative Transfer for Satellite Remote Sensing: Validation and Uncertainty

NASA Technical Reports Server (NTRS)

Marshak, Alexander

2007-01-01

My presentation will begin with the discussion of the Intercomparison of three-dimensional (3D) Radiative Codes (13RC) project that has been started in 1997. I will highlight the question of how well the atmospheric science community can solve the 3D radiative transfer equation. Initially I3RC was focused only on algorithm intercomparison; now it has acquired a broader identity providing new insights and creating new community resources for 3D radiative transfer calculations. Then I will switch to satellite remote sensing. Almost all radiative transfer calculations for satellite remote sensing are one-dimensional (1D) assuming (i) no variability inside a satellite pixel and (ii) no radiative interactions between pixels. The assumptions behind the 1D approach will be checked using cloud and aerosol data measured by the MODerate Resolution Imaging Spectroradiometer (MODIS) on board of two NASA satellites TERRA and AQUA. In the discussion, I will use both analysis technique: statistical analysis over large areas and time intervals, and single scene analysis to validate how well the 1D radiative transfer equation describes radiative regime in cloudy atmospheres.

Sensitivity Analysis and Optimization of Enclosure Radiation with Applications to Crystal Growth

NASA Technical Reports Server (NTRS)

Tiller, Michael M.

1995-01-01

In engineering, simulation software is often used as a convenient means for carrying out experiments to evaluate physical systems. The benefit of using simulations as 'numerical' experiments is that the experimental conditions can be easily modified and repeated at much lower cost than the comparable physical experiment. The goal of these experiments is to 'improve' the process or result of the experiment. In most cases, the computational experiments employ the same trial and error approach as their physical counterparts. When using this approach for complex systems, the cause and effect relationship of the system may never be fully understood and efficient strategies for improvement never utilized. However, it is possible when running simulations to accurately and efficiently determine the sensitivity of the system results with respect to simulation to accurately and efficiently determine the sensitivity of the system results with respect to simulation parameters (e.g., initial conditions, boundary conditions, and material properties) by manipulating the underlying computations. This results in a better understanding of the system dynamics and gives us efficient means to improve processing conditions. We begin by discussing the steps involved in performing simulations. Then we consider how sensitivity information about simulation results can be obtained and ways this information may be used to improve the process or result of the experiment. Next, we discuss optimization and the efficient algorithms which use sensitivity information. We draw on all this information to propose a generalized approach for integrating simulation and optimization, with an emphasis on software programming issues. After discussing our approach to simulation and optimization we consider an application involving crystal growth. This application is interesting because it includes radiative heat transfer. We discuss the computation of radiative new factors and the impact this mode of heat transfer has on our approach. Finally, we will demonstrate the results of our optimization.

Post impact behavior of mobile reactor core containment systems

NASA Technical Reports Server (NTRS)

Puthoff, R. L.; Parker, W. G.; Vanbibber, L. E.

1972-01-01

The reactor core containment vessel temperatures after impact, and the design variables that affect the post impact survival of the system are analyzed. The heat transfer analysis includes conduction, radiation, and convection in addition to the core material heats of fusion and vaporization under partially burial conditions. Also, included is the fact that fission products vaporize and transport radially outward and condense outward and condense on cooler surfaces, resulting in a moving heat source. A computer program entitled Executive Subroutines for Afterheat Temperature Analysis (ESATA) was written to consider this complex heat transfer analysis. Seven cases were calculated of a reactor power system capable of delivering up to 300 MW of thermal power to a nuclear airplane.

Simulation of abuse tolerance of lithium-ion battery packs

NASA Astrophysics Data System (ADS)

Spotnitz, Robert M.; Weaver, James; Yeduvaka, Gowri; Doughty, D. H.; Roth, E. P.

A simple approach for using accelerating rate calorimetry data to simulate the thermal abuse resistance of battery packs is described. The thermal abuse tolerance of battery packs is estimated based on the exothermic behavior of a single cell and an energy balance than accounts for radiative, conductive, and convective heat transfer modes of the pack. For the specific example of a notebook computer pack containing eight 18650-size cells, the effects of cell position, heat of reaction, and heat-transfer coefficient are explored. Thermal runaway of the pack is more likely to be induced by thermal runaway of a single cell when that cell is in good contact with other cells and is close to the pack wall.

Ignition and combustion characteristics of metallized propellants

NASA Technical Reports Server (NTRS)

Mueller, D. C.; Turns, Stephen R.

1992-01-01

During this reporting period, theoretical work on the secondary atomization process was continued and the experimental apparatus was improved. A one-dimensional model of a rocket combustor, incorporating multiple droplet size classes, slurry combustion, secondary atomization, radiation heat transfer, and two-phase slip between slurry droplets and the gas flow was derived and a computer code was written to implement this model. The STANJAN chemical equilibrium solver was coupled with this code to yield gas temperature, density, and composition as functions of axial location. Preliminary results indicate that the model is performing correctly, given current model assumptions. Radiation heat transfer in the combustion chamber is treated as an optically-thick participating media problem requiring a solution of the radiative transfer equation. A cylindrical P sub 1 approximation was employed to yield an analytical expression for chamber-wall heat flux at each axial location. The code exercised to determine the effects of secondary atomization intensity, defined as the number of secondary drops produced per initial drop, on chamber burnout distance and final Al2O3 agglomerate diameter. These results indicate that only weak secondary atomization is required to significantly reduce these two parameters. Stronger atomization intensities were found to yield decreasing marginal benefits. The experimental apparatus was improved to reduce building vibration effects on the optical system alignment. This was accomplished by mounting the burner and the transmitting/receiving optics on a single frame supported by vibration-isolation legs. Calibration and shakedown tests indicate that vibration problems were eliminated and that the system is performing correctly.

SHAPEMOL: Modelling molecular line emission in protoplanetary and planetary nebulae with SHAPE

NASA Astrophysics Data System (ADS)

Santander-García, M.; Bujarrabal, V.; Steffen, W.; Koning, N.

2014-04-01

Modern instrumentation in radioastronomy constitutes a valuable tool for studying the Universe: ALMA will reach unprecedented sensitivities and spatial resolution, while Herschel/HIFI has opened a new window for probing molecular warm gas (˜50-1000 K). On the other hand, the SHAPE software has emerged in the last few years as the standard tool for determining the morphology and velocity field of different kinds of gaseous emission nebulae via spatio-kinematical modelling. Standard SHAPE implements radiative transfer solving, but it is only available for atomic species and not for molecules. Being aware of the growing importance of the development of tools for easying the analyses of molecular data from new era observatories, we introduce the computer code shapemol, a plug-in for SHAPE v5.0 with which we intend to fill the so far empty molecular niche. Shapemol enables spatio-kinematic modeling with accurate non-LTE calculations of line excitation and radiative transfer in molecular species. This code has been succesfully tested in the study of the excitation conditions of the molecular envelope of the young planetary nebula NGC 7027 using data from Herschel/HIFI and IRAM 30m. Currently, it allows radiative transfer solving in the 12CO and 13CO J=1-0 to J=17-16 lines. Shapemol, used along SHAPE, allows to easily generate synthetic maps to test against interferometric observations, as well as synthetic line profiles to match single-dish observations.

MULTI2D - a computer code for two-dimensional radiation hydrodynamics

NASA Astrophysics Data System (ADS)

Ramis, R.; Meyer-ter-Vehn, J.; Ramírez, J.

2009-06-01

Simulation of radiation hydrodynamics in two spatial dimensions is developed, having in mind, in particular, target design for indirectly driven inertial confinement energy (IFE) and the interpretation of related experiments. Intense radiation pulses by laser or particle beams heat high-Z target configurations of different geometries and lead to a regime which is optically thick in some regions and optically thin in others. A diffusion description is inadequate in this situation. A new numerical code has been developed which describes hydrodynamics in two spatial dimensions (cylindrical R-Z geometry) and radiation transport along rays in three dimensions with the 4 π solid angle discretized in direction. Matter moves on a non-structured mesh composed of trilateral and quadrilateral elements. Radiation flux of a given direction enters on two (one) sides of a triangle and leaves on the opposite side(s) in proportion to the viewing angles depending on the geometry. This scheme allows to propagate sharply edged beams without ray tracing, though at the price of some lateral diffusion. The algorithm treats correctly both the optically thin and optically thick regimes. A symmetric semi-implicit (SSI) method is used to guarantee numerical stability. Program summaryProgram title: MULTI2D Catalogue identifier: AECV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 151 098 No. of bytes in distributed program, including test data, etc.: 889 622 Distribution format: tar.gz Programming language: C Computer: PC (32 bits architecture) Operating system: Linux/Unix RAM: 2 Mbytes Word size: 32 bits Classification: 19.7 External routines: X-window standard library (libX11.so) and corresponding heading files (X11/*.h) are required. Nature of problem: In inertial confinement fusion and related experiments with lasers and particle beams, energy transport by thermal radiation becomes important. Under these conditions, the radiation field strongly interacts with the hydrodynamic motion through emission and absorption processes. Solution method: The equations of radiation transfer coupled with Lagrangian hydrodynamics, heat diffusion and beam tracing (laser or ions) are solved, in two-dimensional axial-symmetric geometry ( R-Z coordinates) using a fractional step scheme. Radiation transfer is solved with angular resolution. Matter properties are either interpolated from tables (equations-of-state and opacities) or computed by user routines (conductivities and beam attenuation). Restrictions: The code has been designed for typical conditions prevailing in inertial confinement fusion (ns time scale, matter states close to local thermodynamical equilibrium, negligible radiation pressure, …). Although a wider range of situations can be treated, extrapolations to regions beyond this design range need special care. Unusual features: A special computer language, called r94, is used at top levels of the code. These parts have to be converted to standard C by a translation program (supplied as part of the package). Due to the complexity of code (hydro-code, grid generation, user interface, graphic post-processor, translator program, installation scripts) extensive manuals are supplied as part of the package. Running time: 567 seconds for the example supplied.

Chemical vapor deposition fluid flow simulation modelling tool

NASA Technical Reports Server (NTRS)

Bullister, Edward T.

1992-01-01

Accurate numerical simulation of chemical vapor deposition (CVD) processes requires a general purpose computational fluid dynamics package combined with specialized capabilities for high temperature chemistry. In this report, we describe the implementation of these specialized capabilities in the spectral element code NEKTON. The thermal expansion of the gases involved is shown to be accurately approximated by the low Mach number perturbation expansion of the incompressible Navier-Stokes equations. The radiative heat transfer between multiple interacting radiating surfaces is shown to be tractable using the method of Gebhart. The disparate rates of reaction and diffusion in CVD processes are calculated via a point-implicit time integration scheme. We demonstrate the use above capabilities on prototypical CVD applications.

Final Report: SciDAC Computational Astrophysics Consortium (at Princeton University)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrows, Adam

Supernova explosions are the central events in astrophysics. They are the major agencies of change in the interstellar medium, driving star formation and the evolution of galaxies. Their gas remnants are the birthplaces of the cosmic rays. Such is their brightness that they can be used as standard candles to measure the size and geometry of the universe and their investigation draws on particle and nuclear physics, radiative transfer, kinetic theory, gravitational physics, thermodynamics, and the numerical arts. Hence, supernovae are unrivaled astrophysical laboratories. We will develop new state-of-the-art multi-dimensional radiation hydrodynamic codes to address this and other related astrophysicalmore » phenomena.« less

Transport And Chemical Effects On Concurrent And Opposed-Flow Flame Spread At Microgravity

NASA Technical Reports Server (NTRS)

Son, Y.; Zouein, G.; Ronney, P. D.; Gokoglu, S.

2003-01-01

Flame spread over flat solid fuel beds is a useful means of understanding more complex two-phase non-premixed spreading flames, such as those that may occur due to accidents in inhabited buildings and orbiting spacecraft. The role of buoyant convection on flame spread is substantial, especially for thermally-thick fuels. With suitable assumptions, deRis showed that the spread rate (S(sub f)) is proportional to the buoyant or forced convection velocity (U) and thus suggests that S(sub f) is indeterminate at mu g (since S(sub f) = U) unless a forced flow is applied. (In contrast, for thermally thin fuels, the ideal S(sub f) is independent of U.) The conventional view, as supported by computations and space experiments, is that for quiescent g conditions, S(sub f) must be unsteady and decreasing until extinction occurs due to radiative losses. However, this view does not consider that radiative transfer to the fuel surface can enhance flame spread. In recent work we have found evidence that radiative transfer from the flame itself can lead to steady flame spread at mu g over thick fuel beds. Our current work focuses on refining these experiments and a companion modeling effort toward the goal of a space flight experiment called Radiative Enhancement Effects on Flame Spread (REEFS) planned for the International Space Station (ISS) c. 2007.

Towards Improved Radiative Transfer Simulations of Hyperspectral Measurements for Cloudy Atmospheres

NASA Astrophysics Data System (ADS)

Natraj, V.; Li, C.; Aumann, H. H.; Yung, Y. L.

2016-12-01

Usage of hyperspectral measurements in the infrared for weather forecasting requires radiative transfer (RT) models that can accurately compute radiances given the atmospheric state. On the other hand, it is necessary for the RT models to be fast enough to meet operational processing processing requirements. Until recently, this has proven to be a very hard challenge. In the last decade, however, significant progress has been made in this regard, due to computer speed increases, and improved and optimized RT models. This presentation will introduce a new technique, based on principal component analysis (PCA) of the inherent optical properties (such as profiles of trace gas absorption and single scattering albedo), to perform fast and accurate hyperspectral RT calculations in clear or cloudy atmospheres. PCA is a technique to compress data while capturing most of the variability in the data. By performing PCA on the optical properties, we limit the number of computationally expensive multiple scattering RT calculations to the PCA-reduced data set, and develop a series of PC-based correction factors to obtain the hyperspectral radiances. This technique has been showed to deliver accuracies of 0.1% of better with respect to brute force, line-by-line (LBL) models such as LBLRTM and DISORT, but is orders of magnitude faster than the LBL models. We will compare the performance of this method against other models on a large atmospheric state data set (7377 profiles) that includes a wide range of thermodynamic and cloud profiles, along with viewing geometry and surface emissivity information. 2016. All rights reserved.

Coherent backscattering of light by complex random media of spherical scatterers: numerical solution

NASA Astrophysics Data System (ADS)

Muinonen, Karri

2004-07-01

Novel Monte Carlo techniques are described for the computation of reflection coefficient matrices for multiple scattering of light in plane-parallel random media of spherical scatterers. The present multiple scattering theory is composed of coherent backscattering and radiative transfer. In the radiative transfer part, the Stokes parameters of light escaping from the medium are updated at each scattering process in predefined angles of emergence. The scattering directions at each process are randomized using probability densities for the polar and azimuthal scattering angles: the former angle is generated using the single-scattering phase function, whereafter the latter follows from Kepler's equation. For spherical scatterers in the Rayleigh regime, randomization proceeds semi-analytically whereas, beyond that regime, cubic spline presentation of the scattering matrix is used for numerical computations. In the coherent backscattering part, the reciprocity of electromagnetic waves in the backscattering direction allows the renormalization of the reversely propagating waves, whereafter the scattering characteristics are computed in other directions. High orders of scattering (~10 000) can be treated because of the peculiar polarization characteristics of the reverse wave: after a number of scatterings, the polarization state of the reverse wave becomes independent of that of the incident wave, that is, it becomes fully dictated by the scatterings at the end of the reverse path. The coherent backscattering part depends on the single-scattering albedo in a non-monotonous way, the most pronounced signatures showing up for absorbing scatterers. The numerical results compare favourably to the literature results for nonabsorbing spherical scatterers both in and beyond the Rayleigh regime.

Pediatric patients transferred for operative management of appendicitis: are they at a disadvantage?

PubMed

Farach, Sandra M; Danielson, Paul D; Walford, N Elizabeth; Harmel, Richard P; Chandler, Nicole M

2015-09-01

Many pediatric patients are initially diagnosed with appendicitis at referring hospitals and are subsequently transferred to pediatric facilities. We aimed to compare outcomes of patients transferred to a pediatric referral center to those who present primarily for operative management of appendicitis. A retrospective review of 326 patients with operative appendicitis from July 2012 to July 2013 was performed. Demographic data, clinical parameters, and outcomes were analyzed. Transferred (n=222, 68%) and primary patients (n=104, 32%) were similar except for mean age (primary 12.4 vs. transferred 11.2 years, p<0.01). Computed tomography scans were performed in 80% of transferred compared to 40% of primary patients. Primary patients were more likely to present between the hours of 09:00 and 17:59 (52%), while transferred arrived equally across all hours. Both groups were more likely to present with acute appendicitis (primary 56% vs. transfer 61%, p=NS). There was no difference in time of diagnosis to time of appendectomy, length of hospital stay, or 30 day complications (primary 8.6% vs. transfer 5.8%, p=NS). Patients transferred for definitive care of appendicitis are not found to have more advanced disease or have increased complications; however, they are exposed to significantly more ionizing radiation during evaluation for appendicitis. Copyright © 2015 Elsevier Inc. All rights reserved.

Radiation Effects on Flow Characteristics in Combustion Chambers

NASA Technical Reports Server (NTRS)

Brewster, M. Q.; Gross, Klaus W.

1989-01-01

A JANNAF sponsored workshop was held to discuss the importance and role of radiative heat transfer in rocket combustion chambers. The potential impact of radiative transfer on hardware design, reliability, and performance was discussed. The current state of radiative transfer prediction capability in CFD modeling was reviewed and concluded to be substantially lacking in both the physical models used and the radiative property data available. There is a clear need to begin to establish a data base for making radiation calculations in rocket combustion chambers. A natural starting point for this effort would be the NASA thermochemical equilibrium code (CEC).

Super-Planckian far-field radiative heat transfer

NASA Astrophysics Data System (ADS)

Fernández-Hurtado, V.; Fernández-Domínguez, A. I.; Feist, J.; García-Vidal, F. J.; Cuevas, J. C.

2018-01-01

We present here a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. To guide the search for super-Planckian far-field radiative heat transfer, we make use of the theory of fluctuational electrodynamics and derive a relation between the far-field radiative heat transfer and the directional absorption efficiency of the objects involved. Guided by this relation, and making use of state-of-the-art numerical simulations, we show that the far-field radiative heat transfer between highly anisotropic objects can largely overcome the black-body limit when some of their dimensions are smaller than the thermal wavelength. In particular, we illustrate this phenomenon in the case of suspended pads made of polar dielectrics like SiN or SiO2. These structures are widely used to measure the thermal transport through nanowires and low-dimensional systems and can be employed to test our predictions. Our work illustrates the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nanodevices.

The Role of DYNAMO in Situ Observations in Improving NASA Ceres-like Daily Surface and Atmospheric Radiative Flux Estimates

NASA Technical Reports Server (NTRS)

Wang, Hailan; Su, Wenying; Loeb, Norman G.; Achuthavarier, Deepthi; Schubert, Siegfried D.

2017-01-01

The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earths RadiantEnergy System (CERES) Synoptic 1 degree (SYN1deg) Ed3A are among the most widely used data to studycloud-radiative feedback. The CERES SYN1deg data are based on Fu-Liou radiative transfer computations thatuse specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO)reanalyses as inputs and are therefore subject to the quality of those fields. This study uses in situ Q and Tobservations collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign toaugment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES dailysurface and atmospheric longwave estimates. The results show that the assimilation of DYNAMOobservations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stationsby moistening and warming the lower troposphere and upper troposphere and drying and cooling themid-upper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downwardlongwave flux increases by about 5 W m(exp -2), due mainly to the warming and moistening in the lowertroposphere; the computed daily top-of-atmosphere (TOA) outgoing longwave radiation increases by2-3 W m(exp -2) during dry periods only. Correspondingly, the estimated local atmospheric longwave radiativecooling enhances by about 5 W m(exp -2) (7-8 W m(exp -2)) during wet (dry) periods. These changes reduce the bias inthe CERES SYN1deg-like daily longwave estimates at both the TOA and surface and represent animprovement over the DYNAMO region.

Computational Investigation of Soot and Radiation in Turbulent Reacting Flows

NASA Astrophysics Data System (ADS)

Lalit, Harshad

This study delves into computational modeling of soot and infrared radiation for turbulent reacting flows, detailed understanding of both of which is paramount in the design of cleaner engines and pollution control. In the first part of the study, the concept of Stochastic Time and Space Series Analysis (STASS) as a numerical tool to compute time dependent statistics of radiation intensity is introduced for a turbulent premixed flame. In the absence of high fidelity codes for large eddy simulation or direct numerical simulation of turbulent flames, the utility of STASS for radiation imaging of reacting flows to understand the flame structure is assessed by generating images of infrared radiation in spectral bands dominated by radiation from gas phase carbon dioxide and water vapor using an assumed PDF method. The study elucidates the need for time dependent computation of radiation intensity for validation with experiments and the need for accounting for turbulence radiation interactions for correctly predicting radiation intensity and consequently the flame temperature and NOx in a reacting fluid flow. Comparison of single point statistics of infrared radiation intensity with measurements show that STASS can not only predict the flame structure but also estimate the dynamics of thermochemical scalars in the flame with reasonable accuracy. While a time series is used to generate realizations of thermochemical scalars in the first part of the study, in the second part, instantaneous realizations of resolved scale temperature, CO2 and H2O mole fractions and soot volume fractions are extracted from a large eddy simulation (LES) to carry out quantitative imaging of radiation intensity (QIRI) for a turbulent soot generating ethylene diffusion flame. A primary motivation of the study is to establish QIRI as a computational tool for validation of soot models, especially in the absence of conventional flow field and measured scalar data for sooting flames. Realizations of scalars from the LES are used in conjunction with the radiation heat transfer equation and a narrow band radiation model to compute time dependent and time averaged images of infrared radiation intensity in spectral bands corresponding to molecular radiation from gas phase carbon dioxide and soot particles exclusively. While qualitative and quantitative comparisons with measured images in the CO2 radiation band show that the flame structure is correctly computed, images computed in the soot radiation band illustrate that the soot volume fraction is under predicted by the computations. The effect of the soot model and cause of under prediction is investigated further by correcting the soot volume fraction using an empirical state relationship. By comparing default simulations with computations using the state relation, it is shown that while the soot model under-estimates the soot concentration, it correctly computes the intermittency of soot in the flame. The study of sooting flames is extended further by performing a parametric analysis of physical and numerical parameters that affect soot formation and transport in two laboratory scale turbulent sooting flames, one fueled by natural gas and the other by ethylene. The study is focused on investigating the effect of molecular diffusion of species, dilution of fuel with hydrogen gas and the effect of chemical reaction mechanism on the soot concentration in the flame. The effect of species Lewis numbers on soot evolution and transport is investigated by carrying out simulations, first with the default equal diffusivity (ED) assumption and then by incorporating a differential diffusion (DD) model. Computations using the DD model over-estimate the concentration of the soot precursor and soot oxidizer species, leading to inconsistencies in the estimate of the soot concentration. The linear differential diffusion (LDD) model, reported previously to consistently model differential diffusion effects is implemented to correct the over prediction effect of the DD model. It is shown that the effect of species Lewis number on soot evolution is a secondary phenomenon and that soot is primarily transported by advection of the fluid in a turbulent flame. The effect of hydrogen dilution on the soot formation and transport process is also studied. It is noted that the decay of soot volume fraction and flame length with hydrogen addition follows trends observed in laminar sooting flame measurements. While hydrogen enhances mixing shown by the laminar flamelet solutions, the mixing effect does not significantly contribute to differential molecular diffusion effects in the soot nucleation regions downstream of the flame and has a negligible effect on soot transport. The sensitivity of computations of soot volume fraction towards the chemical reaction mechanism is shown. It is concluded that modeling reaction pathways of C3 and C4 species that lead up to Polycyclic Aromatic Hydrocarbon (PAH) molecule formation is paramount for accurate predictions of soot in the flame. (Abstract shortened by ProQuest.).

Near-Field Thermal Radiation for Solar Thermophotovoltaics and High Temperature Thermal Logic and Memory Applications

NASA Astrophysics Data System (ADS)

Elzouka, Mahmoud

This dissertation investigates Near-Field Thermal Radiation (NFTR) applied to MEMS-based concentrated solar thermophotovoltaics (STPV) energy conversion and thermal memory and logics. NFTR is the exchange of thermal radiation energy at nano/microscale; when separation between the hot and cold objects is less than dominant radiation wavelength (˜1 mum). NFTR is particularly of interest to the above applications due to its high rate of energy transfer, exceeding the blackbody limit by orders of magnitude, and its strong dependence on separation gap size, surface nano/microstructure and material properties. Concentrated STPV system converts solar radiation to electricity using heat as an intermediary through a thermally coupled absorber/emitter, which causes STPV to have one of the highest solar-to-electricity conversion efficiency limits (85.4%). Modeling of a near-field concentrated STPV microsystem is carried out to investigate the use of STPV based solid-state energy conversion as high power density MEMS power generator. Numerical results for In 0.18Ga0.82Sb PV cell illuminated with tungsten emitter showed significant enhancement in energy transfer, resulting in output power densities as high as 60 W/cm2; 30 times higher than the equivalent far-field power density. On thermal computing, this dissertation demonstrates near-field heat transfer enabled high temperature NanoThermoMechanical memory and logics. Unlike electronics, NanoThermoMechanical memory and logic devices use heat instead of electricity to record and process data; hence they can operate in harsh environments where electronics typically fail. NanoThermoMechanical devices achieve memory and thermal rectification functions through the coupling of near-field thermal radiation and thermal expansion in microstructures, resulting in nonlinear heat transfer between two temperature terminals. Numerical modeling of a conceptual NanoThermoMechanical is carried out; results include the dynamic response under write/read cycles for a practical silicon-based device. NanoThermoMechanical rectification is achieved experimentally--for the first time--with measurements at a high temperature of 600 K, demonstrating the feasibility of NanoThermoMechanical to operate in harsh environments. The proof-of-concept device has shown a maximum rectification of 10.9%. This dissertation proposes using meshed photonic crystal structures to enhance NFTR between surfaces. Numerical results show thermal rectification as high as 2500%. Incorporating these structures in thermal memory and rectification devices will significantly enhance their functionality and performance.

Three-dimensional aspects of radiative transfer in remote sensing of precipitation: Application to the 1986 COHMEX storm

NASA Technical Reports Server (NTRS)

Haferman, J. L.; Krajewski, W. F.; Smith, T. F.

1994-01-01

Several multifrequency techniques for passive microwave estimation of precipitation based on the absorption and scattering properties of hydrometers have been proposed in the literature. In the present study, plane-parallel limitations are overcome by using a model based on the discrete-ordinates method to solve the radiative transfer equation in three-dimensional rectangular domains. This effectively accounts for the complexity and variety of radiation problems encountered in the atmosphere. This investigation presents result for plane-parallel and three-dimensional radiative transfer for a precipitating system, discusses differences between these results, and suggests possible explanations for these differences. Microphysical properties were obtained from the Colorado State University Regional Atmospehric Modeling System and represent a hailstorm observed during the 1986 Cooperative Huntsville Meteorological Experiment. These properties are used as input to a three-dimensional radiative transfer model in order to simulate satellite observation of the storm. The model output consists of upwelling brightness temperatures at several of the frequencies on the Special Sensor Microwave/Imager. The radiative transfer model accounts for scattering and emission of atmospheric gases and hydrometers in liquid and ice phases. Brightness temperatures obtained from the three-dimensional model of this investigation indicate that horizontal inhomogeneities give rise to brightness temperature fields that can be quite different from fields obtained using plane-parallel radiative transfer theory. These differences are examined for various resolutions of the satellite sensor field of view. In adddition, the issue of boundary conditions for three-dimensional atmospheric radiative transfer is addressed.

Fast multilevel radiative transfer

NASA Astrophysics Data System (ADS)

Paletou, Frédéric; Léger, Ludovick

2007-01-01

The vast majority of recent advances in the field of numerical radiative transfer relies on approximate operator methods better known in astrophysics as Accelerated Lambda-Iteration (ALI). A superior class of iterative schemes, in term of rates of convergence, such as Gauss-Seidel and Successive Overrelaxation methods were therefore quite naturally introduced in the field of radiative transfer by Trujillo Bueno & Fabiani Bendicho (1995); it was thoroughly described for the non-LTE two-level atom case. We describe hereafter in details how such methods can be generalized when dealing with non-LTE unpolarised radiation transfer with multilevel atomic models, in monodimensional geometry.

The Eighth International Symposium On Radiative Transfer

NASA Astrophysics Data System (ADS)

Lemonnier, Denis; Webb, Brent W.; Mengüç, M. Pınar

2017-08-01

This Special Issue of The Journal of Quantitative Spectroscopy and Radiative Transfer is based on the papers selected from RAD-16, the Eighth International Symposium on Radiative Transfer, which was held June 2016, in Cappadocia, Turkey. This Symposium is a follow-up of the seven previous meetings held in Kuşadası in 1995, 1997, and 2013; Antalya in 2001 and 2010; Istanbul in 2004; and Bodrum in 2007, all in Turkey. The Symposium was another enjoyable opportunity for the international radiation transfer community to assemble in a comfortable setting to present and discuss the state-of-the-art in research and application.

Laser Plasma Heating.

DTIC Science & Technology

The heating of a plasma by a laser is studied, assuming the classical inverse bremsstrahlung mechanism for transfer of energy from laser photons to electron thermal energy. Emphasis is given to CO2 laser heating of the dense plasma focus (DPF) device. Particular attention is paid to the contribution of impurities to the radiation output of the DPF. A steady-state CORONA model is discussed and used to generate a computer program, CORONA, which calculates species densities as a function of electron temperature. (Author)

An improved technique for determining reflection from semi-infinite atmospheres with linearly anisotropic phase functions. [radiative transfer

NASA Technical Reports Server (NTRS)

Fricke, C. L.

1975-01-01

A solution to the problem of reflection from a semi-infinite atmosphere is presented, based upon Chandrasekhar's H-function method for linearly anisotropic phase functions. A modification to the Gauss quadrature formula which gives about the same accuracy with 10 points as the conventional Gauss quadrature does with 100 points was developed. A computer program achieving this solution is described and results are presented for several illustrative cases.

Be discs in coplanar circular binaries: Phase-locked variations of emission lines

NASA Astrophysics Data System (ADS)

Panoglou, Despina; Faes, Daniel M.; Carciofi, Alex C.; Okazaki, Atsuo T.; Baade, Dietrich; Rivinius, Thomas; Borges Fernandes, Marcelo

2018-01-01

In this paper, we present the first results of radiative transfer calculations on decretion discs of binary Be stars. A smoothed particle hydrodynamics code computes the structure of Be discs in coplanar circular binary systems for a range of orbital and disc parameters. The resulting disc configuration consists of two spiral arms, and this can be given as input into a Monte Carlo code, which calculates the radiative transfer along the line of sight for various observational coordinates. Making use of the property of steady disc structure in coplanar circular binaries, observables are computed as functions of the orbital phase. Some orbital-phase series of line profiles are given for selected parameter sets under various viewing angles, to allow comparison with observations. Flat-topped profiles with and without superimposed multiple structures are reproduced, showing, for example, that triple-peaked profiles do not have to be necessarily associated with warped discs and misaligned binaries. It is demonstrated that binary tidal effects give rise to phase-locked variability of the violet-to-red (V/R) ratio of hydrogen emission lines. The V/R ratio exhibits two maxima per cycle; in certain cases those maxima are equal, leading to a clear new V/R cycle every half orbital period. This study opens a way to identifying binaries and to constraining the parameters of binary systems that exhibit phase-locked variations induced by tidal interaction with a companion star.

Advanced Machine Learning Emulators of Radiative Transfer Models

NASA Astrophysics Data System (ADS)

Camps-Valls, G.; Verrelst, J.; Martino, L.; Vicent, J.

2017-12-01

Physically-based model inversion methodologies are based on physical laws and established cause-effect relationships. A plethora of remote sensing applications rely on the physical inversion of a Radiative Transfer Model (RTM), which lead to physically meaningful bio-geo-physical parameter estimates. The process is however computationally expensive, needs expert knowledge for both the selection of the RTM, its parametrization and the the look-up table generation, as well as its inversion. Mimicking complex codes with statistical nonlinear machine learning algorithms has become the natural alternative very recently. Emulators are statistical constructs able to approximate the RTM, although at a fraction of the computational cost, providing an estimation of uncertainty, and estimations of the gradient or finite integral forms. We review the field and recent advances of emulation of RTMs with machine learning models. We posit Gaussian processes (GPs) as the proper framework to tackle the problem. Furthermore, we introduce an automatic methodology to construct emulators for costly RTMs. The Automatic Gaussian Process Emulator (AGAPE) methodology combines the interpolation capabilities of GPs with the accurate design of an acquisition function that favours sampling in low density regions and flatness of the interpolation function. We illustrate the good capabilities of our emulators in toy examples, leaf and canopy levels PROSPECT and PROSAIL RTMs, and for the construction of an optimal look-up-table for atmospheric correction based on MODTRAN5.

On the use of seminumerical simulations in predicting the 21-cm signal from the epoch of reionization

NASA Astrophysics Data System (ADS)

Majumdar, Suman; Mellema, Garrelt; Datta, Kanan K.; Jensen, Hannes; Choudhury, T. Roy; Bharadwaj, Somnath; Friedrich, Martina M.

2014-10-01

We present a detailed comparison of three different simulations of the epoch of reionization (EoR). The radiative transfer simulation (C2-RAY) among them is our benchmark. Radiative transfer codes can produce realistic results, but are computationally expensive. We compare it with two seminumerical techniques: one using the same haloes as C2-RAY as its sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS). These are vastly more computationally efficient than C2-RAY, but use more simplistic physical assumptions. We evaluate these simulations in terms of their ability to reproduce the history and morphology of reionization. We find that both Sem-Num and CPS+GS can produce an ionization history and morphology that is very close to C2-RAY, with Sem-Num performing slightly better compared to CPS+GS. We also study different redshift-space observables of the 21-cm signal from EoR: the variance, power spectrum and its various angular multipole moments. We find that both seminumerical models perform reasonably well in predicting these observables at length scales relevant for present and future experiments. However, Sem-Num performs slightly better than CPS+GS in producing the reionization history, which is necessary for interpreting the future observations. The CPS+GS scheme, however, has the advantage that it is not restricted by the mass resolution of the dark matter density field.

Accelerating NLTE radiative transfer by means of the Forth-and-Back Implicit Lambda Iteration: A two-level atom line formation in 2D Cartesian coordinates

NASA Astrophysics Data System (ADS)

Milić, Ivan; Atanacković, Olga

2014-10-01

State-of-the-art methods in multidimensional NLTE radiative transfer are based on the use of local approximate lambda operator within either Jacobi or Gauss-Seidel iterative schemes. Here we propose another approach to the solution of 2D NLTE RT problems, Forth-and-Back Implicit Lambda Iteration (FBILI), developed earlier for 1D geometry. In order to present the method and examine its convergence properties we use the well-known instance of the two-level atom line formation with complete frequency redistribution. In the formal solution of the RT equation we employ short characteristics with two-point algorithm. Using an implicit representation of the source function in the computation of the specific intensities, we compute and store the coefficients of the linear relations J=a+bS between the mean intensity J and the corresponding source function S. The use of iteration factors in the ‘local’ coefficients of these implicit relations in two ‘inward’ sweeps of 2D grid, along with the update of the source function in other two ‘outward’ sweeps leads to four times faster solution than the Jacobi’s one. Moreover, the update made in all four consecutive sweeps of the grid leads to an acceleration by a factor of 6-7 compared to the Jacobi iterative scheme.

An Epoch of Reionization simulation pipeline based on BEARS

NASA Astrophysics Data System (ADS)

Krause, Fabian; Thomas, Rajat M.; Zaroubi, Saleem; Abdalla, Filipe B.

2018-10-01

The quest to unlock the mysteries of the Epoch of Reionization (EoR) is well poised with many experiments at diverse wavelengths beginning to gather data. Albeit these efforts, we are yet uncertain about the various factors that influence the EoR which include, the nature of the sources, their spectral characteristics (blackbody temperatures, power-law indices), clustering property, efficiency, duty cycle etc. Given these physical uncertainties that define the EoR, we need fast and efficient computational methods to model and analyze the data in order to provide confidence bounds on the parameters that influence the brightness temperature at 21-cm. Towards this goal we developed a pipeline that combines dark matter-only N-body simulations with exact 1-dimensional radiative transfer computations to approximate exact 3-dimensional radiative transfer. Because these simulations are about two to three orders of magnitude faster than the exact 3-dimensional methods, they can be used to explore the parameter space of the EoR systematically. A fast scheme like this pipeline could be incorporated into a Bayesian framework for parameter estimation. In this paper we detail the construction of the pipeline and describe how to use the software which is being made publicly available. We show the results of running the pipeline for four test cases of sources with various spectral energy distributions and compare their outputs using various statistics.

Spectral collocation method with a flexible angular discretization scheme for radiative transfer in multi-layer graded index medium

NASA Astrophysics Data System (ADS)

Wei, Linyang; Qi, Hong; Sun, Jianping; Ren, Yatao; Ruan, Liming

2017-05-01

The spectral collocation method (SCM) is employed to solve the radiative transfer in multi-layer semitransparent medium with graded index. A new flexible angular discretization scheme is employed to discretize the solid angle domain freely to overcome the limit of the number of discrete radiative direction when adopting traditional SN discrete ordinate scheme. Three radial basis function interpolation approaches, named as multi-quadric (MQ), inverse multi-quadric (IMQ) and inverse quadratic (IQ) interpolation, are employed to couple the radiative intensity at the interface between two adjacent layers and numerical experiments show that MQ interpolation has the highest accuracy and best stability. Variable radiative transfer problems in double-layer semitransparent media with different thermophysical properties are investigated and the influence of these thermophysical properties on the radiative transfer procedure in double-layer semitransparent media is also analyzed. All the simulated results show that the present SCM with the new angular discretization scheme can predict the radiative transfer in multi-layer semitransparent medium with graded index efficiently and accurately.

Detailed modeling analysis for soot formation and radiation in microgravity gas jet diffusion flames

NASA Technical Reports Server (NTRS)

Ku, Jerry C.; Tong, LI; Greenberg, Paul S.

1995-01-01

Radiation heat transfer in combustion systems has been receiving increasing interest. In the case of hydrocarbon fuels, a significant portion of the radiation comes from soot particles, justifying the need for detailed soot formation model and radiation transfer calculations. For laminar gas jet diffusion flames, results from this project (4/1/91 8/22/95) and another NASA study show that flame shape, soot concentration, and radiation heat fluxes are substantially different under microgravity conditions. Our emphasis is on including detailed soot transport models and a detailed solution for radiation heat transfer, and on coupling them with the flame structure calculations. In this paper, we will discuss the following three specific areas: (1) Comparing two existing soot formation models, and identifying possible improvements; (2) A simple yet reasonably accurate approach to calculating total radiative properties and/or fluxes over the spectral range; and (3) Investigating the convergence of iterations between the flame structure solver and the radiation heat transfer solver.

Quantification of the water vapor greenhouse effect: setup and first results of the Zugspitze radiative closure experiment

NASA Astrophysics Data System (ADS)

Reichert, Andreas; Sussmann, Ralf; Rettinger, Markus

2014-05-01

Uncertainties in the knowledge of atmospheric radiative processes are among the main limiting factors for the accuracy of current climate models. Being the primary greenhouse gas in the Earth's atmosphere, water vapor is of crucial importance in atmospheric radiative transfer. However, water vapor absorption processes, especially the contribution attributed to the water vapor continuum, are currently not sufficiently well quantified. The aim of this study is therefore to obtain a more exact characterization of the water vapor radiative processes throughout the IR by means of a so-called radiative closure study at the Zugspitze/Schneefernerhaus observatory and thereby validate the radiative transfer codes used in current climate models. For that purpose, spectral radiance is measured at the Zugspitze summit observatory using an AERI-ER thermal emission radiometer (covering the far- and mid-infrared) and a solar absorption FTIR spectrometer (covering the near-infrared), respectively. These measurements are then compared to synthetic radiance spectra computed by means of the Line-By-Line Radiative Transfer Model (LBLRTM, Clough et al., 2005), a high resolution model widely used in the atmospheric science community. This line-by-line code provides the foundation of RRTM, a rapid radiation code (Mlawer et al., 1997) used in various weather forecast models or general circulation models like ECHAM. To be able to quantify errors in the description of water vapor radiative processes from spectral residuals, i.e. difference spectra between measured and calculated radiance, the atmospheric state used as an input to LBLRTM has to be constrained precisely. This input comprises water vapor columns, water vapor profiles, and temperature profiles measured by an LHATPRO microwave radiometer along with total column information on further trace gases (e.g. CO2 and O3) measured by the solar FTIR. We will present the setup of the Zugspitze radiative closure experiment. Due to its high-altitude location and the available permanent instrumentation, the Zugspitze observatory meets the necessary requirements to determine highly accurate water vapor continuum absorption parameters in the far- and mid-infrared spectral range from a more extensive set of closure measurements compared to previous campaign-based studies. Furthermore, we will present a novel radiometric calibration strategy for the solar FTIR spectral radiance measurements based on a combination of the Langley method and measurements of a high-temperature blackbody source that allows for the determination of continuum absorption parameters in the near-infrared spectral region, where previously no precise measurements under atmospheric conditions were available. This improved quantification of water vapor continuum absorption parameters allows us to further validate the current standard continuum model MT_CKD (Mlawer et al., 2012). Acknowledgements: Funding by KIT/IMK-IFU, the State Government of Bavaria as well as by the Deutsche Bundesstiftung Umwelt (DBU) is gratefully acknowledged. References: Clough, S. A., Shephard, M. W., Mlawer, E. J., Delamere, J. S., Iacono, M. J., Cady-Pereira, K., Boukabara, S., and Brown, P. D: Atmospheric radiative transfer modeling: a summary of the AER codes, Short Communication, J. Quant. Spectrosc. Radiat. Transfer, 91, 233-244, 2005. Mlawer, E. J., Taubman, J., Brown, P.D., Iacono, M.J, and Clough, S.A.: RRTM, a validated correlated-k model for the longwave. J. Geophys. Res., 102, 16,663-16,682, 1997. Mlawer, E. J., Payne V. H., Moncet, J., Delamere, J. S., Alvarado, M. J. and Tobin, D.C.: Development and recent evaluation of the MT_CKD model of continuum absorption, Phil. Trans. R. Soc. A, 370, 2520-2556, 2012.

In Vivo 18-FDG/18-Choline-Mediated Cerenkov Radiation Energy Transfer (CRET) Multiplexed Optical Imaging for Human Prostate Carcinoma Detection and Staging

DTIC Science & Technology

2014-10-01

Transfer ( CRET ) Multiplexed Optical Imaging for Human Prostate Carcinoma Detection and Staging PRINCIPAL INVESTIGATOR: Susan L. Deutscher...SUBTITLE 5a. CONTRACT NUMBER In Vivo 18-FDG/18-Choline-Mediated Cerenkov Radiation Energy Transfer ( CRET ) Multiplexed Optical Imaging for Human...internal illumination via 18F-fluorocholine Cerenkov radiation energy transfer ( CRET ) coupled with TF- and ErbB2/3- molecularly targeted near-infrared

Modeling of Radiative Heat Transfer in an Electric Arc Furnace

NASA Astrophysics Data System (ADS)

Opitz, Florian; Treffinger, Peter; Wöllenstein, Jürgen

2017-12-01

Radiation is an important means of heat transfer inside an electric arc furnace (EAF). To gain insight into the complex processes of heat transfer inside the EAF vessel, not only radiation from the surfaces but also emission and absorption of the gas phase and the dust cloud need to be considered. Furthermore, the radiative heat exchange depends on the geometrical configuration which is continuously changing throughout the process. The present paper introduces a system model of the EAF which takes into account the radiative heat transfer between the surfaces and the participating medium. This is attained by the development of a simplified geometrical model, the use of a weighted-sum-of-gray-gases model, and a simplified consideration of dust radiation. The simulation results were compared with the data of real EAF plants available in literature.