Showing papers on "Radiative transfer published in 1981"

Thermal radiation heat transfer

Abstract: A comprehensive discussion of heat transfer by thermal radiation is presented, including the radiative behavior of materials, radiation between surfaces, and gas radiation. Among the topics considered are property prediction by electromagnetic theory, the observed properties of solid materials, radiation in the presence of other modes of energy transfer, the equations of transfer for an absorbing-emitting gas, and radiative transfer in scattering and absorbing media. Also considered are radiation exchange between black isothermal surfaces, radiation exchange in enclosures composed of diffuse gray surfaces and in enclosures having some specularly reflecting surfaces, and radiation exchange between nondiffuse nongray surfaces. The use of the Monte Carlo technique in solving radiant-exchange problems and problems of radiative transfer through absorbing-emitting media is explained.

Structure of the solar chromosphere. III. Models of the EUV brightness components of the quiet sun

Abstract: The described investigation is concerned with the solution of the non-LTE optically thick transfer equations for hydrogen, carbon, and other constituents to determine semiempirical models for six components of the quiet solar chromosphere. For a given temperature-height distribution, the solution is obtained of the equations of statistical equilibrium, radiative transfer for lines and continua, and hydrostatic equilibrium to find the ionization and excitation conditions for each atomic constituent. The emergent spectrum is calculated, and a trial and error approach is used to adjust the temperature distribution so that the emergent spectrum is in best agreement with the observed one. The relationship between semiempirical models determined in this way and theoretical models based on radiative equilibrium is discussed by Avrett (1977). Harvard Skylab EUV observations are used to determine models for a number of quiet-sun regions.

Bidirectional reflectance spectroscopy: 1. Theory

Abstract: An approximate analytic solution is derived for the radiative transfer equation describing particulate surface light scattering, taking into account multiple scattering and mutual shadowing. Analytical expressions for the following quantities are found: bidirectional reflectance, radiance coefficient and factor, the normal, Bond, hemispherical, and physical albedos, integral phase function and phase integral, and limb-darkening profile. Scattering functions for mixtures can be calculated, as well as corrections for comparisons of experimental transmission or reflection spectra with observational planetary spectra. The theory should be useful for the interpretation of reflectance spectroscopy of laboratory surfaces and the photometry of solar system objects.

An introduction to atmospheric radiation

Abstract: Fundamentals of Radiation for Atmospheric Applications. Solar Radiation at the Top of the Atmosphere. Absorption and Scattering of Solar Radiation in the Atmosphere. Thermal Infrared Radiation Transfer in the Atmosphere. Light Scattering by Atmospheric Particulates. Principles of Radiative Transfer in Planetary Atmospheres. Application of Radiative Transfer Principles to Remote Sensing. Radiation and Climate.

The radiation regime and architecture of plant stands

Abstract: one: Plant stand architecture.- 1.1 Role of Phytometric Investigations in The Studies of Plant Stand Architecture and Radiation Regime.- 1.2 Principal Phytometric Characteristics of Stands.- 1.2.1 Phytometric characteristics of leaf and other plant organs.- 1.2.2 Phytometric characteristics of an individual plant.- 1.2.3 Phytometric characteristics of a pure stand.- 1.2.4 Plant stand as a horizontal layer.- 1.3 Phytometrical Methods.- 1.3.1 Determination of leaf area.- 1.3.2 The measurement of leaf orientation.- 1.3.3 Inclined point quadrats method.- 1.3.4 Stratifying clip method.- 1.3.5 The methods of statistical measurements.- 1.3.6 Numerical methods for determination of foliage area vertical distribution.- 1.3.7 A rational method for determining phytometric characteristics of stand architecture and productivity.- 1.4 Statistical Characteristics of A Stand.- 1.4.1 Parameters of statistical characteristics.- 1.4.2 Correlation between statistical characteristics.- 1.5 Spatial Distribution of Phytoelements in Stands.- 1.5.1 General.- 1.5.2 Space-time variability of transition functions.- 1.5.3 Vertical distribution of phytomass and phytoarea.- 1.5.4 Horizontal distribution of phytomass and phytoarea.- 1.6 Foliage Area Orientation in Stands.- 1.6.1 General.- 1.6.2 Distribution functions of leaf inclination and azimuth orientation.- 1.6.3 G-function of leaf orientation.- 1.7 Plant Stand Architecture, Photosynthesis and Productivity.- two: Radiation regime in plant stand.- II.1 Radiation Field in a Plant Stand and The Problem of Its Mathematical Modelling.- II.1.1 General.- II. 1.2 Basic characteristics of the radiation field.- II. 1.3 Optical characteristics of phytoelements.- II. 1.4 Optical characteristics of plate medium.- II. 1.5 The radiation transfer equation for an optically anisotropic plate medium.- IL 1.6 Plant stand as a plate medium.- IL 1.7 The radiation transfer equation for a plant stand.- II. 1.8 Leaf and plant stand absorption functions.- II. 1.9 Statistical character of the radiation field in plant stands.- 11.2 Incident Radiation.- II.2.1 General.- IL2.2 Incoming direct solar radiation.- 11.2.3 Incoming diffuse sky radiation.- 11.2.4 Incoming total solar radiation.- 11.2.5 Incoming long-wave radiation of the atmosphere.- 11.2.6 Photosynthetically active radiation.- 11.3 Optical Properties of Phytoelements.- 11.3.1 General.- 11.3.2 Optical models of the leaf.- 11.3.3 Scattering phase function of the leaf.- 11.3.4 Spectral optical properties of phytoelements.- 11.3.5 Integral coefficients of leaf reflection, transmission and absorption for short-wave radiation and PAR.- 11.3.6 Optical properties of phytoelements in the long-wave spectral region.- 11.4 Penetration of Direct Solar Radiation into a Plant Stand.- 11.4.1 General.- 11.4.2 Statistical character of penetration of direct radiation in a plant stand. Penumbras.- 11.4.3 Theoretical expressions for direct solar radiation penetration.- 11.4.4 Penetration theory for direct solar radiation in horizontally inhomogeneous plant stands.- 11.4.5 Calculated penetration of direct solar radiation and its dependence on various factors.- 11.4.6 Methods of experimental investigation.- 11.4.7 Experimental data on penetration.- 11.5 Penetration of Diffuse Sky Radiation Into Plant Stand.- 11.5.1 General.- 11.5.2 Penetration formulae.- 11.5.3 Calculation of intensities and zonal radiation.- 11.5.4 Calculation of downward fluxes.- 11.5.5 Method of hemispherical photographs.- 11.5.6 Statistical character of the penetration of diffuse sky radiation.- 11.6 Scattering of Radiation Inside Plant Stands.- 11.6.1 General.- 11.6.2 Scattering and absorption coefficients for an elementary volume in a plant stand. Scattering phase function.- 11.6.3 Solution of radiation transfer equation for horizontal leaves.- 11.6.4 The Schwarzschild approximation for modified radiative transfer equation.- 11.6.5 Approximation for single scattering.- 11.6.6 Leaf scattering coefficient ?L and the complementary radiation field.- 11.6.7 Calculation of the complementary PAR field.- 11.6.8 Calculation of the complementary NIR field.- 11.7 Total Radiation Field in Plant Stands.- 11.7.1 General.- 11.7.2 Intensities of total radiation field.- 11.7.3 Total vertical fluxes.- 11.7.4 Angular distribution of total radiation flux.- 11.7.5 Leaf absorption in total radiation field.- 11.7.6 Radiation in a plant stand with horizontal leaves.- 11.7.7 Errors of the approximate methods of calculation.- 11.7.8 New theories.- 11.7.9 Monte Carlo simulation models.- 11.8 Semiempirical Formulae for Total Radiation Fluxes.- 11.8.1 General.- 11.8.2 Exponential and binomial semiempirical formulae.- 11.8.3 New semiempirical formulae.- 11.9 Albedo of Plant Stand.- 11.9.1 General.- 11.9.2 Formulae for the albedo and brightness coefficient.- 11.9.3 Albedo and its dependence on various factors.- 11.9.4 Comparison of calculated and experimental data.- 11.10 Calculation of Long-Wave Radiation in A Stand.- 11.11 Net Radtation in Plant Stands.- Conclusion.- Supplement. Description of Field Experiments.- References.- Author Index.

Inhibited Spontaneous Emission

Abstract: The radiative properties of an atom in a cavity differ fundamentally from the atom's radiative properties in free space. Spontaneous emission is inhibited if the cavity has characteristic dimensions which are small compared to the radiation wavelength, and enhanced if the cavity is resonant. The cavity causes slight shifts in the energies of the atom, analogous to radiative shifts. Experiments are proposed for observing these effects.

Spectroscopic properties of molecules interacting with small dielectric particles

Abstract: Optical properties of small dielectric spheroids with or without adsorbed molecules are studied theoretically. Expressions for the absorption line shapes, the radiative and nonradiative decay rates, and quantum yields are derived. In the case of a molecule near a spheroid the magnitudes differ dramatically from the corresponding case of a molecule near a plane.

A flux-limited diffusion theory

Abstract: A diffusion theory for radiative transfer is derived which is naturally flux limited. i.e., the magnitude of the flux can be no greater than the density times the maximum transport speed. Numerical comparisons with exact solutions of the equation of transfer indicate that this approximate theory is significantly more accurate than classical isotopic diffusion theory (the Eddington approximation) and asymptotic diffusion theory.

Microwave Remote Sensing - Active and Passive - Volume I - Microwave Remote Sensing Fundamentals and Radiometry

Abstract: The three components of microwave remote sensing (sensor-scene interaction, sensor design, and measurement techniques), and the applications to geoscience are examined. The history of active and passive microwave sensing is reviewed, along with fundamental principles of electromagnetic wave propagation, antennas, and microwave interaction with atmospheric constituents. Radiometric concepts are reviewed, particularly for measurement problems for atmospheric and terrestrial sources of natural radiation. Particular attention is given to the emission by atmospheric gases, clouds, and rain as described by the radiative transfer function. Finally, the operation and performance characteristics of radiometer receivers are discussed, particularly for measurement precision, calibration techniques, and imaging considerations.

Radiative cooling to low temperatures: General considerations and application to selectively emitting SiO films

Abstract: Radiative cooling occurs because the atmospheric emittance is low in the wavelength interval 8–13 μm particularly if the air is dry. We derive expressions which specify the optical properties demanded for a surface capable of being cooled to low temperatures. The key factor is infrared selectivity with low reflectance in the 8–13 μm ’’window’’ but high reflectance elsewhere. Considering only radiation balance, ideal surfaces of this type can yield temperature differences of ∼50 °C while the cooling power at near‐ambient temperatures is ∼100 W/m2. However, nonradiative exchange limits the practically achievable temperature difference. SiO films on Al were investigated as an example of an infrared‐selective surface. The infrared optical properties of SiO were determined by a novel and accurate technique. These data were used to compute the spectral radiative properties of Al coated with SiO films of different thicknesses. The spectral selectivity was largest for 1.0‐μm‐thick films. This kind of surface was produced by evaporation of SiO onto smooth Al. The measured reflectance agreed with computations. Practical tests of radiative cooling were performed using a SiO‐coated Al plate placed under transparent polyethylene films in a polystyrene box. An identical panel containing a blackbody radiator was used for comparison. The performance of the panels was tested during clear nights. It was in good qualitative agreement with theoretical expectations.

Radiative heating and cooling with spectrally selective surfaces.

Abstract: Matter continuously exchanges energy with its surroundings. This exchange can be dominated by radiation, conduction, or convection. In this brief review we discuss how proper design of radiative surface properties can be used for heating and cooling purposes. The desired properties can be understood once it is realized that solar and terrestrial radiation take place in different wavelength ranges and that only part of the solar spectrum is useful for vision and for photosynthesis in plants. These facts allow the possibility of tailoring the spectral absorptance, emittance, reflectance, and transmittance of a surface to meet different demands in different wavelength intervals, i.e., to take advantage of spectral selectivity. One example is the selective surface for efficient photothermal conversion of solar energy, which has high absorptance over the solar spectrum but low emittance for the longer wavelengths relevant to thermal reradiation. Below we discuss the pertinent spectral radiative properties of our ambience. These data are then used as background to the subsequent sections treating four examples of spectrally selective surfaces. The first example is the previously mentioned selective surface for converting solar radiation to useful heat. The second example considers surfaces capable of reaching low temperatures by benefiting from the spectral emittance of the clear night sky. The third example concerns two related types of transparent heat mirror. The fourth example, finally, treats radiative cooling of green leaves; this part is included since it gives a nice example of how nature solves a difficult problem in an elegant and efficient way. This example hence provides an interesting background to the other cruder types of artificial selective surfaces. Throughout our discussion we treat the ideal spectral properties, give an illustrative experimental example of how well this goal can be realized, and—where this is possible—show a corresponding theoretical curve indicating to what extent the measured results can be theoretically understood.

Radiative transfer in the surfaces of atmosphereless bodies. I - Theory. II - Interpretation of phase curves

Abstract: A generalized theory of radiative transfer is presented which includes single and multiple scattering of light in particulate surfaces, and is applicable to both the surfaces of atmosphereless bodies and to laboratory samples. Single scattering is described in terms of the effects of porosity and roughness, and is formulated by means of a probabilistic method. It is shown that, for low-albedo surfaces, the effects of porosity and roughness are separable, the opposition effect is caused by the former, and the slope of the linear part of the phase curve is mainly controlled by the latter. The theory, which is applicable to all albedos and phase angles, may be used in both surface brightness and integrated brightness studies. The limiting case of roughness and volume density tending to zero yields the results of classical radiative transfer theory.

The distribution and morphology of X-ray emitting gas in the core of the Perseus cluster.

Abstract: An unresolved source has been found coincident with the nucleus of NGC 1275 in a high-resolution X-ray image of the core of the Perseus cluster. Absorption in the optical features at high velocity with respect to NGC 1275, which are thought to be associated with a foreground galaxy, does not produce any detectable X-ray absorption. The emission tends to become asymmetric in the presence of the lower-velocity filaments, but no obvious, detailed correlation is found between X-ray enhancements and individual filaments. Deprojection of surface brightness to yield temperature and density profiles of the intracluster gas shows results consistent with a quasi-hydrostatic radiative accretion flow onto NGC 1275, and the pressure-driven mass inflow onto the central galaxy is then 200-400 solar masses/yr. The possibility of a problem in the relation of line-of-sight velocity dispersion to cluster gravitational mass is confirmed.

A New Look at the Discrete Ordinate Method for Radiative Transfer Calculations in Anisotropically Scattering Atmospheres

Abstract: The difficulties inherent in the conventional numerical implementation of the discrete ordinate method (following Chandrasekhar's prescription) for solving the radiative transfer equation are discussed. A matrix formulation is developed to overcome these difficulties, and it is specifically shown that the order of the algebraic eigenvalue problem can be reduced by a factor of 2. An expression for the source function is derived and used to obtain angular distributions. By appealing to the reciprocity principle, it is shown that substantial computational shortcuts are possible if only integrated quantities such as albedo and transmissivity are required. Comparison of fluxes calculated by the present approach with those obtained by other methods shows that low-order discrete ordinate approximations yield very accurate results. Thus, the present approach offers an efficient and reliable computational scheme that lends itself readily to the solution of a variety of radiative transfer problems in reali...

On mapping the magnetic field direction in molecular clouds by polarization measurements

Abstract: We predict that interstellar radio-frequency lines possess a few percent linear polarization, provided that (1) the radiative transition rate is at least comparable to the collision rate, (2) the optical depth is moderate. and anisotropic, and (3) the number of extrema of the velocity component along the line of sight through the source is small. If the Zeeman splitting exceeds both the collisional frequency and the radiative transition rate, then the polarization is aligned either perpendicular to or parallel to the projection of the magnetic field on the plane of the sky.

Absorption and dispersion in the O2 microwave spectrum at atmospheric pressures

Abstract: Calculations are performed for absorption and phase dispersion at various frequencies within the 60 GHz band of O2 from low pressures where the spectral lines are isolated, to atmospheric pressures where they merge to form a continuum band. A perturbation theory proposed by Rosenkranz was tested and found to be valid for pressures up to 100 kPa (1 atm). The ’’line coupling coefficients’’, which describe the transfer of excitation from one radiating state to another, are also studied and various methods for evaluating these coefficients are analyzed and compared with experimental data. It is found that dispersion measurements are extremely sensitive to these coefficients and an experimental procedure for systematically measuring them is outlined; it is shown that such measurements can provide a very sensitive test for theoretical calculations of inelastic transition amplitudes.

Electromagnetic Scattering and its Applications

Abstract: 1. Scattering of Radiation by Particles.- 1.1 Interaction of radiation with single particles.- 1.2 Interaction of radiation with particle clouds.- 1.3 Electromagnetic wave propagation.- 1.4 General scattering relationships.- 1.5 General scattering theory.- 1.5.1 The boundary condition method.- The sphere.- The infinite cylinder.- The ellipsoid.- 1.5.2 The extended boundary condition method.- 1.5.3 The integral equation method.- 1.6 Approximation methods in scattering.- 1.6.1 Very small particles (Rayleigh scattering).- 1.6.2 Higher order expansions.- 1.6.3 Rayleigh-Gans-Debye or Born approximation.- The sphere.- The cylinder.- The ellipsoid.- 1.6.4 The integral formulation.- 1.6.5 Fraunhofer diffraction.- 1.6.6 Anomalous diffraction.- 1.6.7 Geometrical optics.- 1.7 Multiple scattering and radiative transfer.- 1.8 Anisotropy.- 1.9 Irregular particles.- 2. Radiative Transfer in Particle Clouds.- 2.1 Radiation emitted by sources.- 2.2 Radiative transfer between source and sink.- 2.3 The equation of radiative transfer.- 2.4 Radiative transfer in the absence of multiple scattering.- 2.5 Radiative transfer in the presence of multiple scattering.- 2.5.1 The method of successive singular scattering.- 2.5.2 The zone method.- 2.5.3 The discrete ordinate method.- Allowance for anisotropic scattering.- 2.5.4 The method of moments.- 2.5.5 The flux method in dense systems.- 2.5.6 Light beam propagation in scattering media.- 3. Methods of Measuring Particle Size Distribution.- 3 1 Methods of measuring dispersity of solid and liquid particles.- 3 2 Photographic and holographic methods for measuring particle sizes.- 3.3 Methods based on the Fraunhofer diffraction pattern.- 3.3.1 The method developed by Swithenbank et al..- 3.3.2 Shifrin's method.- 3.3.3 The Shifrin-Kolmakov method.- 3.3.4 Petrov's method.- 3.4 Methods based on anomalous diffraction.- 3.4.1 The Shifrin-Perelman method.- 3.4.2 The Shifrin-Kolmakov-Chernyshov method.- 3.5 The Phillips-Twomey inversion method.- 3.6 The Backus-Gilbert inversion method.- 3.7 Comparison of the inversion methods.- 4. Measuring Instruments and Data Processing for the Determination of Particle Size Distribution.- 4.1 Swithenbank's method.- 4.2 Shifrin's method.- 4.2.1 Measuring instruments.- 4.2.2 Experimental data processing to obtain the particle size distribution.- 4.2.3 Measurement errors and the testing of equipment.- 4.2.4 Selecting components for devices and calculating their parameters.- 4.3 The Shifrin-Kolmakov method.- 4.4 The Shifrin-Perelman method.- 5. Other Measurements using Light Scattering.- 5.1 Laser fringe anemometry.- 5.2 Measurement of refractive index.- 5.3 Measurement of anisotropy.- 6. Measurement of Particle Characteristics in Industry and Research.- 6.1 A study of steam turbine operation.- 6.2 A study of gas turbine blade cooling.- 6.3 Determination of drop size spectrum in sprays.- 6.4 Determination of the size distribution of drops in a natural gas stream.- 6.5 Determination of contamination in oil products.- 6.6 Determination of the spectrum of mercury drop sizes in HV gas discharge devices.- 6.7 Measurement of particle size in a flame.- 6.7.1 Methods based on the Fraunhofer diffraction pattern.- 6.7.2 Diffusion broadening spectroscopy.- 6.8 Estimation of aggregate size of carbon black by the dispersion quotient method.- 6.9 Measurement of crystal growth rates.- 6.10 Determination of the size distribution of liquid aerosols.- 6.11 Kinetic measurements in aerosols.- 6.12 Determination of the size distribution of atmospheric aerosols.- 6.13 Determination of particle size in seawater.- 6.14 A study of the efficiency of dust collectors.- 6.15 A study of processes taking place in wet scrubbers.- 6.15.1 A study of the break-down of liquids by a gas flow.- 6.15.2 Determining an analytical expression for the drop size distribution.- 6.15.3 A study of the repeated break-down of drops in a turbulent flow.- 6.15.4 A study of the coagulation of drops.- References.- Author index.

Radiative transfer in the surfaces of atmosphereless bodies. II. Interpretation

Abstract: A glass composition particularly adapted for use with ceramic materials in electronic module applications having a thermal coefficient of expansion substantially matching the thermal coefficient of expansion of ceramic material, and a low dielectric constant less than 4.5. The composition is a borosilicate glass consisting essentially of SiO2, B2O3, CaO, A12O3, Na2O, K2O, BaO, ZrO2, and MgO in relatively precise amounts.

Semianalytic Monte Carlo radiative transfer model for oceanographic lidar systems

Abstract: A semianalytic Monte Carlo radiative transfer model (SALMON) has been developed which is particularly well-suited for addressing oceanographic lidar systems. SALMON is based on the method of expected values in which an analytical estimate is made of the probability of collection by a remote receiver of scattered or emitted photons at appropriate points in the stochastically constructed underwater photon trajectory. Sample results indicate that a substantial reduction in both variance and computer resources can be realized by using SALMON, as compared with more conventional Monte Carlo approaches, to study radiative transfer mechanisms associated with lidar systems.

The Jupiter hot plasma torus - Observed electron temperature and energy flows

Abstract: The detection of the optical emission /O I/ 6300 A (8 + or - 4 R) and /S III/ 6312 A (48 + or - 5 R) is reported. It is noted that these emissions are indicators of the ion source morphology and the plasma physical state and that the S III emitters have a kinetic temperature of approximately 10 to the 6th K. When combined with observations of UV lines from the same species, the optical measurements separately imply effective electron temperatures for radiative processes that are mutually consistent (approximately 50,000 K).

Laser ionization based on resonance saturation—a simple model description

Abstract: We have developed a simple physical model of laser ionization based on resonance saturation that involves the most important collisional and radiative interactions, yet lends itself to analytical solutions that enable the time history of the free electron density to be evaluated. We have been able to demonstrate that in the case of sodium the predictions of this simple model are within 15% of the values calculated by our extensive LIBORS computer code. The model has also been used to estimate the ionization time for each of the alkali metals over a wide range of conditions. These results are found to be consistent with several experimental observations.

Radiative heat transfer in rotary kilns

Abstract: Radiative heat transfer between a nongray freeboard gas and the interior surfaces of a rotary kiln has been studied by evaluating the fundamental radiative exchange integrals using numerical methods. Direct gas-to-surface exchange, reflection of the gas radiation by the kiln wall, and kiln wall-to-solids exchange have been considered. Graphical representations of the results have been developed which facilitate the determination of the gas mean beamlength and the total heat flux to the wall and to the solids. These charts can be used to account for both kiln size and solids fill ratio as well as composition and temperature of the gas. Calculations using these charts and an equimolar CO2−H2O mixture at 1110 K indicate that gas-to-surface exchange is a very localized phenomenon. Radiation to a surface element from gas more than half a kiln diameter away is quite small and, as a result, even large axial gas temperature gradients have a negligible effect on total heat flux. Results are also presented which show that the radiant energy either reflected or emitted by a surface element is limited to regions less than 0.75 kiln diameters away. The radiative exchange integrals have been used, together with a modified reflection method, to develop a model for the net heat flux to the solids and to the kiln wall from a nongray gas. This model is compared to a simple resistive network/gray-gas model and it is shown that substantial errors may be incurred by the use of the simple models.

Radiative Transfer in a Strongly Magnetized Plasma - Part Two - Effects of Comptonization

Abstract: We present results of numerical calculations of radiative transfer in hot, strongly magnetized plasma, including Comptonization and redistribution of photons in the cyclotron line. Polarization, angle, and frequency dependent differential scattering cross sections were obtained in the nonrelativistic approximation. An approximate, two-stream transfer equation was solved for homogeneous radiating slabs of various optical depths using Feautrier's method. For intermediate optical depths (slab transparent in the wings of the line) we obtained the asymmetric, self-reversed emission line recently predicted by Wasserman and Salpeter. However, the line shape can be changed significantly due to the presence of ordinary photons, which have weaker resonances in their cross sections. For very large optical depths we find an absorption line superposed ont he usual Wien continuum. We conclude that the cyclotron line in the Her X-1 spectrum is more likely to be an absorption line than an emission line.