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Results for “Radiative transfer equation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Advanced Moisture and Temperature Sounder (AMTS) study

Retrieval of tropospheric humidity profiles from satellite-based upwelling radiances are shown to be improved by using physical methods for obtaining first-guess profiles as well as for inverting the radiative transfer equation by relaxation. The first guess is based on an empirically verified hypothesis, from theoretical considerations, that the brightness temperature corresponding to the radiance should be approximately equal to the actual temperatue at a channel-invariant optical depth provided that the surface and stratospheric contributions to the radiance are small. Even greater improvement of retrieved humidity profiles can be accomplished by increasing the number of channels used and by selecting their spectral location and bandpass to obtain sharper independent weighting functions. For example, the AMTS system, with high resolution water channels at 1650, 1700, 1839, 1850 and 1930 cm, is shown to be capable of reducing the retrieved water vapor errors in 200 mb thick layers by a factor of two or three relative to the HIRS-2 system errors. Expected AMTS errors in tropical layer water content are particularly low, less than 20% at all levels, and of the order of 10% or less in the middle troposphere.

Kaplan, L. D.↗
NASA NTRS1984

Introduction to ocean optics

In this introductory survey of optical oceanography, the fundamental inherent and apparent optical properties of natural waters are presented. Relationships between these inherent and apparent optical properties, as related through the radiative transfer equation, are then examined. Following the first three theoretical sections, brief discussions describing the application of ocean optics to geophysics, biological oceanography, and ocean remote sensing are then presented.

Gordon, H. R.↗
NASA NTRS1986

Reflection and emission models for deserts derived from Nimbus-7 ERB scanner measurements

Broadband shortwave and longwave radiance measurements obtained from the Nimbus-7 Earth Radiation Budget scanner were used to develop reflectance and emittance models for the Sahara-Arabian, Gibson, and Saudi Deserts. The models were established by fitting the satellite measurements to analytic functions. For the shortwave, the model function is based on an approximate solution to the radiative transfer equation. The bidirectional-reflectance function was obtained from a single-scattering approximation with a Rayleigh-like phase function. The directional-reflectance model followed from integration of the bidirectional model and is a function of the sum and product of cosine solar and viewing zenith angles, thus satisfying reciprocity between these angles. The emittance model was based on a simple power-law of cosine viewing zenith angle.

Staylor, W. F.↗
NASA NTRS1986

Scattering from a random layer embedded with dielectric needles

Intensity scattering from a random layer imbedded with small dielectric needles is studied for applications to coniferous vegetation. The phase matrix of a thin needle whose length may be appreciable compared to the incident wavelength is presented. The effects of needle orientation on scattering is taken into account by averaging the phase function over angles of orientation. The backscattering coefficient from the layer is computed by solving the radiative transfer equation. The effects of operating frequency, orientation and size of a needle on like- and cross-backscattering are demonstrated. It was found that in backscattering angular trends are mainly controlled by the orientation of the needles.

Eom, H. J.↗
NASA NTRS1985

Observed and computed stellar line profiles - The roles played by partial redistribution, geometrical extent and expansion

Partial redistribution (PRD) radiative transfer is reviewed with emphasis on the complex interaction of observations and theoretical predictions of spectral line shapes. Although the physics of PRD was understood and formal solutions to the radiative transfer equation including PRD were published as early as 1962, more than a decade elapsed before the clear inconsistency between observed and theoretical profiles calculated with the restrictive assumption of complete redistribution stimulated the development and use of PRD semiempirical spectral analysis for the solar Lyman alpha, Ca II, and Mg II resonance lines. Work is summarized that led to 'realistic' plane parallel static chromospheric models for the sun and other late type stars, with emphasis on the determination of the temperature minimum at the base of the chromosphere and the physical basis for resonance line limb darkening, the brightness of the line wings, and the width of the emission features. Finally the various roles played by atmospheric extension and expansion (winds) in determining resonance line profile shapes are discussed, and the existing PRD calculations for late type stars are summarized.

Linsky, J. L.↗
NASA NTRS1986

Technology for active laser remote sensing from space

The requirements for the experiments to be performed on the laser atmospheric sounder and altimeter facility of the polar orbiting platform are considered. The proposed instruments for the Lidar In-Space Technology Experiment designed to calibrate and verify the radiative transfer equation for laser energies at wavelengths of 1060, 532, and 355 nm, and to measure the vertical distribution of aerosols, the optical thickness of high altitude clouds, and the top of clouds are described. Research in the area of tunable laser materials and Lidar transmitters, in particular Ti:Al2O3 materials and Lidar transmitters, aimed at increasing wavelength tunability, efficiency, and the lifetime of solid-state lasers for utilization on Space Station polar orbiting platforms is discussed.

Sokoloski, M. M.↗
NASA NTRS1987

The derivation of vector magnetic fields from Stokes profiles - Integral versus least squares fitting techniques

The results of two methods for deriving photospheric vector magnetic fields from the Zeeman effect, as observed in the Fe I line at 6302.5 A at high spectral resolution (45 mA), are compared. The first method does not take magnetooptical effects into account, but determines the vector magnetic field from the integral properties of the Stokes profiles. The second method is an iterative least-squares fitting technique which fits the observed Stokes profiles to the profiles predicted by the Unno-Rachkovsky solution to the radiative transfer equation. For sunspot fields above about 1500 gauss, the two methods are found to agree in derived azimuthal and inclination angles to within about + or - 20 deg.

Ronan, R. S.↗
NASA NTRS1988

Finite element discrete ordinates method for radiative transfer in non-rotationally invariant scattering media - Application to the leaf canopy problem

A finite element discrete ordinates method for solving the radiative transfer equation in nonrotationally invariant scattering media has been applied to the lead-canopy problem, and results are presented on the cross sections and the reflection functions. The method is based on a unique implementation of the Galerkin integral law formulation of the transport equation. For both near-normal and grazing incidences, the transfer functions of leaf canopies are found to be strongly anisotropic, with relatively more scattered flux in the vertical directions. It is suggested that the assumption of isotropic scattering in leaf canopies is not valid.

Myneni, Ranga B.↗
NASA NTRS1989

Simulation studies of improved sounding systems

Two instrument designs for indirect satellite sounding of the atmosphere in the infrared are represented by the High Resolution Infra-Red Sounder, Model 2 (HIRS-2) and by the Advanced Meteorological Temperature Sounder (AMTS). The relative capabilities of the two instruments were tested by simulating satellite measurements from a group of temperature soundings, allowing the two participants to retrieve the temperature profiles from the simulated data, and comparing the results with the original temperature profiles. Four data sets were produced from radiosondes data extrapolated to a suitable altitude, representing continents and oceans, between 30S and 30N. From the information available, temperature profiles were retrieved by two different methods, statistical regression and inversion of the radiative transfer equation. Results show the consequence of greater spectral purity, concomitant increase in the number of spectral intervals, and the better spatial resolution in partly clouded areas. At the same time, the limitation of the HIRS-2 without its companion instrument leads to some results which should be ignored in comparing the two instruments. A clear superiority of AMTS results is shown.

Yates, H.↗
NASA NTRS1988

Relations between VAS physical retrievals and their first guess input

The Smith (1983) physical retrieval algorithm, which is designed to yield mesoscale soundings through a blending of first-guess limited fine mesh-derived profiles with VISSR Atmospheric Sounder (VAS) detected radiance data by means of an inversion of the radiative transfer equation, yields retrievals that may be better related to ground truth data than the guess profiles at some levels. At other levels, the first-guess profiles were slightly superior to the retrievals. Correlation functions related to the window and midtropospheric temperature channels indicate that magnitudes and orientations of retrieval gradients were intermediate to those of the guess data and brightness temperatures.

Beven, John L.↗
NASA NTRS1989

Feasibility of determining the vertical profile of carbon monoxide from a space platform

The results of a feasibility study conducted to determine the possibility of passively measuring the vertical profile of carbon monoxide in the troposphere on a global basis are presented. The instrument considered is a nadir-viewing gas correlation filter radiometer (GCFR). The basic instrument concept and radiative transfer equations are presented. The calculated signal functions, signal levels, sensitivity, and system noise levels of a spaceborne GCFR instrument are presented and discussed. It is concluded that a three- or four-level measurement of the atmospheric carbon monoxide mixing ratio in the troposphere is possible with this type of instrument.

Reichle, Henry, Jr.↗
NASA NTRS1989

Absorption and emission line shapes in the O2 atmospheric bands - Theoretical model and limb viewing simulations

A multiple scattering radiative transfer model has been developed to carry out a line-by-line calculation of the absorption and emission limb measurements that will be made by the High Resolution Doppler Imager to be flown on the Upper Atmosphere Research Satellite. The multiple scattering model uses the doubling and adding methods to solve the radiative transfer equation, modified to take into account a spherical inhomogeneous atmosphere. Representative absorption and emission line shapes in the O2 1Sigma(+)g - 3Sigma(-)g atmospheric bands (A,B, and gamma) and their variation with altitude are presented. The effects of solar zenith angle, aerosol loading, surface albedo, and cloud height on the line shapes are also discussed.

Abreu, Vincent J.↗
NASA NTRS1989

Radiative transfer theory for inhomogeneous media with random extinction and scattering coefficients

The small-angle scattering approximation of the scalar radiative transfer equation (RTE) is examined for the case where the extinction and scattering coefficients have a component that is a deterministic function of position along the propagation path and a component that is a random function of position transverse to the propagation direction. It is found that the resulting stochastic RTE can be reduced to a system of two stochastic integrodifferential equations for the average and fluctuating components of the radiant intensity. Two transfer equations are obtained describing the average radiant intensity and the spatial correlation function of the intensity fluctuations. The average intensity equation is then solved and applied to a simple propagation scenario. An approximate solution is also derived for the equation giving the correlation function. The developed equations can be applied to problems involving short wavelength electromagnetic wave propagation through media possessing the variable characteristics of turbulence and turbidity, such as plasmas, the atmosphere, and the ocean.

Manning, Robert M.↗
NASA NTRS1990

The circumstellar dust envelopes of red giant stars. I - M giant stars with the 10-micron silicate emission band

Spherical dust envelope models of red giant stars are constructed by solving the radiative transfer equations of the generalized two-stream Eddington approximation. The IRAS observations of M giant stars which show the 10-micron silicate emission band in IRAS LRS spectra are explained by the models with the dirty silicate grains with K proportional to lambda exp -1.5 for lambda greather than 28 microns. Under the assumption of steady mass flow in the envelope, this model analysis gives the following conclusions: (1) the strength of the silicate emission peak at 10 microns is a good indicator of the mass loss rate of the star, (2) no stars with the 10-microns silicate emission feature are observed in the range of mass loss rate smaller than 7 x 10 to the -8th solar mass/yr, and (3) the characteristic time of the mass loss process of M stars does not exceed a few 10,000 years.

Hashimoto, O.↗
NASA NTRS1990

Calculation of infrared limb emission by ozone in the terrestrial middle atmosphere. I - Source functions. II - Emission calculations

The departure from LTE in the vibration-rotation bands of ozone in the middle atmosphere is analyzed using two statistical equilibrium models: the energy gap model and the simplified single model. The diurnal variations in the fundamental band source functions nu(1) and nu(3) is determined by the diurnal change in the rate of ozone photolysis by the solar radiation. Source functions are presented for the vibration-rotation bands of ozone that emit in the 9-11-micron spectral interval, over an altitude range of 1-110 km. Results are also reported of the evaluation of the radiative transfer equation incorporating these source functions and energy level populations. Using the results of the two statistical equilibrium models, calculations are carried out of the spectrally integrated limb radiance for the limb viewing geometry for daytime conditions. Results indicate that the interpretation of the measurements of spectrally integrated limb radiance from ozone will be greatly complicated by the breakdown of LTE in the vibration-rotational bands of ozone.

Mlynczak, Martin G.↗
NASA NTRS1978

A Radiative Transfer Model for Microwave Emission from Soils

The radiative transfer equation for an absorbing medium is used to develop a model for microwave emission from soils. The model calculates the microwave emission intensity in terms of the brightness temperature as a function of the soil moisture and temperature. The consistency of the model is verified by a comparative study of the present model with other microwave emission models. The effect of surface roughness on the brightness temperature is studied by modifying the Fresnel reflection coefficient and by including the surface depolarization effect. The quantitative effect of the surface roughness is studied and it is demonstrated that the brightness temperatures observed for a natural agricultural terrain can be explained through the inclusion of the roughness effect. The surface roughness effect is further analyzed to obtain formulae which are useful in the analysis of the brightness temperatures, particularly, to obtain soil moisture information from the brightness. temperatures. The sensitivity of the brightness temperature to the soil temperature variations is studied both qualitatively and quantitatively. A simple formula is obtained to calculate the soil temperature dependence of the brightness temperature in terms of the surface and the deep soil temperatures. An algorithm to normalize the brightness temperatures so as to compare microwave observations under different soil temperature conditions is also discussed. A program listing of the model is given in the appendix.

Choudhury, B. J.↗
NASA NTRS1989

Infrared emission from ultracompact H II regions

Models of circumstellar dust shells around ultracompact (UC) H II regions were constructed that accurately fit the observed IR flux distributions. The models assume spherically symmetric dust shells illuminated by stars whose bolometric luminosity is inferred from the integrated FIR flux densities. Assuming ionization by a single zero age main sequence (ZAMS) star, the relations of Panagia were used to infer the stellar radius and effective temperature for a given luminosity. The grain mixture in the dust shell consists of bare graphite and silicate grains with the optical properties of Draine and Lee and the size distribution of Mathis et al. The computer code of Wolfire et al was used to solve the radiative transfer equations through a spherical dust shell. The model provides monochromatic luminosities, dust temperatures, and opacities through the shell. Aside from the stellar and dust properties, the only other input parameters to the model are the distance to the shell, the form of its density distribution, and its outer radius. Predictions of the model are compared with observations of a typical UC H II region and the run of dust temperature with radius and the optical depth with frequency are discussed.

Churchwell, ED↗
NASA NTRS1989

Radiative transfer theory for active remote sensing of a forested canopy

A canopy is modeled as a two-layer medium above a rough interface. The upper layer stands for the forest crown, with the leaves modeled as randomly oriented and distributed disks and needles and the branches modeled as randomly oriented finite dielectric cylinders. The lower layer contains the tree trunks, modeled as randomly positioned vertical cylinders above the rough soil. Radiative-transfer theory is applied to calculate EM scattering from such a canopy, is expressed in terms of the scattering-amplitude tensors (SATs). For leaves, the generalized Rayleigh-Gans approximation is applied, whereas the branch and trunk SATs are obtained by estimating the inner field by fields inside a similar cylinder of infinite length. The Kirchhoff method is used to calculate the soil SAT. For a plane wave exciting the canopy, the radiative-transfer equations are solved by iteration to the first order in albedo of the leaves and the branches. Numerical results are illustrated as a function of the incidence angle.

Karam, M. A.↗