SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Sunspot structure from two dimensional radiative transfer analysis of center limb intensity profiles made at several heliocentric angles
An extension of the Chahine relaxation method (1970) for inverting the radiative transfer equation is presented. This method is superior to the original method in that it takes into account in a realistic manner the shape of the kernel function, and its extension to nonlinear systems is much more straightforward. A comparison of the new method with a matrix method due to Twomey (1965), in a problem involving inference of vertical distribution of ozone from spectroscopic measurements in the near ultraviolet, indicates that in this situation this method is stable with errors in the input data up to 4%, whereas the matrix method breaks down at these levels. The problem of non-uniqueness of the solution, which is a property of the system of equations rather than of any particular algorithm for solving them, remains, although it takes on slightly different forms for the two algorithms.
In order to make the Wu-Kaplan longwave radiative transfer parameterization (Krishnamurthy, 1982) presently used in the 9 layer GLAS GCM more suitable for use at higher horizontal and vertical resolutions, the fixed CO2 transmittance tables and climatological O3 transmittances are replaced with appropriate models. Results of off line tests of simple models of CO2 transmittance as a function of atmospheric temperature profile and surface pressure, based on the technique used by Susskind et al. (1983) in the GLAS physical retrieval scheme are given. The models are evaluated in terms of tansmittance error, flux divergence error, and equilibrium temperature error. The transmittances of CO2 averaged over each of the spectral bands 500-660 cm-1 and 660-800 cm-1 are modeled, following Susskind et al., 1983, as products of effective layer transmittances.
Using a three-dimensional radiative transfer model combined with cloud-resolving model output, we simulate active and passive sensor observations of clouds and precipitaiton. This combination of tools allows us to diagnose the contributions of various hydrometeor types. Radar multiple scattering is most closely associated with the presence of graupel. At Wband, massive amounts multiple scattering in deep convection can decorrelate the reflectivity profile from the vertical structure, but for less intense events, multiple scattering could be a useful indicator of riming. For passive sensors, polarization differences at 166 GHz indicate the presence of horizontally aligned frozen particles with pronounced aspect ratios, while high concentrations of more isotropic aggregates and graupel dampen the polarization difference while also contributing to the lowest brightness temperature depressions. The insights into remote sensing measurements will facilitate the development of improved algorithms and advanced sensors.
Intensity of emergent radiation for finite homogeneous slab which absorbs radiation and scatters it isotropically
Intensity of emergent radiation in finite homogeneous slab absorbing and scattering it isotropically, viewed as boundary value problem determined by imbedding techniques
Radiative temperature changes for molecular gases under non local thermodynamic equilibrium
In this paper, we take a data-driven approach and apply machine learning to the moment closure problem for the radiative transfer equation in slab geometry. Instead of learning the unclosed high order moment, we propose to directly learn the gradient of the high order moment using neural networks. This new approach is consistent with the exact closure we derive for the free streaming limit and also provides a natural output normalization. Finally, a variety of benchmark tests, including the variable scattering problem, the Gaussian source problem with both periodic and reflecting boundaries, and the two-material problem, show both good accuracy and generalizability of our machine learning closure model.
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.
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.
Radiative transfer in plane-parallel atmospheres - invariance principles for anisotropic scattering
Radiative transfer effects in low Reynolds number or merged layer regime of hypersonic flow about axisymmetric blunt bodies, including thin shock layer theory
In this paper we treat the multiple scattering theory of radiative transfer in plane-parallel inhomogeneous atmospheres. The treatment presented here may be adopted to model atmospheres characterized by an optical depth dependent coherent scattering phase function. For the purpose of illustration we consider the semi-infinite medium in which the absorption property of the atmosphere is characterized by an exponential function. The methodology employed here is the extension of the case treated previously by the author for homogeneous atmospheres.
The reported investigation has the objective to develop an accurate radiative transfer model for the thermal infrared region using a quasi-random band model. It is intended to use this model to examine the sensitivity of the outgoing radiance and flux density to the perturbations of such meteorological parameters on the surface emittance and temperature, atmospheric water vapor distribution, cloud altitude and fractional cover, and the concentrations of other infrared active constituents. It is found that the combined effect of N2O and CH4 on the flux is significant and exceeds 1 percent. These two constituents should, therefore, not be neglected in accurate modeling work. The effect of ozone on the flux is too large to be neglected and was partly responsible for the discrepancy between earlier model results and measurements. The effect of cloud depth should be taken into account to obtain better agreement with the measured limb darkening functions.
The reported investigation had the objective to develop an accurate radiative transfer model for the thermal infrared region using a quasi-random band model. It is intended to use this model to examine the sensitivity of the outgoing radiance and flux density to the perturbations of such meteorological parameters as the surface emittance and temperature, atmospheric water vapor distribution, cloud altitude and fractional cover, and the concentrations of other infrared active constituents. The outgoing infrared flux and limb darkening functions obtained from this model agree well with the satellite measured data. Important sensitivity parameters obtained agree with the results of the various empirical and theoretical models. It is concluded that the effect of cloud depth should be taken into account to obtain better agreement with the measured limb darkening functions.
Schuster's two-stream approximation (1905) is first derived from Chandrasekhar's radiative transfer equation (1950), and then extended to an arbitrary number of streams. The resulting technique for solving the transfer function similar to the discrete ordinate and spherical harmonic methods, is useful for modeling atmospheres with complicated phase functions and moderate optical depths. The resulting n coupled linear differential equations are simple and consume less computer time than other approximations, yet have the same required accuracy. The approximation is also flexible with respect to the choice of patch functions, and no approximations are made on the form of the phase function, other than its expansion into Legendre polynomials. A four-stream approximation is evaluated for a Henyey-Greenstein phase function with an asymmetry factor equal to 0.5.
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 cloud-dominated atmospheres the total extinction and total scattering phase function vary only weakly with wavelength. We identify the conditions under which the spectrally-invariant approximation can accurately describe the extinction and scattering properties of cloudy atmospheres. Validity of the assumptions and accuracy of the approximation is tested with radiative transfer calculations. We discuss the physics behind this phenomenon and possible applications to remote sensing, climate, and the EarthCare, mission in particular.
Abstract Recent studies develop the SPeedy Algorithm for Radiative TrAnsfer through CloUd Sides (SPARTACUS) to handle the influence of horizontal RT on vertical radiative fluxes within an atmospheric column. The present study applies SPARTACUS to large eddy simulation (LES)‐generated cloud fields across the stratocumulus to trade cumulus transition (STCT) regime with coarse and fine vertical resolutions. The results show that, as the vertical resolution increases, radiation simulations show increasingly stronger cloud‐top longwave (LW) radiative cooling. Consequently, the sharp radiative heating gradient across the cloud layer in the LES‐like resolution simulations cannot be resolved with the coarse resolution simulations. Including the horizontal RT typically enhances cloud LW radiative cooling rate by less than 10% for all the cloud fields but more significantly in the cloud fields during the STCT. The enhanced cloud LW radiative cooling also occurs in the lower cloud layer in the decoupled cumulus cloud regime.