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Radiative transfer
About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.
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TL;DR: HERACLES as discussed by the authors is a three-dimensional radiation hydrodynamics code that uses an original moment method to solve the radiative transfer, which is very well suited to studying many astrophysical problems such as radiative shocks, molecular jets of young stars, fragmentation and formation of dense cores in the interstellar medium, and protoplanetary discs.
Abstract: Aims. We present a new three-dimensional radiation hydrodynamics code called HERACLES that uses an original moment method to solve the radiative transfer. Methods. The radiation transfer is modelled using a two-moment model and a closure relation that allows large angular anisotropies in the radiation field to be preserved and reproduced. The radiative equations thus obtained are solved by a second-order Godunov-type method and integrated implicitly by using iterative solvers. HERACLES has been parallelized with the MPI library and implemented in Cartesian, cylindrical, and spherical coordinates. To characterize the accuracy of HERACLES and to compare it with other codes, we performed a series of tests including purely radiative tests and radiation-hydrodynamics ones. Results. The results show that the physical model used in HERACLES for the transfer is fairly accurate in both the diffusion and transport limit, but also for semi-transparent regions. Conclusions. This makes HERACLES very well-suited to studying many astrophysical problems such as radiative shocks, molecular jets of young stars, fragmentation and formation of dense cores in the interstellar medium, and protoplanetary discs.
267 citations
TL;DR: The methodology is based on the maximum a posteriori estimate, which mathematically requires the minimization of the difference between observed spectral radiances and a nonlinear model of radiative transfer of the atmospheric state subject to the constraint that the estimated state must be consistent with an a priori probability distribution for that state.
Abstract: We describe the approach for the estimation of the atmospheric state, e.g., temperature, water, ozone, from calibrated, spectral radiances measured from the Tropospheric Emission Spectrometer (TES) onboard the Aura spacecraft. The methodology is based on the maximum a posteriori estimate, which mathematically requires the minimization of the difference between observed spectral radiances and a nonlinear model of radiative transfer of the atmospheric state subject to the constraint that the estimated state must be consistent with an a priori probability distribution for that state. The minimization techniques employed here are based on the trust-region Levenberg-Marquardt algorithm. An analysis of the errors for this estimate include smoothing, random, spectroscopic, "cross-state", representation, and systematic errors. In addition, several metrics and diagnostics are introduced that assess the resolution, quality, and statistical significance of the retrievals. We illustrate this methodology for the retrieval of atmospheric and surface temperature, water vapor, and ozone over the Gulf of Mexico on November 3, 2004.
267 citations
TL;DR: The state-of-the-art on radiative transfer modeling in vegetation canopies and the application of such models to the interpretation and analysis of remotely sensed optical data is summarized.
267 citations
TL;DR: The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) was designed to reduce this uncertainty by measuring and analyzing aerosol properties and effects on the United States eastern seaboard, where one of the world's major plumes of urban/industrial haze moves from the continent over the Atlantic Ocean.
Abstract: Aerosol effects on atmospheric radiation are a leading source of uncertainty in predicting climate change. The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) was designed to reduce this uncertainty by measuring and analyzing aerosol properties and effects on the United States eastern seaboard, where one of the world's major plumes of urban/industrial haze moves from the continent over the Atlantic Ocean. The TARFOX intensive field campaign was conducted July 10–31, 1996. It included coordinated measurements from four satellites (GOES-8, NOAA-14, ERS-2, Landsat), four aircraft (ER-2, C-130, C-131A, and a modified Cessna), land sites, and ships. A variety of aerosol conditions was sampled, ranging from relatively clean, behind frontal passages, to moderately polluted, with aerosol optical depths exceeding 0.5 at midvisible wavelengths. Gradients of aerosol optical thickness were sampled to aid in separating aerosol effects from other radiative effects and to more tightly constrain closure tests, including those of satellite retrievals. Early results from TARFOX include demonstration of the unexpected importance of carbonaceous compounds and water condensed on aerosol in the United States East Coast haze plume, chemical apportionment of the aerosol optical depth, measurements of aerosol-induced changes in upwelling and downwelling shortwave radiative fluxes, and generally good agreement between measured flux changes and those calculated from measured aerosol properties. This overview presents the TARFOX objectives, rationale, overall experimental approach, and key initial findings as a guide to the more complete results reported in this special section and elsewhere.
267 citations
TL;DR: In this paper, a detailed summary of the Lyman Alpha (Lya) radiative processes is presented, including collisional-excitation & recombination, and basic radiative transfer concepts, including e.g., partially coherent scattering, frequency diffusion, resonant versus wing scattering, optically thick versus 'extremely' optically thin media, and multiphase media.
Abstract: The Epoch of Reionization (EoR) represents a milestone in the evolution of our Universe. Star-forming galaxies that existed during the EoR likely emitted a significant fraction (~5-40%) of their bolometric luminosity as Lyman Alpha (Lya) line emission. However, neutral intergalactic gas that existed during the EoR was opaque to Lya emission that escaped from galaxies during this epoch, which makes it difficult to observe. The neutral intergalactic medium (IGM) may thus reveal itself by suppressing the Lya flux from background galaxies. Interestingly, a `sudden' reduction in the observed Lya flux has now been observed in galaxies at z >6. This review contains a detailed summary of Lya radiative processes: I describe (i) the main Lya emission processes, including collisional-excitation & recombination (and derive the famous factor `0.68'), and (ii) basic radiative transfer concepts, including e.g. partially coherent scattering, frequency diffusion, resonant versus wing scattering, optically thick versus 'extremely' optically thick (static/outflowing/collapsing) media, and multiphase media. Following this review, I derive expressions for the Gunn-Peterson optical depth of the IGM during (inhomogeneous) reionization and post-reionization. I then describe why current observations appear to require a very rapid evolution of volume-averaged neutral fraction of hydrogen in the context of realistic inhomogeneous reionization models, and discuss uncertainties in this interpretation. Finally, I describe how existing & futures surveys and instruments can help reduce these uncertainties, and allow us to fully exploit Lya emitting galaxies as a probe of the EoR.
265 citations