This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Light scattering in planetary atmospheres

We review the data and models describing the production of the electrons, termed secondary electrons, that initiate the secondary and subsequent feedback avalanches required for the growth of current during breakdown and for the maintenance of low-current, cold-cathode discharges in argon First we correlate measurements of the production of secondary electrons at metallic cathodes, ie the yields of electrons induced by Ar+ ions, fast Ar atoms, metastable atoms and vuv photons The yields of electrons per ion, fast atom and photon vary greatly with particle energy and surface condition Then models of electron, ion, fast atom, excited atom and photon transport and kinetics are fitted to electrical-breakdown and low-current, discharge-maintenance data to determine the contributions of various cathode-directed species to the secondary electron production Our model explains measured breakdown and low-current discharge voltages for Ar over a very wide range of electric field to gas density ratios E/n, ie 15 Td to 100 kTd We review corrections for nonequilibrium electron motion near the cathode that apply to our local-field model of these discharges Analytic expressions for the cross sections and reaction coefficients used by this and related models are summarized

https://iopscience.iop.org/article/10.1088/0963-0252/8/3/201/pdf

Cold-cathode discharges and breakdown in argon: surface and gas phase production of secondary electrons

The aim of the Round Table (RT) ”Problems in modelling stellar atmospheres“ was that of giving a panoramic view of the state of art on the atmospheric models used to predict observations of stars from T to A spectral type, the Sun included.

/pdf/round-table-summary-problems-in-modelling-stellar-48jvhmkdq4.pdf

Round Table Summary: Problems in Modelling Stellar Atmospheres

The use of the Monte Carlo method in radiative heat transfer is reviewed. The review covers surface-surface, enclosure, and participating media problems. Discussio. is included of research on the fundamentals of the method and on applications to surface-surface interchange in enclosures, exchange between surfaces with roughness characteristics, determination of configuration factors, inverse design, transfer through packed beds and fiber layers, participating media, scattering, hybrid methods, spectrally dependent problems including media with line structure, effects of using parallel algorithms, practical applications, and extensions of the method. Conclusions are presented on needed future work and the place of Monte Carlo techniques in radiative heat transfer computations

The Monte Carlo Method in Radiative Heat Transfer

Recent advances in cloud microphysical models have led to realistic three-dimensional distributions of cloud constituents. Radiative transfer schemes can make use of this detailed knowledge in order to study the effects of horizontal as well as vertical inhomogeneities within clouds. This study looks specifically at the differences between three-dimensional radiative transfer results and those obtained by plane parallel, independent pixel approximations in the microwave spectrum. A three-dimensional discrete ordinates method as well as a backward Monte Carlo method are used to calculate realistic radiances emerging from the cloud. Analyses between these models and independent pixel approximations reveal that plane parallel approximations introduce two distinct types of errors. The first error is physical in nature and is related to the fact that plane parallel approximations do not allow energy to leak out of dense areas into surrouding areas. In general, it was found that these errors are quite small for emission-dominated frequencies (37 GHz and lower) and that physical errors are highly pronounced only at scattering frequencies (85 GHz) where large deviations and biases up to 8 K averaged over the entire cloud were found. The second error is more geometric in nature and is related to the fact that plane parallel approximations cannot accommodate physical boundaries in the horizontal dimension for off-nadir viewing angles. The geometric errors were comparable in magnitude for all frequencies. Their magnitude, however, depends on a number of factors including the scheme used to deal with the edge, the nature of the surface, and the viewing angle.

Microwave radiative transfer through horizontally inhomogeneous precipitating clouds

A general review is given of the application of the Monte Carlo method to the numerical calculations of non-equilibrium radiation transport. With the aid of a general flow chart, the various steps required in such Monte Carlo calculations are detailed. Advanced techniques which improve efficiency of calculations such as weighting and biasing are also discussed. Although specific results are not given in the text, references to recent Monte Carlo calculations of radiation transport are included.

The Monte Carlo technique applied to radiative transfer.

The transfer of resonance line radiation in homogeneous cylinders of various shapes and optical thicknesses is studied by means of the Monte Carlo method in order to investigate the effects of geometry on (non-LTE) source functions and emergent line intensity profiles. It is found that increasing the larger cylinder dimension (radius or length) produces no change in the source function except to extend it at a constant level. For cylinders with the same axial optical thickness as a slab, we find that the axial source function is effectively the same as that of a slab whenever the radius of the cylinder exceeds its length. Further, when the length exceeds the radius, the radial source function approximates the source function for a slab of optical thickness equal to that of the cylinder radius, provided this is less than a thermalization length. Emergent line shapes are calculated and are found to be strongly dependent upon the position and aspect. Scaling laws are given which permit estimation of the source function at an arbitrary point in a cylinder without a detailed solution of the transfer problem.

L.L. House

Papers

The Monte Carlo technique applied to radiative transfer.

Radiative transport in finite homogenous cylinders by the Monte Carlo technique

The Monte Carlo Technique Applied to Radiative Transfer