Light-transmittance predictions under multiple-light-scattering conditions. I. Direct problem: hybrid-method approximation.

Our aim is to present a method of predicting light transmittances through dense three-dimensional layered media. A hybrid method is introduced as a combination of the four-flux method with coefficients predicted from a Monte Carlo statistical model to take into account the actual three-dimensional geometry of the problem under study. We present the principles of the hybrid method, some exemplifying results of numerical simulations, and their comparison with results obtained from Bouguer-Lambert-Beer law and from Monte Carlo simulations.

Light-transmittance predictions under multiple-light-scattering conditions. II. Inverse problem: particle size determination.

Our aim is to present the application of the hybrid method presented in part I to an inverse procedure to determine particle size and concentration under multiple-scattering conditions. The hybrid method is introduced as a combination of the four-flux method with coefficients obtained from Monte Carlo statistical simulations to take into account the actual three-dimensional geometry. Then an inversion scheme is expanded to enable the application of the hybrid method to particle size and concentration determination. We present the inversion method as well as exemplifying results of spectrum inversions.

Four-flux model for a multilayer, plane absorbing and scattering medium: application to the optical degradation of white paint in a space environment.

We generalize the four-flux radiative transfer model to the case of a multilayer medium. A concrete application, that of the study of the optical degradation of white paint in a simulated space environment, is presented. The degraded material is decomposed in a damaged layer and in an unaffected layer, and we assume that the degradation is due to a variation Dkappa of the imaginary part of the refractive index in the damaged layer. Then we find an empirical law for variation Dkappa with dose, taking into account possible saturation.

Comparison of iterative and monte carlo methods for calculation of the Aureole about a point source in the earth's atmosphere.

Point sources in the atmosphere are surrounded by aureoles because of atmospheric scattering. The properties of an aureole were calculated by use of a Monte Carlo approach and an iterative method for an isotropic source and an axially symmetric emission source inside an infinite homogeneous atmosphere. The influence of single-scattering albedo, optical depth between source and observer, and source intensity anisotropy were studied from both approaches. For each situation, the limits and advantages of the Monte Carlo technique and the iterative method are described.