SIMULATION OF MULTIPLY SCATTERING MEDIA

The radiative transport in a multiply scattering medium differs strong ly from that in a weakly scattering medium, so it should be described by the rigorously derived equation of radiative transfer. This integro -differential equation cannot be solved analytically. With the Monte-C arlo method (MCM) and the N-flux method (NFM) presented here, the tran smission, reflection and absorption properties of a multiply scatterin g layer can be calculated for a given set of input parameters. Using M CM, a specific measurement geometry can be considered in the simulatio n. Since measurements of strongly scattering media can be very much in error due to radiation that is scattered beyond the instrument apertu re or lateral sample boundaries, MCM provides a possibility to correct for this ''missing radiation''. Thermotropic layers can protect solar apertures against overheating or, more generally, control solar radia tion by switching from a transparent state to a strongly scattering st ate with rising temperature. Simulation results for the optical proper ties of thermotropic layers in the diffusely back-scattering state are presented and compared with measured values. These results can be use d to optimise the back-scattering of solar radiation as well as to ana lyse the sub-micron internal structure of the layers. (C) 1998 Elsevie r Science B.V. All rights reserved.