Integrating transport equations by combining transfer matrices, transmission-reflection matrices, and Green's matrices, in the context of light propagation in foliage

Abstract

In many problems, it is necessary to integrate a transport equation. Here we consider specifically light incident on a horizontally homogeneous foliage ('the canopy'), modeled as a turbid medium. This is often treated by integrating numerically the light transport equation, assuming initial values for the reflected radiances, and iterating until the radiances stabilize. We here present a method combining transfer matrices, transmission-reflection matrices, and Green's matrices (TTRG). This method is both fast and accurate, especially if one must do many computations on the same canopy, for different incident fluxes and internal emissions. There exist (artificial) extreme light trapping situations for which iterative integration is hardly practical, while TTRG remains as efficient.