  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.
