Normalized horizontal flux
A flux expresses an amount of energy crossing a unit area per unit time. Within RAMI it is assumed that all model simulation do yield quantities per unit time (even though actual runs may last much longer). The normalized horizontal flux term, thus is the total flux passing through one of the lateral sides (either in or out of a voxel of given dimensions), divided by the total incoming flux through the upper side of that voxel.
By definition all voxels within RAMI are aligned with the cartesian coordinate system of the scene. Since every voxel is composed of six sides, they can be labelled as upper (u) and lower (l) sides with respect to the cartesian coordinate whose value is constant within them.
Xl thus refers to the lower voxel side that has constant X values (its face is oriented perpendicular to the X axis vector) and whose absolute x-coordinate values are lower than those of the upper voxel side with the same orientation (Xu). Similarly Yl and Yu are the lower and upper voxel sides oriented perpendicular to the Y axis. Zu is the top of the canopy voxel side (oriented horizontally), whereas Zl is the side of the voxel that is located just above (and parallel to) the soil/background.
Since every voxel has 4 lateral sides, and fluxes may both enter (Fin) or exit (Fout) a voxel, 8 different horizontal fluxes will have to be computed: 4 for radiation passing through the voxel sides perpendicular to the X-axis, and another 4 for radiation passing through the voxel sides perpendicular to the Y-axis. In addition, the incoming flux at the top-of-canopy level is also required. The latter is needed to convert the actual horizontal flux terms into the corresponding normalized horizontal flux term quantities.
For example, the outgoing normalized horizontal flux term for the Xu voxel side (nhorflxoutXu) thus is the ratio of the outgoing flux (Fout) passing through the upper voxel side perpendicular to the direction of the X-axis (Xu), divided by the incoming flux at the top-of-canopy level, i.e., Fin(Zu): nhorflxoutXu = Fout(Xu) ⁄ Fin(Zu)
Overall 8 normalized total horizontal flux term quantities have to be computed for every voxel location: eg
|Header line content||Header line format|
|# columns in file||%4d|
*: if available, otherwise set to −1.000000.
1 8 0.123456 0.123456 0.123456 0.123456 0.123456 0.123456 0.123456 0.123456