Phase: RAMI4PILPS
The MixFor-3D (MixFor3D) model [Olchev et al., 2009] consists of several closely coupled 3-D submodels describing the structure of a forest stand; the radiative transfer in a forest canopy; the turbulent transfer of sensible heat and water vapor between ground surface, trees and the atmospheric surface layer; and the heat and moisture transfer in soil.
Mixfor3D has a horizontal resolution of 2 x 2 m2, a vertical canopy resolution of 1 m, a vertical soil resolution of 0.1 m and a primary time step of 1 h.
The model algorithm describing solar radiation transfer through a forest canopy considers direct and diffuse radiation penetrating through gaps in the canopy, transmitted by leaves and reflected from leaves, bark and soil surface.
It uses information about the 3-D structure of each tree species in the forest stand, and about the optical properties of their leaves and bark.
It takes into account clumping and gapping of foliage, spatial variations in leaf orientation angles and site topography.
The calculation of the direct solar radiation fluxes within the canopy is based on estimating the probability that a ray of light passing through the foliage reaches a given level within the canopy without interception [e.g., Myneni et al., 1989].
Hemispheric transmission and reflection for photosynthetically active and near-infrared radiation are calculated for each grid unit of a plant canopy with the two-stream approximation approach [e.g., Dickinson, 1983; Pinty et al., 2006] taking into consideration the local PAD and LAD, as well as optical spectral properties of the grid phytoelements.
Total radiation fluxes for each grid point of a forest canopy are calculated using a “step-by-step” algorithm going from the upper canopy layers to the lower canopy layers.
Since it is well established that canopy structure affects the radiative properties [e.g., Cescatti, 1988; Rautiainen et al., 2004; Smolander and Stenberg, 2005; Widlowski et al., 2005b], one can anticipate that the approximation of spherical objects with box-shaped 1 m3 voxels will have an impact on the simulation results of the MixFor3D model (for 3-D cases).
