These experiments were suggested to simulate the radiative transfer regime in the red and near infra-red spectral bands for heterogeneous environments. Within RAMI an environment is deemed heterogeneous if its properties must be considered dependent of geographical location (horizontal spatial coordinates). The description of the 3-D foliage structure can then either be done in a deterministic manner (discrete case), that is, the location and orientation of every individual scatterer is known, or else, using a statistical approach where volumes with particular foliage properties are defined at specified locations within the scene. Within these volumes, scatterers can then either be finite-sized or else non-dimensional (turbid case). Please click on the links below to have access to the various description pages of the 3-D scenes.
Heterogeneous environments are typically represented with 3-dimensional models. If applicable by the RT model at hand, cyclic boundary conditions must be applied to all test cases unless specified otherwise on the individual measurement description pages. Furthermore, the various measurements that are required to be carried for each test case, are always defined with respect to a reference plane which - unless specified otherwise - covers the entire test case area (known as the "scene"), and is located at the top-of-the-canopy, that is, just above the highest structural element in the scene.
Prior to the performing of any RT model simulations, please refer to the 'definitions' pages for detailed instructions regarding the angular sign conventions for BRF simulations, as well as precise definitions of the required leaf normal distributions and other RT model technicalities. Also read the relevant file naming and formatting conventions that must be adhered to by all participants.
The following Figure shows the envelope of a series of histograms of local angular model deviation values estimated for viewing conditions in the principal plane (left panels), cross plane (middle panels) and the principal and cross planes together (right panels) for the ensemble of discrete heterogeneous test cases. The top, center and bottom panels display the results obtained at the red, the near-infrared and, at the red and near-infrared wavelengths together, respectively. It can be seen that the values generated by four conceptually different three-dimensional models range from 3 to 6%.
The following Figure shows the detailed contributions of the individual models to a series of histograms of local angular model deviation values estimated for viewing conditions in the principal plane (left panels), cross plane (middle panels) and the principal and cross planes together (right panels) for the ensemble of discrete heterogeneous test cases. The top, center and bottom panels display the results obtained at the red, the near-infrared and, at the red and near-infrared wavelengths together, respectively.
The bottom right panel of this Figure summarizes the values of the local angular deviations when summed up over the two wavelengths and viewing planes. Here again, the RAMI exercise permitted the identification of one model deviating from the others. The particular behavior of the DART model in the near-infrared wavelength and additional results from RAMI lead to further corrections and upgrades of this model in its treatment of multiple scattering processes.