RAMI2 phase
These experiments were suggested to simulate the radiative transfer regime in the red and near infra-red spectral bands for heterogeneous environments. The representation of the 3-D foliage structure is to be done either 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).
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.
The following two Figures show the various contributions of the RT models to a series of histograms of local angular model deviation for discrete homogeneous environments with erectophile and planophile leaf normal distributions, respectively. Values were estimated for viewing conditions in the principal plane (left panels), cross plane (middle panels) and the principal and cross planes together (right panels) as well as for LAI values of 1 (top), 2 (center) and 5 (bottom).
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 and cross planes, in both the red and near-infrared wavelengths, for the ensemble of the discrete representations of the "Floating Spheres" heterogeneous test cases. Clockwise from the top left panel are shown: the total, the multiple scattered, the single-scattered by vegetation, and the single-scattered by soil BRF components.
The next Figure shows the same series of histograms but after removing the models GORT, LIM and frt, which were identifiable to be rather different from the ensemble of other participating models in the above graph.
The Figure below shows the angular deviations of the various models (with respect to each other) as a function of viewing angle, averaged over both turbid and discrete "Floating Spheres" experiments along the principal plane, two solar zenith angles (20 and 50 degree), and for both the red and near-infrared wavelengths:
The following figure is similar to the previous but shows the angular deviations of the various models (with respect to each other) as a function of viewing angle, averaged over both turbid and discrete "Floating Spheres" experiments along the orthogonal plane, two solar zenith angles (20 and 50 degree), and for both the red and near-infrared wavelengths:
The various testcases that are defined within this phase of the RAMI initiative can be visualized on their respective description pages: