This set of experiments is proposed in order to simulate the radiative transfer regime for two spatially homogeneous leaf canopies - of different structural and spectral properties - that meet along a common (straight line) interface. The overall scene architecture thus is similar to that of two spatially homogeneous forest stands that meet along some straight separation line, or, a meadow that lies at the edge of a forest.
Each canopy part is composed of a large number of non overlapping disc-shaped objects representing the foliage elements. The structural and spectral properties of the scatterers are different from one canopy part to the other. The underlying background is Lambertian. To address the needs of different RT models, both a statistical scene description, as well as a file with the exact coordinates of every single scatterer in the canopy is provided. 1D models may want to use the Independent Pixel Approach (IPA), that is to simulate the contribution of each canopy separately and then merge the results, in order to participate in these test cases. Any other approach used by plane parallel models is obviously welcome too.
The foliage objects in both canopy parts are randomly distributed finite size disc-shaped scatterers characterized by their specified radiative properties (reflectance, transmittance), and the orientation of the normals to the scatterers follows both erectophile and planophile distribution functions (for LAD definitions see here).
The interface between the two canopy types lies always along the y axis, i.e. x=0 and the canopy with an erectophile leaf normal distribution has leaf centers with negative abscissa (x) values (Figure 1).
The erectophile and planophile adjacent canopies are both 1m in height, and are formed by a disc-shaped scatterer with a radius of 0.05m which follows a Bi-Lambertian scattering law. Other structural and spectral properties are, however, different between the erectophile and planophile canopy parts as listed in the table below for the HOM29 (sparse ERE/dense PLA) and HOM30 (medium ERE/sparse PLA) scenes.
For 3D RT models capable of using the deterministic position and orientation of all scatterers in the scenes an ASCII file is available here for HOM29 and here for HOM30. These files contain the leaf normal distribution type, LND (where ERE=erectophile and PLA=planophile), the leaf/disc radius (R), the leaf/disc centre coordinates (Xc,Yc,Zc), and the cosine directions (Dx,Dy,Dz) of every single leaf/disc in a 50×50 $m^2$ canopy section.
The size of these ASCII files are several Mbytes and the format of their header is LND Radius Xc Yc Zc Dx Dy Dz.
|Experiment identifier tag
|ERE canopy LAI||1.0 $m^2/m^2$||3.0 $m^2/m^2$|
|ERE canopy Height||1.0 m||2.0 m|
|ERE number of scatterers||159154||477464|
|ERE spectral properties||LEAF2_||LEAF2_|
|PLA canopy LAI||5.0 $m^2/m^2$||1.0 $m^2/m^2$|
|PLA canopy Height||1.0 m||1.0 m|
|PLA number of scatterers||795774||159154|
|PLA spectral properties||LEAF1_||LEAF1_|
|Scatterer Radius (ERE & PLA)||0.05 m||0.05 m|
The planophile leaf spectral properties are indicated by the values labeled as LEAF1_ in the optical properties file, while erectophile properties are labeled as LEAF2_. As usual both bi-lambertian reflectance and transmittance are provided.
The surface reflectance is determined by SOIL2 values of the same file and is assumed to be lambertian.
The illumination conditions are very likely dependent on the kind of measurement in RAMI-V more than in previous RAMI phases. For brf*, dhr, fabs*, ftran* measurements, except brf_sat, the illumination were listed in the description of measure brfpp, and duplicated in other measure description pages. For these geometries the tag will be _zZZaAAA_ with ZZ and AAA defining $\theta_i$ and $\phi_i$, respectively. In addition, diffuse isotropic illumination is foreseen for bhr, fabs*, ftran* measures (geometry tag will then be _DIFFUSE_).