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Anisotropic background


This set of scenes are provided to simulate the radiative transfer regimes in the RAMI-V spectral bands for two heterogeneous canopies composed of a large number of identical and non-overlapping spherical objects (plant crowns) distributed over a horizontal background surface with different non-lambertian reflectance properties. Six flavors of the scene originates from the combination of two by three different surface parameterizations as listed in Table 1.

HETnn_DIS_d1r Overstorey Surface properties (BRF model)
HET10_DIS_S1A sparse A (soil, RPV4_)
HET11_DIS_S1B sparse B (snow, RPV8_)
HET12_DIS_S1C sparse C (understorey vegetation, RPVS_)
HET20_DIS_D1A dense A
HET21_DIS_D1B dense B
HET22_DIS_D1C dense C
Table 1: scenes flavors as a combination of two vegetation densities and three surface reflectance properties.

Sparse scene
Figure 1: Sparse scene.
Dense scene
Figure 2: Dense scene.

These spherical objects have a radius of 0.5m and their centres are located 0.51 ± 0.0001 meters above the background plane (random height distribution) to yield a maximum canopy height of ~1.01m. 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 are provided.

Two different fractional coverages are proposed: sparse with fractional coverage of 0.2 and dense (0.4). Each individual sphere contains a 'cloud' of oriented finite-sized particles representing the foliage.

The leaf area index (LAI) of a single sphere (LAI = area of leaves/maximum cross section of sphere) is fixed and amounts to 5.0m2/m2.

The orientation of the normals of the foliage elements (scatterers) follows a uniform (or spherical) distribution function, i.e., the probability to be intercepted by a leaf is independent of the direction of travel of the radiation (see the definitions page).

Tables 2 provides the details of the vegetation part for sparse (HET10,11,12) and dense (HET 20,21,22) scenes. The optical properties of the leaf (standard green leaf, STDL) and of the underlying surfaces (flavor: A, B, C) are given in the Spectral characteristics section.

An ASCII file with the radius (R), centre coordinates (Xc,Yc,Zc), and direction cosines (Dx,Dy,Dz) of every single leaf in a spherical volumes centered at 0,0,0 can be found here. This file, meant to build an individual crown contains 49999 leaf instances. Its header is R Xc Yc Zc Dx Dy Dz.

Each tree should then be translated in space accordingly to the two different files for sparse and dense scene flavors given in Table 2 (Tree positions).

Properties Sparse Dense
( X × Y × Z) 101.0 × 101.0 × 1.01 [m × m × m]
(Xmin, Ymin, Zmin) −50.5, −50.5, 0.0 [m, m, m]
(Xmax, Ymax, Zmax)+50.5, +50.5, 1.0101 [m, m, m]
Scatterer shapeDisc of negligible thickness
Scatterer radius0.005 [m]
LAI of individual sphere5.0
Scatterer normal distributionUniform
Foliage scattering lawBi-Lambertian
Sphere radius0.5 [m]
Minimum sphere center height0.5099 [m]
Maximum sphere center height0.5101 [m]
Background BRF patternNon-Lambertian (see tables below)
Number of spheres2547 5093
Fractional scene area coverage of spheres 0.1961 0.3921
Tree position link link
Table 2: physical properties of the canopy (vegetation).

Top SPARSE scene
Figure 3: Top view rendering of the SPARSE scene.
Top DENSE scene
Figure 4: Top view rendering of the DENSE scene.

Within a given sphere the Bi-Lambertian foliage elements are characterized by specified radiative properties (reflectance, transmittance) defined by STDL_REFL and STDL_TRAN spectral values given here for each RAMI-V spectral band.

The BRF of the anisotropic scattering background (which is intended to represent bare soil, snow, and understorey vegetation conditions) is expressed in terms of $\rho_0$,k and $\Theta$ parameters of the RPV model. The parameters labeled with RPV4_ should be used for HET10, HET20 (soil background), RPV8_ for HET11, HET21 (snow background) and RPVS_ for HET12, HET22 (understorey vegetation) scenes, can be found here.



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_).