This set of experiments is suggested to simulate the radiative transfer regime in the red and near infra-red spectral bands for heterogeneous leaf canopies composed of two structurally different layers. Each of these layers are represented by a large number of identical, non-overlapping spherical objects, respectively, that are located over and only partially covering a horizontal plane standing for the underlying background surface. The structural properties of these spherical objects are different between the upper (overstorey) and lower (understorey) layers. In the understorey layer, the spherical objects have a radius of 0.5m and their centers are located 0.51 ± 0.0001 meters above the background plane (random height distribution). In the overstorey layer the spherical objects have a radius of 5m and center coordinates that vary between 7 and 11 meter above the background level (such that the maximum canopy height is 16m). To address the needs of different RT models, both a statistical scene description, as well as ASCII files with the exact coordinates of the scatterers in the sphere (or the sphere locations in the scene) are provided.

Overall three different overstorey densities and two understorey densities will be presented. 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 5.0 [m² ⁄ m²] both in the overstorey and understorey. Within a given sphere the Bi-Lambertian foliage elements are characterized by specified radiative properties (reflectance, transmittance) defined separately for both the visible and near-infrared spectral domains.

The orientation of the normals of the foliage elements (scatterers) follows a uniform (or what is sometimes called a 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).

All canopy constituents obey Lambertian scattering laws.

Heterogeneous two-layer canopy with sparse understorey

The tables below provide the details required to build and run a RT model on the two-layer heterogeneous canopy with a sparse understorey.

Scene properties:

where the Leaf Area Index (LAI) is calculated as follows:

LAI = (# of leaves × one-sided area of single leaf) ⁄ (π × square of the radius of sphere)

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 is available for both understorey and overstorey spheres.
These files (are ~ 2.7 Mbytes and) contain 49999 lines of format R Xc Yc Zc Dx Dy Dz that may serve as input to your scene creation process (provided that you are able to create multiple instances of its content, each one of which is then translated to the actual locations of the sphere centers in the scene. The coordinates (X, Y, Z) of the various UNDERSTOREY sphere centers for the sparse UNDERSTOREY scene can be found here.

The tables below provide detailed information regarding the illumination conditions and spectral properties of the foliage and background constituents of the sparse canopy scenarios. Every table is preceeded by the corresponding experiment identifier tag <EXP> that is needed in the naming of the various measurement results files (see file naming and formatting conventions). Two spectral bands (red and NIR) and two illumination conditions (direct only with SZA=20° and 50°) are proposed for three different background anisotropy scenarios, referred to as HET16, HET17 and HET18 in the tables below. The difference between experiments HET16, HET17 and HET18 thus lies only in the density of the overstorey (i.e., the number of overstorey spheres).

Heterogeneous two-layer canopy with dense understorey

The tables below provide the details required to build and run a RT model on the two-layer heterogeneous canopy with a dense understorey.

Scene properties:

where the Leaf Area Index (LAI) is calculated as follows:

LAI = (# of leaves × one-sided area of single leaf) ⁄ (π × square of the radius of sphere)

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 is available for both understorey and overstorey spheres.
These files (are ~ 2.7 Mbytes and) contain 49999 lines of format R Xc Yc Zc Dx Dy Dz that may serve as input to your scene creation process (provided that you are able to create multiple instances of its content, each one of which is then translated to the actual locations of the sphere centers in the scene. The coordinates (X, Y, Z) of the various UNDERSTOREY sphere centers for the sparse UNDERSTOREY scene can be found here.

The tables below provide detailed information regarding the illumination conditions and spectral properties of the foliage and background constituents of the sparse canopy scenarios. Every table is preceeded by the corresponding experiment identifier tag <EXP> that is needed in the naming of the various measurement results files (see file naming and formatting conventions). Two spectral bands (red and NIR) and two illumination conditions (direct only with SZA=20° and 50°) are proposed for three different background anisotropy scenarios, referred to as HET26, HET27 and HET28 in the tables below. The difference between experiments HET26, HET27 and HET28 thus lies only in the density of the overstorey (i.e., the number of overstorey spheres).