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Homogeneous discrete cases composed of two adjacent canopies: HOM29 and HOM30

This set of experiments is suggested 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 LND definitions see here). The particular values selected for the various input variables represent typical plant canopy conditions.

The following figure exhibits a graphical representation of such a scene:

The tables below provide the details required to implement and perform each of the experiments in this category. Every table is preceded 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). For illumination purposes it is imperative to note that 1) the interface between the two canopy types lies always along the y axis, i.e. x=0, 2) the canopy with an erectophile leaf normal distributions has leaf centers with negative x coordinate values, 3) the canopy with a planophile leaf normal distributions has leaf centers with positive x coordinate values, and 4) a positive (illumination) azimuth angle is counted from the positive X axis towards the positive Y axis as indicated in the image below.

The first set of spatially homogeneous adjacent canopy experiments refers to a vegetation environment where both canopy parts have a height of 1m, a scatterer radius of 0.05m and follow Bi-Lambertian scattering laws. Other structural and spectral properties are, however, different between the erectophile and planophile canopy parts. The erectophile canopy part has leaf centers with negative x coordinate values, whereas the planophile canopy part has leaf centers with positive x coordinate values. The background scattering law is also Lambertian. Two spectral bands (red and NIR) and two illumination conditions (direct only with SZA=20° and 50°) are proposed for three different azimuthal illumination conditions that is, the solar azimuth is 0, 90, and 180 degree. For any given table below, the solar azimuth is thus the only changing parameter from one column to the next.

For 3D RT models capable of using the deterministic position and orientation of all scatterers in the scenes an ASCII file is available here This file (47.3 Mbytes) contains 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 direction cosines (Dx,Dy,Dz) of every single leaf/disc in a 50×50 m² canopy section. The size of these ASCII files is several Mbytes and the format of its content is LND R Xc Yc Zc Dx Dy Dz.

The next set of spatially homogeneous adjacent canopy experiments refers to a vegetation environment where both canopy parts have a scatterer radius of 0.05m and follow Bi-Lambertian scattering laws. Other structural and spectral properties are, however, different between the erectophile and planophile canopy parts. The erectophile canopy part has leaf centers with negative x coordinate values, whereas the planophile canopy part has leaf centers with positive x coordinate values. The background scattering law is also Lambertian. Two spectral bands (red and NIR) and two illumination conditions (direct only with SZA=20° and 50°) are proposed for three different azimuthal illumination conditions that is, the solar azimuth is 0, 90, and 180 degree. For any given table below, the solar azimuth is thus the only changing parameter from one column to the next.

For 3D RT models capable of using the deterministic position and orientation of all scatterers in the scenes an ASCII file is available here This file (31.9 Mbytes) contains 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 direction cosines (Dx,Dy,Dz) of every single leaf/disc in a 50×50 m² canopy section. The size of these ASCII files is several Mbytes and the format of its content is LND R Xc Yc Zc Dx Dy Dz.

Below is a list of the various measurements that are required for these test cases:

• BRF in cross plane (total)
• BRF in cross plane for multiple-scattered radiation
• BRF in cross plane for single collided radiation
• BRF in cross plane for uncollided radiation
• BRF in principal plane (total)
• BRF in principal plane for multiple-scattered radiation
• BRF in principal plane for single collided radiation
• BRF in principal plane for uncollided radiation
• Collided by canopy only transmission at lower boundary level for direct illumination only
• Directional Hemispherical Reflectance (Black Sky Albedo)
• Foliage absorption
• Total transmission at lower boundary level for direct illumination only
• Uncollided transmission at lower boundary level for direct illumination only
• Vertical profile of total transmission through canopy