HET23,24/HET33,34
This set of experiments is proposed in order to simulate the radiative transfer regime in the RAMI-V spectral bands for heterogeneous leaf canopies situated on an incline of constant slope. For energy conservation purposes the virtual tree-crowns are inclined and the background is kept horizontal rather than having a background that is sloping and trees that are upright. The canopy is thus represented by a large number of identical, non-overlapping and inclinded cylindrical objects that are located over a horizontal plane standing for the underlying background.
| HETnn_DIS_dss | Tree density | Tree inclination |
|---|---|---|
| HET23_DIS_S15 | sparse | 15° |
| HET24_DIS_D15 | dense | 15° |
| HET33_DIS_S30 | sparse | 30° |
| HET34_DIS_D30 | dense | 30° |
Each individual cylinder contains a 'cloud' of oriented finite-sized disc-shaped scatterers representing the foliage. These 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 definition page). The background surface follows the Lambertian scattering law.
As can be seen in the image below, the cylindrical objects (when placed upright) have a height of 3.0 m, a radius of 1.0 m, and a leaf area index of 4.05 m² ⁄ m². Two different inclinations of the cylinders are envisaged: 15° and 30°, respectively. These inclinations can be obtained by rotation the cylinder (centered at the origin 0,0,0 ) along the Y axis such that the positive Z axis moves towards the positive X axis. In the canopy the cylindrical objects have their center coordinates located between heights of 2.0099 m and 2.0101 m.
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 and the cylinder locations in the scene are provided.
An ASCII file with the radius (R), centre coordinates (Xc,Yc,Zc), and direction cosines (Dx,Dy,Dz) of every single leaf in a cylindrical volume (centered at 0,0,0 but inclined via a 15° rotation around the Y axis such that the positive z axis moves towards the positive X axis) is available here for the tree inclined by 15° and for the tree inclined by 30°. This files (1.2 Mbytes) contain 17999 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 cylinder centers in the scene.
| Experiment | HET23 | HET24 | HET33 | HET34 |
|---|---|---|---|---|
| ( X × Y × Z) [m × m × m] | 101.30 × 101.0 × 3.58 | |||
| (Xmin, Ymin, Zmin) [m, m, m] | −50.65, −50.5, 0.0 | |||
| (Xmax, Ymax, Zmax) [m, m, m] | +50.65, +50.5, 3.58 | |||
| Scatterer shape | Disc of negligible thickness | |||
| Scatterer radius [m] | 0.0075 | |||
| Foliage scattering law | Bi-Lambertian | |||
| LAI of individual (upright) cylinder | 4.05 | |||
| Radius of cylinder [m] | 0.5 | |||
| Height of (upright) cylinder [m] | 3.0 | |||
| Cylinder center height range [m] | 2.0099 - 2.0101 | |||
| Scatterer normal distribution | Uniform | |||
| Background scattering law | Lambertian | |||
| Number of cylinders | 1274 | 5093 | 1274 | 5093 |
| LAI of scene | 0.396058 | 1.58330 | 0.396058 | 1.58330 |
| Tree definition | file | file | file | file |
| Tree position | file | file | file | file |
| Top-view rendering |  |
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Each leaf is characterized by a Bi-Lambertian optical properties through the STDL_REFL and STDL_TRAN spectral values given in file for each RAMI-V spectral band. The surface reflectance is determined by SOIL2 values of the same file and is assumed to be lambertian.
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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_).
