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17-May-2022   
Path: RAMI-IV : EXPERIMENTS : ABSTRACT CANOPIES : HETEROGENEOUS : TWO LAYER CANOPY
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Abstract heterogeneous canopies with two layers:HET16, HET17, HET18 and HET26, HET27, HET28

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.

The following figures exhibit graphical representations of the two layer heterogeneous canopies:

Heterogeneous two layer canopy with sparse understorey:

The following table provides a graphical overview of the three scenes (having sparse, medium and dense) overstorey layers covering a sparse understorey layer;

HET16 (sparse overstorey - sparse understorey) HET17 (medium overstorey - sparse understorey) HET18 (dense overstorey - 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:

( X × Y × Z) [m × m × m] 101.0 × 101.0 × 15.90
(Xmin, Ymin, Zmin) [m, m, m] −50.5, −50.5, 0.0
(Xmax, Ymax, Zmax) [m, m, m] +50.5, +50.5, 15.90
Scatterer shape Disc of negligible thickness
Scatterer radius [m] 0.005 (understorey) 0.05 (overstorey)
LAI of individual sphere 5.0 (understorey and overstorey)
Scatterer normal distribution Uniform (understorey and overstorey)
Foliage scattering law Bi-Lambertian (understorey and overstorey)
Sphere radius [m] 0.5 (understorey) 5.0 (overstorey)
Number of spheres 2547 (understorey) see below for (overstorey)
sphere center height range [m] 0.5099 - 0.5101 (understorey) 7.0 - 11.0 (overstorey)
Background scattering law Lambertian

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).

Experiment identifier tag <EXP> : HET16_DIS_UNI_RED_20 HET17_DIS_UNI_RED_20 HET18_DIS_UNI_RED_20
Solar Zenith Angle (SZA) 20 [deg] 20 [deg] 20 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.06 0.06 0.06
Leaf scatterer transmittance 0.02 0.02 0.02
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.13 0.13 0.13

Experiment identifier tag <EXP> : HET16_DIS_UNI_NIR_20 HET17_DIS_UNI_NIR_20 HET18_DIS_UNI_NIR_20
Solar Zenith Angle (SZA) 20 [deg] 20 [deg] 20 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.50 0.50 0.50
Leaf scatterer transmittance 0.44 0.44 0.44
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.16 0.16 0.16

Experiment identifier tag <EXP> : HET16_DIS_UNI_RED_50 HET17_DIS_UNI_RED_50 HET18_DIS_UNI_RED_50
Solar Zenith Angle (SZA) 50 [deg] 50 [deg] 50 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.06 0.06 0.06
Leaf scatterer transmittance 0.02 0.02 0.02
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.13 0.13 0.13
background reflectance
0.16 0.16 0.16

Experiment identifier tag <EXP> : HET16_DIS_UNI_NIR_50 HET17_DIS_UNI_NIR_50 HET18_DIS_UNI_NIR_50
Solar Zenith Angle (SZA) 50 [deg] 50 [deg] 50 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.50 0.50 0.50
Leaf scatterer transmittance 0.44 0.44 0.44
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.16 0.16 0.16

Heterogeneous two layer canopy with dense understorey:

The following table provides a graphical overview of the three scenes (having sparse, medium and dense) overstorey layers covering a dense understorey layer;

HET26 (sparse overstorey - dense understorey) HET27 (medium overstorey - dense understorey) HET28 (dense overstorey - 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:

( X × Y × Z) [m × m × m] 101.0 × 101.0 × 15.90
(Xmin, Ymin, Zmin) [m, m, m] −50.5, −50.5, 0.0
(Xmax, Ymax, Zmax) [m, m, m] +50.5, +50.5, 15.90
Scatterer shape Disc of negligible thickness
Scatterer radius [m] 0.005 (understorey) 0.05 (overstorey)
LAI of individual sphere 5.0 (understorey and overstorey)
Scatterer normal distribution Uniform (understorey and overstorey)
Foliage scattering law Bi-Lambertian (understorey and overstorey)
Sphere radius [m] 0.5 (understorey) 5.0 (overstorey)
Number of spheres 5093 (understorey) see below for (overstorey)
sphere center height range [m] 0.5099 - 0.5101 (understorey) 7.0 - 11.0 (overstorey)
Background scattering law Lambertian

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 dense 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).

Experiment identifier tag <EXP> : HET26_DIS_UNI_RED_20 HET27_DIS_UNI_RED_20 HET28_DIS_UNI_RED_20
Solar Zenith Angle (SZA) 20 [deg] 20 [deg] 20 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.06 0.06 0.06
Leaf scatterer transmittance 0.02 0.02 0.02
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.13 0.13 0.13

Experiment identifier tag <EXP> : HET26_DIS_UNI_NIR_20 HET27_DIS_UNI_NIR_20 HET28_DIS_UNI_NIR_20
Solar Zenith Angle (SZA) 20 [deg] 20 [deg] 20 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.50 0.50 0.50
Leaf scatterer transmittance 0.44 0.44 0.44
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.16 0.16 0.16

Experiment identifier tag <EXP> : HET26_DIS_UNI_RED_50 HET27_DIS_UNI_RED_50 HET28_DIS_UNI_RED_50
Solar Zenith Angle (SZA) 50 [deg] 50 [deg] 50 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.06 0.06 0.06
Leaf scatterer transmittance 0.02 0.02 0.02
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.13 0.13 0.13

Experiment identifier tag <EXP> : HET26_DIS_UNI_NIR_50 HET27_DIS_UNI_NIR_50 HET28_DIS_UNI_NIR_50
Solar Zenith Angle (SZA) 50 [deg] 50 [deg] 50 [deg]
Solar Azimuth Angle (SAA) 0 [deg] 0 [deg] 0 [deg]
Leaf scatterer reflectance 0.50 0.50 0.50
Leaf scatterer transmittance 0.44 0.44 0.44
Overstorey sphere number 18 (sparse)
sphere center locations (x y z)
37 (medium)
sphere center locations (x y z)
59 (dense)
sphere center locations (x y z)
background reflectance
0.16 0.16 0.16


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


Prior to the performing of any RT model simulations, please refer to the 'definitions' pages for detailed instructions regarding the angular sign conventions for BRF simulations, as well as other RT model technicalities. Also read the relevant file naming and formatting conventions that must be adhered to by all participants. In addition, RAMI-IV offers participants the possibility to test the compliance of their model-generated results files with these file-naming and formatting convention, prior to their submission via ftp: To do so follow the on-line format checker link that appears in the top navigation bar during the active submission period.

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