Abstract heterogeneous two-layer canopies

This set of experiments is proposed in order to simulate the radiative transfer regime in the RAMI-V spectral bands for heterogeneous leaf canopies composed of two structurally different layers with three (overstories) and two (understories) different densities, respectively. Each of these layers is represented by a large number of identical, non-overlapping spherical objects that are located over a horizontal background surface with uniform lambertian reflectance.

HETnn_DIS_d2d	Overstories density	Understories density
HET16_DIS_S2S	sparse	sparse
HET17_DIS_M2S	medium	sparse
HET18_DIS_D2S	dense	sparse
HET26_DIS_S2D	sparse	dense
HET27_DIS_M2D	medium	dense
HET28_DIS_D2D	dense	dense

Physical properties

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 0.5 m and their centers are located 0.51 ± 0.0001 meters above the background plane (random height distribution). In the overstorey layer the spherical objects (crowns) have a radius of 5 m and center coordinates that vary between 7 and 11 meter above the background level (such that the maximum canopy height is 16m).

Sphere definition

Each individual sphere contains a cloud of 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 to 5.0 $m^2/m^2$ for both the overstorey and understorey. 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 definition page). 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. This set of experiments is proposed in order to simulate the radiative transfer regime in the RAMI-V spectral bands for heterogeneous leaf canopies composed of two structurally different layers. Each of these layers is represented by a large number of identical, non-overlapping spherical objects 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.

These files contain 49999 lines with the values of R Xc Yc Zc Dx Dy Dz for each single leaf instance, to define a single crown.

Each crown should then be translated in space accordingly to the Table 2 and Table 3 below (Tree position property).

Trees position

Overall, three different overstorey and two understorey densities are defined. As the spheres are identical copies of the two model defined above for understorey and overstorey, the overall canopy density is defined by the number of spheres (crowns) instantiated.

Understorey	Sparse	Dense
( X × Y × Z) [m × m × m]	101.0 × 101.0 × ~1.01
(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
LAI of individual sphere	5.0
Scatterer normal distribution	Uniform
Foliage scattering law	Bi-Lambertian
Sphere radius [m]	0.5
Sphere center height range [m]	0.5099 - 0.5101
Background scattering law	Lambertian
Number of spheres	2547	5093
LAI understorey ($m^2/m^2$)	0.196	0.392
Tree position	link	link

Overstories	Sparse	Medium	Dense
( 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]	0.05
LAI of individual sphere	5.0
Scatterer normal distribution	Uniform
Foliage scattering law	Bi-Lambertian
Sphere radius [m]	5.0
Number of spheres	see below for (overstorey)
Sphere center height range [m]	7.0 - 11.0
Background scattering law	Lambertian
Number of trees	18	37	59
LAI overstorey ($m^2/m^2$)	0.69	1.42	2.27
Tree position	link	link	link

Spectral properties

Within a given sphere the Bi-Lambertian foliage elements of the overstorey layer are characterized by specified radiative properties (reflectance, transmittance) defined by STDL_REFL and STDL_TRAN spectral values given in file for each RAMI-V spectral bands. The corresponding optical properties of the understorey layer are defined by the values labelled as LEAF2_REFL and LEAF2_TRAN.

The soil background is characterized by a lambertian reflectance defined by the SOIL2 values given in the optical properties file.

Illumination characteristics

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_).