This set of experiments was suggested to simulate the radiative transfer regime in the red and near infra-red spectral bands for spatially heterogeneous scenes resembling boreal birch stands. In addition to the standard RAMI measurements, a local transmission measurement is to be applied along a transect of 21 m both parallel and perpendicular to the azimuth of the illumination direction. More details regarding this measurement will be found at the end of this page. At this stage, further information on the structural and spectral properties of the scene will be provided first.
A large number of non-overlapping tree-like entities of different sizes and spectral properties were randomly located across (and only partially covering) a planar surface that represented the underlying soil. Individual tree objects were represented by an ellipsoidal crown located (just) above a cylindrical trunk. The finite sized foliage was randomly distributed within the ellipsoidal volumes that represented the tree crowns, and was characterized by radiative properties (reflectance, transmittance) that are typical for birch trees.
The zero azimuth line was defined along the northern direction and coincides with the positive X-axis as indicated below:
The overall architectural characteristics of the scene are as follows:
|Scene dimensions: ( ΔX × ΔY × ΔZ)||100.0 × 100.0 × 14.5 [m × m × m]|
|(Xmin, Ymin, Zmin)||−50.0, −50.0, 0.0 [m, m, m]|
|(Xmax, Ymax, Zmax)||+50.0, +50.0, +14.50 [m, m, m]|
|Scatterer shape||Disc of negligible thickness|
|Scatterer radius||0.05 [m]|
|Scatterer normal distribution in tree crown||Uniform|
|Number of trees in scene||1800|
|Fractional scene coverage of ellipsoids||0.289|
|LAI of scene||0.388|
|Spatial distribution of tree locations (X,Y) in scene||Random (Tree locations are given below)|
|Stem density [tree/hectare]||1800|
|Mean tree height in scene||8.007 [m]|
The architecture of this scene contains tree-like entities that are composed of an ellipsoidal crown sitting on top of a cylindrical trunk - which reaches down to the underlying background. The ellipsoidal crowns have circular crossections and reach their maximum width half-way along their vertical length. These geometrical primitives do not overlap and exist in five classes (A - E) with different spectral and structural properties each.
The following table provides the structural properties of the various tree classes:.
|Tree height [m]||2.5||5.5||8.5||11.5||14.5|
|Single Tree LAI [m² ⁄ m²]||0.751||1.081||1.340||1.575||1.805|
|Crown height [m]||1.237||2.952||4.919||7.137||9.606|
|Crown width [m]||0.611||0.995||1.43||1.937||2.538|
|Trunk height [m]||1.263||2.548||3.581||4.363||4.894|
|Trunk width [m]||0.014||0.033||0.054||0.078||0.107|
|Tree number [/scene]||38||507||981||261||13|
Within the 100×100 m² scene the X,Y location of these tree-like entities is generated in a random manner (Poisson distribution). For the purpose of this RAMI exercise, it is however recommended to utilize the X,Y tree center coordinates as described in the files accessible from the table below:
|Tree X,Y centers||class A||class B||class C||class D||class E|
Notice that each of the above tree classes (A - E) features its own spectral properties. The table below provides the spectral properties of the various scene constituents for the red spectral band:
A local transmission transect is defined as series of total (direct + diffuse) transmission measurements carried out at the level of the canopy background (i.e., soil). Twenty-one reference areas of 1 by 1 m² each make up a local transmission transect. For each one of these unit-area surfaces centered at some x,y position, the direct and diffuse radiation impinging upon it at the level of the canopy floor (z = 0) has to be ratio'ed with the radiation impinging upon a similar (1 by 1 m²) reference area centered at the same x,y coordinates but located at the top of the canopy (z = zmax).
Two local transmission transects, centered at the x=0, y=0 coordinates have been specified: The first one is called the X-transect because its various reference areas follow the X-axis (i.e., the transect lies parallel to the incident radiation azimuth), whilst the second one is called the Y-transect and follows the Y-axis (i.e., the transect lies perpendicular to the incident radiation azimuth). Graphical illustration of the X-transect locations at the bottom of the canopy and at the top-of-the canopy, as well as for the Y-transect locations at the bottom of the canopy and at the top-of-the canopy are available.