This page provides descriptions of the architectural, spectral and illumination related properties of a 49 year old Betula pendula stand located near 58° 16′ 38.67″ N 27° 20′ 30.38″ E.
The stand was inventoried in summer 2007 by Andres Kuusk, Joel Kuusk, Mait Lang, Tõnu Lükk, Matti Mõttus, Tiit Nilson, Miina Rautiainen, and Alo Eenmäe of the Tartu Observatory, in Tõravere, Estonia as well as the Estonian University of Life Sciences, Tartu, Estonia.
Potential RAMI participants thus are to treat the information presented on this page as actual 'inventory data', that is, they should identify/extract those parameters and characteristics that are required as input to their canopy reflectance models.
In some cases this may mean that simplifications have to be made to the available information, or, that parts of the available information can not be exploited with a given radiative transfer model. Whatever the case may be, all potential RAMI participants should mimic the standard practices that they use when matching actual field measurements to the required set(s) of input parameters of their model(s). If this means that you need more information than provided, please do not hesitate in contacting us. Last but not least, for those 3D models capable of maintaining architectural fidelity down to the individual shoot and branch level a series of ASCII (text) files containing the Cartesian coordinates of various geometric primitives (triangles, spheres and cylinders) and their transformations will be given. This should facilitate the reconstruction of the birch canopy architecture as it is described on this page.
Järvselja Birch Stand (Winter) scene description.
Järvselja Birch Stand (Winter) scene description.
Järvselja Birch Stand (Winter) scene description.
Architectural information
The Järvselja birch forest inventory was carried out over a 100×100 m² area placing the origin of the coordinate system at its south-western end. In order to include also the tree crowns of the inventoried tree locations within the RAMI birch Stand representation it was necessary to expand the scene area slightly beyond one hectare. Maintaining the origin of the tree location coordinate system thus resulted in some negative x,y values in the table below. Overall architectural characteristics of the scene are thus as follows:
*The LAI of the pine trees is computed using half the total area of the needles in a shoot.
**The fractional cover is defined as 1 - direct transmission at zero solar zenith angle.
Foliage structure
The table below provides the structural characteristics of the Norway spruce shoots that are part of the RAMI Järvselja winter birch-stand scene. RT models capable of representing the detailed architecture of individual foliage elements may want to use the information provided in the ASCII (text) files accessible from the last row in each table below.
o: the foliage length is measured from the bottom of the twig to the tip of the upper needles, i.e., it is the maximum vertical distance on the image displayed in the first row of this table
+: the maximum radial foliage extension is defined as the maximum distance from the axis connecting the bottom of the twig to the tip of the elementary foliage unit, i.e., along the vertical in the pictures displayed in the first row of this table).
#: a detailed description of the structural characteristics of the Picea abies shoot structure can be found in the header of the structural description file accessible via the link at the bottom of this table column.
x: in the case of the Picea Abies shoots this one-sided foliage area value is half the total needle surface area (i.e., the value obtained when summing up the silhouette areas of all individual needles in the shoot). Here needles are assumed to be elongated spheres. If individual needles are represented as cylinders (with discs as endcaps) then the total needle area of the shoot will be different and the number of shoots per pine tree should be adjusted accordingly.
Tree structure
The Järvselja Birch forest is generated on the basis of 18 individual tree representations. These are distributed among the following tree species: ACPL=maple (Acer Platenoides), BEPE1-4=birch (Betula Pendula), ALGL1-4=alder (Almus Glutinosa), TICO1-5=linden (Tilio Cordata), POTR1-2=poplar (Populus Tremuloides), PIAB=Norway spruce (Picea Abies), and FREX=ash (Fraxinus Exelsior). Only the Norway spruce trees contain foliage. The two tables below provides an overview of some structural characteristics of these 18 tree representations. NOTE: all footnotes are listed at the end of the second table. For those RT models capable of representing the 3D architecture of a given tree through a series of geometric primitives, the last lines of each table contain links to data files with detailed specifications of the foliage and wood structural properties of the Järvselja Birch forest (Winter) trees.
=: for shoots the zenith angle of the foliage normal is defined as the angle between the vertical and the normal of the inner twig of the shoot (for a shoot axis aligned along the z-axis the normal was arbitrarily chosen to lie along the y-axis). Rather than spanning the full range of possible zenith angles (i.e., from 0 to 180 degree) as could be expected for non-flat asymmetric objects, it was chosen to follow the convention of foliage normals pointing only into the upper hemisphere. This is because RAMI participants, that make use of this foliage normal distribution information, will in all likelihood have models where scatterers are represented as flat (disc or equilateral triangle shaped) objects. However, should your model require a description of the foliage normal zenith angle distribution up to 180 degrees then please do not hesitate in contacting us and we will provide this information to you. For both the zenith and azimuth angle distributions the 'graph' link shows an image of the normalised foliage normal distribution versus zenith (or azimuth) angle of the foliage normal. The 'data' files for the zenith and azimuth angle distribution have three columns indicating
the upper value of the zenith (or azimuth) angle in a given bin,
the fraction of foliage area having a normal in this zenith (or azimuth) angle range, and
the fraction of wood area having a normal that falls in this zenith (or azimuth) angle range.
Bin angle widths were chosen to be 5 degrees and 10 degrees for zenith and azimuth angles, respectively.
x: the crown radius of actual trees is varying with azimuth angle. This can be seen in the various pictures showing a perspective-free nadir view of a given tree located at x=0,y=0 (concentric circles indicate the distance from the origin in steps of 0.25m). The mean and maximum values were computed from the triangle objects making up the 3D trees depicted in the picture in the the fourth-last row of each table column.
*: tThe graphs show the maximum radial distance of foliage elements in a given height interval plotted against the upper height level of that height interval. The data files have five columns: lower-height-of-bin-in-units-of-meters upper-height-of-bin-in-units-of-meters minimum_radial-distance_of_foliage-in-units-of-m maximum_radial-distance_of_foliage-in-units-of-m. mean_radial-distance_of_foliage-in-units-of-m
#: this value corresponds to the one-sided leaf area for flat leaves. For Norway spruce trees it corresponds to the sum of the (maximum) silhouettes of all the individual needles in the tree (i.e., half the total needle area per tree).
o: the data files have 3 columns: lower-height-of-bin-in-units-of-meters upper-height-of-bin-in-units-of-meters area-of-wood-or-foliage-in-units-of-m2.
+: this is the nominal value derived from the inventory data for a tree of this height. The actual value of the tree representations provided in the ASCII files at the bottom of this table might be slightly different.
Stand structure
The Järvselja Birch forest (winter) is composed of 1120 individual trees. The following two tables indicates how these trees are distributed among the above tree classes and specifies their respective x,y locations of the tree centers of each tree class in the forest stand. The last row of each table contains an ASCII file with tree rotation and translation information for those RT models capable of ingesting the detailed 3D architecture of the tree models specified in the previous section.
x: these files contain pseudo code to rotate individual trees around their z axis and translate them from the origin to the x,y locations specified in the data files of the previous row of this table. Positive rotation angles in these files indicate that when looking down from the positive Z axis towards the origin of the coordinate system a counterclockwise rotation will result in moving the positive x axis towards the positive y axis. The angle of rotation is in the 7th column of these data files (starting from the count from 1).
RAMI participants with 3D RT models capable of representing objects using geometric primitives can download a single compressed ZIP archive with all the tree architectural ASCII information that is listed in the above tables by clicking HERE. Note: The size of the compressed archive is about 22 megabytes. It contains 44 ASCII files and can be unzipped using 'WINZIP' on windows or 'unzip' on linux/unix operating systems. Beware that the inflated archive will take up 184.9 Megabytes of storage.
Tree species and locations for the Järvselja birch stand (winter). The origin of the coordinate system is in the lower left hand side corner of the image.
Spectral canopy characteristics
Only the foliage and woody components in the Järvselja birch stand (Winter) scene feature LAMBERTIAN scattering properties. The background properties on the other hand are NON-LAMBERTIAN. To capture the directional variability of the hemispherical directional reflectance factor (HDRF) of snow, the RPV model has been fitted to a series of actual goniometer observations. The tables below contains the magnitudes of the reflectance and transmission characteristics of the various canopy components for nineteen different spectral bands as well as the RPV parameters describing the anisotropy of the background HDRF. The experimental identifier for the Järvselja Birch Stand (Winter) scene is given by HET15_JBS_WIN_B**_54 where B** relates to the spectral bands (B01, B02, …, B19). An ASCII (text) file that resumes all of the information in this table can be found here.
Illumination characteristics
The illumination conditions for the Järvselja Birch stand (winter) relate to the 1st April at GMT 9:45. More specifically the illumination features both direct and isotropic diffuse components. Direct solar light is characterised by a solar zenith angle (SZA) of 54.0 degree and a solar azimuth angle of 291.3 degree. The table below indicates the ratio of isotropically diffuse to total incident radiation for the nineteen different spectral bands:
The figure below shows perspective-free view of the Järvselja birch stand with the Cartesian coordinate system and direction of the incident solar radiation (blue arrow) superimposed. Azimuth angles are counted in an anti-clockwise direction from the positive X-axis towards the positive Y-axis as indicated by the (dotted blue) arc around the origin.
