5-Scale is a combination of 4-Scale by Chen and Leblanc (1997) and LIBERTY by Dawson et al. (1998). It's main goal is to compute the reflectance of a vegetated surface from the remote sensing point of view. 5-Scale is geometric-optical radiative-transfer model that was developed with emphasis on the structural composition of forest canopies at different scales. Although developed for boreal forest applications [2], it can be applied to other types of vegetation.

5-Scale employs the following methodologies:

(1) The model simulates tree crowns as discrete geometrical objects: cone and cylinder for conifers, and spheroid for deciduous species. The non-random spatial distribution of trees is simulated using the Neyman (1939) type A distribution that creates patchiness of a forest stand. The size of the crowns decreases when the trees are found in large clusters and the tree locations can also be subject to a repulsion effect (i.e., no vertical overlaps occur) to better represent the competition for light;

(2) Inside the crown, a branch architecture defined by a single inclination angle is included (Chen and Black, 1991). A branch is in turn composed of foliage elements (individual leaves in deciduous and shoots in conifer canopies) with a given angle distribution pattern;

(3) The hotspot is computed both on the ground and on the foliage with gap size distributions between and inside the crowns, respectively;

(4) The tree surface created by the crown volume (cone and cylinder, or spheroid) is treated as a complex medium rather than a smooth surface so that shadowed foliage can be observed on the sunlit side and sunlit foliage on the shaded side.

(5) A multiple scattering scheme using view factors is used to compute the "shaded reflectivities."

(6) If canopy and background spectra are available, 5-Scale can output the bidirectional hyperspectral reflectance at any combination of sun and view geometries. The default input format for the foliage spectrum corresponds to the LIBERTY model by Dawson et al.(1998). LIBERTY is part of 5-Scale and can be used to simulate foliage reflectivity based on chlorophyl, water content, etc. A few measured spectra are also given with 5-Scale.

Scales of plant canopy architecture considered in reflectance models:

  • 1-scale: turbid media;
  • 2-scale: randomly distributed discrete objects containing turbid media;
  • 3-scale: non-random discrete objects containing turbid media;
  • 4-scale: non-random discrete objects with internal structures (such as branches and shoots).
  • 5-scale: 4-Scale + radiation transfer inside the foliage is considered

© Revised: Feb., 2006