## Materials and Methods
### General Methodology
#### 2.3.3 DART and PROSPECT Radiative Transfer Models Parametrization  
DART version 5.7.3v1078 was used to simulate canopy reflectances and build the LUT. DART is a radiative transfer model able to simulate light interactions and multiple scattering effects within the modeling of a 3D scene, including the topography and the atmosphere. The 3D scene is a made of voxels whose size can be set by the user to simulate various scene elements. These elements can be represented through planar elements (triangles, allowing for precise modeling) and/or turbid  
Figure 3: Steps used for the mask building using the AVIRIS-NG image and masking of the AVIRIS-C images. voxels (statistical representation of fluids and vegetation). In the case of vegetation, these turbid voxels properties are determined by the canopy leaf area and its spatial distribution, the leaf angle distribution (LAD), and leaf optical properties. A more precise description of the DART model can be found in [PERSON] et al. (2012) and [PERSON] et al. (2013). DART makes it possible to define trees with simplified representations such as turbid crowns of conic, spherical, or ellipsoidal shape and allows for tuning of the fraction on full voxels within the crown as well as branches and twigs modeling. Therefore, trees are defined by structural parameters such as the shape and size of their crown and the distribution of their branches and leaf cells, as well as optical parameters with the optical properties of leaf voxels and branches. The scene modeling done in this study is based on a simplified forest representation. A repetitive pattern of four trees with ellipsoidal crowns was used ([PERSON] et al., 2013). Crown size and height were set to the Tonzi site average values ([PERSON] et al., 2013). Branches and twigs were neglected to reduce modeling complexity and introduction of errors if not correctly set. Trunk reflectance was set to the value measured in-field. Canopy cover variations were obtained by increasing the scene dimensions. The trees were placed so that the scene bidirectional reflectance factor (BRF) is the closest to a forest BRF, following the pattern given in [PERSON] et al. (2013) and [PERSON] et al. (2013). Trees and scene characteristics are given in Table 3. The forest understory was represented as a lambertian surface whose optical properties were determined by pure soil pixels selected within the AVIRIS-C images in open parts of the site, at least one pixel (18 m) away from canopy pixels and several pixels wide. These open parts were visually chosen using QGIS high-resolution Microsoft Bing Maps satellite backgrounds. Leaf optical properties were simulated through the PROSPECT model ([PERSON] et al., 2013) implemented in DART, using the input parameters described in Table 4. The leaf structure parameter N was set to 1.8. Sun and atmosphere were the only radiation sources. The sun positions were set so that they match with the AVIRIS-C images based on site location and hours of acquisition. The simulations used a rural aerosol model with a visibility of 23 km corresponding to mid-latitude summer standard atmosphere. A total of 168 bands with a spectral bandwidth of 0.010 um were simulated between 0.36 and 2.45 um to cover both the visible and short wave infrared (SWIR) spectral ranges.