4.3. Hyperspectral Reflectance

The full range (350–2500 nm) leaf reflectance profiles were collected by an ASD FieldSpec 4 spectroradiometer (Analytical Spectral Devices, Boulder, CO, USA), using a leaf clip with an internal halogen light source attached to a plant probe. The measurements were acquired on four areas (randomly selected, ∅ 1 cm) of the adaxial surface of each leaf, with one measurement per area, and the collections were combined to produce an average leaf spectrum. The relative reflectance of each leaf was determined from the measurement of the leaf radiance divided by the radiance of a white reference panel included in the leaf clip, measured before each plant (i.e., four spectral collections) when collecting spectra for modeling, or every four plants (i.e., 16 spectral collections) when collecting spectra for hyperspectral phenotyping.