2.2.2. Hyperspectral Data Acquisition

The reflectance spectra of maize leaves were determined in an indoor measurement unit using a spectroradiometer (SVC HR~1024 i) with a spectral range of 350–2500 nm and a view of 25◦. First, the reflectivity of the white reference plate was measured for spectral correction. Then, the leaves were placed into the clamp to measure 10 spectra of each leaf, and the average value was calculated as the actual spectrum. Finally, the spectral resolution was resampled to 1 nm and then a continuous smooth reflection spectrum was obtained by Savitzky–Golay smoothing. Considering that the wavelengths of plant pigments are concentrated in the visible and near-infrared regions and that the constituent wavelengths of vegetation indices commonly used for estimating plant physiological and biochemical parameters are within these region [34], we only studied the spectra at 400–1000 nm.
