2.3. Hyperspectral images acquisition and calibration
After drying, samples were taken out of the desiccator for
hyperspectral images scanning. Two line-scan reflectance hyperspectral
imaging systems were employed in the study. One was
performed in visible-near infrared (Vis–NIR) spectral range (400–
1000 nm with a spectral resolution of 5 nm), and the other was
performed in near infrared (NIR) spectral range (880–1720 nm
with a spectral resolution of 7 nm). Major components of the systems
were described elsewhere (He, Wu, & Sun, 2013). The
obtained raw images were calibrated automatically by the system
using a white and a dark reference image. The white image was
obtained by scanning a uniform white ceramic tile and the dark
reference was obtained with the light off by covering the lens.