Regression models were obtained
using the Modified Partial Least Squared (MPLSR) method (Shenk
& Westerhaus, 1995b). With MPLSR, the NIR residuals at each
wavelength, obtained after each factor is calculated, are standardised
(divided by the standard deviations of the residuals at a wavelength)
before calculating the next factor (Shenk & Westerhaus,
1995a). Separate MPLSR calibrations were performed for each
parameter using the PLS1 algorithm.