ON THE SCALES ASSOCIATED WITH NEAR-INFRARED REFLECTANCE DIFFERENCE SPECTRA

Scale differences of individual near-infrared spectra are identified w hen set-independent standard normal variate (SNV) and de-trend (DT) tr ansformations are applied in either SNV followed by DT or DT then SNV order. The relationship of set-dependent multiplicative scatter correc tion (MSC) to SNV is also referred to. A simple correction factor is p roposed to convert derived spectra from one order to the other. It is suggested that the suitable order for the study of changes using diffe rence spectra (when removing baselines) should be DT followed by SNV, which leads to all derived spectra on the scale of mean zero and varia nce equal to one. If baselines are identical, then SNV scale spectra c an be used to calculate differences.