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Non-Linearity Problems in NIR Spectroscopy

In previous contributions to this column we have mainly considered linear calibration techniques, Le. methods that combine the spectral readings in a linear prediction formula. Such methods are the most simple and surprisingly often they work well in practice. In some cases, however, especially when the span of one or more of the constituents is large, nonlinear methods can give quite substantial improvements.1 The present contribution is the first in a series of articles about nonlinearity problems in calibration and how they can be solved.