Abstract: NIR spectra are often pre-processed in order to remove systematic noise such as base-line varation and multiplicative scauer effects. This is done by differentiating the spectra to first or second derivatives, by Mtltiplicative Siga Correction (MSC), or by sirnilar filtering methods. This pre-processinp may, however, also remove infosmaion fror The spectra regarding Y (the measured response variable in multivarate calibration applications). Provided is a variant ofPLS that can be used to achieve a signal correction that is as close to orthogonal as possible to a given Y-vector or Y-matrix (430). Thus, ensung that the signal correction removes as little information as possible regarding Y. In the case when the number of X-variables, in an X matrix, K exceeds the number of observations N, strict orthogonality is obtined. A filter (470) according to the present invention is named Orthogonal Signal Correction (OSC).