Standardization of near-infrared spectra in the wavelet domain

A new standardization method based on transferring near-infrared (NIR) spectra in the wavelet domain is proposed. For each NIR spectrum, wavelet transform coefficients are computed, and the transfer step is performed by relating the wavelet transform coefficients of spectra obtained on both instruments with univariate linear models. This method is applied to two different data sets, and its performance is compared with the piecewise direct standardization method. The results obtained with this new method are better than those obtained by PDS, the biggest improvement occurring when very few standardization samples were used to estimate the standardization parameters. Both PDS and wavelet approaches offer advantages only when the spectral differences are local. When spectral differences are global, other methods such as the slope/bias correction function as well.