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Pre-processing of NIR. Åsmund Rinnan. Introduction NIR. Fructose. Glucose. 25 50 75. 75 50 25. Introduction NIR. Baseline with a slope/ curve. Nonlinearity. Fructose. Glucose. 25 50 75. 75 50 25. A “fat” baseline. Reference dependent O-PLS OSC OS SIS.
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Pre-processing of NIR Åsmund Rinnan
IntroductionNIR Fructose Glucose 25 50 75 75 50 25
IntroductionNIR Baseline with a slope/ curve Nonlinearity Fructose Glucose 25 50 75 75 50 25 A “fat” baseline
Reference dependent O-PLS OSC OS SIS Reference independent MSC/ ISC EMSC/ EISC SNV Detrend Normalization Savitzky-Golay Norris-Williams Finite difference IntroductionTechniques
Correction of light scatter MSC EMSC Detrend SNV Derivation Finite difference Savitzky-Golay IntroductionTechniques
Effect of pre-processingBefore Specular effect
MSC Raw Reference
MSC Raw Reference
MSC Raw spectrum b = Slope a = Intercept Reference • P Geladi, D MacDougal, H Martens (1985): Linearization and scatter correction for near-infrared reflectance spectra of meat, Applied Spectroscopy, 39, 491-500
Extended MSC Wavelength correction Slope & Intercept Known spectra = Detrend = Basic MSC • H. Martens, E. Stark (1991): Extended multiplicative signal correction and spectral interference subtraction: new preprocessing methods for near infrared spectroscopy, Journal of Pharmaceutical and Biomedicinal Analysis, 9, 625-635
Extended MSC Calculated The correction Step 1: Step 2: • H. Martens, E. Stark (1991): Extended multiplicative signal correction and spectral interference subtraction: new preprocessing methods for near infrared spectroscopy, Journal of Pharmaceutical and Biomedicinal Analysis, 9, 625-635
Extended MSCSummary X X • Parameter setting • Parameter setting • Paraemter setting MSC Detrend
SNV • R.J. Barnes, M.S. Dhanoa, S.J. Lister (1989): Standard Normal Variate Transformation and De-trending of Near-Infrared Diffuse Reflectance Spectra, Applied Spectroscopy, 43, 772-777
SNV vs MSC MSC SNV
SNV vs. MSC MSC Reference needed Outlier sensitive Only similar spectra No normalization SNV Normalization No reference
DerivationSavitzky-Golay • A Savitsky, M J E Golay (1964): Smoothing and differentiation of data by simplified least squares procedures, Analytical Chemistry, 36 (8), 1627-1639
DerivationSavitzky-Golay Smoothing 11 9 7 5 3 • A Savitsky, M J E Golay (1964): Smoothing and differentiation of data by simplified least squares procedures, Analytical Chemistry, 36 (8), 1627-1639
DerivationSavitzky-Golay Smoothing Polynomial 7 4 2 5 3 1 • A Savitsky, M J E Golay (1964): Smoothing and differentiation of data by simplified least squares procedures, Analytical Chemistry, 36 (8), 1627-1639
DerivationSavitzky-Golay 7 point smoothing 15 point smoothing 2nd order derivative
Run the following for near to optimal results MSC with Only 1st order reference correction or SNV 1st order reference correction and 2nd order wavelength correction Only 2nd order wavelength correction Savitzky-Golay derivation with 2nd order polynomial smoothing 7 points smoothing for the 1st derivative 9 points smoothing for the 2nd derivative SummaryPre-processing of NIR