Abstract
Both spectral noise and reference method noise affect the accuracy and the precision NIR predicted values. The reference noise is often neglected, and the few reports dealing with it only consider random noise artificially added to the original sound reference data. A calibration for lignin content of maritime pine (Pinus pinaster Ait.) wood meal was developed, but due to low precision and accuracy in the reference data set, NIR partial least-squares regression (PLSR) yielded a slope of 0.51 and an intercept at 14% Klason lignin. We demonstrate with an independent data set for external validation, obtained with higher precision and accuracy, that the NIR PLSR model based on the noisy reference data led to better results. The slope of the correlation between predicted and reference values was 0.89 and the intercept was 3.9. Thus, the model performed much better than expected from the cross-validation results. The predictability can be explained by the facts that the loadings of the first principal component (PC) of the calibration and test samples are very similar and dominated by lignin-related bands, and that most of the variation in the test set can be explained by the first PC. This only explains why the Klason lignin content could be predicted with the model without giving many spectral outliers, but not the good result of the external validation. We show that the latter can be explained by the inverse calibration used for PLSR and that predicted values can be more accurate and precise than the reference values used for calibration.
References
Antti, H., Sjöström, M., Wallbäcks, L. (1996) Multivariate calibration models using NIR spectroscopy on pulp and paper industrial applications. J. Chemometr.10:591–603.10.1002/(SICI)1099-128X(199609)10:5/6<591::AID-CEM474>3.0.CO;2-LSearch in Google Scholar
Bruker (1996) Spektroskopiesoftware OPUS. Multivariate Kalibration. OPUS/QUANT-2, Bruker.Search in Google Scholar
Conlin, A.K., Martin, E.B., Morris, A.J. (1998) Data augmentation: an alternative approach to the analysis of spectroscopic data. Chemometr. Intell. Lab.44:161–173.10.1016/S0169-7439(98)00071-9Search in Google Scholar
da Silva Perez, D., Guillemain, A., Chantre, G., Alazard, P., Alves, A., Rodrigues, J.C., Rozenberg, P., Plomion, C., Robin, E. (2005) Improvement of wood, pulp and paper quality of maritime pine (Pinus pinaster Ait.) by combining rapid assessment techniques and genetics. In: Proceedings of the 13th International Symposium on Wood, Fibre and Pulping Chemistry (ISWFPC), Auckland.Search in Google Scholar
DiFoggio, R. (1995) Examination of some misconceptions about near-infrared analysis. Appl. Spectrosc.49:67–75.10.1366/0003702953963247Search in Google Scholar
Estienne, F., Pasti, L., Centner, V., Walczak, B., Despagne, F., Rimbaud, D.J., deNoord, O.E., Massart, D.L. (2001) A comparison of multivariate calibration techniques applied to experimental NIR data sets Part II. Predictive ability under extrapolation conditions. Chemometr. Intell. Lab.58:195–211Search in Google Scholar
Geladi, P. (2002) Some recent trends in the calibration literature. Chemometr. Intell. Lab.60:211–224.10.1016/S0169-7439(01)00197-6Search in Google Scholar
Gierlinger, N., Jacques, D., Schwanninger, M., Wimmer, R., Paques, L.E. (2004) Heartwood extractives and lignin content of different larch species (Larix sp.) and relationships to brown-rot decay-resistance. Trees18:230–236.Search in Google Scholar
Lu, J., McClure, W.F. (1998) Effect of random noise on the performance of NIR calibrations. J. Near Infrared Spectrosc.6:77–87.10.1255/jnirs.124Search in Google Scholar
Michell, A.J., Schimleck, L.R. (1996) NIR spectroscopy of woods from Eucalyptus globulus. Appita J.49:23–26.Search in Google Scholar
Næs, T., Isaksson, T., Fearn, T., Davies, T. A User-Friendly Guide to Multivariate Calibration and Classification. Chichester, NIR Publications, 2002.Search in Google Scholar
Pot, D., Chantre, G., Rozenberg, P., Rodrigues, J.C., Jones, G.L., Pereira, H., Hannrup, B., Cahalan, C., Plomion, C. (2002) Genetic control of pulp and timber properties in maritime pine (Pinus pinaster Ait.). Ann. For. Sci.59:563–575.10.1051/forest:2002042Search in Google Scholar
Raymond, C.A., Schimleck, L.R. (2002) Development of near infrared reflectance analysis calibrations for estimating genetic parameters for cellulose content in Eucalyptus globulus. Can. J. For. Res.32:170–176.10.1139/x01-174Search in Google Scholar
Savitzky, A., Golay, M.J.E. (1964) Smoothing and differentiation of data by simplified least squares procedures. Anal. Chem.36:1627–1639.10.1021/ac60214a047Search in Google Scholar
Schwanninger, M., Hinterstoisser, B. (2001) Determination of the lignin content in wood by FT-NIR. In: Proceedings of the 11th International Symposium on Wood and Pulping Chemistry, Nice. ATIP, Paris, France.Search in Google Scholar
Schwanninger, M., Hinterstoisser, B. (2002) Klason lignin: modifications to improve the precision of the standardized determination. Holzforschung56:161–166.10.1515/HF.2002.027Search in Google Scholar
Schwanninger, M., Hinterstoisser, B., Gradinger, C., Messner, K., Fackler, K. (2004) Examination of spruce wood biodegraded by Ceriporiopsis subvermispora using near and mid infrared spectroscopy. J. Near Infrared Spectrosc.12:397–409.10.1255/jnirs.449Search in Google Scholar
Sørensen, L.K. (2002) True accuracy of near infrared spectroscopy and its dependence on precision of reference data. J. Near Infrared Spectrosc.10:15–25.10.1255/jnirs.317Search in Google Scholar
Tappi (1994–1995) T 222. Om-88, Acid-insoluble lignin in wood and pulp.Search in Google Scholar
Wright, J.A., Birkett, M.D., Gambino, M.J.T. (1990) Prediction of pulp yield and cellulose content from wood samples using near infrared reflectance spectroscopy. Tappi J.73:164–166.Search in Google Scholar
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