Improving spatial synchronization between X-ray and near-infrared spectra information to predict wood density profiles
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Improving spatial synchronization between X‑ray and near‑infrared spectra information to predict wood density profiles Ana Alves1 · Andrea Hevia2,3 · Rita Simões1 · Juan Majada2 · Ricardo Alia4 · José Rodrigues1 Received: 10 January 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Wood density is one of the most important physical properties of the wood, used in improvement programs for wood quality of major timber species. Traditional core sampling of standing trees has been widely used to assess wood density profiles at high spatial resolution by X-ray microdensitometry methods, but alternative methods to predict wood properties quality are also needed. Near-infrared (NIR) spectroscopy, a non-destructive technique, is being increasingly used for wood property assessment and has already been demonstrated to be able to predict wood density. However, the estimation of wood density profiles by NIR has not yet been extensively studied, and improved models using spectra information (NIR) and X-ray data need to be developed. To this end, partial least square regression (PLS-R) models for predicting wood density were developed at a 1.4 mm spatial resolution on Pinus pinaster wood cores, with an improved spatial synchronization along the tangential and radial directions of the strip, between X-ray data and NIR spectra. The validation of the best model showed a high coefficient of determination (0.95), low error (0.026) and no outlier. Compression wood samples were not detected as outliers and were correctly predicted by the model. However, pith spectra were detected as outliers and its predicted values were overestimated by 33% due to unusual spectra suggesting a diverse chemical composition. The results suggest that NIR-PLS models obtained can be used for screening maritime pine wood density profiles along the radii at 1.4 mm spatial resolution.
Ana Alves and Andrea Hevia have contributed equally to this work and should be regarded as cofirst authors. * José Rodrigues [email protected] Extended author information available on the last page of the article
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Wood Science and Technology
Introduction Wood density has long been recognized as one of the most important wood physical properties. It has a direct impact on most wood utilizations, but it also is a common indicator of wood quality since it is related to other wood properties such as timber strength and shrinkage, fibre properties, pulp yield and properties or calorific values (Macdonald and Hubert 2002; Mäkinen et al. 2002; Saranpää 2003; Zobel and van Buijtenen 1989). In addition, wood density is one of the simplest and easiest wood properties to asses without the need for complex or expensive equipment, although more sophisticated equipment is required for detailed studies aimed at intra-ring density analysis, like the indirect X-ray microdensitometer (Hevia et al. 2020; Jacquin et al. 2017; Louzada and Fonseca 2002; Louzada 2003; Rozenberg et al. 2001). The procedure developed by Polge (1966) provides a
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