Abstract

The use of near infrared (NIR) diffuse reflectance spectroscopy for the estimation of basic density and moisture content of loblolly pine (Pinus taeda L.) logs was explored. A total of 219 wood disks representing the large and small ends of 146 merchantable logs 4.87 m in length, ranging in age from 13 years to 19 years, were analysed. NIR spectra were obtained from the transverse surface of the disks when the wood was green using a Foss XDS NIR System coupled with a Smart Probe Analyser. Each disk was divided into four quadrants and two spectra were collected per quadrant (one representing juvenile wood and one mature wood). NIR calibration models were fitted using pre-processed spectra with multiplicative scatter correction and the dimensionality of the models was kept constant for comparison purposes. Successful models based on an average of all spectra collected from both ends of the logs were obtained for basic density (R²_c = 0.84) and moisture content (R²_c = 0.85) using nine factors for both properties. The predictive ability of the calibrations was acceptable, with mean square errors of 22.8 kg m⁻³ for basic density and 2.1% for moisture content. It was found that the number of spectra per disk could be reduced to four readings but further reductions increased prediction errors considerably. Calibration models based only on spectra collected from one of the log ends were also examined. Using large-end diameter spectra only, the fit statistics for basic density models fell to R²c=0.76 for (eight spectra) and R²_c=0.71 (four spectra). Similarly, the fit statistics for moisture content calibrations dropped to R²_c=0.76 for (eight spectra) and R²_c=0.72 (four spectra). Calibrations based only on small-end diameter spectra were considerably weaker than those based on large-end diameter spectra.

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