Potential of near-infrared spectroscopy to characterize wood products1This article is a contribution to the series The Role of Sensors in the New Forest Products Industry and Bioeconomy.

Abstract

Near infrared spectroscopy (NIRS) has high potential as a rapid nondestructive approach to identifying wood species and estimating properties that affect their utilization. This study found that NIRS could differentiate certain wood species groups. True firs (balsam fir ( Abies balsamea (L.) Mill.) and subalpine fir ( Abies lasiocarpa (Hook.) Nutt.)) could be distinguished from pine and spruce in eastern and western spruce–pine–fir, respectively, more than 95% of the time. Western hemlock ( Tsuga heterophylla (Raf.) Sarg.) could be differentiated from amabilis fir ( Abies amabilis Douglas ex J. Forbes) in the Hem–Fir species group with about 90% accuracy. Average wood moisture content (MC) of air-dried southern pine and western redcedar ( Thuja plicata Donn ex D. Don) samples wood could be estimated by NIRS ±10%–30% at high moisture contents and more accurately (±2%–5%) below 30% MC. Conditioned samples of amabilis fir had predicted MCs within 2%–3% of measured values in the 0%–30% MC range. However, the broad applicability and response of NIRS to a number of factors may be its greatest weakness, since measurements for a specific response, such as MC or species differentiation, may be confounded by the effects of other variables, such as surface roughness and localized density differences. It is recommended that instrumentation with a relatively large probe (large illumination area) be used to average such variables in the sample.