Assessing trees, wood and derived products with near infrared spectroscopy: hints and tips

Wood is a renewable and valuable resource for a variety of end-use application areas. However, rapid and reliable assessments are needed to identify the quality of the tree, timber or wood product at all stages of production and processing. The ideal technology for assessing wood and wood products must provide reliable data, be user-friendly, cost-competitive and provide a rapid analysis. The ulti- mate application of near infrared (NIR) spectroscopy of wood or wood products is to substitute for costly and time-consuming reference measurements in order to aid process optimisation or determine properties and genetic traits on large numbers of individual samples. Increased interest in the application of NIR spectroscopy in various research fields including wood is observed nowadays. A vast number of publications highlight the potential of NIR spectroscopy for the characterisation of wood in a broad area of uses. The Journal of Near Infrared Spectroscopy has published two special issues on the application of NIR to forestry and wood research in 2010 and 2011 and a recent literature search yielded in excess of 556,000 results which can be easily found by using the search terms "NIR" and "wood". This mass of published data may suggest that the technique of NIR spectroscopy is widely understood and broadly adopted by the timber industry, but even in recent papers it is evident that there is still a need to better understand the fundamental issues regarding sample selection and preparation, instrument choice, correct measurement and spectral interpretation. In this paper we draw on more than 40 years of collective experience and summarise state-of-the-art knowledge regarding instrumentation, spectral acquisition and data mining in regard to wood science and technology. The goal of this tutorial is two-fold: first, to inform early career wood scientists of the critical steps in utilising NIR spectroscopy to assess the quality of wood. Second, to alert managers to the level of operator skill required for the successful adoption of NIR technology. Some basic information is presented here, but due to the limited size of the manuscript, reference to more specific and detailed literature is provided in each section.