Abstract
Portable spectroscopic instruments are an interesting alternative for in-field and on-line measurements. However, the practical implementation of visible-near infrared (VIS-NIR) portable sensors in the forest sector is challenging due to operation in harsh environmental conditions and natural variability of wood itself. The objective of this work was to use spectroscopic methods as an alternative to visual grading of wood quality. Three portable spectrometers covering visible and near infrared range were used for the detection of selected naturally occurring wood defects, such as knots, decay, resin pockets and reaction wood. Measurements were performed on wooden discs collected during the harvesting process, without any conditioning or sample preparation. Two prototype instruments were developed by integrating commercially available micro-electro-mechanical systems with for-purpose selected lenses and light source. The prototype modules of spectrometers were driven by an Arduino controller. Data were transferred to the PC by USB serial port. Performance of all tested instruments was confronted by two discriminant methods. The best performing was the microNIR instrument, even though the performance of custom prototypes was also satisfactory. This work was an essential part of practical implementation of VIS-NIR spectroscopy for automatic grading of logs directly in the forest. Prototype low-cost spectrometers described here formed the basis for development of a prototype hyperspectral imaging solution tested during harvesting of trees within the frame of a practical demonstration in mountain forests.
Highlights
Wood log grading is an action used to determine a set of characteristics regarding wood quality that are later used by forest resources managers, traders and manufacturers
Visual grading is the traditional method for determining log quality and is based on types, sizes and positions of physical characteristics that are not allowed for each quality class
Knots are the portion of a branch or limb that has been surrounded by subsequent xylem grown during tree life
Summary
Wood log grading is an action used to determine a set of characteristics regarding wood quality that are later used by forest resources managers, traders and manufacturers. The grader’s challenge is to properly assess all visible characteristics of each log, including the log’s geometry and presence/location of defects. The expert can identify the quality class corresponding to such a unique set of characteristics. Strict following of clearly defined assessment procedures as well as an objective grading verdict corresponding to established grading rules must be guaranteed along the whole inspection. The role of the expert grader is to assure proper assessment and, determine the log’s gross dimensions to estimate what portion of the log is available to produce a given product and evaluate the quality of the product that could be produced from the log
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