Development of Low-Cost Portable Spectrometers for Detection of Wood Defects

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.

Log end face image and stem tapering indicate maximum bow height on Norway spruce bottom logs

“…Thus, the detection of reaction wood from a standard RGB image is challenging without staining methods, which involve dyeing the wood surface with acid or alcohol (Gardiner et al 2014). Devices that operate beyond visible wavelengths, such as hyperspectral sensors (Hagman 1996) and portable spectrometers (Sandak et al 2020), hold great potential to decrease the bias of max. bow height predictions through the better detection of the reaction wood from the fresh log end face.…”

Principles and Applications of Miniaturized Near‐Infrared (NIR) Spectrometers

“…Recent literature in this field notes that a particular requirement for ruggedness and capacity to operate in a harsh environment appears for the portable instrument [115] . This creates the need for the development of specialized, yet cost‐effective, spectrometers by utilizing modules existing on the market.…”

“…A prototype instrument developed by Sandak et al. in 2020 used a rugged metal case, while maintaining low‐power consumption, high cost‐effectiveness, and performance levels suitable for detecting wood defects [115] . Importantly, the specialized instrument implements adjustable focusing optics to improve its applicability to collecting NIR spectra of chained wood logs that feature profound surface roughness and irregularities.…”

Rapid Quality Control of Woodchip Parameters Using a Hand-Held Near Infrared Spectrophotometer

“…For example, research on bamboo wood demonstrated that it could be considered as renewable resources due to its chemical and physical properties investigated by NIR spectroscopy [30]. Moreover, different studies have employed the MicroNIR instrument in industrial pulp production [31] and in forestry sector for assessing the economic value of wood and forest management [32], taking advantages of its portability.…”