Accuracy of predicting the moisture content of three types of wood sections using near infrared spectroscopy

The moisture content of wood affects its physical properties. Many researchers have attempted to measure wood moisture contents nondestructively using near-infrared (NIR) spectroscopy. Wood is a natural material with anisotropic characteristics. There are three section types of cut wood surfaces, namely cross, radial, and tangential sections. In this study the NIR spectra of all three types of wood sections were measured and compared to determine how accurately the water content of softwood could be predicted. Two wood species were chosen and were cut into 30-mm cubes. The wood samples were stored for two weeks under various humidity conditions before they underwent NIR spectroscopy. The NIR spectra were obtained from three wood sections and principal component regression (PCR) was performed. Good calibration models for the three types of sections were then obtained. Furthermore, to expand the application of the PCR model for each section type, combinations of calibration models and prediction sets of the other sections were implemented. For the cross section models, there was no clear prediction capability when the test sets from the other two section types were used. However, for the radial and tangential sections, a high prediction accuracy was obtained using the other test set.