Determination of Dry Matter Content and Basic Density of Norway Spruce by near Infrared Reflectance and Transmittance Spectroscopy

Abstract

The purpose of the study was to investigate the feasibility of using near infrared (NTR) spectroscopy in reflectance and transmittance modes for the determination of dry matter content and basic density of Norway spruce ( Picea abies (L.) Karst). The 169 samples varied in moisture content (below fibre saturation, green and fully saturated) and in form (solid wood and shavings). Calibration models were produced using partial least squares regression and the resulting models were validated using test sets. The calibration models for dry matter content showed good predictive ability. The root mean square error of prediction (RMSEP) was 1–2% for dry matter contents ranging between 35 and 95%, corresponding to a relative error between 1 and 6%. Calibration models for basic density were less precise, having RMSEP values between 15 and 26 kg m⁻³ for basic density values ranging from 313 to 495 kg m⁻³ (relative error 3–8%). The reason for the limited predictive ability of the basic density models is probably that the part of each sample scanned with NIR spectroscopy was not representative of the whole sample of which the basic density had been determined by the reference method. No marked differences in the predictive ability of calibration models were found between reflectance and transmittance.