Development of Wood Property Calibrations Using near Infrared Spectra Having Different Spectral Resolutions

A range of important wood properties can be predicted using calibrations obtained using SilviScan data and diffuse reflectance near infrared (NIR) spectra collected from wooden strips cut from increment cores. The ease of NIR measurements and the rapid provision of SilviScan data provides the opportunity to establish extremely large data sets, causing calibration problems. An option is to reduce the number of data points representing an individual NIR spectrum. NIR spectra were collected in 10 mm increments from the radial longitudinal face of 89 Pinus taeda L. (loblolly pine) breast height (1.30 m) wooden strips using a Foss NIRSystems 5000 [wavelength range 1100–2498 nm, spectral sampling interval (SSI) 2 nm]. Air-dry density, microfibril angle (MFA) and stiffness calibrations were obtained using SSIs ranging from 2 to 64 nm. Calibrations developed using NIR spectra having SSIs of 4 or 8 nm performed as well as those obtained at 2 nm. As resolution was decreased (SSI increased), the quality of the calibrations associated with the various wood properties was affected to different degrees. The MFA calibration was the most affected and air-dry density the least.