Directional Characteristics of Near Infrared Light Reflected from Wood

Abstract

A near infrared auto-goniophotometer was designed to acquire detailed information on optical characteristics of a biological material which had a cellular structure, such as wood. The reflected light, which originated from the irradiation of polarized near infrared light, was separated into an unpolarized and a polarized component by using two polarizing filters. The standardized reflected intensities of each component at various incident angles q and observation angles h, r up (q, h) and r p (q, h), were measured. Sitka spruce samples with various thicknesses were used. The measurements showed that the directional characteristics of the unpolarized component were affected significantly by the irradiation conditions and the sample thickness. Particularly, these varied with the wavelength of incident light l. This shows that the directional characteristics models we proposed previously are reasonable. On the other hand, matrices of the directional characteristics for polarized components typically show an elliptical shape which is strongly affected by incident angle and only slightly by l. Based on these results, the effects of sample thickness on the spectral directional characteristics were determined.

Fungal decay of spruce and beech wood assessed by near-infrared spectroscopy in combination with uni- and multivariate data analysis

“…This model, however, is not directly applicable to solid wood surfaces in the tangential direction because smooth surfaces scatter less IR radiation (Tsuchikawa and Tsutsumi 1999;Tsuchikawa et al 2001). We assumed that (1) linear correlation of this minimum with total lignin can be adapted to spectra collected from solid wood and (2) surface spectra represent the total lignin content of a sample after a given incubation time.…”

Surface quality sensing of trembling aspen (Populus tremuloidesMichx.) veneer products by near infrared spectroscopy

“…The best prediction occurred for the aspen CIE b* colour space parameter (R 2 = 0.68; Figure 3), and the CIE L* colour space parameter (R 2 = 0.43) obtained in the range 400-900 nm confirmed that surface inactivation due to high temperature exposure induces veneer coloration changes (Gaintantzopoulou et al 2009). These changes are attributed to chemistry changes related to the disruption of hydrogen bonding and structural damage produced by the heat treatment (Tsuchikawa et al 2001, Meder et al 2002. Koumbi-Mounanga et al (2013) also found a good prediction of the CIE L* colour space parameter (R 2 = 0.54) using 400-900 nm spectral data for Douglas-fir (Pseudotsuga menziesii var.…”

Using near-infrared hyperspectral images on subalpine fir board. Part 1: Moisture content estimation

“…First, it has a limited penetration depth in solid wood, from 1 mm to 5 mm depending on surface roughness and the wavelength used (Tsuchikawa et al 1996, 2001, Sykes et al 2005. More penetrating radiations, such as microwaves should be tested for estimating bulk MC of boards.…”

“…Further work is needed to test a more deterministic approach that uses optical models like the one of the Tsuchikawa et al (2001). Also, in this study, we derived board MC images from NIR-HSI.…”