Construction of novel measurement method of wood property by TOF-NIR densitometory

介绍了一种以条纹相机和半导体激光器为主要组成部分的新型光学测量系统，从飞行时间近红外光谱的角度阐明了木材的光学特性。另外，还构建了由连续型LED近红外激光器和光电探测器组成的系统。透射光强度在早木和晚木之间存在差异，这是由于密度的差异造成的。密度和细胞结构直接影响传输的时间分辨剖面。基于光输运方程的正反向模型，从时间分辨剖面的变化计算木材的吸收和散射系数。我们知道木材的吸收和散射系数随样品表层和内部湿度的变化而变化。多变量统计作为时间分辨剖面的解释变量表明，与传统的近红外光谱相比，木材含水率的估计精度更高。基于辐射传递方程的扩散近似的光学模型证明对厚样品是有用的，尽管木材是一种具有非均匀细胞结构的结构材料，但厚样品在光学上可以被视为理想的扩散器。

A new optical measurement system, the main components of which are a streak camera and semiconductor laser , was introduced to clarify the optical characteristics of wood from the viewpoint of time-of-flight near infrared (TOF-NIR) spectroscopy. Another system, which is composed of LED NIR laser (CW type) and photodetector, was also constructed. Intensity of transmitted light varied with early wood and late wood, which was due to the difference of density. The density and cellular structure directly affected the transmitted time-resolved profile. Absorption and scattering coefficient of wood were calculated from the variation of time-resolved profile based on the forward and backward model of light transportation equations. It was known thatabsorption and scattering coefficient of wood were varied with the moisture condition of subsurface layer and inside of the sample. Multivariate statistics as the explanatory variables of time-resolved profile showed high accurate estimation of moisture content of wood compared to that of traditional NIR spectroscopy. The optical model based on the diffusion approximation to the radiative transfer equation proved to be useful for thick samples, which can be optically regarded as an ideal diffuser, although wood is a structural material with non-homogeneous cellularstructure.