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

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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.