Directional Characteristics Model and Light-Path Model for Biological Material Having Cellular Structure

Abstract

Nondestructive measurements, based on NIRS (near-infrared spectroscopy), on biological material having cellular structure, such as wood, require a nontraditional approach. In this respect, a truly nondestructive measurement system that can accurately monitor the physical condition and chemical components of materials is very desirable. Supported by a series of experiments, we constructed optical characteristic concepts that account for the cellular structure of a sample. The system was successfully modeled by following theoretically the sequential propagation of light in a sample (specifically, scattering, reflection, absorption, and transmission), which varies according to the angle of the fibers with respect to the direction of incident light, θ, and with its wavelength. A set of optical models, which consists of a directional characteristics model and a light-path model, has been developed to describe the various steps in the sequence. On the basis of these models, the leakage ratios of diffusely reflected light from the aggregate width of semi-infinite tracheids, S(θ), for various conditions of irradiation were calculated. These values were in good agreement with the actual values obtained from the measured values of absorbance through the judicious use of a semi-theoretical equation.

Prediction of Oriented Strand Board Wood Strand Density by near Infrared and Fourier Transform Infrared Reflectance Spectroscopy

“…35 additionally, as the particle size of the ground sample decreases, the absorbance of light decreases but, for solid samples, the absorbance of light varies as a function of pore/lumen direction with respect to the light path. 36,37 this should, theoretically, equate to higher prediction errors for wood flakes in which the surface presented is randomly distributed.…”

A review of near-infrared spectroscopy for monitoring moisture content and density of solid wood

“…Because wood is an anisotropic cellular material that is not an ideal scattering medium, the observed absorbances deviate from those that are calculated using the equations of the K-M theory (Tsuchikawa 1998(Tsuchikawa ,2001Tsuchikawa and Tsutsumi 1999b). Indeed, the K-M theory assumes that (i) the incident radiation is completely diffusively reflected in order that the Lambert cosine law can be applied, (ii) the particles in the wood samples are randomly distributed, and (iii) the sample is subjected only to diffuse illumination (Tsuchikawa 1998, Tsuchikawa and Tsutsumi 1999a. To correct for these deviations, four sub-models have been added to the K-M based modeling.…”

“…The relationship between absorbance and θ is expressed by the leakage ratio of diffusely reflected radiation S(θ) that is the ratio of the radiant power of diffusely reflected radiation escaping from the trimmed edge of the tracheid aggregates to the total radiant power of diffusely reflected radiation from the lumens of the tracheids. S(θ) is computed for various conditions of illumination differently for the three directional characteristics models (D, M and R) that differ as a function of the spectral domain (see computation details in Tsuchikawa and Tsutsumi 1999a). Similar to the directional characteristics model, this model assumes that the effect of the specular component of the reflected radiation from the plane interface of the lumen is negligible.…”

Application of Time-of-Flight Near-Infrared Spectroscopy to Wood with Anisotropic Cellular Structure

“…Thus, we constructed a nondestructive measurem ent system applicable to wood materials that allows development of optical characteristics m odels to describe such a situation. 1,2 By a series of theoretical examinations, near-infrared spectroscopy (NIRS) m ade it possible to analyze both physical conditions and chemical components of wood retaining its cellular structure.…”