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.