Experimental Study of Optical Scattering and Fiber Orientation Determination of Softwood and Hardwood with Different Surface Finishes

Abstract

Optical scattering from wood of different surface finishes has been experimentally investigated. It has been found that for planed-Hemlock samples the scattering intensity distribution in the direction across the wood fibers is very close to perfect diffuse reflection, while that in the direction along the fibers appears as the combination of diffuse and specular reflection. The increase of wood surface roughness reduces the difference between these two scattering intensity distributions. The difference provides the basis for determining wood fiber orientation by measuring the scattering intensity variation with fiber orientation. When the sample surface becomes very rough, such as a rough sawn or porous hardwood sample, the scattering from the uneven surface overwhelms the difference and creates a difficulty in fiber orientation measurement. To solve the problem, we have been employed optical polarization detection in the investigation. With this detection method, for the samples used in this work, the intensity variation of the scattering vs. fiber orientation appears periodic despite the different surface finishes. With the help of Fourier analysis, fiber orientations of the rough sawn softwood and porous hardwood samples under investigation can be precisely measured.