In this report, a newly designed apparatus, that is, a near infrared auto-goniophotometer, was introduced to acquire detailed optical information about biological material having a cellular structure like wood. Such information allows us to analyse the three-dimensional physical condition of a sample and confirm the suitability of proposed optical models. The directional characteristics could be found on the basis of the intensity of reflected or transmitted light at each observation angle. In these experiments, Sitka spruce (Picea sitchensis Carr.) with various thicknesses were used. Results of these measurements showed the directional characteristics which were affected significantly by the illumination conditions and sample thickness. Particularly, these varied characteristically with the wavelength of the incident light. This result supports the validity of the proposed optical models which vary with wavelength. Throughout these analyses, the relationships between the physical aspects of a sample and the emitted light from it is being clarified.

A near infrared auto-goniophotometer was designed to acquire detailed information on optical characteristics of a biological material which had a cellular structure, such as wood. The reflected light, which originated from the irradiation of polarized near infrared light, was separated into an unpolarized and a polarized component by using two polarizing filters. The standardized reflected intensities of each component at various incident angles q and observation angles h, r up (q, h) and r p (q, h), were measured. Sitka spruce samples with various thicknesses were used. The measurements showed that the directional characteristics of the unpolarized component were affected significantly by the irradiation conditions and the sample thickness. Particularly, these varied with the wavelength of incident light l. This shows that the directional characteristics models we proposed previously are reasonable. On the other hand, matrices of the directional characteristics for polarized components typically show an elliptical shape which is strongly affected by incident angle and only slightly by l. Based on these results, the effects of sample thickness on the spectral directional characteristics were determined.