Versatile four-axis gonioreflectometer for bidirectional reflectance distribution function measurements on anisotropic material surfaces

Abstract

The bidirectional reflectance distribution function (BRDF) data are essential for analyzing and modeling the material appearance of anisotropic surfaces. In order to acquire four-dimensional BRDF on the anisotropic material surfaces, a four-axis gonioreflectometer was designed and implemented. The instrument consists of a collimated, broadband light source, a four-axis rotation mechanism, a spectroradiometer, and a control system. The instrument is able to carry out spectral BRDF measurements over most of the incident and reflection hemispheres and the entire visible spectrum. One thousand twenty-four samples are obtained over the spectral range of 380 to 760 nm. The angular resolution of the BRDF measurement is <0.1 deg with good repeatability. A relative calibration method was adopted to obtain the absolute values of BRDFs. Various scanning schemes can be carried out by the instrument to scan the designated angular domains, enabling the instrument to capture material appearance with strong, distinctive anisotropic highlights and translucency. The obtained BRDF data of a textile sample demonstrate the instrument capability of capturing complex light scattering behaviors, including off-specular reflection peaks, off-plane reflection peaks, and backscattering.

Optical Material Characterisation of Prepreg CFRP for Improved Composite Inspection

“…These information are used for the investigations in this paper. Thus this is in accordance with the conclusions from both publications from Li et al [32,54], Rabal et al [33] as well as Martinez and Hartmann [34]. In particular, the angle-restricted BRDF modelling applied in this paper is very well suited to determine the required reflection characteristics for this application.…”

“…In this context, the measuring principle and different applications of a Gonioreflectometer are discussed. Li et al [32], Rabal et al [33] as well as Martinez and Hartmann [34] all mentioned the need for tools to measure optical material properties especially for materials and coatings research. They also explain the relevance of spectrally resolved measured values for these optical material properties.…”

“…Their utilised Gonioreflectometer system can perform spectrally resolved BRDF measurements in the wavelength range from 240 nm to 2000 nm, with a resolution of 15 bit and a measurement uncertainty of 3 nm. Li et al [32] measure with their spectroradiometer in the spectral range from 380 nm to 760 nm with 1024 spectral bands. They digitise with 16 bit A/D resolution and have a spectral resolution between 0.82 nm and 3.3 nm.…”

Developmental Trends in the Application and Measurement of the Bidirectional Reflection Distribution Function

“…Traditional measurement devices measure the sample by using a mechanical structure to rotate the detector and the light source around it at a certain spatial angle. The most common structural form of such a device features a combination of the zenith of the motion structure, the azimuthal circular track [32,[71][72][73][74][75][76], and a cantilever structure forms [38,41,[77][78][79][80][81][82][83] for BRDF measurements. With the development of robotics, the advantages of automated measurements have been expanded by combining robots with BRDF measurement devices [44,84].…”

Effects of rotation errors on goniometric measurements

“…Li et al [15] considered the angular accuracy of the rotation stages in their gonioreflectometer, and estimated the size of the angular accuracy error. Earlier, Leloup et al [7] derived expressions for the actual positions of their sample, light source, and detector using rotation matrices, then converted these into spherical coordinates to calculate the BRDF.…”