Multispectral gonioreflectometer facility for directional reflectance measurements and its use on materials and paints

Improvement of remote sensing technologies brings associated challenges in other research and production areas. In the field of coating and material science is an increase in the requirements to the reflectance properties. For many applications the spectral characterization alone no longer suffices and more knowledge about the directional reflectance characteristic is necessary. This directional information, where the ideal description is given by the bidirectional reflectance distribution function (BRDF), requires costly and complex measurement facilities called gonioreflectometers in order to extract it. We report on the realization of such a facility at Fraunhofer IOSB. The system consists of three parts: a rotation stage holding the sample, a semi-circular metal arm carrying the illumination source and a robot arm accommodating the sensor. The facility is highly adaptable to a variety of measurements, being capable of measuring anisotropy and retroreflection, which for several applications is of critical importance. Examples of measurements performed on several metallic paints in use on naval and inland applications will be shown as well as a lambertian reflectance reference for comparison.