We present an alternative measurement method for BRDF characterization. It is based on imaging instead of angular sampling. Under illumination, the reflectance characteristic of the analyzed material is projected onto a hemispheric diffuse reflective dome surrounding the probe. Images of the dome are taken to capture the directional distribution of the reflected light. This shows the main advantage of the new method: The simultaneous capture of the reflectance within a hemispherical sector, therefore accelerating greatly the data acquisition. However, some additional processing steps have to be implemented to achieve results comparable to the sampling method. Captures with different integration times have to be merged into a high dynamic range (HDR) image and a pixel mapping to absolute scattering angles in spherical coordinates (elevation and azimuth) has to be registered. Measurements acquired with this fist simple approach are quantitatively compared to the aforementioned established sampling acquisition method for two different materials: A diffuse Lambertian reference and a higher gloss degree material. These results are discussed in the last section and will serve as guidelines for future iteration developments of the proposed method.
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.