Evaluation of Surface Roughness with Reduced Data of BRDF Pattern

Traditional non-destructive measurement of surface roughness exploits complete data of bidirectional reflective distribution function (BRDF). The instrument is normally bulky and the process should be conducted off-line, hence it is time-consuming. If only a part of BRDF data can be sufficient to determine the surface roughness, both the measurement equipment and processing time can be significantly reduced. This paper proposes a compact device capable of detecting multiple angular intensities of reflective scattering with different incident angles from different spatial points of the target object at the same time. It is used to evaluate the surface roughness of a standard specimen with arithmetic mean roughness (Ra) values ranging from 0.13 µm to 2.1 µm. The case of measuring two spatial points of the specimen is used for illustrating the calibration procedure of the device and how the data were searched and processed to increase the reliability and robustness for evaluating the surface roughness with reduced data of BRDF. Similar methodologies can be applicable for other real-time detection methods based on the scattering process.