Bidirectional reflectance scale comparison between NIST and PTB

Abstract

Interlaboratory comparisons, referred to as key comparisons, are completed for many metrological units within the framework of the mutual recognition arrangement of the Bureau International des Poids et Mesures. These comparisons are the responsibility of consultative committees of the different metrological areas. In the case of the Consultative Committee for Photometry and Radiometry, there are currently about 20 key comparisons for various measurands. While interest in the field of bidirectional reflectance has been growing in recent years among users in industry and research and development, there is currently no dedicated key comparison to demonstrate scale conformity. This is the basis of the comparison of the bidirectional reflectance scales between the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). Measurements of two distinct sets of white diffuse reflectance standards, two sintered polytetrafluoroethylene samples and two matte ceramic samples, were performed using the common and widely used 0∶45 geometry. The wavelength range of the comparison spans the ultraviolet (λ≥330  nm) to the near infrared (λ≤1150  nm), a technically important region. In total, five different facilities participated in this bilateral investigation. The results of the comparison show good agreement within the combined uncertainties.