Comparison of absolute d/O diffuse reflectance factor scales of the NRC and the PTB

A comparison of the absolute diffuse reflectance factor scales of the National Research Council (NRC, Canada) and the Physikalisch-Technische Bundesanstalt (PTB, Germany) for radiance factor measurements in the d/0 geometry was carried out in 1996. The spectral range of the comparison was 360 nm to 830 nm. The transfer standards exchanged were two matte opal glasses, one of which was similar to those used in a 1981 international comparison between the NRC, the NBS, and the PTB. The current NRC/PTB agreement is within 0,15 % from 370 nm to 830 nm, which is well within the combined relative standard uncertainties for the two laboratories. These results are generally in good agreement with those of the 1981 exchange but are significantly improved for wavelengths below 420 nm, where discrepancies of up to 0,5 % were previously reported at 390 nm. The improvement at shorter wavelengths is largely due to improvements in the uniformity of the radiance of the sphere wall and out-of-band blocking of the interference filters used for wavelength separation.