Improved comparison of the World Radiometric Reference and the SI radiometric scale

A few years ago, we compared for the first time the World Radiometric Reference, which is used as reference for meteorological radiometry, and the Système International (SI) radiometric scale realized at the National Physical Laboratory with cryogenic radiometers. We present an improved comparison which used as transfer standard a trap detector calibrated to the NPL primary standard cryogenic radiometer. As a realization of the World Radiometric Reference, we used an electrical substitution radiometer traceable to the WRR and used in solar radiometry. The method of transfer has been improved and the results confirm those of the first comparison but with much lower uncertainty.