Improvement and extension of the black-body-based spectral irradiance scale

Using a new, high-temperature black-body radiator developed by the All-Russian Institute for Optophysical Measurements (VNIIOFI), Moscow, and applying newly developed methods and equipment, the black-body-based spectral irradiance scale of the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, has been extended and its uncertainties have been reduced compared with previous results. The pyrolytic-graphite Planckian radiator BB3200pg, which can be operated at temperatures up to over 3300 K, is presented and characterized along with modifications to optimize uniformity and stability. The determination of the radiometric black-body temperatures is already well established by measuring the weighted irradiance using filter detectors without imaging systems. This method is compared and verified with results based on self-consistent spectral irradiance measurements using fast-scanning spectroradiometers. In addition, a laser-based method for the determination of the radiometric temperature is presented and compared with conventional procedures of radiation-temperature measurement. The implementation of this additional method into the radiometric chain of the PTB is illustrated. Improvements in the uncertainty budget of the spectral irradiance scale are discussed.