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

Using a new, high-temperature black-body radiator developed by the All-Russ ian Institute for Optophysical Measurements (VNIIOFI), Moscow, and applying newly developed methods and equipment, the black-body-based spectral irrad iance scale of the Physikalisch-Technische Bundesanstalt (PTB), Braunschwei g, 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 charac terized along with modifications to optimize uniformity and stability. The determination of the radiometric black-body temperatures is already well es tablished by measuring the weighted irradiance using filter detectors witho ut imaging systems. This method is compared and verified with results based on self-consistent spectral irradiance measurements using fast-scanning sp ectroradiometers. In addition, a laser-based method for the determination o f the radiometric temperature is presented and compared with conventional p rocedures of radiation-temperature measurement. The implementation of this additional method into the radiometric chain of the PTB is illustrated. Imp rovements in the uncertainty budget of the spectral irradiance scale are di scussed.