A radiometric method to measure high temperatures of black bodies using broadband-filter detectors is presented. Results of temperature measurements using a linear pyrometer and filter detectors, respectively, are compared. The performance of the black-body source and the realization of an interim detector-based spectralirradiance scale are described and discussed. The new scale is compared with the results of the 1990 Comité Consultatif de Photométrie et Radiométrie intercomparison of spectral-irradiance measurements.

High-temperature black bodies used as primary standards of spectral irradiance have to meet several requirements. One important demand is that the spectral irradiance of the black body is uniquely determined by Planck's radiation law, where the (radiometric) temperature of the black body is the only parameter that determines its relative spectral distribution. By combining determinations of the radiometric temperature of a black body over a wide temperature range with the corresponding spectral measurements, black-body spectra for different temperatures can be compared. This allows the use of self-consistency checks to ascertain whether (i) the temperature determinations are coherent over a wide temperature range; and (ii) the different spectral distributions show any deviation from Planck's law. Using this method of self-consistent calibrations, new absorption bands in the spectrum of a black body were discovered at very high temperatures. The level of absorption increases with temperature and depends on the operating conditions and imperfections of the black-body system. Possible origins of this effect are discussed and modifications proposed to avoid such absorption bands.

Subcomparison CCPR-K1.b of the CCPR key comparison of spectral irradiance covering 200 nm to 400 nm will be carried out in 2002/03 piloted by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. Deuterium arc lamps will be used as transfer standards of spectral irradiance, although they are known to have, in general, poor stability and reproducibility. PTB investigated a variety of deuterium lamps to test their capability (stability and reproducibility) for use as transfer standards. A measurement facility capable of characterizing up to three lamps at a time has been set up. Investigations of the spectral ageing pattern will help to interpolate between different reference measurements to markedly reduce the influence of ageing effects. The application of an external SiC photodiode as a monitor detector was tested. Spatial characterization of the irradiance of each lamp was also carried out. All this all helped us to find suitable types of lamp, producing reasonable irradiance homogeneously enough to be non-sensitive to small misalignments.

In a new facility, the use of thermal radiators such as FEL lamps and very-high-temperature black bodies as standards of spectral irradiance has been extended for the first time down to 200 nm, thus covering the whole air-ultraviolet range. This improvement is based on a significant increase of the throughput and signal-to-noise ratio of a spectroradiometer and on a large reduction in the effects from stray light within this new calibration facility. The reliability of this facility is demonstrated in a comparison between calibrations of spectral irradiance using a black body with different radiometric temperatures, and in a comparison of the calibration of an FEL lamp and a deuterium lamp with the existing scale. The uncertainties achieved are as low as or better than those of the standard facility in this spectral range.