ANNUAL REPORT 2007

Methods for improving the extrapolated radiation temperature measurements above the metallic fixed points using linear pyrometers were compared. Four different methods for obtaining the effective wavelength were studied. These include direct measurement of the spectral responsivity of the pyrometer, comparison of two measured pyrometer signals at known temperatures, comparison against a narrow-band filter radiometer operating as an irradiance mode transfer pyrometer, and calculating the effective wavelength using reliable intercomparison data. The improvements obtained using the methods are estimated by comparing the results with extrapolation using the Sakuma-Hattori method and analysis using Planck’s law with the nominal wavelength (651 nm) of the pyrometer tested. Experimental results of the study are based on a large set of intercomparison data resulting from a recent temperature intercomparison between the PTB (Germany) and the MIKES (Finland) in the range of 1570 K to 2770 K. The measurement artifacts include a high temperature black body, a strip lamp used as an ITS-90 reference, two linear pyrometers and various irradiance-mode filter radiometers. It was shown that improper understanding of the pyrometer properties may lead to systematic measurement errors up to several Kelvins. With careful analysis, uncertainties of the order of 1 K are obtainable. Comparison of detector-based spectral irradiance scales using NIR lasers Spectral irradiance measurements using filter radiometers are needed for radiometric temperature determinations. Independent laser-based calibration facilities at the Metrology Research Institute, Finland, and the National Institute of Standards and Technology (NIST), United States, used for the realization of the detector-based spectral irradiance scale have been compared in the near-infrared (NIR) region. The results of the comparison of the laser-based facilities were compared to the spectral irradiance scale obtained with the NIST mono-chromator-based calibration facility. The comparison was carried out by calibrating a narrow-bandwidth filter radiometer on each facility. The results of the comparison showed agreement between the integrated responsivities of the radiometer within 0.1 %, well within the standard uncertainty of the comparison. The work also covers the study of out-of-band responsivity measurements and the ageing properties of the filter radiometer used. The results give additional evidence on the suitability of lasers as sources for the realization of absolute spectral irradiance scales in the NIR region enabling, e.g. the development of the radiometric temperature scales with lower uncertainties.