Towards high-accuracy primary spectral radiometry from 400 K to 1300 K.

We describe the design, construction, calibration and use of a near-infrared thermodynamic radiation thermometer to measure blackbodies from 400 K to 1300 K. The motivation for this work is the pending redefinition of the kelvin and the need for direct, thermodynamic temperature measurements of the fixed-point blackbodies presently used in the realization of the temperature scale. The challenges of accurately measuring Planck radiances which vary greatly in radiance level and spectral shape are discussed. Methods to characterize the components used in the radiation thermometer design are described. The use of this radiation thermometer as a relative primary thermometer and the resulting residuals are shown. We describe radiometric calibration procedures for using the radiation thermometer as an absolute primary thermometer. Preliminary data showing the initial radiometric calibration steps are discussed.