Realization of a spectral irradiance scale in the near infrared at the National Research Council of Canada.

The measurements involved in the realization of a spectral irradiance scale in the near IR are described. Interference filters were used in conjunction with absolute radiometers to calibrate two different types of tungsten-halogen lamp at nine discrete wavelengths in the spectral range of 700-1600 nm. We discuss various aspects of these measurements: the apparatus used and alignment procedures, aging of the lamps and verification of their spectral characteristics, filter properties and measurements, some of the problems associated with the radiometric measurements, and data analysis. In particular it is shown that the interpolation formulas used to obtain spectral irradiance values at other wavelengths must be carefully chosen to avoid spurious errors. Two independent realizations were made; a comparison of the results obtained in the two cases indicated that some of the lamps had anomalous behavior. Finally it is shown that the new scale is in agreement with the scales realized by several other national laboratories within estimated uncertainties.