Radiometric calibration history of visible and near-infrared portable radiometers

The National Institute of Standards and Technology (NIST), with the support of the National Aeronautics and Space Administration (NASA), has built several transfer radiometers that are used in radiometric measurement comparisons to validate spectral-radiance levels assigned to integrating-sphere sources by the end user. The transfer radiometers are characterized and calibrated at the NIST, and function as direct links in the spectral radiance measurement chain. This paper presents a historical analysis of a calibration method that utilizes a broadband source. Previously observed discrepancies between two radiometers are reconciled as a result.