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 sev eral transfer radiometers that are used in radiometric measurement comparis ons to validate spectral-radiance levels assigned to integrating-sphere sou rces by the end user. The transfer radiometers are characterized and calibr ated at the NIST, and function as direct links in the spectral radiance mea surement 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.