In June 2007, a spherical integrating source was calibrated in the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center's (GSFC) Calibration Facility as part of the prelaunch characterization program for the NPOESS Preparatory Program (NPP) Ozone Mapping and Profiler Suite (OMPS) instrument. Before shipment to the instrument vendor, the sphere radiance was measured at the Remote Sensing Laboratory at the National Institute of Standards (NIST) and then returned to the NASA Goddard facility for a second calibration. For the NASA GSFC calibration, the reference was a set of quartz halogen lamps procured from NIST. For the measurement in the Remote Sensing Laboratory, the reference was an integrating sphere that was directly calibrated at NIST's Facility for Spectroradiometric Calibrations (FASCAL). For radiances in the visible and near-infrared (400 nm to 1000 nm), the agreement between the NASA GSFC calibration and the validation measurements at the Remote Sensing Laboratory was at the 1 % level. For radiances in the near ultraviolet (250 nm to 400 nm), the agreement was at the 3 % level.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.