Long Term Repeatability Study of Broadband Radiometers and Spectroradiometers Used for Calibration of Earth Science Optical Instruments

The Goddard Laser for Absolute Measurement of Radiance (GLAMR) has been used to calibrate Earth Science optical instruments over the past ten years. The absolute radiance data is provided by a set of three broadband radiometers, consisting of one silicon, one indium gallium arsenide, and one extended indium gallium arsenide. Two such sets of monitoring radiometers associated with two different integrating spheres and a third set of radiometers used to transfer the calibration provided by NIST allow for a “round robin” intercomparison between these sets, as well as a comparison within each set in their regions of spectral overlap. Additionally, these radiometers were used to calibrate spectroradiometers that provide both radiance and spectral information for one of Goddard’s broadband, NIST-calibrated FEL lamp-illuminated integrating spheres named Grande. This calibration was performed on both of the GLAMR integrating spheres and provides an additional check of consistency between their radiometers. This data allows long term trends in the radiometer sensitivity to be separated from statistical variation of repeated calibrations at NIST, even in cases where changes in an individual radiometer are smaller than the uncertainty of the calibration.