System-level calibration of a transfer radiometer used to validate EOS radiance scales

A number of transfer radiometers have been developed by the National Institute of Standards and Technology (NIST) with the support and funding of the National Aeronautics and Space Administration's (NASA's) satellite sensor calibration programmes. The transfer radiometers travel to NASA satellite builder and calibration facilities and validate the radiance scale of calibration sources at those facilities. One of these instruments, the Earth Observing Systems (EOS) Visible Transfer Radiometer (VXR), was calibrated for spectral responsivity in different facilities at NIST using two types of integrating sphere sources (ISSs): an incandescent lamp-illuminated ISS and a laser-illuminated ISS. The laser-illuminated ISS results in reduced uncertainties and a greater dynamic range in radiance responsivity. We will discuss the calibration procedures using the two types of source, compare results of calibrations of two of the VXR filter channels in the two NIST facilities, and suggest additional irradiance and radiance responsivity calibrations that are now possible using the new laser-illuminated facility.