A CLARREO (Climate Absolute Radiance and Refractivity Observatory) Pathfinder (CPF) mission has been funded todemonstrate retrieval of SI-traceable spectral reflectance with absolute uncertainty <0.3% (k=1). The mission consists ofa Reflected Solar spectrometer that will be hosted on the International Space Station (ISS) in the 2023 timeframe andrely on a ratioing radiometer approach to retrieve the unprecedented accuracy. Demonstrating that the accuracy isachieved through an Independent Calibration effort similar in philosophy to the efforts in metrology laboratories relyingon multiple, independent measurements to improve credibility for a sensor’s absolute and relative uncertainty errorbudgets. These measurements use different traceability paths and multiple instrument approaches and CPF’sIndependent Calibration will be similar in this regard. The Independent Calibration relies on a pre-launch absoluteradiometric calibration obtained from additional testing done after instrument thermal-vacuum (TVAC) testing. Theadded radiometric calibration is combined with a high fidelity instrument model to provide an on-orbit radiometriccalibration independent from the ratioing radiometer approach. The current work describes the post-TVAC testingportion of the CPF Independent Calibration Plan and the Independent Model Development as well as planned on-orbitEvaluation of the Independent Calibration.
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