CLARREO Pathfinder On-orbit Inter-calibration Approach

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder (CPF) mission began in 2016 and will demonstrate essential measurement technologies required to obtain reflected solar (RS) climate observations. The mission includes the flight of a RS spectrometer that is scheduled to begin taking measurements from the International Space Station (ISS) in the 2023 timeframe for at least one year. By measuring spectral reflectance with high accuracy and SI-traceability (0.3% k=1) the CPF instrument will be able to serve as an on-orbit radiometric reference for operational Earth-viewing sensors, including land imaging sensors. Although CPF will be demonstrating its inter-calibration approach with the Clouds and Earth's Radiant Energy System (CERES) broadband shortwave channel and the Visible/Infrared Imaging Radiometer Suite (VIIRS), this approach can readily be applied to other on-orbit shortwave sensors. Two-axis pointing, a spectral range from 350 nm to 2300 nm, and a spectral resolution ≤ 6 nm enable the CLARREO Pathfinder instrument to provide nearly coincident temporal, spatial, angular, and spectral matching of inter-calibration targets, with sampling sufficient to reduce random errors. The inter-calibration method will refine knowledge of target sensors' effective offsets, gain, non-linearity, and spectral response. We will present an overview of CLARREO Pathfinder mission with focus on the development of its inter-calibration approaches and a discussion of its versatility.