CLARREO Pathfinder

NASA’s CLARREO Pathfinder is an International Space Station instrument mission demonstrating highly accurate measurements of reflected sunlight for Earth-observation calibration. Its HySICS imaging spectrometer spans 350–2300 nm, with direct views of the Sun, Earth and Moon used to maintain radiometric traceability. The design targets 0.3% radiometric uncertainty (k=1). For intercalibration, the instrument rotates to closely match another sensor’s viewing geometry and acquires measurements matched in location, time and spectral band. This approach supports transfer of a common reference to instruments such as CERES and VIIRS and more consistent long-term environmental records.