Maintaining MAIA polarimetric and radiometric performance with routine on-board calibrator views

The Multi-Angle Imager for Aerosols (MAIA) mission, scheduled for launch in 2026, will investigate the effects of airborne particulate matter on human health. The satellite instrument contains a spectropolarimetric camera that is pointable in 2 axes, acquires images in 14 wavelength channels between 364 and 2124 nm, and measures linear Stokes parameters Q and U at 440, 646, and 1044 nm. After prelaunch calibration, the instrument demonstrated uncertainty < 0.005 in degree of linear polarization and < 0.4º in angle of linear polarization. Radiometric gain and spatial nonuniformity were also characterized at several temperatures. During operations, the camera will view a dark target several times each orbit and also observe an on-board calibrator (OBC) on most orbits. The OBC consists of a solar diffuser and 12 polarizers at different orientations in a 6 x 2 grid. Polarimetric calibration coefficients can be re-estimated by pointing the camera to view the 12 AOLP domains during a several minutes-long sequence near the orbit’s North pole. These observations will also be used to update the radiometric flat field when all pixels view the same portion of the calibrator. To account for changing solar illumination as the spacecraft moves in its orbit, the domains will be viewed in a varying order on different orbits. Also, for a subset of observations, the gimbal will remain fixed. Frequent updates using onboard data will maintain the high accuracy achieved in ground testing even as thermal fluctuations and exposure to space cause changes in performance.