Polarization ray trace-based modeling using preflight characterization of the Multi-Angle Imager for Aerosols (MAIA) satellite instrument

The Multi-Angle Imager for Aerosols (MAIA) instrument, developed at the Jet Propulsion Laboratory (JPL), is scheduled for launch into low-Earth orbit in 2026 to investigate the connection between aerosols and public health. To retrieve aerosol properties, the MAIA spectropolarimetric camera will capture radiance images across 14 UV-SWIR wavelength channels. The 440, 646, and 1044 nm bands will also measure the linear Stokes parameters Q and U. A division of time polarimeter, MAIA uses a combination of photo-elastic modulators, compound achromatic waveplates, focal plane polarizers, and rapid detector readout to measure a time modulated polarimetric signal. The instrument completed calibration and testing in 2022 and demonstrated degree of linear polarization (DOLP) uncertainty below 0.005. To monitor performance after launch, a polarization ray-tracing model has been created using CODE V and open-source Python packages. This model predicts the camera's field-angle-dependent Mueller matrix (MM). Contributions from coatings, waveplates, optical filters, and polarizers are incorporated into the model by making use of polarization metrology measurements of the as-built optical components. Critically, the model also includes variations in retardance from MAIA’s compound quarter waveplates as a function of both wavelength and angle. Model output is compared to the measured polarimetric calibration coefficients and used to estimate the clocking alignment of the polarization-critical optics. In orbit, this model will be used with MAIA’s polarized onboard calibrator (OBC) to track any changes in the polarization properties of the camera optics over time.