Polarimetry in the longwave infrared is currently absent from NASA’s suite of spaceborne observ-ing systems. Thermal polarimetry provides unique sensitivity to surface and ice crystal optical properties, offering a new pathway for constraining cloud microphysics and radiative effects. Ice clouds play a critical role in regulating large-scale atmospheric circulation, influencing high-impact phenomena such as the position and strength of the Northern Hemisphere jet stream and the varia-bility of the El Niño–Southern Oscillation.
The goal of the CHanneled InfraRed Polarimeter (CHIRP) team is to establish a pathway toward achieving the polarimetric accuracy required for ice cloud remote sensing and to advance thermal polarimetry to higher technology readiness levels. CHIRP is a wavelength-channeled polarimeter designed for robustness and flight compatibility, with no moving parts. A single metasurface polar-ization grating enables simultaneous spectroscopy and polarimetry in a compact, common-path configuration. The first diffracted orders encode orthogonal polarization states, which are co-registered onto a single focal plane, simplifying calibration and enhancing system stability.
In this work, we present laboratory characterization of the CHIRP instrument alongside simula-tions of ice cloud top-of-atmosphere observations. Calibration accuracy and system stability re-quirements are driven by tropical ice cloud-top temperatures near 200 K, where the expected polar-ized radiance is only a few kelvin. To meet this performance goal, we develop an end-to-end cali-bration and validation framework spanning a broad temperature range. This framework includes methods for quantifying polarization sensitivity, assessing thermal stability, and identifying sys-tematic error sources under mission-relevant environmental conditions.