Where sky meets sea: Integrated aerosol and ocean color retrieval from PACE SPEXone multi-angle polarimetry

Global aerosol and ocean color properties are simultaneously retrieved from multi-angle polarimetric measurements acquired by the SPEXone instrument aboard NASA’s PACE mission. These coupled retrievals are enabled by the FastMAPOL algorithm, which combines optimal estimation with deep neural network forward models to achieve efficient and accurate operational processing. Ocean remote-sensing reflectance ( R r s ) is derived through multi-angle atmospheric correction, introducing an explicit angular dimension for characterizing aquatic optical properties. Since early 2024, both Level-2 and Level-3 global products have been generated in near real time and are publicly distributed through the NASA Earthdata archive. Validation against the Aerosol Robotic Network (AERONET) and associated AERONET-Ocean Color (OC) observations demonstrates robust performance for both atmospheric and oceanic retrievals. Retrieved aerosol optical depth (AOD) exhibits overall uncertainties (RMSD) of approximately 0.06, with mean biases smaller than 0.01, while 63% of retrievals satisfy the uncertainty threshold of max ( 0.04 , 10 % ) , across a wide range of aerosol loadings and water conditions. Retrieved R r s exhibits uncertainties of approximately 0.001 – 0.002 sr − 1 and biases on the order of 0.001 sr − 1 across phytoplankton-dominated waters. R r s retrieval uncertainties increase with aerosol loading, whereas AOD retrieval uncertainties increase with water complexities, highlighting the coupled nature of aerosol and ocean color retrievals. Moreover, global gridded analyses reveal realistic spatial patterns of aerosol type, absorption, and ocean color variability. The angular variability of multi-angle R r s is further examined across latitudes and seasons, including a closure assessment based on a self-consistent bidirectional reflectance correction. This study provides a comprehensive validation of the FastMAPOL SPEXone V3 data products and establishes a baseline for the expected improvements in aerosol and R r s retrievals with the upcoming V4 release, which incorporates updated radiometric calibration. PACE multi-angle polarimetry thus establishes a new capability for fully integrated global aerosol and ocean color retrievals, enhancing our ability to characterize aerosol–ocean interactions and advance understanding of the coupled Earth system.