Aerosol and ocean color retrievals from FastMAPOL/component algorithm using NASA’s PACE polarimetric measurements

We present the validation of aerosol and ocean color retrieval results from the Fast Multi-Angular Polarimetric Ocean coLor/component (FastMAPOL/component) algorithm using Spectropolarimeter for Planetary EXploration one (SPEXone) measurements onboard NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, launched in February 2024. FastMAPOL/component is an enhanced version of the FastMAPOL algorithm, which parametrizes aerosol by type, and has a more detailed coastal waters bio-optical model. The validated parameters include spectral aerosol optical depth (AOD) and remote sensing reflectance ( R rs ) across eight Aerosol Robotic Network for Ocean Color (AERONET-OC) stations in North America and Europe. The results are from 34 matchups co-located between the SPEXone measurements and AERONET-OC stations. Aerosol optical depth was retrieved with RMSE of less than 0.025 for all wavelengths, and R rs was retrieved with RMSE less than 0.0012 sr −1 for all wavelengths studied. More than 90% of the retrieved AOD meet the PACE and Global Climate Observing System (GCOS) uncertainty requirements, whereas the R rs retrieval uncertainties were slightly higher than the PACE requirements. In addition to AOD, the angstrom exponent (AE) and single scattering albedo (SSA) retrievals were also compared against the AERONET retrievals. However, because AERONET retrieved SSA and AE exhibit high uncertainties at low AODs, a full estimation of their uncertainty from our retrievals remains a topic for future studies, although their actual impact on ocean color in the current cases is minimal due to these low aerosol loadings. Furthermore, the AERONET-OC R rs are grouped to represent different levels of water complexities: clear, moderately clear, moderately complex and highly complex waters to assess algorithm’s performance over those water types. The retrieved R rs spectra aligned well with AERONET observations in terms of the angular distances with values of 0.11, 0.24, 0.18, and 0.23 radians for clear, moderately clear, moderately complex, and highly complex waters, respectively. This suggests that the employed bio-optical models are largely sufficient for modeling these diverse water conditions. Ultimately, the coupled aerosol and ocean color information derived from this algorithm have broad applicability, ranging from the detection and tracking of algal blooms to the evaluation of aerosol properties for air quality assessments and their impacts on the global radiative energy budget on a changing climate.