Inversion of multi-angular polarimetric measurements over coastal waters from the ACEPOL campaign: an application to improve atmospheric correction for hyperspectral ocean color retrievals

NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, scheduled for launch in the timeframe of late 2022 to early 2023, will carry a hyperspectral Ocean Color Instrument (OCI) and two Multi-Angle Polarimeters (MAP): the UMBC Hyper-Angular Rainbow Polarimeter (HARP-2) and the SRON Spectro-Polarimeter for Planetary EXploration one (SPEXone). MAP measurements have been demonstrated to contain rich information on the microphysical properties of aerosols and hydrosols, and therefore can be used to obtain more accurate aerosol properties for complex atmosphere and ocean systems. With its three-instrument payload, PACE will provide new opportunities to advance atmospheric correction for the OCI ocean color retrievals using aerosol information retrieved from collocated polarimeter measurements. To date, it has not been demonstrated that the use of polarimeter data can aid the atmospheric correction of collocated ocean color measurements. During the Aerosol Characterization from Polarimeter and Lidar (ACEPOL) field campaign in 2017, four MAPs, including SPEX airborne and RSP (Research Scanning Polarimeter), were flown together in the same aircraft. Like OCI, SPEX is also a hyperspectral radiometer, and thus has potential to be used as an OCI proxy for ocean color algorithm development and assessment. In this work, we perform aerosol retrievals from the RSP measurements collected during the ACEPOL field campaign using the Multi-Angular Polarimetric Ocean coLor (MAPOL) algorithm. MAPOL is a joint aerosol and water-leaving radiance retrieval algorithm that enables accurate retrieval of aerosol properties over both open-ocean and complex coastal waters. We apply the retrieved aerosol properties to the collocated hyperspectral measurements from SPEX airborne. The corresponding hyperspectral water-leaving signals are computed and compared with the collocated AERONET-OC and MODIS Ocean Color products. In this study we aim to demonstrate the concept of using MAPs on PACE to improve the performance of the OCI atmospheric correction for more accurate retrieval of ocean color radiometery.