Atmospheric correction for hyperspectral radiometers over the ocean using multi-angle polarimetric retrievals

Abstract:

Hyperspectral radiometers applied to ocean color remote sensing from space have the potential to significantly advance our understanding of marine biogeochemistry on Earth. Relative to traditional multi-spectral instruments, the enhanced spectral information content of such sensors will improve our ability to identify and differentiate phytoplankton species, quantify CDOM, and monitor harmful algal blooms. The robustness of satellite ocean color retrievals depends on the accuracy of atmospheric correction, which degrades in the presence of absorbing aerosols and complex coastal waters. The heritage atmospheric correction approach employed by NASA has the potential to be applied to hyperspectral sensors, but improvements are required to fully exploit the measurements over optically complex scenes. For the Ocean Color Instrument (OCI) that will be carried on the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, the rich information content of the two multi-angle polarimeters (MAPs); SPEXone and Hyper-Angular Rainbow Polarimeter 2 (HARP2) can be utilized to improve the atmospheric correction of OCI. We have developed a fast and accurate atmospheric correction scheme for hyperspectral measurements: the POLYnomial-based Atmospheric Correction (POLYAC) algorithm, which is based on the parameterization of the atmospheric path radiance using aerosol and surface properties retrieved from co-located multi-wavelength MAP measurements. It has been applied to collocated SPEX airborne and RSP measurements as proxy for a hyperspectral radiometer and a MAP, respectively. The MAP retrieval is based on the Multi-Angular Polarimetric Ocean coLor (MAPOL) algorithm. The hyperspectral remote sensing reflectance obtained from POLYAC compares accurately with the Aerosol Robotic Network (AERONET), and Visible Infrared Imaging Radiometer Suite (VIIRS) ocean color products. It is also planned to be applied with other instrument synergies such as RSP – GCAS, AirHARP – SPEX airborne and AirMSPI – SPEX airborne in the future. POLYAC can provide a robust alternative atmospheric correction scheme for future ocean color missions synergistic instrument payloads, such as the PACE mission, in conditions where the performance of the heritage atmospheric correction scheme is degraded.