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ROSES Proposals

Hyperspectral Algorithms for PACE OCI Water Leaving Reflectances and UV Penetration Depths

PI: Nick Krotkov - NASA Goddard Space Flight Center
Co-Is: Patricia Castellanos (NASA Goddard Space Flight Center (GSFC)); Zachary Fasnacht (Science Systems and Applications, Inc. (SSAI)); David Haffner (SSAI); Joanna Joiner (NASA GSFC); Jungbin Mok (SSAI); Omar Torres (NASA GSFC); Alexander Vasilkov (SSAI)
As compared with heritage and current ocean color imagers, the PACE OCI spectrometer will additionally measure hyperspectral reflectances in the ultraviolet (UV-A) to help characterize UV-absorbing aerosols (e.g., “Brown Carbon”), as well as phytoplankton composition and harmful algal blooms. Our team will apply multi-year experience producing operational aerosol, cloud and trace gas (NO2, ozone) products from the hyperspectral UV-Vis Ozone Monitoring Instrument (OMI) on EOS Aura satellite (2004- current) to develop and evaluate a novel OCI algorithms for the hyperspectral water leaving reflectances (WLRs) from 350 to 500nm and UV biological action spectra weighted penetration depths for different biological processes.

Our innovative hyperspectral WLR algorithm is based on the state-of-the-art atmospheric-ocean Vector Linearized Radiative Transfer Model (VLIDORT), which analytically calculates Jacobians with respect to the atmospheric (vertically resolved aerosols, trace gases) and ocean (wind speed, WLRs) parameters. To explicitly account for aerosols, we propose to use spatiotemporally resolved 3D aerosol optical properties (including newly developed BrC parameterization) from the NASA's Global Modeling and Assimilation Office (GMAO) analyses and forecasts combined with the on-line VLIDORT computations that account for polarization of multiple scattered radiation and anisotropic reflection of solar light from ocean water and rough surface accounting for wind speed and direction.

Quantifying the penetration of UV solar radiation into the ocean is important for the study of ocean biology, including evaluation of possible damage of UV radiation to the photosynthetic apparatus of phytoplankton, and biogeochemistry, e.g. evaluation of carbonyl sulfide production in the ocean. Our semi-analytical UV-visible spectral inherent optical property model previously developed for the heritage ozone (TOMS) and ocean color (SeaWiFS) measurements will be adapted for calculation of the biological action spectra-weighted UV penetration depths using VLIDORT calculation of the downwelling spectral irradiance at the ocean surface and GMAO stratospheric ozone fields.

We will demonstrate proposed algorithms and estimate uncertainties using satellite measured top-of-the-atmosphere reflectance spectra (Level 1B) from the current LEO UV-Vis spectrometers (EOS Aura/OMI and EU/ESA Copernicus Sentinel 5 Precursor /TROPOMI) an upcoming GEO spectrometer (GEMS).

We will compare OMI-retrieved WLRs with our semi-analytical spectral inherent optical property model in the UVA wavelengths and with the traditional ocean color retrievals from MODIS and SeaWiFS at the visible wavelengths.