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ROSES Proposals

PACE UV Retrieval of Ocean and Atmosphere Data-Products (PACE UV ROAD): CDM, BrC and BC Polarimetry

PI: Jacek Chowdhary - Columbia University and NASA Goddard Institute for Space Studies
Co-PIs: Li Liu (Columbia University); Matteo Ottaviani (Terra Research, Inc / NASA Goddard Institute for Space Studies (GISS)); Kostas Tsigaridis (Columbia University and NASA GISS)
PACE data sets will offer unprecedented opportunities to improve, and even provide new, aerosol and ocean products from inversions of space-borne observations. Of particular interest will be the synergy between UV radiometry (from the OCI sensor) and UV-VIS multi-angle polarimetry (from the SPEXone and HARP2 sensors). Enhanced multiple scattering (EMS) in the atmosphere, which results from an increase in molecular optical depth, causes space-borne UV radiance to be more sensitive to absorbing aerosols such as Black Carbon (BC) and Brown Carbon (BrC). At the same time, EMS increases the diffuse skylight illuminating the ocean, and therefore the radiative coupling between ocean and atmosphere. Hence, satellite retrievals of atmospheric and oceanic UV products must be carried out simultaneously; such inversions provide as an added bonus a rigorous evaluation of associated uncertainty budgets. The radiative coupling between atmosphere and ocean also highlights the importance of absorption by colored detrital matter (CDM) in the ocean. CDM exhibits similar absorption spectra as BrC aerosols and therefor has a similar impact on space-borne UV radiance. An advantage of polarized radiance is that it is less sensitive to multiple scattering, and thus to radiative coupling of atmosphere and ocean. Hence, polarimetric measurements constitute a crucial asset in simultaneous retrievals of BC/BrC and CDM UV products from space-borne observations.

The objective of our proposal is to perform simultaneous retrievals of CDM, BC and BrC products from (i) combined OCI-SPEXone data sets; and (ii) combined OCI-HARP2 data sets. OCI observations cover the UV down to 350 nm, but its radiance data sets are sensitive to variations in both atmospheric and oceanic properties. SPEXone observations complement OCI observations by also providing multi-angle polarized radiance observations down to 385 nm; however, the swath of SPEXone observations is significantly smaller than OCI's. HARP2 observations complement OCI observations by providing multi-angle polarized radiance observations for a swath similar to that of OCI observations; however, HARP2 observations capture the spectrum down to only 440 nm. Hence, for HARP2 we will focus on how the CDM/BC/BrC product retrievals from OCI-SPEXone data sets can be applied to analyses of OCI-HARP2 data sets obtained over a larger swath.

We will use the MAPP retrieval algorithm, which was developed to retrieve aerosol and ocean color properties from airborne multiangle polarimetry observations down to 410 nm by our RSP instrument. We will apply this algorithm to both simulated PACE data sets and available airborne data sets to develop and optimize the retrieval of CDM/BC/BrC UV products from PACE observations. MAPP will be extended to include (a) variations in phytoplankton absorption in the UV; (b) variations in spectral slopes of CDM absorption and in underwater light scattering coefficient; (c) variations in complex refractive indices for BrC aerosols. We will use MAPP inversions of (1) OCI radiance in the VIS to select appropriate phytoplankton absorption spectra for use in the UV; and (2) SPEXone/HARP2 VIS polarized radiance to mask dust-contaminated scenes.

We will use existing in-situ, airborne, and simulated space-borne data sets for our analyses of information content on, and retrieval uncertainties of, atmospheric and oceanic properties. For the in-situ and airborne data sets, we will focus on the SABOR and NAAMES campaigns where RSP observations were coordinated with ship measurements. For the NAAMES campaign, we will also use UV hyperspectral measurements from the airborne GCAS that were co-located with RSP observations. To simulate PACE observations, we will use SeaWiFS retrievals for extrapolation of UV ocean properties, and GISS ModelE results for global variations in aerosol UV properties.