Polarimetric remote sensing of the atmosphere in the PACE UV-VIS spectrum: Modeling scattering and absorption by Brown Carbon

The NASA Aerosol Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, scheduled for launch in 2023, will carry two instruments that measure UV radiance emerging from the top of the atmosphere (TOA): the Ocean Color Instrument (OCI) and the Spectro-Polarimeter for Planetary Exploration (SPEXone) instrument. OCI will provide single-view, hyperspectral radiometric data with a spectral resolution of 5 nm, whereas SPEXone will provide multiangle, multispectral polarimetric data with a degree of linear polarization accuracy of 0.3%. Together, these instruments will be the most advanced in NASAs history for the combined observation of ocean color and atmospheric aerosols in the UV, and they will therefore provide unprecedented research opportunities for the ocean color and atmospheric aerosol communities. In particular, UV observations are best suited to constrain Colored Dissolved Organic Matter (CDOM) in the ocean, and Brown Carbon (BrC) aerosols in the atmosphere. However, both CDOM and BrC exhibit very similar absorption spectra in the UV-VIS; hence, care must be taken in accurately modeling these spectra for analyses of OCI and SPEXone measurements [1,2]. In this talk, we present a simple but highly-accurate 3-parameter model for hyper-spectral variations in the complex refractive index of BrC in the UV-VIS, and we discuss the impact of those variations on PACE-like total and polarized multiangle radiances. References: [1] Chowdhary, J., P.-W. Zhai, E. Boss, H. Dierssen, R. Frouin, A. Ibrahim, Z. Lee, L.A. Remer, M. Twardowski, F. Xu, X. Zhang, M. Ottaviani, W.R. Espinosa, and D. Ramon, 2019: Modeling atmosphere-ocean radiative transfer: A PACE mission perspective. Front. Earth Sci., 7, 100, doi:10.3389/feart.2019.00100. [2] Frouin, R.J., B.A. Franz, A. Ibrahim, K. Knobelspiesse, Z. Ahmad, B. Cairns, J. Chowdhary, H.M. Dierssen, J. Tan, O. Dubovik, X. Huang, A.B. Davis, O. Kalashnikova, D.R. Thompson, L.A. Remer, E. Boss, O. Coddington, P.-Y. Deschamps, B.-C. Gao, L. Gross, O. Hasekamp, A. Omar, B. Pelletier, D. Ramon, F. Steinmetz, and P.-W. Zhai, 2019: Atmospheric correction of satellite ocean-color imagery during the PACE Era. Front. Earth Sci., 7, 145, doi:10.3389/feart.2019.00145.