613 Seminar: Pengwang Zhai


Scheduled to launch in 2022, NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission aims to extend key climate data records including ocean color, aerosol, and cloud parameters and to address new and emerging science goals. The primary instrument is called the Ocean Color Instrument, an advanced spectrometer that makes radiometric measurements with continuous spectral coverage from the ultraviolet (350 nm) to near-infrared (890 nm), plus a set of discrete shortwave infrared bands (940, 1038, 1250, 1378, 1615, 2130, and 2260 nm). OCI is capable of capturing fine spectral variations of the ocean color signal, which can be used to explore exciting new sciences in characterizing phytoplankton function groups, quantifying colored dissolved organic matter (CDOM), studying primary productivity and phytoplankton physiology, and much more. In addition, the PACE mission plans to include two multi-angle polarimeters: the UMBC Hyper Angular Rainbow Polarimeter (HARP-2) and the SRON Spectro-polarimeter for Planetary Exploration (SPEXone), which can determine aerosol and cloud microphysical parameters, aid in atmospheric correction for ocean color remote sensing, and explore 3-D effects of inhomogeneous clouds and land surfaces, to just name a few.

To best extract information contained in both the spectrometer and polarimeters, we have been dedicated in developing a PACE simulator that is based on a vector radiative transfer package for coupled atmosphere and ocean systems that is flexible in both atmospheric and ocean compositions, includes both elastic and inelastic scattering, and incorporates atmospheric gas absorptions. The PACE simulator has been used to study the sensitivity of the OCI spectral signals in response to different atmospheric and ocean configurations. It is particularly interesting to study the different contributions of water leaving radiance signals to the top-of-atmosphere measurements for different ocean water types. Also, the PACE simulator can be used to quantitatively study phytoplankton fluorescence with different chlorophyll a concentrations, quantum yields, and most interestingly, non-photochemical quenching effects. Moreover, we are also developing a joint retrieval algorithm of aerosols and water leaving radiances for polarimeter measurements. The algorithm is versatile in aerosol composition and size distribution parameters, and can also deal with coastal waters in which the inherent optical properties decouple with the chlorophyll a concentration. The algorithm has been validated with both synthetic radiative transfer datasets and airborne polarimeter measurements acquired by the Research Scanning Polarimeter (RSP). We will present the properties of aerosols and water leaving radiances retrieved from the RSP data and share the lessons that we have learned from this retrieval activity.

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